| SPEECHSC | D. Burnett |
| Internet-Draft | Voxeo |
| Intended status: Standards Track | S. Shanmugham |
| Expires: January 13, 2012 | Cisco Systems, Inc. |
| July 12, 2011 |
Media Resource Control Protocol Version 2 (MRCPv2)
draft-ietf-speechsc-mrcpv2-25
The MRCPv2 protocol allows client hosts to control media service resources such as speech synthesizers, recognizers, verifiers and identifiers residing in servers on the network. MRCPv2 is not a "stand-alone" protocol - it relies on other protocols, such as Session Initiation Protocol (SIP) to rendezvous MRCPv2 clients and servers and manage sessions between them, and the Session Description Protocol (SDP) to describe, discover and exchange capabilities. It also depends on SIP and SDP to establish the media sessions and associated parameters between the media source or sink and the media server. Once this is done, the MRCPv2 protocol exchange operates over the control session established above, allowing the client to control the media processing resources on the speech resource server.
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Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.
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This Internet-Draft will expire on January 13, 2012.
Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.
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The MRCPv2 protocol is designed to allow a client device to control media processing resources on the network. Some of these media processing resources include speech recognition engines, speech synthesis engines, speaker verification and speaker identification engines. MRCPv2 enables the implementation of distributed Interactive Voice Response platforms using VoiceXML [W3C.REC-voicexml20-20040316] browsers or other client applications while maintaining separate back-end speech processing capabilities on specialized speech processing servers. MRCPv2 is based on the earlier Media Resource Control Protocol (MRCP) [RFC4463] developed jointly by Cisco Systems, Inc., Nuance Communications, and Speechworks Inc.
The protocol requirements of SPEECHSC [RFC4313] include that the solution be capable of reaching a media processing server and setting up communication channels to the media resources, and sending and receiving control messages and media streams to/from the server. The Session Initiation Protocol (SIP) [RFC3261] meets these requirements.
The proprietary version of MRCP ran over the Real Time Streaming Protocol (RTSP) [RFC2326]. At the time work on MRCPv2 was begun, the consensus was that this use of RTSP would break the RTSP protocol or cause backward-compatibility problems, something forbidden by Section 3.2 of the above mentioned requirements document. This is the reason why MRCPv2 does not run over RTSP.
MRCPv2 leverages these capabilities by building upon SIP and the Session Description Protocol (SDP) [RFC4566]. MRCPv2 uses SIP to setup and tear down media and control sessions with the server. In addition, the client can use a SIP re-INVITE method (an INVITE dialog sent within an existing SIP Session) to change the characteristics of these media and control session while maintaining the SIP dialog between the client and server. SDP is used to describe the parameters of the media sessions associated with that dialog. It is mandatory to support SIP as the session establishment protocol to ensure interoperability. Other protocols can be used for session establishment by prior agreement. This document only describes the use of SIP and SDP.
MRCPv2 uses SIP and SDP to create the speech client/server dialog and set up the media channels to the server. It also uses SIP and SDP to establish MRCPv2 control sessions between the client and the server for each media processing resource required for that dialog. The MRCPv2 protocol exchange between the client and the media resource is carried on that control session. MRCPv2 protocol exchanges do not change the state of the SIP dialog, the media sessions, or other parameters of the dialog initiated via SIP. It controls and affects the state of the media processing resource associated with the MRCPv2 session(s).
MRCPv2 defines the messages to control the different media processing resources and the state machines required to guide their operation. It also describes how these messages are carried over a transport layer protocol such as the Transmission Control Protocol (TCP) [RFC0793] or the Transport Layer Security (TLS) Protocol [RFC5246] (Note: the Stream Control Transmission Protocol (SCTP) [RFC4960] is a viable transport for MRCPv2 as well, but the mapping onto SCTP is not described in this specification).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
Since many of the definitions and syntax are identical to those for the HTTP/1.1 (Hypertext Transfer Protocol (HTTP/1.1) [RFC2616]), this specification refers to the section where they are defined rather than copying it. For brevity, [HX.Y] is to be taken to refer to Section X.Y of RFC 2616.
All the mechanisms specified in this document are described in both prose and an augmented Backus-Naur form (ABNF [RFC5234]).
The complete message format in ABNF form is provided in Section 15 and is the normative format definition. Note that productions may be duplicated within the main body of the document for reading convenience. If a production in the body of the text conflicts with one in the normative definition, the latter rules.
The state-machine diagrams in this document do not show every possible method call. Rather, they reflect the state of the resource based on the methods that have moved to IN-PROGRESS or COMPLETE states (see Section 5.3). Note that since PENDING requests essentially have not affected the resource yet and are in queue to be processed, they are not reflected in the state-machine diagrams.
This document defines many protocol headers that contain URIs (Uniform Resource Identifier (URI) [RFC3986]) or lists of URIs for referencing media. The entire document, including the Security Considerations section (Section 12), assumes that HTTP or HTTP over TLS (HTTPS) [RFC2818] will be used as the URI addressing scheme unless otherwise stated. However, implementations MAY support other schemes (such as "file") provided they have addressed any security considerations described in this document and any others particular to the specific scheme. For example, implementations where the client and server both reside on the same physical hardware and the file system is secured by traditional user-level file access controls could be reasonable candidates for supporting the "file" scheme.
A system using MRCPv2 consists of a client that requires the generation and/or consumption of media streams and a media resource server that has the resources or "engines" to process these streams as input or generate these streams as output. The client uses SIP and SDP to establish an MRCPv2 control channel with the server to use its media processing resources. MRCPv2 servers are addressed using SIP URIs.
The session initiation protocol (SIP) uses SDP with the offer/answer model described in RFC3264 [RFC3264] to set up the MRCPv2 control channels and describe their characteristics. A separate MRCPv2 session is needed to control each of the media processing resources associated with the SIP dialog between the client and server. Within a SIP dialog, the individual resource control channels for the different resources are added or removed through SDP offer/answer carried in a SIP re-INVITE transaction.
The server, through the SDP exchange, provides the client with an unambiguous channel identifier and a TCP port number. The client MAY then open a new TCP connection with the server on this port number. Multiple MRCPv2 channels can share a TCP connection between the client and the server. All MRCPv2 messages exchanged between the client and the server carry the specified channel identifier that the server MUST ensure is unambiguous among all MRCPv2 control channels that are active on that server. The client uses this channel identifier to indicate the media processing resource associated with that channel. For information on message framing, see Section 5.
The session initiation protocol (SIP) also establishes the media sessions between the client (or other source/sink of media) and the MRCPv2 server using SDP m-lines. One or more media processing resources may share a media session under a SIP session, or each media processing resource may have its own media session.
The following diagram shows the general architecture of a system that uses MRCPv2. To simplify the diagram only a few resources are shown.
MRCPv2 client MRCPv2 Media Resource Server
|--------------------| |------------------------------------|
||------------------|| ||----------------------------------||
|| Application Layer|| ||Synthesis|Recognition|Verification||
||------------------|| || Engine | Engine | Engine ||
||Media Resource API|| || || | || | || ||
||------------------|| ||Synthesis|Recognizer | Verifier ||
|| SIP | MRCPv2 || ||Resource | Resource | Resource ||
||Stack | || || Media Resource Management ||
|| | || ||----------------------------------||
||------------------|| || SIP | MRCPv2 ||
|| TCP/IP Stack ||---MRCPv2---|| Stack | ||
|| || ||----------------------------------||
||------------------||----SIP-----|| TCP/IP Stack ||
|--------------------| || ||
| ||----------------------------------||
SIP |------------------------------------|
| /
|-------------------| RTP
| | /
| Media Source/Sink |------------/
| |
|-------------------|
An MRCPv2 server may offer one or more of the following media processing resources to its clients.
The MRCPv2 server is a generic SIP server, and is thus addressed by a SIP URI (RFC 3261 [RFC3261]).
For example:
sip:mrcpv2@example.net
MRCPv2 requires a connection-oriented transport layer protocol such as TCP or SCTP to guarantee reliable sequencing and delivery of MRCPv2 control messages between the client and the server. In order to meet the requirements for security enumerated in SpeechSC Requirements [RFC4313], clients and servers MUST implement TLS as well. One or more connections between the client and the server can be shared among different MRCPv2 channels to the server. The individual messages carry the channel identifier to differentiate messages on different channels. MRCPv2 protocol encoding is text based with mechanisms to carry embedded binary data. This allows arbitrary data like recognition grammars, recognition results, synthesizer speech markup etc. to be carried in MRCPv2 messages. For information on message framing, see Section 5.
MRCPv2 employs a session establishment and management protocol such as SIP in conjunction with SDP. The client reaches an MRCPv2 server using conventional INVITE and other SIP requests for establishing, maintaining, and terminating SIP dialogs. The SDP offer/answer exchange model over SIP is used to establish a resource control channel for each resource. The SDP offer/answer exchange is also used to establish media sessions between the server and the source or sink of audio.
The client needs a separate MRCPv2 resource control channel to control each media processing resource under the SIP dialog. A unique channel identifier string identifies these resource control channels. The channel identifier is an unambiguous, opaque string followed by an "@", then by a string token specifying the type of resource. The server generates the channel identifier and MUST make sure it does not clash with the identifier of any other MRCP channel currently allocated by that server. MRCPv2 defines the following IANA-registered types of media processing resources. Additional resource types, their associated methods/events and state machines may be added as described below in Section 13.
| Resource Type | Resource Description | Described in |
|---|---|---|
| speechrecog | Speech Recognizer | Section 9 |
| dtmfrecog | DTMF Recognizer | Section 9 |
| speechsynth | Speech Synthesizer | Section 8 |
| basicsynth | Basic Synthesizer | Section 8 |
| speakverify | Speaker Verification | Section 11 |
| recorder | Speech Recorder | Section 10 |
The SIP INVITE or re-INVITE transaction and the SDP offer/answer exchange it carries contain m-lines describing the resource control channel to be allocated. There MUST be one SDP m-line for each MRCPv2 resource to be used in the session. This m-line MUST have a media type field of "application" and a transport type field of either "TCP/MRCPv2" or "TCP/TLS/MRCPv2". (The usage of SCTP with MRCPv2 may be addressed in a future specification). The port number field of the m-line MUST contain the "discard" port of the transport protocol (port 9 for TCP) in the SDP offer from the client and MUST contain the TCP listen port on the server in the SDP answer. The client may then either set up a TCP or TLS connection to that server port or share an already established connection to that port. Since MRCPv2 allows multiple sessions to share the same TCP connection, multiple m-lines in a single SDP document may share the same port field value; MRCPv2 servers MUST NOT assume any relationship between resources using the same port other than the sharing of the communication channel.
MRCPv2 resources do not use the port or format field of the m-line to distinguish themselves from other resources using the same channel. The client MUST specify the resource type identifier in the resource attribute associated with the control m-line of the SDP offer. The server MUST respond with the full Channel-Identifier (which includes the resource type identifier and an unambiguous string) in the "channel" attribute associated with the control m-line of the SDP answer. To remain backwards compatible with conventional SDP usage, the format field of the m-line MUST have the arbitrarily-selected value of "1".
When the client wants to add a media processing resource to the session, it issues a new SDP offer, according to the procedures of RFC 3264 [RFC3264], in a SIP re-INVITE request. The SDP offer/answer exchange carried by this SIP transaction contains one or more additional control m-lines for the new resources to be allocated to the session. The server, on seeing the new m-line, allocates the resources (if they are available) and responds with a corresponding control m-line in the SDP answer carried in the SIP response. If the new resources are not available, the re-INVITE receives an error message, and existing media processing going on before the re-INVITE will continue as it was before.
MRCPv2 clients and servers using TCP as a transport protocol MUST use the procedures specified in RFC 4145 [RFC4145] for setting up the TCP connection, with the considerations described hereby. Similarly, MRCPv2 clients and servers using TCP/TLS as a transport protocol MUST use the procedures specified in RFC 4572 [RFC4572] for setting up the TLS connection, with the considerations described hereby. The a=setup attribute, as described in RFC 4145 [RFC4145], MUST be "active" for the offer from the client and MUST be "passive" for the answer from the MRCPv2 server. The a=connection attribute MUST have a value of "new" on the very first control m-line offer from the client to an MRCPv2 server. Subsequent control m-line offers from the client to the MRCP server MAY contain "new" or "existing", depending on whether the client wants to set up a new connection or share an existing connection, respectively. If the client specifies a value of "new", the server MUST respond with a value of "new". If the client specifies a value of "existing", the server MAY respond with a value of "existing" if it prefers to share an existing connection or can answer with a value of "new", in which case the client MUST initiate a new transport connection.
When the client wants to de-allocate the resource from this session, it issues a new SDP offer, according to RFC 3264 [RFC3264], where the control m-line port MUST be set to 0. This SDP offer is sent in a SIP re-INVITE request. This de-allocates the associated MRCPv2 identifier and resource. The server MUST NOT close the TCP, SCTP or TLS connection if it is currently being shared among multiple MRCP channels. When all MRCP channels that may be sharing the connection are released and/or the associated SIP dialog is terminated, the client or server terminates the connection.
When the client wants to tear down the whole session and all its resources, it MUST issue a SIP BYE request to close the SIP session. This will de-allocate all the control channels and resources allocated under the session.
All servers MUST support TLS. Servers MAY support TCP without TLS in physically secure environments. It is up to the client, through the SDP offer, to choose which transport it wants to use for an MRCPv2 session. Aside from the exceptions given above, when using TCP the m-lines MUST conform to RFC4145 [RFC4145], which describes the usage of SDP for connection-oriented transport. When using TLS the SDP m-line for the control stream MUST conform to comedia over TLS [RFC4572], which specifies the usage of SDP for establishing a secure connection-oriented transport over TLS.
This first example shows the power of using SIP to route to the appropriate resource. In the example, note the use of a request to a domain's speech server service in the INVITE to mresources@example.com. The SIP routing machinery in the domain locates the actual server, mresources@server.example.com, which gets returned in the 200 OK. Note that "cmid" is defined in Section 4.4.
This example exchange adds a resource control channel for a synthesizer. Since a synthesizer also generates an audio stream, this interaction also creates a receive-only Real-Time Protocol (RTP) [RFC3550] media session for the server to send audio to. The SIP dialog with the media source/sink is independent of MRCP and is not shown.
C->S: INVITE sip:mresources@example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf1
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314161 INVITE
Contact:<sip:sarvi@client.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=sarvi 2890844526 2890844526 IN IP4 192.0.2.12
s=-
c=IN IP4 192.0.2.12
t=0 0
m=application 9 TCP/MRCPv2 1
a=setup:active
a=connection:new
a=resource:speechsynth
a=cmid:1
m=audio 49170 RTP/AVP 0
a=rtpmap:0 pcmu/8000
a=recvonly
a=mid:1
S->C: SIP/2.0 200 OK
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf1;received=192.0.32.10
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314161 INVITE
Contact:<sip:mresources@server.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=- 2890842808 2890842808 IN IP4 192.0.2.11
s=-
c=IN IP4 192.0.2.11
t=0 0
m=application 32416 TCP/MRCPv2 1
a=setup:passive
a=connection:new
a=channel:32AECB234338@speechsynth
a=cmid:1
m=audio 48260 RTP/AVP 0
a=rtpmap:0 pcmu/8000
a=sendonly
a=mid:1
C->S: ACK sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf2
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314161 ACK
Content-Length:0
This example exchange continues from the previous figure and allocates an additional resource control channel for a recognizer. Since a recognizer would need to receive an audio stream for recognition, this interaction also updates the audio stream to sendrecv, making it a 2-way RTP media session.
C->S: INVITE sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf3
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314162 INVITE
Contact:<sip:sarvi@client.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=sarvi 2890844526 2890844527 IN IP4 192.0.2.12
s=-
c=IN IP4 192.0.2.12
t=0 0
m=application 9 TCP/MRCPv2 1
a=setup:active
a=connection:existing
a=resource:speechsynth
a=cmid:1
m=audio 49170 RTP/AVP 0 96
a=rtpmap:0 pcmu/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=sendrecv
a=mid:1
m=application 9 TCP/MRCPv2 1
a=setup:active
a=connection:existing
a=resource:speechrecog
a=cmid:1
S->C: SIP/2.0 200 OK
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf3;received=192.0.32.10
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314162 INVITE
Contact:<sip:mresources@server.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=- 2890842808 2890842809 IN IP4 192.0.2.11
s=-
c=IN IP4 192.0.2.11
t=0 0
m=application 32416 TCP/MRCPv2 1
a=setup:passive
a=connection:existing
a=channel:32AECB234338@speechsynth
a=cmid:1
m=audio 48260 RTP/AVP 0 96
a=rtpmap:0 pcmu/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=sendrecv
a=mid:1
m=application 32416 TCP/MRCPv2 1
a=setup:passive
a=connection:existing
a=channel:32AECB234338@speechrecog
a=cmid:1
C->S: ACK sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf4
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314162 ACK
Content-Length:0
This example exchange continues from the previous figure and de-allocates the recognizer channel. Since a recognizer no longer needs to receive an audio stream, this interaction also updates the RTP media session to recvonly.
C->S: INVITE sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf5
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314163 INVITE
Contact:<sip:sarvi@client.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=sarvi 2890844526 2890844528 IN IP4 192.0.2.12
s=-
c=IN IP4 192.0.2.12
t=0 0
m=application 9 TCP/MRCPv2 1
a=resource:speechsynth
a=cmid:1
m=audio 49170 RTP/AVP 0
a=rtpmap:0 pcmu/8000
a=recvonly
a=mid:1
m=application 0 TCP/MRCPv2 1
a=resource:speechrecog
a=cmid:1
S->C: SIP/2.0 200 OK
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf5;received=192.0.32.10
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314163 INVITE
Contact:<sip:mresources@server.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=- 2890842808 2890842810 IN IP4 192.0.2.11
s=-
c=IN IP4 192.0.2.11
t=0 0
m=application 32416 TCP/MRCPv2 1
a=channel:32AECB234338@speechsynth
a=cmid:1
m=audio 48260 RTP/AVP 0
a=rtpmap:0 pcmu/8000
a=sendonly
a=mid:1
m=application 0 TCP/MRCPv2 1
a=channel:32AECB234338@speechrecog
a=cmid:1
C->S: ACK sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf6
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:314163 ACK
Content-Length:0
Since MRCPv2 resources either generate or consume media streams, the client or the server needs to associate media sessions with their corresponding resource or resources. More than one resource could be associated with a single media session or each resource could be assigned a separate media session. Also note that more than one media session can be associated with a single resource if need be, but this scenario is not useful for the current set of resources. For example, a synthesizer and a recognizer could be associated to the same media session (m=audio line), if it is opened in "sendrecv" mode. Alternatively, the recognizer could have its own "sendonly" audio session and the synthesizer could have its own "recvonly" audio session.
The association between control channels and their corresponding media sessions is established using a new "resource channel media identifier" media-level attribute ("cmid"). Valid values of this attribute are the values of the "mid" attribute defined in RFC 5888 [RFC5888]. If there is more than 1 audio m-line, then each audio m-line MUST have a "mid" attribute. Each control m-line MAY have one or more "cmid" attributes that match the resource control channel to the "mid" attributes of the audio m-lines it is associated with. Note that if a control m-line does not have a "cmid" attribute it will not be associated with any media. The operations on such a resource will hence be limited. For example, if it was a recognizer resource, the RECOGNIZE method requires an associated media to process while the INTERPRET method does not. The formatting of the "cmid" attribute is described by the following ABNF:
cmid-attribute = "a=cmid:" identification-tag identification-tag = token
To allow this flexible mapping of media sessions to MRCPv2 control channels, a single audio m-line can be associated with multiple resources or each resource can have its own audio m-line. For example, if the client wants to allocate a recognizer and a synthesizer and associate them with a single 2-way audio stream, the SDP offer would contain two control m-lines and a single audio m-line with an attribute of "sendrecv". Each of the control m-lines would have a "cmid" attribute whose value matches the "mid" of the audio m-line. If, on the other hand, the client wants to allocate a recognizer and a synthesizer each with its own separate audio stream, the SDP offer would carry two control m-lines (one for the recognizer and another for the synthesizer) and two audio m-lines (one with the attribute "sendonly" and another with attribute "recvonly"). The "cmid" attribute of the recognizer control m-line would match the "mid" value of the "sendonly" audio m-line and the "cmid" attribute of the synthesizer control m-line would match the "mid" attribute of the "recvonly" m-line.
When a server receives media (e.g. audio) on a media session that is associated with more than one media processing resource, it is the responsibility of the server to receive and fork the media to the resources that need to consume it. If multiple resources in an MRCPv2 session are generating audio (or other media) to be sent on a single associated media session, it is the responsibility of the server to either multiplex the multiple streams onto the single RTP session or contain an embedded RTP mixer (see RFC 3550 [RFC3550]) to combine the multiple streams into one. In the former case, the media stream will contain RTP packets generated by different sources, and hence the packets will have different Synchronization Source identifiers (SSRCs). In the latter case, the RTP packets will contain multiple Contributing Source Identifiers (CSRCs) corresponding to the original streams before being combined by the mixer. An MRCPv2 implementation MUST either multiplex or mix unless it cannot correctly do either, in which case the server MUST disallow the client from associating multiple such resources to a single audio stream by rejecting the SDP offer with a SIP 488 "Not Acceptable" error. Note that there is a large installed base that will return a SIP 501 "Not Implemented" error in this case. To facilitate interoperability with this installed base, new implementations should consider adding configuration to treat a 501 in this context as a 488 when it is received from an element known to be a legacy implementation.
The MRCPv2 messages defined in this document are transported over a TCP, TLS or SCTP (in the future) connection between the client and the server. The method for setting up this transport connection and the resource control channel is discussed in Section 4.1 and Section 4.2. Multiple resource control channels between a client and a server that belong to different SIP dialogs can share one or more TLS, TCP or SCTP connections between them; the server and client MUST support this mode of operation. The individual MRCPv2 messages carry the MRCPv2 channel identifier in their Channel-Identifier header field, which MUST be used to differentiate MRCPv2 messages from different resource channels (see Section 6.2.1 for details). All MRCPv2 servers MUST support TLS. Servers MAY support TCP without TLS in physically secure environments. It is up to the client to choose which mode of transport it wants to use for an MRCPv2 session.
Most examples from here on show only the MRCPv2 messages and do not show the SIP messages that may have been used to establish the MRCPv2 control channel.
If an MRCP client notices that the underlying connection has been closed for one of its MRCP channels, and it has not previously initiated a re-INVITE to close that channel, it MUST send a BYE to close down the SIP dialog and all other MRCP channels. If an MRCP server notices that the underlying connection has been closed for one of its MRCP channels, and it has not previously received and accepted a re-INVITE closing that channel, then it MUST send a BYE to close down the SIP dialog and all other MRCP channels.
MRCPv2 messages are textual using the ISO 10646 character set in the UTF-8 encoding (RFC3629 [RFC3629]) to allow many different languages to be represented. However, to assist in compact representations, MRCPv2 also allows message bodies to be represented in other character sets such as ISO 8859-1 [ISO.8859-1.1987]. This may be useful for languages such as Chinese where the default character set for most documents is not UTF-8. The MRCPv2 protocol headers (the first line of an MRCP message) and header field names use only the US-ASCII subset of UTF-8. Internationalization only applies to certain fields like grammar, results, speech markup etc, and not to MRCPv2 as a whole.
Lines are terminated by CRLF. Also, some parameters in the message may contain binary data or a record spanning multiple lines. Such fields have a length value associated with the parameter, which indicates the number of octets immediately following the parameter.
The MRCPv2 message set consists of requests from the client to the server, responses from the server to the client and asynchronous events from the server to the client. All these messages consist of a start-line, one or more header fields, an empty line (i.e. a line with nothing preceding the CRLF) indicating the end of the header fields, and an optional message body.
generic-message = start-line
message-header
CRLF
[ message-body ]
message-body = *OCTET
start-line = request-line / response-line / event-line
message-header = 1*(generic-header / resource-header / generic-field)
resource-header = synthesizer-header
/ recognizer-header
/ recorder-header
/ verifier-header
The message-body contains resource-specific and message-specific data. The actual Media Types used to carry the data are specified later in the sections defining the individual messages. Generic header fields are described in Section 6.2.
If a message contains a message body, the message MUST contain content-headers indicating the Media Type and encoding of the data in the message body.
Request, response and event messages (described in following sections) include the version of MRCP that the message conforms to. Version compatibility rules follow [H3.1] regarding version ordering, compliance requirements, and upgrading of version numbers. The version information is indicated by "MRCP" (as opposed to "HTTP" in [H3.1]) or "MRCP/2.0" (as opposed to "HTTP/1.1" in [H3.1]). To be compliant with this specification, clients and servers sending MRCPv2 messages MUST indicate an mrcp-version of "MRCP/2.0". ABNF productions using mrcp-version can be found in Section 5.2, Section 5.3, and Section 5.5.
mrcp-version = "MRCP" "/" 1*2DIGIT "." 1*2DIGIT
The message-length field specifies the length of the message in octets, including the start-line, and MUST be the 2nd token from the beginning of the message. This is to make the framing and parsing of the message simpler to do. This field specifies the length of the message including data that may be encoded into the body of the message. Note that this value MAY be printed as a fixed-length integer that is zero-padded in front in order to eliminate or reduce inefficiency in cases where the message-length value would change as a result of the length of the message-length token itself. This value, as with all lengths in MRCP, is to be interpreted as a base-10 number. In particular, leading zeros do not indicate that the value is to be interpreted as a base-8 number.
message-length = 1*19DIGIT
The following sample MRCP exchange demonstrates proper message-length values. The values for message-length have been removed from all other examples in the specification and replaced by '...' to reduce confusion in the case of minor message-length computation errors in those examples.
C->S: MRCP/2.0 877 INTERPRET 543266
Channel-Identifier:32AECB23433801@speechrecog
Interpret-Text:may I speak to Andre Roy
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:661
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C: MRCP/2.0 82 543266 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 634 INTERPRETATION-COMPLETE 543266 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Content-Type:application/nlsml+xml
Content-Length:441
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
All MRCPv2 messages, responses and events MUST carry the Channel-Identifier header field so the server or client can differentiate messages from different control channels that may share the same transport connection.
In the resource-specific header field descriptions in sections 8-11, a header field is disallowed on a method (request, response, or event) for that resource unless specifically listed as being allowed. Also, the phrasing "This header field MAY occur on method X" indicates that the header field is allowed on that method but is not required to be used in every instance of that method.
An MRCPv2 request consists of a Request line followed by the message header section and an optional message body containing data specific to the request message.
The Request message from a client to the server includes within the first line the method to be applied, a method tag for that request and the version of the protocol in use.
request-line = mrcp-version SP message-length SP method-name
SP request-id CRLF
The mrcp-version field is the MRCP protocol version that is being used by the client.
The message-length field specifies the length of the message, including the start-line.
Details about the mrcp-version and message-length fields are given in Section 5.1.
The method-name field identifies the specific request that the client is making to the server. Each resource supports a subset of the MRCPv2 methods. The subset for each resource is defined in the section of the specification for the corresponding resource.
method-name = generic-method
/ synthesizer-method
/ recognizer-method
/ recorder-method
/ verifier-method
The request-id field is a unique identifier representable as an unsigned 32 bit integer created by the client and sent to the server. Consecutive requests within an MRCP session MUST utilize monotonically increasing request-id's. The request-id space is linear, (i.e. not mod(32)) so the space does not wrap and validity can be checked with a simple unsigned comparison operation. The client may choose any initial value for its first request, but a small integer is RECOMMENDED to avoid exhausting the space in long sessions. If the server receives duplicate or out-of-order requests the server MUST reject the request with a response code of 410. Since request-id's are scoped to the MRCP session, they are unique across all TCP connections and all resource channels in the session.
The server resource MUST use the client-assigned identifier in its response to the request. If the request does not complete synchronously, future asynchronous events associated with this request MUST carry the client-assigned request-id.
request-id = 1*10DIGIT
After receiving and interpreting the request message for a method, the server resource responds with an MRCPv2 response message. The response consists of a response line followed by the message header section and an optional message body containing data specific to the method.
response-line = mrcp-version SP message-length SP request-id
SP status-code SP request-state CRLF
The mrcp-version field MUST contain the version of the request if supported; otherwise, it must contain the highest version of the MRCPv2 protocol supported by the server.
The message-length field specifies the length of the message, including the start-line.
Details about the mrcp-version and message-length fields are given in Section 5.1.
The request-id used in the response MUST match the one sent in the corresponding request message.
The status-code field is a 3-digit code representing the success or failure or other status of the request.
status-code = 3DIGIT
The request-state field indicates if the action initiated by the Request is PENDING, IN-PROGRESS or COMPLETE. The COMPLETE status means that the Request was processed to completion and that there will be no more events or other messages from that resource to the client with that request-id. The PENDING status means that the request has been placed on a queue and will be processed in first-in-first-out order. The IN-PROGRESS status means that the request is being processed and is not yet complete. A PENDING or IN-PROGRESS status indicates that further Event messages may be delivered with that request-id.
request-state = "COMPLETE"
/ "IN-PROGRESS"
/ "PENDING"
The status codes are classified under the Success (2XX) codes, Client Failure (4XX) codes, and Server Failure (5XX).
Success Codes
| Code | Meaning |
|---|---|
| 200 | Success |
| 201 | Success with some optional header fields ignored |
Client Failure 4xx Codes
| Code | Meaning |
|---|---|
| 401 | Method not allowed |
| 402 | Method not valid in this state |
| 403 | Unsupported header field |
| 404 | Illegal value for header field. This is the error for a syntax violation. |
| 405 | Resource not allocated for this session or does not exist |
| 406 | Mandatory Header Field Missing |
| 407 | Method or Operation Failed (e.g., Grammar compilation failed in the recognizer. Detailed cause codes might be available through a resource specific header.) |
| 408 | Unrecognized or unsupported message entity |
| 409 | Unsupported Header Field Value. This is a value that is syntactically legal but exceeds the implementation's capabilities or expectations. |
| 410 | Non-Monotonic or Out of order sequence number in request. |
| 411-420 | Reserved for future assignment |
Server Failure 5xx Codes
| Code | Meaning |
|---|---|
| 501 | Server Internal Error |
| 502 | Protocol Version not supported |
| 503 | Reserved for future assignment |
| 504 | Message too large |
The server resource may need to communicate a change in state or the occurrence of a certain event to the client. These messages are used when a request does not complete immediately and the response returns a status of PENDING or IN-PROGRESS. The intermediate results and events of the request are indicated to the client through the event message from the server. The event message consists of an event header line followed by the message header section and an optional message body containing data specific to the event message. The header line has the request-id of the corresponding request and status value. The request-state value is COMPLETE if the request is done and this was the last event, else it is IN-PROGRESS.
event-line = mrcp-version SP message-length SP event-name
SP request-id SP request-state CRLF
The mrcp-version used here is identical to the one used in the Request/Response Line and indicates the version of the MRCPv2 protocol running on the server.
The message-length field specifies the length of the message, including the start-line.
Details about the mrcp-version and message-length fields are given in Section 5.1.
The event-name identifies the nature of the event generated by the media resource. The set of valid event names depends on the resource generating it. See the corresponding resource-specific section of the document.
event-name = synthesizer-event
/ recognizer-event
/ recorder-event
/ verifier-event
The request-id used in the event MUST match the one sent in the request that caused this event.
The request-state indicates whether the Request/Command causing this event is complete or still in progress, and is the same as the one mentioned in Section 5.3. The final event for a request has a COMPLETE status indicating the completion of the request.
MRCPv2 supports a set of methods and header fields that are common to all resources. These are discussed here; resource-specific methods and header fields are discussed in the corresponding resource-specific section of the document.
MRCPv2 supports two generic methods for reading and writing the state associated with a resource.
generic-method = "SET-PARAMS"
/ "GET-PARAMS"
These are described in the following sub-sections.
The SET-PARAMS method, from the client to the server, tells the MRCPv2 resource to define parameters for the session, such as voice characteristics and prosody on synthesizers, recognition timers on recognizers, etc. If the server accepts and sets all parameters it MUST return a response status-code of 200. If it chooses to ignore some optional header fields that can be safely ignored without affecting operation of the server it MUST return 201.
If one or more of the header fields being sent is incorrect, error 403, 404, or 409 MUST be returned as follows:
If both error 404 and another error have occurred, only error 404 MUST be returned. If both errors 403 and 409 have occurred, but not error 404, only error 403 MUST be returned.
If error 403, 404, or 409 is returned, the response MUST include the bad or unsupported header fields and their values exactly as they were sent from the client. Session parameters modified using SET-PARAMS do not override parameters explicitly specified on individual requests or requests that are in-PROGRESS.
C->S: MRCP/2.0 ... SET-PARAMS 543256
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:female
Voice-variant:3
S->C: MRCP/2.0 ... 543256 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
The GET-PARAMS method, from the client to the server, asks the MRCPv2 resource for its current session parameters, such as voice characteristics and prosody on synthesizers, recognition-timer on recognizers, etc. For every header field the client sends in the request without a value, the server MUST include the corresponding header fields and their values in the response. If no parameter header fields are specified by the client then the server MUST return all the settable parameters and their values in the corresponding header section of the response, including vendor-specific parameters. Such wild-card parameter requests can be very processing-intensive, since the number of settable parameters can be large depending on the implementation. Hence, it is RECOMMENDED that the client not use the wildcard GET-PARAMS operation very often. Note that GET-PARAMS returns header field values that apply to the whole session and not values that have a request level scope. For example, Input-Waveform-URI is a request-level header field and thus would not be returned by GET-PARAMS.
If all of the header fields requested are supported, the server MUST return a response status-code of 200. If some of the header fields being retrieved are unsupported for the resource, the server MUST reject the request with a 403 Unsupported Header Field. Such a response MUST include the unsupported header fields exactly as they were sent from the client, without values.
C->S: MRCP/2.0 ... GET-PARAMS 543256
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:
Voice-variant:
Vendor-Specific-Parameters:com.example.param1;
com.example.param2
S->C: MRCP/2.0 ... 543256 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:female
Voice-variant:3
Vendor-Specific-Parameters:com.example.param1="Company Name";
com.example.param2="124324234@example.com"
All MRCPv2 header fields, which include both the generic-headers defined in the following sub-sections and the resource-specific header fields defined later, follow the same generic format as that given in Section 3.1 of RFC5322 [RFC5322]. Each header field consists of a name followed by a colon (":") and the value. Header field names are case-insensitive. The value MAY be preceded by any amount of LWS (linear white space), though a single SP (space) is preferred. Header fields may extend over multiple lines by preceding each extra line with at least one SP or HT (horizontal tab).
generic-field = field-name ":" [ field-value ]
field-name = token
field-value = *LWS field-content *( CRLF 1*LWS field-content)
field-content = <the OCTETs making up the field-value
and consisting of either *TEXT or combinations
of token, separators, and quoted-string>
The field-content does not include any leading or trailing LWS (i.e. linear white space occurring before the first non-whitespace character of the field-value or after the last non-whitespace character of the field-value). Such leading or trailing LWS MAY be removed without changing the semantics of the field value. Any LWS that occurs between field-content MAY be replaced with a single SP before interpreting the field value or forwarding the message downstream.
MRCPv2 servers and clients MUST NOT depend on header field order. It is "good practice" to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header fields. However, MRCPv2 servers and clients MUST be prepared to process the header fields in any order. The only exception to this rule is when there are multiple header fields with the same name in a message.
Multiple header fields with the same name MAY be present in a message if and only if the entire value for that header field is defined as a comma-separated list [i.e., #(values)].
Since vendor-specific parameters may be order-dependent, it MUST be possible to combine multiple header fields of the same name into one "name:value" pair without changing the semantics of the message, by appending each subsequent value to the first, each separated by a comma. The order in which header fields with the same name are received is therefore significant to the interpretation of the combined header field value, and thus an intermediary MUST NOT change the order of these values when a message is forwarded.
generic-header = channel-identifier
/ accept
/ active-request-id-list
/ proxy-sync-id
/ accept-charset
/ content-type
/ content-id
/ content-base
/ content-encoding
/ content-location
/ content-length
/ fetch-timeout
/ cache-control
/ logging-tag
/ set-cookie
/ set-cookie2
/ vendor-specific
All MRCPv2 requests, responses and events MUST contain the Channel-Identifier header field. The value is allocated by the server when a control channel is added to the session and communicated to the client by the "a=channel" attribute in the SDP answer from the server. The header field value consists of 2 parts separated by the '@' symbol. The first part is an unambiguous string identifying the MRCPv2 session. The second part is a string token which specifies one of the media processing resource types listed in Section 3.1. The unambiguous string (first part) MUST be unique among the resource instances managed by the server and is common to all resource channels with that server established through a single SIP dialog.
channel-identifier = "Channel-Identifier" ":" channel-id CRLF channel-id = 1*alphanum "@" 1*alphanum
The Accept header field follows the syntax defined in [H14.1]. The semantics are also identical, with the exception that if no Accept header field is present, the server MUST assume a default value that is specific to the resource type that is being controlled. This default value can be changed for a resource on a session by sending this header field in a SET-PARAMS method. The current default value of this header field for a resource in a session can be found through a GET-PARAMS method. This header field MAY occur on any request.
In a request, this header field indicates the list of request-ids to which the request applies. This is useful when there are multiple requests that are PENDING or IN-PROGRESS and the client wants this request to apply to one or more of these specifically.
In a response, this header field returns the list of request-ids that the method modified or affected. There could be one or more requests in a request-state of PENDING or IN-PROGRESS. When a method affecting one or more PENDING or IN-PROGRESS requests is sent from the client to the server, the response MUST contain the list of request-ids that were affected or modified by this command in its header section.
The Active-Request-Id-List is only used in requests and responses, not in events.
For example, if a STOP request with no Active-Request-Id-List is sent to a synthesizer resource which has one or more SPEAK requests in the PENDING or IN-PROGRESS state, all SPEAK requests MUST be cancelled, including the one IN-PROGRESS. The response to the STOP request contains in the Active-Request-Id-List value the request-ids of all the SPEAK requests that were terminated. After sending the STOP response, the server MUST NOT send any SPEAK-COMPLETE or RECOGNITION-COMPLETE events for the terminated requests.
active-request-id-list = "Active-Request-Id-List" ":"
request-id *("," request-id) CRLF
When any server resource generates a barge-in-able event, it also generates a unique tag. The tag is sent as this header field's value in an event to the client. The client then acts as a intermediary among the server resources and sends a BARGE-IN-OCCURRED method to the synthesizer server resource with the Proxy-Sync-Id it received from the server resource. When the recognizer and synthesizer resources are part of the same session, they may choose to work together to achieve quicker interaction and response. Here the Proxy-Sync-Id helps the resource receiving the event, intermediated by the client, to decide if this event has been processed through a direct interaction of the resources. This header field MAY occur only on events and the BARGE-IN-OCCURRED method. The name of this header field contains the word 'proxy' only for historical reasons and does not imply that a proxy server is involved.
proxy-sync-id = "Proxy-Sync-Id" ":" 1*VCHAR CRLF
See [H14.2]. This specifies the acceptable character sets for entities returned in the response or events associated with this request. This is useful in specifying the character set to use in the Natural Language Semantic Markup Language (NLSML) results of a RECOGNITION-COMPLETE event. This header field is only used on requests.
See [H14.17]. MRCPv2 supports a restricted set of registered Media Types for content, including speech markup, grammar, and recognition results. The content types applicable to each MRCPv2 resource-type are specified in the corresponding section of the document and are registered in the MIME Media Types registry maintained by IANA. The multi-part content type "multi-part/mixed" is supported to communicate multiple of the above mentioned contents, in which case the body parts MUST NOT contain any MRCPv2 specific header fields. This header field MAY occur on all messages.
content-type = "Content-Type" ":" media-type-value CRLF
media-type-value = type "/" subtype *( ";" parameter )
type = token
subtype = token
parameter = attribute "=" value
attribute = token
value = token / quoted-string
This header field contains an ID or name for the content by which it can be referenced. This header field operates according to the specification in RFC 2392 [RFC2392] and is required for content disambiguation in multi-part messages. In MRCPv2 whenever the associated content is stored, by either the client or the server, it MUST be retrievable using this ID. Such content can be referenced later in a session by addressing it with the "session" URI scheme described in Section 13.6. This header field MAY occur on all messages.
The content-base entity-header may be used to specify the base URI for resolving relative URIs within the entity.
content-base = "Content-Base" ":" absoluteURI CRLF
Note, however, that the base URI of the contents within the entity-body may be redefined within that entity-body. An example of this would be multi-part media, which in turn can have multiple entities within it. This header field MAY occur on all messages.
The Content-Encoding entity-header is used as a modifier to the Content-Type. When present, its value indicates what additional content encoding has been applied to the entity-body, and thus what decoding mechanisms must be applied in order to obtain the Media Type referenced by the Content-Type header field. Content-Encoding is primarily used to allow a document to be compressed without losing the identity of its underlying media type. Note that the SDP session can be used to determine accepted encodings (see Section 7). This header field MAY occur on all messages.
content-encoding = "Content-Encoding" ":"
*WSP content-coding
*(*WSP "," *WSP content-coding *WSP )
CRLF
Content-Encoding is defined in [H3.5]. An example of its use is
Content-Encoding:gzip
If multiple encodings have been applied to an entity, the content encodings MUST be listed in the order in which they were applied.
The Content-Location entity-header MAY be used to supply the resource location for the entity enclosed in the message when that entity is accessible from a location separate from the requested resource's URI. Refer to [H14.14].
content-location = "Content-Location" ":"
( absoluteURI / relativeURI ) CRLF
The Content-Location value is a statement of the location of the resource corresponding to this particular entity at the time of the request. This header field is provided for optimization purposes only. The receiver of this header field MAY assume that the entity being sent is identical to what would have been retrieved or might already have been retrieved from the Content-Location URI.
For example, if the client provided a grammar markup inline, and it had previously retrieved it from a certain URI, that URI can be provided as part of the entity, using the content-location header field. This allows a resource like the recognizer to look into its cache to see if this grammar was previously retrieved, compiled and cached. In this case, it might optimize by using the previously compiled grammar object.
If the content-location is a relative URI, the relative URI is interpreted relative to the content-base URI. This header field MAY occur on all messages.
This header field contains the length of the content of the message body (i.e. after the double CRLF (carriage return, then line feed) following the last header field). Unlike in HTTP, it MUST be included in all messages that carry content beyond the header section. If it is missing, a default value of zero is assumed. Otherwise, it is interpreted according to [H14.13]. When a message having no use for a message body contains one, i.e. the Content-Length is non-zero, the receiver MUST ignore the content of the message body. This header field MAY occur on all messages.
content-length = "Content-Length" ":" 1*19DIGIT CRLF
When the recognizer or synthesizer needs to fetch documents or other resources this header field controls the corresponding URI access properties. This defines the timeout for content that the server may need to fetch over the network. The value is interpreted to be in milliseconds and ranges from 0 to an implementation-specific maximum value. The default value for this header field is implementation-specific. This header field MAY occur in DEFINE-GRAMMAR, RECOGNIZE, SPEAK, SET-PARAMS or GET-PARAMS.
fetch-timeout = "Fetch-Timeout" ":" 1*19DIGIT CRLF
If the server implements content caching, it MUST adhere to the cache correctness rules of HTTP 1.1 [RFC2616] when accessing and caching stored content. In particular, the "expires" and "cache-control" header fields of the cached URI or document MUST be honored and take precedence over the Cache-Control defaults set by this header field. The Cache-Control directives are used to define the default caching algorithms on the server for the session or request. The scope of the directive is based on the method it is sent on. If the directive is sent on a SET-PARAMS method, it applies for all requests for external documents the server makes during that session, unless overridden by a Cache-Control header field on an individual request. If the directives are sent on any other requests they apply only to external document requests the server makes for that request. An empty Cache-Control header field on the GET-PARAMS method is a request for the server to return the current Cache-Control directives setting on the server. This header field MAY occur only on requests.
cache-control = "Cache-Control" ":"
[*WSP cache-directive
*( *WSP "," *WSP cache-directive *WSP )]
CRLF
cache-directive = "max-age" "=" delta-seconds
/ "max-stale" [ "=" delta-seconds ]
/ "min-fresh" "=" delta-seconds
delta-seconds = 1*19DIGIT
Here delta-seconds is a decimal time value specifying the number of seconds since the instant the message response or data was received by the server.
The different cache-directive options allow the client to ask the server to override the default cache expiration mechanisms:
The server cache MAY be requested to use stale response/data without validation, but only if this does not conflict with any "MUST"-level requirements concerning cache validation (e.g., a "must-revalidate" Cache-Control directive in the HTTP 1.1 specification pertaining to the corresponding URI).
If both the MRCPv2 Cache-Control directive and the cached entry on the server include "max-age" directives, then the lesser of the two values is used for determining the freshness of the cached entry for that request.
This header field MAY be sent as part of a SET-PARAMS/GET-PARAMS method to set or retrieve the logging tag for logs generated by the server. Once set, the value persists until a new value is set or the session ends. The MRCPv2 server MAY provide a mechanism to subset its output logs so that system administrators can examine or extract only the log file portion during which the logging tag was set to a certain value.
It is RECOMMENDED that clients have some identifying information in the logging tag, so that one can determine which client request generated a given log message at the server.
logging-tag = "Logging-Tag" ":" 1*UTFCHAR CRLF
Since the associated HTTP client on an MRCPv2 server fetches documents for processing on behalf of the MRCPv2 client, the cookie store in the HTTP client of the MRCPv2 server is treated as an extension of the cookie store in the HTTP client of the MRCPv2 client. This requires that the MRCPv2 client and server be able to synchronize their common cookie store as needed. To enable the MRCPv2 client to push its stored cookies to the MRCPv2 server and get new cookies from the MRCPv2 server stored back to the MRCPv2 client, the Set-Cookie and Set-Cookie2 entity-header fields MAY be included in MRCPv2 requests to update the cookie store on a server and be returned in final MRCPv2 responses or events to subsequently update the client's own cookie store. The stored cookies on the server persist for the duration of the MRCPv2 session and MUST be destroyed at the end of the session. To ensure support for the type of cookie header field dictated by the HTTP origin server, MRCPv2 clients and servers MUST support both the Set-Cookie and Set-Cookie2 entity header fields.
set-cookie = "Set-Cookie:" cookies CRLF
cookies = cookie *("," *LWS cookie)
cookie = attribute "=" value *(";" cookie-av)
cookie-av = "Comment" "=" value
/ "Domain" "=" value
/ "Max-Age" "=" value
/ "Path" "=" value
/ "Secure"
/ "Version" "=" 1*19DIGIT
/ "Age" "=" delta-seconds
set-cookie2 = "Set-Cookie2:" cookies2 CRLF
cookies2 = cookie2 *("," *LWS cookie2)
cookie2 = attribute "=" value *(";" cookie-av2)
cookie-av2 = "Comment" "=" value
/ "CommentURL" "=" DQUOTE uri DQUOTE
/ "Discard"
/ "Domain" "=" value
/ "Max-Age" "=" value
/ "Path" "=" value
/ "Port" [ "=" DQUOTE portlist DQUOTE ]
/ "Secure"
/ "Version" "=" 1*19DIGIT
/ "Age" "=" delta-seconds
portlist = portnum *("," *LWS portnum)
portnum = 1*19DIGIT
The Set-Cookie and Set-Cookie2 header fields are specified in RFC 2109 [RFC2109] and RFC 2965 [RFC2965], respectively. The "Age" attribute is introduced in this specification to indicate the age of the cookie and is optional. An MRCPv2 client or server MUST calculate the age of the cookie according to the age calculation rules in the HTTP/1.1 specification [RFC2616] and append the "Age" attribute accordingly.
The MRCPv2 client or server MUST supply defaults for the "Domain" and "Path" attributes if omitted by the HTTP origin server as specified in RFC 2109 (set-cookie) and RFC 2965 (set-cookie2). Note that there is no leading dot present in the "Domain" attribute value in this case. Although an explicitly specified "Domain" value received via the HTTP protocol may be modified to include a leading dot, an MRCPv2 client or server MUST NOT modify the "Domain" value when received via the MRCPv2 protocol.
An MRCPv2 client or server MAY combine multiple cookie header fields of the same type into a single "field-name:field-value" pair as described in Section 6.2.
The Set-Cookie and Set-Cookie2 header fields MAY be specified in any request that subsequently results in the server performing an HTTP access. When a server receives new cookie information from an HTTP origin server, and assuming the cookie store is modified according RFC 2109 or RFC 2965, the server MUST return the new cookie information in the MRCPv2 COMPLETE response or event as appropriate to allow the client to update its own cookie store.
The SET-PARAMS request MAY specify the Set-Cookie and Set-Cookie2 header fields to update the cookie store on a server. The GET-PARAMS request MAY be used to return the entire cookie store of "Set-Cookie" or "Set-Cookie2" type cookies to the client.
This set of header fields allows for the client to set or retrieve Vendor Specific parameters.
vendor-specific = "Vendor-Specific-Parameters" ":"
[vendor-specific-av-pair
*(";" vendor-specific-av-pair)] CRLF
vendor-specific-av-pair = vendor-av-pair-name "="
value
vendor-av-pair-name = 1*UTFCHAR
Header fields of this form MAY be sent in any method (request) and are used to manage implementation-specific parameters on the server side. The vendor-av-pair-name follows the reverse Internet Domain Name convention (see Section 13.1.6 for syntax and registration information). The value of the vendor attribute is specified after the "=" symbol and MAY be quoted. For example:
com.example.companyA.paramxyz=256 com.example.companyA.paramabc=High com.example.companyB.paramxyz=Low
When used in GET-PARAMS to get the current value of these parameters from the server, this header field value may contain a semicolon-separated list of implementation-specific attribute names.
Result data from the server for the Recognizer and Verifier resources is carried as a typed media entity in the MRCPv2 message body of various events. The Natural Language Semantics Markup Language (NLSML), an XML markup based on an early draft from the W3C, is the default standard for returning results back to the client. Hence, all servers implementing these resource types MUST support the Media Type application/nlsml+xml. The Extensible MultiModal Annotation (EMMA) [W3C.REC-emma-20090210] format can be used to return results as well. This can be done by negotiating the format at session establishment time with SDP (a=resultformat:application/emma+xml) or with SIP (Allow/Accept). With SIP, for example, if a client wants results in EMMA, an MRCPv2 server can route the request to another server that supports EMMA by inspecting the SIP header fields, rather than having to introspect into the SDP.
MRCPv2 uses this representation to convey content among the clients and servers that generate and make use of the markup. MRCPv2 uses NSLML specifically to convey recognition, enrollment, and verification results between the corresponding resource on the MRCPv2 server and the MRCPv2 client. Details of this result format are fully described in Section 6.3.1.
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="http://theYesNoGrammar">
<interpretation>
<instance>
<ex:response>yes</ex:response>
</instance>
<input>ok</input>
</interpretation>
</result>
The Natural Language Semantics Markup Language (NLSML) is an XML data structure with elements and attributes designed to carry result information from recognizer (including enrollment) and verifier resources. The normative definition of NLSML is the RelaxNG schema in Section 16.1. Note that the elements and attributes of this format are defined in the MRCPv2 namespace. In the result structure, they must either be prefixed by a namespace prefix declared within the result or must be children of an element identified as belonging to the respective namespace. For details on how to use XML Namespaces, see [W3C.REC-xml-names11-20040204]. Section 2 of [W3C.REC-xml-names11-20040204] provides details on how to declare namespaces and namespace prefixes.
The root element of NLSML is <result>. Optional child elements are <interpretation>, <enrollment-result>, and <verification-result>, at least one of which must be present. A single <result> may contain all of the optional child elements. Details of the <result> and <interpretation> elements and their subelements and attributes can be found in Section 9.6. Details of the <enrollment-result> element and its subelements can be found in Section 9.7. Details of the <verification-result> element and its subelements can be found in Section 11.5.2.
Server resources may be discovered and their capabilities learned by clients through standard SIP machinery. The client MAY issue a SIP OPTIONS transaction to a server, which has the effect of requesting the capabilities of the server. The server MUST respond to such a request with an SDP-encoded description of its capabilities according to RFC3264 [RFC3264]. The MRCPv2 capabilities are described by a single m-line containing the media type "application" and transport type "TCP/TLS/MRCPv2" or "TCP/MRCPv2". There MUST be one "resource" attribute for each media resource that the server supports with the resource type identifier as its value.
The SDP description MUST also contain m-lines describing the audio capabilities and the coders the server supports.
In this example, the client uses the SIP OPTIONS method to query the capabilities of the MRCPv2 server.
C->S:
OPTIONS sip:mrcp@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf7
Max-Forwards:6
To:<sip:mrcp@example.com>
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:63104 OPTIONS
Contact:<sip:sarvi@client.example.com>
Accept:application/sdp
Content-Length:0
S->C:
SIP/2.0 200 OK
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bf7;received=192.0.32.10
To:<sip:mrcp@example.com>;tag=62784
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:63104 OPTIONS
Contact:<sip:mrcp@server.example.com>
Allow:INVITE, ACK, CANCEL, OPTIONS, BYE
Accept:application/sdp
Accept-Encoding:gzip
Accept-Language:en
Supported:foo
Content-Type:application/sdp
Content-Length:...
v=0
o=sarvi 2890844536 2890842811 IN IP4 192.0.2.12
s=-
i=MRCPv2 server capabilities
c=IN IP4 192.0.2.12/127
t=0 0
m=application 0 TCP/TLS/MRCPv2 1
a=resource:speechsynth
a=resource:speechrecog
a=resource:speakverify
m=audio 0 RTP/AVP 0 3
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
This resource processes text markup provided by the client and generates a stream of synthesized speech in real-time. Depending upon the server implementation and capability of this resource, the client can also dictate parameters of the synthesized speech such as voice characteristics, speaker speed, etc.
The synthesizer resource is controlled by MRCPv2 requests from the client. Similarly, the resource can respond to these requests or generate asynchronous events to the client to indicate conditions of interest to the client during the generation of the synthesized speech stream.
This section applies for the following resource types:
The capabilities of these resources are defined in Section 3.1.
The synthesizer maintains a state machine to process MRCPv2 requests from the client. The state transitions shown below describe the states of the synthesizer and reflect the state of the request at the head of the synthesizer resource queue. A SPEAK request in the PENDING state can be deleted or stopped by a STOP request without affecting the state of the resource.
Idle Speaking Paused State State State | | | |----------SPEAK-------->| |--------| |<------STOP-------------| CONTROL | |<----SPEAK-COMPLETE-----| |------->| |<----BARGE-IN-OCCURRED--| | | |---------| | | CONTROL |-----------PAUSE--------->| | |-------->|<----------RESUME---------| | | |----------| |----------| | PAUSE | | BARGE-IN-OCCURRED | |--------->| |<---------| |----------| | | | SPEECH-MARKER | | |<---------| | |----------| |----------| | | STOP | RESUME | | | |<---------| | |<---------| | | |<---------------------STOP-------------------------| |----------| | | | DEFINE-LEXICON | | | | | | |<---------| | | |<---------------BARGE-IN-OCCURRED------------------|
The synthesizer supports the following methods.
synthesizer-method = "SPEAK"
/ "STOP"
/ "PAUSE"
/ "RESUME"
/ "BARGE-IN-OCCURRED"
/ "CONTROL"
/ "DEFINE-LEXICON"
The synthesizer may generate the following events.
synthesizer-event = "SPEECH-MARKER"
/ "SPEAK-COMPLETE"
A synthesizer method may contain header fields containing request options and information to augment the Request, Response or Event it is associated with.
synthesizer-header = jump-size
/ kill-on-barge-in
/ speaker-profile
/ completion-cause
/ completion-reason
/ voice-parameter
/ prosody-parameter
/ speech-marker
/ speech-language
/ fetch-hint
/ audio-fetch-hint
/ failed-uri
/ failed-uri-cause
/ speak-restart
/ speak-length
/ load-lexicon
/ lexicon-search-order
This header field MAY be specified in a CONTROL method and controls the amount to jump forward or backward in an active SPEAK request. A + or - indicates a relative value to what is being currently played. This header field MAY also be specified in a "SPEAK" request as a desired offset into the synthesized speech. In this case, the synthesizer MUST begin speaking from this amount of time into the speech markup. Note that an offset that extends beyond the end of the produced speech will result in audio of length zero. The different speech length units supported are dependent on the synthesizer implementation. If the synthesizer resource does not support a unit or the operation, the resource MUST respond with a status-code of 409 "Unsupported Header Field Value".
jump-size = "Jump-Size" ":" speech-length-value CRLF
speech-length-value = numeric-speech-length
/ text-speech-length
text-speech-length = 1*UTFCHAR SP "Tag"
numeric-speech-length = ("+" / "-") positive-speech-length
positive-speech-length = 1*19DIGIT SP numeric-speech-unit
numeric-speech-unit = "Second"
/ "Word"
/ "Sentence"
/ "Paragraph"
This header field MAY be sent as part of the SPEAK method to enable kill-on-barge-in support. If enabled, the SPEAK method is interrupted by DTMF input detected by a signal detector resource or by the start of speech sensed or recognized by the speech recognizer resource.
kill-on-barge-in = "Kill-On-Barge-In" ":" BOOLEAN CRLF
The client MUST send a BARGE-IN-OCCURRED method to the synthesizer resource when it receives a barge-in-able event from any source. This source could be a synthesizer resource or signal detector resource and MAY be either local or distributed. If this header field is not specified in a SPEAK request or explicitly set by a SET-PARAMS, the default value for this header field is "true".
If the recognizer or signal detector resource is on the same server as the synthesizer and both are part of the same session, the server MAY work with both to provide internal notification to the synthesizer so that audio may be stopped without having to wait for the client's BARGE-IN-OCCURRED event.
It is generally RECOMMENDED when playing a prompt to the user with Kill-On-Barge-In and asking for input, that the client issue the RECOGNIZE request ahead of the SPEAK request for optimum performance and user experience. This way, it is guaranteed that the recognizer is online before the prompt starts playing and the user's speech will not be truncated at the beginning (especially for power users).
This header field MAY be part of the SET-PARAMS/GET-PARAMS or SPEAK request from the client to the server and specifies a URI which references the profile of the speaker. Speaker profiles are collections of voice parameters like gender, accent etc.
speaker-profile = "Speaker-Profile" ":" uri CRLF
This header field MUST be specified in a SPEAK-COMPLETE event coming from the synthesizer resource to the client. This indicates the reason the SPEAK request completed.
completion-cause = "Completion-Cause" ":" 3DIGIT SP
1*VCHAR CRLF
| Cause-Code | Cause-Name | Description |
|---|---|---|
| 000 | normal | SPEAK completed normally. |
| 001 | barge-in | SPEAK request was terminated because of barge-in. |
| 002 | parse-failure | SPEAK request terminated because of a failure to parse the speech markup text. |
| 003 | uri-failure | SPEAK request terminated because access to one of the URIs failed. |
| 004 | error | SPEAK request terminated prematurely due to synthesizer error. |
| 005 | language-unsupported | Language not supported. |
| 006 | lexicon-load-failure | Lexicon loading failed. |
| 007 | cancelled | A prior SPEAK request failed while this one was still in the queue. |
This header field MAY be specified in a SPEAK-COMPLETE event coming from the synthesizer resource to the client. This contains the reason text behind the SPEAK request completion. This header field communicates text describing the reason for the failure, such as an error in parsing the speech markup text.
completion-reason = "Completion-Reason" ":"
quoted-string CRLF
The completion reason text is provided for client use in logs and for debugging and instrumentation purposes. Clients MUST NOT interpret the completion reason text.
This set of header fields defines the voice of the speaker.
voice-parameter = voice-gender
/ voice-age
/ voice-variant
/ voice-name
voice-gender = "Voice-Gender:" voice-gender-value CRLF
voice-gender-value = "male"
/ "female"
/ "neutral"
voice-age = "Voice-Age:" 1*3DIGIT CRLF
voice-variant = "Voice-Variant:" 1*19DIGIT CRLF
voice-name = "Voice-Name:"
1*UTFCHAR *(1*WSP 1*UTFCHAR) CRLF
The Voice- parameters are derived from the similarly-named attributes of the voice element specified in W3C's Speech Synthesis Markup Language Specification (SSML) [W3C.REC-speech-synthesis-20040907]. Legal values for these parameters are as defined in that specification.
These header fields MAY be sent in SET-PARAMS/GET-PARAMS request to define/get default values for the entire session or MAY be sent in the SPEAK request to define default values for that speak request. Note that SSML content can itself set these values internal to the SSML document, of course.
Voice parameter header fields MAY also be sent in a CONTROL method to affect a SPEAK request in progress and change its behavior on the fly. If the synthesizer resource does not support this operation, it MUST reject the request with a status-code of 403 "Unsupported Header Field".
This set of header fields defines the prosody of the speech.
prosody-parameter = "Prosody-" prosody-param-name ":"
prosody-param-value CRLF
prosody-param-name = 1*VCHAR
prosody-param-value = 1*VCHAR
prosody-param-name is any one of the attribute names under the prosody element specified in W3C's Speech Synthesis Markup Language Specification [W3C.REC-speech-synthesis-20040907]. The prosody-param-value is any one of the value choices of the corresponding prosody element attribute specified in the above section.
These header fields MAY be sent in SET-PARAMS/GET-PARAMS request to define/get default values for the entire session or MAY be sent in the SPEAK request to define default values for that speak request. Furthermore, these attributes can be part of the speech text marked up in SSML.
The prosody parameter header fields in the SET-PARAMS or SPEAK request only apply if the speech data is of type text/plain and does not use a speech markup format.
These prosody parameter header fields MAY also be sent in a CONTROL method to affect a SPEAK request in progress and change its behavior on the fly. If the synthesizer resource does not support this operation, it MUST respond back to the client with a status-code of 403 "Unsupported Header Field".
This header field contains timestamp information in a "timestamp" field. This is a Network Time Protocol (NTP) [RFC5905] timestamp, a 64 bit number in decimal form. It MUST be synced with the Real-Time Protocol (RTP) [RFC3550] timestamp of the media stream through the Real-Time Control Protocol (RTCP) [RFC3550].
Markers are bookmarks that are defined within the markup. Most speech markup formats provide mechanisms to embed marker fields within speech texts. The synthesizer generates SPEECH-MARKER events when it reaches these marker fields. This header field MUST be part of the SPEECH-MARKER event and contain the marker tag value after the timestamp, separated by a semicolon. In these events the timestamp marks the time the text corresponding to the marker was emitted as speech by the synthesizer.
This header field MUST also be returned in responses to STOP, CONTROL, and BARGE-IN-OCCURRED methods, in the SPEAK-COMPLETE event, and in an IN-PROGRESS SPEAK response. In these messages, if any markers have been encountered for the current SPEAK, the marker tag value MUST be the last embedded marker encountered. If no markers have yet been encountered for the current SPEAK, only the timestamp is REQUIRED. Note than in these events the purpose of this header field is to provide timestamp information associated with important events within the lifecycle of a request (start of SPEAK processing, end of SPEAK processing, receipt of CONTROL/STOP/BARGE-IN-OCCURRED).
timestamp = "timestamp" "=" time-stamp-value
time-stamp-value = 1*20DIGIT
speech-marker = "Speech-Marker" ":"
timestamp
[";" 1*(UTFCHAR / %x20)] CRLF
This header field specifies the default language of the speech data if the language is not specified in the markup. The value of this header field MUST follow RFC 5646 [RFC5646] for its values. The header field MAY occur in SPEAK, SET-PARAMS or GET-PARAMS requests.
speech-language = "Speech-Language" ":" 1*VCHAR CRLF
When the synthesizer needs to fetch documents or other resources like speech markup or audio files, this header field controls the corresponding URI access properties. This provides client policy on when the synthesizer should retrieve content from the server. A value of "prefetch" indicates the content MAY be downloaded when the request is received, whereas "safe" indicates that content MUST NOT be downloaded until actually referenced. The default value is "prefetch". This header field MAY occur in SPEAK, SET-PARAMS or GET-PARAMS requests.
fetch-hint = "Fetch-Hint" ":" ("prefetch" / "safe") CRLF
When the synthesizer needs to fetch documents or other resources like speech audio files, this header field controls the corresponding URI access properties. This provides client policy whether or not the synthesizer may attempt to optimize speech by pre-fetching audio. The value is either "safe" to say that audio is only fetched when it is referenced, never before; "prefetch" to permit, but not require the implementation to pre-fetch the audio; or "stream" to allow it to stream the audio fetches. The default value is "prefetch". This header field MAY occur in SPEAK, SET-PARAMS or GET-PARAMS requests.
audio-fetch-hint = "Audio-Fetch-Hint" ":"
("prefetch" / "safe" / "stream") CRLF
When a synthesizer method needs a synthesizer to fetch or access a URI and the access fails, the server SHOULD provide the failed URI in this header field in the method response, unless there are multiple URI failures, in which case one of the failed URIs MUST be provided in this header field in the method response.
failed-uri = "Failed-URI" ":" absoluteURI CRLF
When a synthesizer method needs a synthesizer to fetch or access a URI and the access fails the server MUST provide the URI-specific or protocol-specific response code for the URI in the Failed-URI header field in the method response through this header field. The value encoding is UTF-8 (RFC3629 [RFC3629]) to accommodate any access protocol, some of which might have a response string instead of a numeric response code.
failed-uri-cause = "Failed-URI-Cause" ":" 1*UTFCHAR CRLF
When a CONTROL request to jump backward is issued to a currently speaking synthesizer resource, and the target jump point is before the start of the current SPEAK request, the current SPEAK request MUST restart from the beginning of its speech data and the response to the CONTROL request MUST contain this header field with a value of "true" indicating a restart.
speak-restart = "Speak-Restart" ":" BOOLEAN CRLF
This header field MAY be specified in a CONTROL method to control the length of speech to speak, relative to the current speaking point in the currently active SPEAK request. If numeric, the value MUST be a positive integer. If a header field with a Tag unit is specified, then the speech output continues until the tag is reached or the SPEAK request complete, whichever comes first. This header field MAY be specified in a SPEAK request to indicate the length to speak from the speech data and is relative to the point in speech that the SPEAK request starts. The different speech length units supported are synthesizer implementation dependent. If a server does not support the specified unit, the resource MUST respond with a status-code of 409 "Unsupported Header Field Value".
speak-length = "Speak-Length" ":" positive-length-value
CRLF
positive-length-value = positive-speech-length
/ text-speech-length
text-speech-length = 1*UTFCHAR SP "Tag"
positive-speech-length = 1*19DIGIT SP numeric-speech-unit
numeric-speech-unit = "Second"
/ "Word"
/ "Sentence"
/ "Paragraph"
This header field is used to indicate whether a lexicon has to be loaded or unloaded. The default value for this header field is "true". This header field MAY be specified in a DEFINE-LEXICON method.
load-lexicon = "Load-Lexicon" ":" BOOLEAN CRLF
This header field is used to specify a list of active pronunciation lexicon URIs and the search order among the active lexicons. Lexicons specified within the SSML document take precedence over the lexicons specified in this header field. This header field MAY be specified in the SPEAK, SET-PARAMS, and GET-PARAMS methods.
lexicon-search-order = "Lexicon-Search-Order" ":"
"<" absoluteURI ">" *(" " "<" absoluteURI ">") CRLF
A synthesizer message may contain additional information associated with the Request, Response or Event in its message body.
Marked-up text for the synthesizer to speak is specified as a typed media entity in the message body. The speech data to be spoken by the synthesizer can be specified inline by embedding the data in the message body or by reference by providing a URI for accessing the data. In either case the data and the format used to markup the speech needs to be of a content type supported by the server.
All MRCPv2 servers containing synthesizer resources MUST support both plain text speech data and W3C's Speech Synthesis Markup Language [W3C.REC-speech-synthesis-20040907] and hence MUST support the Media Types text/plain and application/ssml+xml. Other formats MAY be supported.
If the speech data is to be fetched by URI reference, the Media Type text/uri-list (see RFC2483 [RFC2483] ) is used to indicate one or more URIs that, when dereferenced, will contain the content to be spoken. If a list of speech URIs is specified, speech data provided by each URI MUST be spoken in the order in which the URIs are specified in the content.
A mix of URI and inline speech data MAY be indicated through the multipart/mixed Media Type, and MRCPv2 clients and servers MUST support the multipart/mixed Media Type. Embedded within the multipart there MAY be content for the text/uri-list, application/ssml+xml and/or text/plain media types. The character set and encoding used in the speech data is specified according to standard Media Type definitions. The multi-part content MAY also contain actual audio data. Clients may have recorded audio clips stored in memory or on a local device and wish to play it as part of the SPEAK request. The audio portions MAY be sent by the client as part of the multi-part content block. This audio is referenced in the speech markup data that is another part in the multi-part content block according to the multipart/mixed Media Type specification.
Content-Type:text/uri-list Content-Length:... http://www.example.com/ASR-Introduction.ssml http://www.example.com/ASR-Document-Part1.ssml http://www.example.com/ASR-Document-Part2.ssml http://www.example.com/ASR-Conclusion.ssml
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Aldine Turnbet
and arrived at <break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is <prosody
rate="-20%">ski trip</prosody></s>
</p>
</speak>
Content-Type:multipart/mixed; boundary="break"
--break
Content-Type:text/uri-list
Content-Length:...
http://www.example.com/ASR-Introduction.ssml
http://www.example.com/ASR-Document-Part1.ssml
http://www.example.com/ASR-Document-Part2.ssml
http://www.example.com/ASR-Conclusion.ssml
--break
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams
and arrived at <break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is <prosody
rate="-20%">ski trip</prosody></s>
</p>
</speak>
--break--
Synthesizer lexicon data from the client to the server can be provided inline or by reference. Either way they are carried as typed media in the message body of the MRCPv2 request message (see Section 8.14).
When a lexicon is specified in-line in the message, the client MUST provide a Content-ID for that lexicon as part of the content header fields. The server MUST store the lexicon associated with that Content-ID for the duration of the session. A stored lexicon can be overwritten by defining a new lexicon with the same Content-ID. Lexicons that have been associated with a Content-ID can be referenced through the "session" URI scheme (see Section 13.6).
If lexicon data is specified by external URI reference, the Media Type text/uri-list (see RFC2483 [RFC2483] ) is used to list the one or more URIs that may be dereferenced to obtain the lexicon data. All MRCPv2 servers MUST support the HTTP and HTTPS uri access mechanisms, and MAY support other mechanisms.
If the data in the message body consists of a mix of URI and inline lexicon data the multipart/mixed Media Type is used. The character set and encoding used in the lexicon data may be specified according to standard Media Type definitions.
The SPEAK Request provides the synthesizer resource with the speech text and initiates speech synthesis and streaming. The SPEAK method MAY carry voice and prosody header fields that alter the behavior of the voice being synthesized, as well as a typed media message body containing the actual marked-up text to be spoken.
The SPEAK method implementation MUST do a fetch of all external URIs that are part of that operation. If caching is implemented, this URI fetching MUST conform to the cache control hints and parameter header fields associated with the method in deciding whether it is to be fetched from cache or from the external server. If these hints/parameters are not specified in the method, the values set for the session using SET-PARAMS/GET-PARAMS apply. If it was not set for the session their default values apply.
When applying voice parameters there are 3 levels of precedence. The highest precedence are those specified within the speech markup text, followed by those specified in the header fields of the SPEAK request and hence apply for that SPEAK request only, followed by the session default values which can be set using the SET-PARAMS request and apply for subsequent methods invoked during the session.
If the resource was idle at the time the SPEAK request arrived at the server and the SPEAK method is being actively processed, the resource responds immediately with a success status code and a request-state of IN-PROGRESS.
If the resource is in the speaking or paused state when the SPEAK method arrives at the server, i.e. it is in the middle of processing a previous SPEAK request, the status returns success with a request-state of PENDING. The server places the SPEAK request in the synthesizer resource request queue. The request queue operates strictly FIFO: requests are processed serially in order of receipt. If the current SPEAK fails, all SPEAK methods in the pending queue are cancelled and each generates a SPEAK-COMPLETE event with a Completion-Cause of "cancelled".
For the synthesizer resource, SPEAK is the only method that can return a request-state of IN-PROGRESS or PENDING. When the text has been synthesized and played into the media stream, the resource issues a SPEAK-COMPLETE event with the request-id of the SPEAK request and a request-state of COMPLETE.
C->S: MRCP/2.0 ... SPEAK 543257
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:neutral
Voice-Age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams and arrived at
<break/>
<say-as interpret-as="vxml:time">0345p</say-as>.
</s>
<s>The subject is
<prosody rate="-20%">ski trip</prosody>
</s>
</p>
</speak>
S->C: MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857206027059
S->C: MRCP/2.0 ... SPEAK-COMPLETE 543257 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Completion-Cause:000 normal
Speech-Marker:timestamp=857206027059
The STOP method from the client to the server tells the synthesizer resource to stop speaking if it is speaking something.
The STOP request can be sent with an Active-Request-Id-List header field to stop the zero or more specific SPEAK requests that may be in queue and return a response status-code of 200 (Success). If no Active-Request-Id-List header field is sent in the STOP request the server terminates all outstanding SPEAK requests.
If a STOP request successfully terminated one or more PENDING or IN-PROGRESS SPEAK requests, then the response MUST contain an Active-Request-Id-List header field enumerating the SPEAK request-ids that were terminated. Otherwise there is no Active-Request-Id-List header field in the response. No SPEAK-COMPLETE events are sent for such terminated requests.
If a SPEAK request that was IN-PROGRESS and speaking was stopped, the next pending SPEAK request, if any, becomes IN-PROGRESS at the resource and enters the speaking state.
If a SPEAK request that was IN-PROGRESS and paused was stopped, the next pending SPEAK request, if any, becomes IN-PROGRESS and enters the paused state.
C->S: MRCP/2.0 ... SPEAK 543258
Channel-Identifier:32AECB23433802@speechsynth
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams and arrived at
<break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is
<prosody rate="-20%">ski trip</prosody></s>
</p>
</speak>
S->C: MRCP/2.0 ... 543258 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857206027059
C->S: MRCP/2.0 ... STOP 543259
Channel-Identifier:32AECB23433802@speechsynth
S->C: MRCP/2.0 ... 543259 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Active-Request-Id-List:543258
Speech-Marker:timestamp=857206039059
The BARGE-IN-OCCURRED method, when used with the synthesizer resource, provides a client which has detected a barge-in-able event a means to communicate the occurrence of the event to the synthesizer resource.
This method is useful in two scenarios,
If a SPEAK request is active with kill-on-barge-in enabled (see Section 8.4.2), and the BARGE-IN-OCCURRED event is received, the synthesizer MUST immediately stop streaming out audio. It MUST also terminate any speech requests queued behind the current active one, irrespective of whether they have barge-in enabled or not. If a barge-in-able SPEAK request was playing and it was terminated, the response MUST contain the an Active-Request-Id-List header field listing the request-ids of all SPEAK requests that were terminated. The server generates no SPEAK-COMPLETE events for these requests.
If there were no SPEAK requests terminated by the synthesizer resource as a result of the BARGE-IN-OCCURRED method, the server responds to the BARGE-IN-OCCURRED with a status-code of 200 success, and the response MUST NOT contain an Active-Request-Id-List header field.
If the synthesizer and recognizer resources are part of the same MRCPv2 session, they can be optimized for a quicker kill-on-barge-in response if the recognizer and synthesizer interact directly. In these cases, the client MUST still react to a START-OF-INPUT event from the recognizer by invoking the BARGE-IN-OCCURRED method to the synthesizer. The client MUST invoke the BARGE-IN-OCCURRED if it has any outstanding requests to the synthesizer resource in either the PENDING or IN-PROGRESS state.
C->S: MRCP/2.0 ... SPEAK 543258
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:neutral
Voice-Age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams and arrived at
<break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is
<prosody rate="-20%">ski trip</prosody></s>
</p>
</speak>
S->C: MRCP/2.0 ... 543258 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857206027059
C->S: MRCP/2.0 ... BARGE-IN-OCCURRED 543259
Channel-Identifier:32AECB23433802@speechsynth
Proxy-Sync-Id:987654321
S->C:MRCP/2.0 ... 543259 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Active-Request-Id-List:543258
Speech-Marker:timestamp=857206039059
The PAUSE method from the client to the server tells the synthesizer resource to pause speech output if it is speaking something. If a PAUSE method is issued on a session when a SPEAK is not active the server MUST respond with a status-code of 402 "Method not valid in this state". If a PAUSE method is issued on a session when a SPEAK is active and paused the server MUST respond with a status-code of 200 "Success". If a SPEAK request was active the server MUST return an Active-Request-Id-List header field whose value contains the request-id of the SPEAK request that was paused.
C->S: MRCP/2.0 ... SPEAK 543258
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:neutral
Voice-Age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams and arrived at
<break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is
<prosody rate="-20%">ski trip</prosody></s>
</p>
</speak>
S->C: MRCP/2.0 ... 543258 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857206027059
C->S: MRCP/2.0 ... PAUSE 543259
Channel-Identifier:32AECB23433802@speechsynth
S->C: MRCP/2.0 ... 543259 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Active-Request-Id-List:543258
The RESUME method from the client to the server tells a paused synthesizer resource to resume speaking. If a RESUME request is issued on a session with no active SPEAK request, the server MUST respond with a status-code of 402 "Method not valid in this state". If a RESUME request is issued on a session with an active SPEAK request that is speaking (i.e., not paused) the server MUST respond with a status-code of 200 "Success". If a SPEAK request was paused the server MUST return an Active-Request-Id-List header field whose value contains the request-id of the SPEAK request that was resumed.
C->S: MRCP/2.0 ... SPEAK 543258
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:neutral
Voice-age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams and arrived at
<break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is
<prosody rate="-20%">ski trip</prosody></s>
</p>
</speak>
S->C: MRCP/2.0 ... 543258 200 IN-PROGRESS@speechsynth
Channel-Identifier:32AECB23433802
Speech-Marker:timestamp=857206027059
C->S: MRCP/2.0 ... PAUSE 543259
Channel-Identifier:32AECB23433802@speechsynth
S->C: MRCP/2.0 ... 543259 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Active-Request-Id-List:543258
C->S: MRCP/2.0 ... RESUME 543260
Channel-Identifier:32AECB23433802@speechsynth
S->C: MRCP/2.0 ... 543260 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Active-Request-Id-List:543258
The CONTROL method from the client to the server tells a synthesizer that is speaking to modify what it is speaking on the fly. This method is used to request the synthesizer to jump forward or backward in what it is speaking, change speaker rate, speaker parameters, etc. It affects only the currently IN-PROGRESS SPEAK request. Depending on the implementation and capability of the synthesizer resource it may or may not support the various modifications indicated by header fields in the CONTROL request.
When a client invokes a CONTROL method to jump forward and the operation goes beyond the end of the active SPEAK method's text, the CONTROL request still succeeds. The active SPEAK request completes and returns a SPEAK-COMPLETE event following the response to the CONTROL method. If there are more SPEAK requests in the queue, the synthesizer resource starts at the beginning of the next SPEAK request in the queue.
When a client invokes a CONTROL method to jump backward and the operation jumps to the beginning or beyond the beginning of the speech data of the active SPEAK method, the CONTROL request still succeeds. The response to the CONTROL request contains the speak-restart header field, and the active SPEAK request restarts from the beginning of its speech data.
These two behaviors can be used to rewind or fast-forward across multiple speech requests, if the client wants to break up a speech markup text to multiple SPEAK requests.
If a SPEAK request was active when the CONTROL method was received the server MUST return an active-request-id-list header field with the Request-id of the SPEAK request that was active.
C->S: MRCP/2.0 ... SPEAK 543258
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:neutral
Voice-age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams
and arrived at <break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is <prosody
rate="-20%">ski trip</prosody></s>
</p>
</speak>
S->C: MRCP/2.0 ... 543258 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857205016059
C->S: MRCP/2.0 ... CONTROL 543259
Channel-Identifier:32AECB23433802@speechsynth
Prosody-rate:fast
S->C: MRCP/2.0 ... 543259 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Active-Request-Id-List:543258
Speech-Marker:timestamp=857206027059
C->S: MRCP/2.0 ... CONTROL 543260
Channel-Identifier:32AECB23433802@speechsynth
Jump-Size:-15 Words
S->C: MRCP/2.0 ... 543260 200 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Active-Request-Id-List:543258
Speech-Marker:timestamp=857206039059
This is an Event message from the synthesizer resource to the client indicating that the corresponding SPEAK request was completed. The request-id header field matches the request-id of the SPEAK request that initiated the speech that just completed. The request-state field is set to COMPLETE by the server, indicating that this is the last event with the corresponding request-id. The Completion-Cause header field specifies the cause code pertaining to the status and reason of request completion such as the SPEAK completed normally or because of an error, kill-on-barge-in etc.
C->S: MRCP/2.0 ... SPEAK 543260
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:neutral
Voice-age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams
and arrived at <break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is
<prosody rate="-20%">ski trip</prosody></s>
</p>
</speak>
S->C: MRCP/2.0 ... 543260 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857206027059
S->C: MRCP/2.0 ... SPEAK-COMPLETE 543260 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Completion-Cause:000 normal
Speech-Marker:timestamp=857206039059
This is an event generated by the synthesizer resource to the client when the synthesizer encounters a marker tag in the speech markup it is currently processing. The request-id field in the header field matches the corresponding SPEAK request. The request-state field indicates IN-PROGRESS as the speech is still not complete. The value of the speech marker tag hit, describing where the synthesizer is in the speech markup, is returned in the speech-marker header field, along with an NTP timestamp indicating the instant in the output speech stream that the marker was encountered. The SPEECH-MARKER event MUST also be generated with a null marker value and output NTP timestamp when a SPEAK request in Pending-State (i.e. in the queue) changes state to IN-PROGRESS and starts speaking. The NTP timestamp MUST be synchronized with the RTP timestamp used to generate the speech stream through standard RTCP machinery.
C->S: MRCP/2.0 ... SPEAK 543261
Channel-Identifier:32AECB23433802@speechsynth
Voice-gender:neutral
Voice-age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams
and arrived at <break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<mark name="here"/>
<s>The subject is
<prosody rate="-20%">ski trip</prosody>
</s>
<mark name="ANSWER"/>
</p>
</speak>
S->C: MRCP/2.0 ... 543261 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857205015059
S->C: MRCP/2.0 ... SPEECH-MARKER 543261 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857206027059;here
S->C: MRCP/2.0 ... SPEECH-MARKER 543261 IN-PROGRESS
Channel-Identifier:32AECB23433802@speechsynth
Speech-Marker:timestamp=857206039059;ANSWER
S->C: MRCP/2.0 ... SPEAK-COMPLETE 543261 COMPLETE
Channel-Identifier:32AECB23433802@speechsynth
Completion-Cause:000 normal
Speech-Marker:timestamp=857207689259;ANSWER
The DEFINE-LEXICON method, from the client to the server, provides a lexicon and tells the server to load or unload the lexicon (see Section 8.4.16). The media type of the lexicon is provided in the Content-Type header (see Section 8.5.2). One such media type is PLS [W3C.REC-pronunciation-lexicon-20081014].
If the server resource is in the speaking or paused state, the server MUST respond with a failure status-code of 402 "Method not valid in this state".
If the resource is in the idle state and is able to successfully load/unload the lexicon the status MUST return a 200 "Success" status-code and the request-state MUST be COMPLETE.
If the synthesizer could not define the lexicon for some reason, for example because the download failed or the lexicon was in an unsupported form, the server MUST respond with a failure status-code of 407, and a Completion-Cause header field describing the failure reason.
The speech recognizer resource receives an incoming voice stream and provides the client with an interpretation of what was spoken in textual form.
The recognizer resource is controlled by MRCPv2 requests from the client. The recognizer resource can both respond to these requests and generate asynchronous events to the client to indicate conditions of interest during the processing of the method.
This section applies to the following resource types.
The difference between the above two resources is in their level of support for recognition grammars. The "dtmfrecog" resource type is capable of recognizing only DTMF digits and hence accepts only DTMF grammars. It only generates barge-in for DTMF inputs and ignores speech. The "speechrecog" resource type can recognize regular speech as well as DTMF digits and hence MUST support grammars describing either speech or DTMF. This resource generates barge-in events for speech and/or DTMF. By analyzing the grammars that are activated by the RECOGNIZE method, it determines if a barge-in should occur for speech and/or DTMF. When the recognizer decides it needs to generate barge-in it also generates a START-OF-INPUT event to the client. The recognition resource may support recognition in the normal or hotword modes or both (although note that a single speechrecog resource does not perform normal and hotword mode recognition simultaneously). For implementations where a single recognition resource does not support both modes, or simultaneous normal and hotword recognition is desired, the two modes can be invoked through separate resources allocated to the same SIP dialog (with different MRCP session identifiers) and share the RTP audio feed.
The capabilities of the recognition resource are enumerated below:
Voice Enrollment has the concept of an enrollment session. A session to add a new phrase to a personal grammar involves the initial enrollment followed by a repeat of enough utterances before committing the new phrase to the personal grammar. Each time an utterance is recorded, it is compared for similarity with the other samples and a clash test is performed against other entries in the personal grammar to ensure there are no similar and confusable entries.
Enrollment is done using a recognizer resource. Controlling which utterances are to be considered for enrollment of a new phrase is done by setting a header field (see Section 9.4.39) in the Recognize request.
Interpretation is accomplished through the INTERPRET method (Section 9.20) and the interpret-text header field (Section 9.4.30).
The recognizer resource maintains a state machine to process MRCPv2 requests from the client.
Idle Recognizing Recognized State State State | | | |---------RECOGNIZE---->|---RECOGNITION-COMPLETE-->| |<------STOP------------|<-----RECOGNIZE-----------| | | | | |--------| |-----------| | START-OF-INPUT | GET-RESULT | | |------->| |---------->| |------------| | | | DEFINE-GRAMMAR |----------| | |<-----------| | START-INPUT-TIMERS | | |<---------| | |------| | | | INTERPRET | | |<-----| |------| | | | RECOGNIZE | |-------| |<-----| | | STOP | |<------| | |<-------------------STOP--------------------------| |<-------------------DEFINE-GRAMMAR----------------|
If a recognition resource supports voice enrolled grammars, starting an enrollment session does not change the state of the recognizer resource. Once an enrollment session is started, then utterances are enrolled by calling the RECOGNIZE method repeatedly. The state of the speech recognizer resource goes from IDLE to RECOGNIZING state each time RECOGNIZE is called.
The recognizer supports the following methods.
recognizer-method = recog-only-method
/ enrollment-method
recog-only-method = "DEFINE-GRAMMAR"
/ "RECOGNIZE"
/ "INTERPRET"
/ "GET-RESULT"
/ "START-INPUT-TIMERS"
/ "STOP"
It is OPTIONAL for a recognizer resource to support voice enrolled grammars. If the recognizer resource does support voice enrolled grammars it MUST support the following methods.
enrollment-method = "START-PHRASE-ENROLLMENT"
/ "ENROLLMENT-ROLLBACK"
/ "END-PHRASE-ENROLLMENT"
/ "MODIFY-PHRASE"
/ "DELETE-PHRASE"
The recognizer may generate the following events.
recognizer-event = "START-OF-INPUT"
/ "RECOGNITION-COMPLETE"
/ "INTERPRETATION-COMPLETE"
A recognizer message may contain header fields containing request options and information to augment the Method, Response or Event message it is associated with.
recognizer-header = recog-only-header
/ enrollment-header
recog-only-header = confidence-threshold
/ sensitivity-level
/ speed-vs-accuracy
/ n-best-list-length
/ no-input-timeout
/ input-type
/ recognition-timeout
/ waveform-uri
/ input-waveform-uri
/ completion-cause
/ completion-reason
/ recognizer-context-block
/ start-input-timers
/ speech-complete-timeout
/ speech-incomplete-timeout
/ dtmf-interdigit-timeout
/ dtmf-term-timeout
/ dtmf-term-char
/ failed-uri
/ failed-uri-cause
/ save-waveform
/ media-type
/ new-audio-channel
/ speech-language
/ ver-buffer-utterance
/ recognition-mode
/ cancel-if-queue
/ hotword-max-duration
/ hotword-min-duration
/ interpret-text
/ dtmf-buffer-time
/ clear-dtmf-buffer
/ early-no-match
If a recognition resource supports voice enrolled grammars, the following header fields are also used.
enrollment-header = num-min-consistent-pronunciations
/ consistency-threshold
/ clash-threshold
/ personal-grammar-uri
/ enroll-utterance
/ phrase-id
/ phrase-nl
/ weight
/ save-best-waveform
/ new-phrase-id
/ confusable-phrases-uri
/ abort-phrase-enrollment
For enrollment-specific header fields that can appear as part of SET-PARAMS or GET-PARAMS methods, the following general rule applies: the START-PHRASE-ENROLLMENT method must be invoked before these header fields may be set through the SET-PARAMS method or retrieved through the GET-PARAMS method.
Note that the Waveform-URI header field of the Recognizer resource can also appear in the response to the END-PHRASE-ENROLLMENT method.
When a recognition resource recognizes or matches a spoken phrase with some portion of the grammar, it associates a confidence level with that match. The confidence-threshold header field tells the recognizer resource what confidence level the client considers a successful match. This is a float value between 0.0-1.0 indicating the recognizer's confidence in the recognition. If the recognizer determines that there is no candidate match with a confidence that is greater than the confidence threshold, then it MUST return no-match as the recognition result. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS. The default value for this header field is implementation specific, as is the interpretation of any specific value for this header field. Although values for servers from different vendors are not comparable, it is expected that clients will tune this value over time for a given server.
confidence-threshold = "Confidence-Threshold" ":" FLOAT CRLF
To filter out background noise and not mistake it for speech, the recognizer may support a variable level of sound sensitivity. The sensitivity-level header field is a float value between 0.0 and 1.0 and allows the client to set the sensitivity level for the recognizer. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS. A higher value for this header field means higher sensitivity. The default value for this header field is implementation specific, as is the interpretation of any specific value for this header field. Although values for servers from different vendors are not comparable, it is expected that clients will tune this value over time for a given server.
sensitivity-level = "Sensitivity-Level" ":" FLOAT CRLF
Depending on the implementation and capability of the recognizer resource it may be tunable towards Performance or Accuracy. Higher accuracy may mean more processing and higher CPU utilization, meaning fewer active sessions per server and vice versa. The value is a float between 0.0 and 1.0. A value of 0.0 means fastest recognition. A value of 1.0 means best accuracy. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS. The default value for this header field is implementation specific. Although values for servers from different vendors are not comparable, it is expected that clients will tune this value over time for a given server.
speed-vs-accuracy = "Speed-Vs-Accuracy" ":" FLOAT CRLF
When the recognizer matches an incoming stream with the grammar, it may come up with more than one alternative match because of confidence levels in certain words or conversation paths. If this header field is not specified, by default, the recognition resource returns only the best match above the confidence threshold. The client, by setting this header field, can ask the recognition resource to send it more than 1 alternative. All alternatives must still be above the confidence-threshold. A value greater than one does not guarantee that the recognizer will provide the requested number of alternatives. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS. The minimum value for this header field is 1. The default value for this header field is 1.
n-best-list-length = "N-Best-List-Length" ":" 1*19DIGIT CRLF
When the recognizer detects barge-in-able input and generates a START-OF-INPUT event, that event MUST carry this header field to specify whether the input that caused the barge-in was DTMF or speech.
input-type = "Input-Type" ":" inputs CRLF
inputs = "speech" / "dtmf"
When recognition is started and there is no speech detected for a certain period of time, the recognizer can send a RECOGNITION-COMPLETE event to the client with a Completion-Cause of "no-input-timeout" and terminate the recognition operation. The client can use the no-input-timeout header field to set this timeout. The value is in milliseconds and may range from 0 to an implementation specific maximum value. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS. The default value is implementation specific.
no-input-timeout = "No-Input-Timeout" ":" 1*19DIGIT CRLF
When recognition is started and there is no match for a certain period of time, the recognizer can send a RECOGNITION-COMPLETE event to the client and terminate the recognition operation. The Recognition-Timeout header field allows the client to set this timeout value. The value is in milliseconds. The value for this header field ranges from 0 to an implementation specific maximum value. The default value is 10 seconds. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
recognition-timeout = "Recognition-Timeout" ":" 1*19DIGIT CRLF
If the Save-Waveform header field is set to true, the recognizer MUST record the incoming audio stream of the recognition into a stored form and provide a URI for the client to access it. This header field MUST be present in the RECOGNITION-COMPLETE event if the Save-Waveform header field was set to true. The value of the header field MUST be empty if there was some error condition preventing the server from recording. Otherwise, the URI generated by the server MUST be unambiguous across the server and all its recognition sessions. The content associated with the URI MUST be available to the client until the MRCPv2 session terminates.
Similarly, if the Save-Best-Waveform header field is set to true, the recognizer MUST save the audio stream for the best repetition of the phrase that was used during the enrollment session. The recognizer MUST then record the recognized audio and make it available to the client by returning a URI in the Waveform-URI header field in the response to the END-PHRASE-ENROLLMENT method. The value of the header field MUST be empty if there was some error condition preventing the server from recording. Otherwise, the URI generated by the server MUST be unambiguous across the server and all its recognition sessions. The content associated with the URI MUST be available to the client until the MRCPv2 session terminates. See the discussion on the sensitivity of saved waveforms in Section 12.
The server MUST also return the size in octets and the duration in milliseconds of the recorded audio wave-form as parameters associated with the header field.
waveform-uri = "Waveform-URI" ":" ["<" uri ">"
";" "size" "=" 1*19DIGIT
";" "duration" "=" 1*19DIGIT] CRLF
This header field MAY be specified in the SET-PARAMS, GET-PARAMS or the RECOGNIZE methods and tells the server resource the Media Type in which to store captured audio or video such as the one captured and returned by the Waveform-URI header field.
media-type = "Media-Type" ":" media-type-value
CRLF
This optional header field specifies a URI pointing to audio content to be processed by the RECOGNIZE operation. This enables the client to request recognition from a specified buffer or audio file.
input-waveform-uri = "Input-Waveform-URI" ":" uri CRLF
This header field MUST be part of a RECOGNITION-COMPLETE, event coming from the recognizer resource to the client. It indicates the reason behind the RECOGNIZE method completion. This header field MUST be sent in the DEFINE-GRAMMAR and RECOGNIZE responses, if they return with a failure status and a COMPLETE state. In the ABNF below, the 'cause-code' contains a numerical value selected from the Cause-Code column of the following table. The 'cause-name' contains the corresponding token selected from the Cause-Name column.
completion-cause = "Completion-Cause" ":" cause-code SP
cause-name CRLF
cause-code = 3DIGIT
cause-name = *VCHAR
| Cause-Code | Cause-Name | Description |
|---|---|---|
| 000 | success | RECOGNIZE completed with a match or DEFINE-GRAMMAR succeeded in downloading and compiling the grammar |
| 001 | no-match | RECOGNIZE completed, but no match was found |
| 002 | no-input-timeout | RECOGNIZE completed without a match due to a no-input-timeout |
| 003 | hotword-maxtime | RECOGNIZE in hotword mode completed without a match due to a recognition-timeout |
| 004 | grammar-load-failure | RECOGNIZE failed due grammar load failure. |
| 005 | grammar-compilation-failure | RECOGNIZE failed due to grammar compilation failure. |
| 006 | recognizer-error | RECOGNIZE request terminated prematurely due to a recognizer error. |
| 007 | speech-too-early | RECOGNIZE request terminated because speech was too early. This happens when the audio stream is already "in-speech" when the RECOGNIZE request was received. |
| 008 | success-maxtime | RECOGNIZE request terminated because speech was too long but whatever was spoken till that point was a full match. |
| 009 | uri-failure | Failure accessing a URI. |
| 010 | language-unsupported | Language not supported. |
| 011 | cancelled | A new RECOGNIZE cancelled this one, or a prior RECOGNIZE failed while this one was still in the queue. |
| 012 | semantics-failure | Recognition succeeded but semantic interpretation of the recognized input failed. The RECOGNITION-COMPLETE event MUST contain the Recognition result with only input text and no interpretation. |
| 013 | partial-match | Speech Incomplete timeout expired before there was a full match. But whatever that was spoken till that point was a partial match to one or more grammars. |
| 014 | partial-match-maxtime | The Recognition-Timer expired before full match was achieved. But whatever was spoken till that point was a partial match to one or more grammars. |
| 015 | no-match-maxtime | The Recognition-Timer expired. Whatever was spoken till that point either did not match any of the grammars. This cause could also be returned if the recognizer does not support detecting partial grammar matches. |
| 016 | grammar-definition-failure | any DEFINE-GRAMMAR error other than grammar-load-failure and grammar-compilation-failure. |
This header field MAY be specified in a RECOGNITION-COMPLETE event coming from the recognizer resource to the client. This contains the reason text behind the RECOGNIZE request completion. The server uses this header field to communicate text describing the reason for the failure, such as the specific error encountered in parsing a grammar markup.
The completion reason text is provided for client use in logs and for debugging and instrumentation purposes. Clients MUST NOT interpret the completion reason text.
completion-reason = "Completion-Reason" ":"
quoted-string CRLF
This header field MAY be sent as part of the SET-PARAMS or GET-PARAMS request. If the GET-PARAMS method contains this header field with no value, then it is a request to the recognizer to return the recognizer context block. The response to such a message MAY contain a recognizer context block as a typed media message body. If the server returns a recognizer context block, the response MUST contain this header field and its value MUST match the Content-ID of the corresponding media block.
If the SET-PARAMS method contains this header field, it MUST also contain a message body containing the recognizer context data, and a Content-ID matching this header field value. This Content-ID MUST match the Content-ID that came with the context data during the GET-PARAMS operation.
An implementation choosing to use this mechanism to hand off recognizer context data between servers MUST distinguish its implementation-specific block of data by using an IANA-registered content type in the IANA Media Type vendor tree.
recognizer-context-block = "Recognizer-Context-Block" ":"
[1*VCHAR] CRLF
This header field MAY be sent as part of the RECOGNIZE request. A value of false tells the recognizer to start recognition, but not to start the no-input timer yet. The recognizer MUST NOT start the timers until the client sends a START-INPUT-TIMERS request to the recognizer. This is useful in the scenario when the recognizer and synthesizer engines are not part of the same session. In such configurations, when a kill-on-barge-in prompt is being played (see Section 8.4.2), the client wants the RECOGNIZE request to be simultaneously active so that it can detect and implement kill-on-barge-in. However, the recognizer SHOULD NOT start the no-input timers until the prompt is finished. The default value is "true".
start-input-timers = "Start-Input-Timers" ":" BOOLEAN CRLF
This header field specifies the length of silence required following user speech before the speech recognizer finalizes a result (either accepting it or generating a nomatch event). The speech-complete-timeout value applies when the recognizer currently has a complete match against an active grammar, and specifies how long the recognizer MUST wait for more input before declaring a match. By contrast, the incomplete timeout is used when the speech is an incomplete match to an active grammar. The value is in milliseconds.
speech-complete-timeout = "Speech-Complete-Timeout" ":" 1*19DIGIT CRLF
A long speech-complete-timeout value delays the result to the client and therefore makes the application's response to a user slow. A short speech-complete-timeout may lead to an utterance being broken up inappropriately. Reasonable speech complete timeout values are typically in the range of 0.3 seconds to 1.0 seconds. The value for this header field ranges from 0 to an implementation specific maximum value. The default value for this header field is implementation specific. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
This header field specifies the required length of silence following user speech after which a recognizer finalizes a result. The incomplete timeout applies when the speech prior to the silence is an incomplete match of all active grammars. In this case, once the timeout is triggered, the partial result is rejected (with a Completion-Cause of "partial-match"). The value is in milliseconds. The value for this header field ranges from 0 to an implementation specific maximum value. The default value for this header field is implementation specific.
speech-incomplete-timeout = "Speech-Incomplete-Timeout" ":" 1*19DIGIT
CRLF
The speech-incomplete-timeout also applies when the speech prior to the silence is a complete match of an active grammar, but where it is possible to speak further and still match the grammar. By contrast, the complete timeout is used when the speech is a complete match to an active grammar and no further spoken words can continue to represent a match.
A long speech-incomplete-timeout value delays the result to the client and therefore makes the application's response to a user slow. A short speech-incomplete-timeout may lead to an utterance being broken up inappropriately.
The speech-incomplete-timeout is usually longer than the speech-complete-timeout to allow users to pause mid-utterance (for example, to breathe). This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
This header field specifies the inter-digit timeout value to use when recognizing DTMF input. The value is in milliseconds. The value for this header field ranges from 0 to an implementation specific maximum value. The default value is 5 seconds. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
dtmf-interdigit-timeout = "DTMF-Interdigit-Timeout" ":" 1*19DIGIT CRLF
This header field specifies the terminating timeout to use when recognizing DTMF input. The DTMF-Term-Timeout applies only when no additional input is allowed by the grammar; otherwise, the DTMF-Interdigit-Timeout applies. The value is in milliseconds. The value for this header field ranges from 0 to an implementation specific maximum value. The default value is 10 seconds. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
dtmf-term-timeout = "DTMF-Term-Timeout" ":" 1*19DIGIT CRLF
This header field specifies the terminating DTMF character for DTMF input recognition. The default value is NULL which is indicated by an empty header field value. This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
dtmf-term-char = "DTMF-Term-Char" ":" VCHAR CRLF
When a recognizer needs to fetch or access a URI and the access fails the server SHOULD provide the failed URI in this header field in the method response, unless there are multiple URI failures, in which case one of the failed URIs MUST be provided in this header field in the method response.
failed-uri = "Failed-URI" ":" absoluteURI CRLF
When a recognizer method needs a recognizer to fetch or access a URI and the access fails the server MUST provide the URI specific or protocol specific response code for the URI in the Failed-URI header field through this header field in the method response. The value encoding is UTF-8 (RFC3629 [RFC3629]) to accommodate any access protocol, some of which might have a response string instead of a numeric response code.
failed-uri-cause = "Failed-URI-Cause" ":" 1*UTFCHAR CRLF
This header field allows the client to request the recognizer resource to save the audio input to the recognizer. The recognizer resource MUST then attempt to record the recognized audio, without endpointing, and make it available to the client in the form of a URI returned in the Waveform-URI header field in the RECOGNITION-COMPLETE event. If there was an error in recording the stream or the audio content is otherwise not available, the recognizer MUST return an empty Waveform-URI header field. The default value for this field is "false". This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS. See the discussion on the sensitivity of saved waveforms in Section 12.
save-waveform = "Save-Waveform" ":" BOOLEAN CRLF
This header field MAY be specified in a RECOGNIZE request and allows the client to tell the server that, from this point on, further input audio comes from a different audio source, channel or speaker. If the recognition resource had collected any input statistics or adaptation state, the recognition resource MUST do what is appropriate for the specific recognition technology, which includes but is not limited to discarding any collected input statistics or adaptation state before starting the RECOGNIZE request. Note that if there are multiple resources that are sharing a media stream and are collecting or using this data, and the client issues this header field to one of the resources, the reset operation applies to all resources that use the shared media stream. This helps in a number of use cases, including where the client wishes to reuse an open recognition session with an existing media session for multiple telephone calls.
new-audio-channel = "New-Audio-Channel" ":" BOOLEAN
CRLF
This header field specifies the language of recognition grammar data within a session or request, if it is not specified within the data. The value of this header field MUST follow RFC 5646 [RFC5646] for its values. This MAY occur in DEFINE-GRAMMAR, RECOGNIZE, SET-PARAMS or GET-PARAMS request.
speech-language = "Speech-Language" ":" 1*VCHAR CRLF
This header field lets the client request the server to buffer the utterance associated with this recognition request into a buffer available to a co-resident verifier resource. The buffer is shared across resources within a session and is allocated when a verifier resource is added to this session. The client MUST NOT send this header field unless a verifier resource is instantiated for the session. The buffer is released when the verifier resource is released from the session.
This header field specifies what mode the RECOGNIZE method will operate in. The value choices are "normal" or "hotword". If the value is "normal", the RECOGNIZE starts matching speech and DTMF to the grammars specified in the RECOGNIZE request. If any portion of the speech does not match the grammar, the RECOGNIZE command completes with a no-match status. Timers may be active to detect speech in the audio (see Section 9.4.14), so the RECOGNIZE method may complete because of a timeout waiting for speech. If the value of this header field is "hotword", the RECOGNIZE method operates in hotword mode, where it only looks for the particular keywords or DTMF sequences specified in the grammar and ignores silence or other speech in the audio stream. The default value for this header field is "normal". This header field MAY occur on the RECOGNIZE method.
recognition-mode = "Recognition-Mode" ":"
normal-value / hotword-value CRLF
normal-value = "normal"
hotword-value = "hotword"
This header field specifies what will happen if the client attempts to invoke another RECOGNIZE method when this RECOGNIZE request is already in progress for the resource. The value for this header field is Boolean. A value of "true" means the server MUST terminate this RECOGNIZE request, with a Completion-Cause of "cancelled", if the client issues another RECOGNIZE request for the same resource. A value of "false" for this header field indicates to the server that this RECOGNIZE request will continue to completion and if the client issues more RECOGNIZE requests to the same resource, they are queued. When the currently active RECOGNIZE request is stopped or completes with a successful match, the first RECOGNIZE method in the queue becomes active. If the current RECOGNIZE fails, all RECOGNIZE methods in the pending queue are cancelled and each generates a RECOGNITION-COMPLETE event with a Completion-Cause of "cancelled". This header field MUST be present in every RECOGNIZE request. There is no default value.
cancel-if-queue = "Cancel-If-Queue" ":" BOOLEAN CRLF
This header field MAY be sent in a hotword mode RECOGNIZE request. It specifies the maximum length of an utterance (in seconds) that will be considered for Hotword recognition. This header field, along with Hotword-Min-Duration, can be used to tune performance by preventing the recognizer from evaluating utterances that are too short or too long to be one of the hotwords in the grammar(s). The value is in milliseconds. The default is implementation dependent. If present in a RECOGNIZE request specifying a mode other than "hotword", the header field is ignored.
hotword-max-duration = "Hotword-Max-Duration" ":" 1*19DIGIT
CRLF
This header field MAY be sent in a hotword mode RECOGNIZE request. It specifies the minimum length of an utterance (in seconds) that will be considered for Hotword recognition. This header field, along with Hotword-Max-Duration, can be used to tune performance by preventing the recognizer from evaluating utterances that are too short or too long to be one of the hotwords in the grammar(s). The value is in milliseconds. The default value is implementation dependent. If present in a RECOGNIZE request specifying a mode other than "hotword", the header field is ignored.
hotword-min-duration = "Hotword-Min-Duration" ":" 1*19DIGIT CRLF
The value of this header field is used to provide a pointer to the text for which a natural language interpretation is desired. The value is either a URI or text. If the value is a URI, it MUST be a Content-ID that refers to an entity of type text/plain in the body of the message. Otherwise, the server MUST treat the value as the text to be interpreted. This header field MUST be used when invoking the INTERPRET method.
interpret-text = "Interpret-Text" ":" 1*VCHAR CRLF
This header field MAY be specified in a GET-PARAMS or SET-PARAMS method and is used to specify the size in time, in milliseconds, of the typeahead buffer for the recognizer. This is the buffer that collects DTMF digits as they are pressed even when there is no RECOGNIZE command active. When a subsequent RECOGNIZE method is received it MAY look to this buffer to match the RECOGNIZE request. If the digits in the buffer is not sufficient then it can continue to listen to more digits to match the grammar. The default size of this DTMF buffer is platform specific.
dtmf-buffer-time = "DTMF-Buffer-Time" ":" 1*19DIGIT CRLF
This header field MAY be specified in a RECOGNIZE method and is used to tell the recognizer to clear the DTMF type-ahead buffer before starting the recognize. The default value of this header field is FALSE, which does not clear the typeahead buffer before starting the RECOGNIZE method. If this header field is specified to be TRUE, then the recognize will clear the DTMF buffer before starting recognition. This means digits pressed by the caller before the RECOGNIZE command was issued are discarded.
clear-dtmf-buffer = "Clear-DTMF-Buffer" ":" BOOLEAN CRLF
This header field MAY be specified in a RECOGNIZE method and is used to tell the recognizer that it MUST NOT wait for the end of speech before processing the collected speech to match active grammars. A value of TRUE indicates the recognizer MUST do early matching. The default value for this header field if not specified is FALSE. If the recognizer does not support the processing of the collected audio before the end of speech this header field can be safely ignored.
early-no-match = "Early-No-Match" ":" BOOLEAN CRLF
This header field MAY be specified in a START-PHRASE-ENROLLMENT, SET-PARAMS, or GET-PARAMS method and is used to specify the minimum number of consistent pronunciations that must be obtained to voice enroll a new phrase. The minimum value is 1. The default value is implementation specific and MAY be greater than 1.
num-min-consistent-pronunciations =
"Num-Min-Consistent-Pronunciations" ":" 1*19DIGIT CRLF
This header field MAY be sent as part of the START-PHRASE-ENROLLMENT, SET-PARAMS, or GET-PARAMS method. Used during voice-enrollment, this header field specifies how similar to a previously enrolled pronunciation of the same phrase an utterance needs to be in order to be considered "consistent." The higher the threshold, the closer the match between an utterance and previous pronunciations must be for the pronunciation to be considered consistent. The range for this threshold is a float value between is 0.0 to 1.0. The default value for this header field is implementation specific.
consistency-threshold = "Consistency-Threshold" ":" FLOAT CRLF
This header field MAY be sent as part of the START-PHRASE-ENROLLMENT, SET-PARAMS, or GET-PARAMS method. Used during voice-enrollment, this header field specifies how similar the pronunciations of two different phrases can be before they are considered to be clashing. For example, pronunciations of phrases such as "John Smith" and "Jon Smits" may be so similar that they are difficult to distinguish correctly. A smaller threshold reduces the number of clashes detected. The range for this threshold is float value between 0.0 and 1.0. The default value for this header field is implementation specific. Clash testing can be turned off completely by setting the Clash-Threshold header field value to 0.
clash-threshold = "Clash-Threshold" ":" FLOAT CRLF
This header field specifies the speaker-trained grammar to be used or referenced during enrollment operations. Phrases are added to this grammar during enrollment. For example, a contact list for user "Jeff" could be stored at the Personal-Grammar-URI "http://myserver.example.com/myenrollmentdb/jeff-list". The generated grammar syntax MAY be implementation specific. There is no default value for this header field. This header field MAY be sent as part of the START-PHRASE-ENROLLMENT, SET-PARAMS, or GET-PARAMS method.
personal-grammar-uri = "Personal-Grammar-URI" ":" uri CRLF
This header field MAY be specified in the RECOGNIZE method. If this header field is set to "true" and an Enrollment is active, the RECOGNIZE command MUST add the collected utterance to the personal grammar that is being enrolled. The way in which this occurs is engine-specific and may be an area of future standardization. The default value for this header field is "false".
enroll-utterance = "Enroll-Utterance" ":" BOOLEAN CRLF
This header field in a request identifies a phrase in an existing personal grammar for which enrollment is desired. It is also returned to the client in the RECOGNIZE complete event. This header field MAY occur in START-PHRASE-ENROLLMENT, MODIFY-PHRASE or DELETE-PHRASE requests. There is no default value for this header field.
phrase-id = "Phrase-ID" ":" 1*VCHAR CRLF
This string specifies the interpreted text to be returned when the phrase is recognized. This header field MAY occur in START-PHRASE-ENROLLMENT and MODIFY-PHRASE requests. There is no default value for this header field.
phrase-nl = "Phrase-NL" ":" 1*UTFCHAR CRLF
The value of this header field represents the occurrence likelihood of a phrase in an enrolled grammar. When using grammar enrollment, the system is essentially constructing a grammar segment consisting of a list of possible match phrases. This can be thought of to be similar to the dynamic construction of a <one-of> tag in the W3C grammar specification. Each enrolled-phrase becomes an item in the list that can be matched against spoken input similar to the <item> within a <one-of> list. This header field allows you to assign a weight to the phrase (i.e., <item> entry) in the <one-of> list that is enrolled. Grammar weights are normalized to a sum of one at grammar compilation time, so a weight value of 1 for each phrase in an enrolled grammar list indicates all items in that list have the same weight. This header field MAY occur in START-PHRASE-ENROLLMENT and MODIFY-PHRASE requests. The default value for this header field is implementation specific.
weight = "Weight" ":" weight-value CRLF
weight-value = FLOAT
This header field allows the client to request the recognizer resource to save the audio stream for the best repetition of the phrase that was used during the enrollment session. The recognizer MUST attempt to record the recognized audio and make it available to the client in the form of a URI returned in the Waveform-URI header field in the response to the END-PHRASE-ENROLLMENT method. If there was an error in recording the stream or the audio data is otherwise not available, the recognizer MUST return an empty Waveform-URI header field. This header field MAY occur in the START-PHRASE-ENROLLMENT, SET-PARAMS, and GET-PARAMS methods.
save-best-waveform = "Save-Best-Waveform" ":" BOOLEAN CRLF
This header field replaces the id used to identify the phrase in a personal grammar. The recognizer returns the new id when using an enrollment grammar. This header field MAY occur in MODIFY-PHRASE requests.
new-phrase-id = "New-Phrase-ID" ":" 1*VCHAR CRLF
This header field specifies a grammar that defines invalid phrases for enrollment. For example, typical applications do not allow an enrolled phrase that is also a command word. This header field MAY occur in RECOGNIZE requests that are part of an enrollment session.
confusable-phrases-uri = "Confusable-Phrases-URI" ":" uri CRLF
This header field can optionally be specified in the END-PHRASE-ENROLLMENT method to abort the phrase enrollment, rather than committing the phrase to the personal grammar.
abort-phrase-enrollment = "Abort-Phrase-Enrollment" ":"
BOOLEAN CRLF
A recognizer message may carry additional data associated with the request, response or event. The client may provide the grammar to be recognized in DEFINE-GRAMMAR or RECOGNIZE requests. When one or more grammars are specified using the DEFINE-GRAMMAR method, the server MUST attempt to fetch, compile and optimize the grammar before returning a response to the DEFINE-GRAMMAR method. A RECOGNIZE request MUST completely specify the grammars to be active during the recognition operation, except when the RECOGNIZE method is being used to enroll a grammar. During grammar enrollment, such grammars are optional. The server resource may send the recognition results in the RECOGNITION-COMPLETE event or the GET-RESULT response. Grammars and recognition results are carried in the message body of the corresponding MRCPv2 messages.
Recognizer grammar data from the client to the server can be provided inline or by reference. Either way, grammar data is carried as typed media entities in the message body of the RECOGNIZE or DEFINE-GRAMMAR request. All MRCPv2 servers MUST accept grammars in the XML form (Media Type application/srgs+xml) of the W3C's XML-based Speech Grammar Markup Format (SRGS) [W3C.REC-speech-grammar-20040316] and MAY accept grammars in other formats. Examples include but are not limited to:Semantic Interpretation for Speech Recognition (SISR) [W3C.REC-semantic-interpretation-20070405] specification.
Additionally, MRCPv2 servers MAY support the
When a grammar is specified inline in the request, the client MUST provide a Content-ID for that grammar as part of the content header fields. If there is no space on the server to store the inline grammar, the request MUST return with a Completion-Cause code of 016 "grammar-definition-failure". Otherwise, the server MUST associate the inline grammar block with that Content-ID and MUST store it on the server for the duration of the session. However, if the Content-ID is redefined later in the session through a subsequent DEFINE-GRAMMAR, the inline grammar previously associated with the Content-ID MUST be freed. If the Content-ID is redefined through a subsequent DEFINE-GRAMMAR with an empty message body (i.e. no grammar definition), then in addition to freeing any grammar previously associated with the Content-ID the server MUST clear all bindings and associations to the Content-ID. Unless and until subsequently redefined, this URI MUST be interpreted by the server as one that has never been set.
Grammars that have been associated with a Content-ID can be referenced through the "session" URI scheme (see Section 13.6). For example:
session:help@root-level.store
Grammar data MAY be specified using external URI references. To do so, the client uses a body of Media Type text/uri-list (see RFC 2483 [RFC2483] ) to list the one or more URIs that point to the grammar data. The client can use a body of Media Type text/grammar-ref-list (see Section 13.5.1) if it wants to assign weights to the list of grammar URI. All MRCPv2 servers MUST support grammar access using the HTTP and HTTPS URI schemes.
If the grammar data the client wishes to be used on a request consists of a mix of URI and inline grammar data the client uses the multipart/mixed Media Type to enclose the text/uri-list, application/srgs or application/srgs+xml content entities. The character set and encoding used in the grammar data are specified using to standard Media Type definitions.
When more than one grammar URI or inline grammar block is specified in a message body of the RECOGNIZE request, the server interprets this as a list of grammar alternatives to match against.
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
<!-- multiple language attachment to a token -->
<rule id="people1">
<token lexicon="en-US,fr-CA"> Robert </token>
</rule>
<!-- the equivalent single-language attachment expansion -->
<rule id="people2">
<one-of>
<item xml:lang="en-US">Robert</item>
<item xml:lang="fr-CA">Robert</item>
</one-of>
</rule>
</grammar>
Content-Type:text/uri-list Content-Length:... session:help@root-level.store http://www.example.com/Directory-Name-List.grxml http://www.example.com/Department-List.grxml http://www.example.com/TAC-Contact-List.grxml session:menu1@menu-level.store
Content-Type:multipart/mixed; boundary="break"
--break
Content-Type:text/uri-list
Content-Length:...
http://www.example.com/Directory-Name-List.grxml
http://www.example.com/Department-List.grxml
http://www.example.com/TAC-Contact-List.grxml
--break
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
<!-- multiple language attachment to a token -->
<rule id="people1">
<token lexicon="en-US,fr-CA"> Robert </token>
</rule>
<!-- the equivalent single-language attachment expansion -->
<rule id="people2">
<one-of>
<item xml:lang="en-US">Robert</item>
<item xml:lang="fr-CA">Robert</item>
</one-of>
</rule>
</grammar>
--break--
Recognition results are returned to the client in the message body of the RECOGNITION-COMPLETE event or the GET-RESULT response message as described in Section 6.3). Element and attribute descriptions for the recognition portion of the NLSML format are provided in Section 9.6 with a normative definition of the schema in Section 16.1.
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="http://www.example.com/theYesNoGrammar">
<interpretation>
<instance>
<ex:response>yes</ex:response>
</instance>
<input>ok</input>
</interpretation>
</result>
Enrollment results are returned to the client in the message body of the RECOGNITION-COMPLETE event as described in Section 6.3). Element and attribute descriptions for the enrollment portion of the NLSML format are provided in Section 9.7 with a normative definition of the schema in Section 16.2.
When a client changes servers while operating on the behalf of the same incoming communication session, this header field allows the client to collect a block of opaque data from one server and provide it to another server. This capability is desirable if the client needs different language support or because the server issued a redirect. Here the first recognizer resource may have collected acoustic and other data during its execution of recognition methods. After a server switch, communicating this data may allow the recognition resource on the new server to provide better recognition. This block of data is implementation-specific and MUST be carried as Media Type application/octets in the body of the message.
This block of data is communicated in the SET-PARAMS and GET-PARAMS method/response messages. In the GET-PARAMS method, if an empty recognizer-context-block header field is present, then the recognizer SHOULD return its vendor-specific context block, if any, in the message body as an entity of Media Type application/octets with a specific Content-ID. The Content-ID value MUST also be specified in the recognizer-context-block header field in the GET-PARAMS response. The SET-PARAMS request wishing to provide this vendor-specific data MUST send it in the message body as a typed entity with the same Content-ID that it received from the GET-PARAMS. The Content-ID MUST also be sent in the recognizer-context-block header field of the SET-PARAMS message.
Each speech recognition implementation choosing to use this mechanism to hand off recognizer context data among servers MUST distinguish its implementation-specific block of data from other implementations by choosing a Content-ID that is recognizable among the participating servers and unlikely to collide with values chosen by another implementation.
The recognizer portion of NLSML (see Section 6.3.1) represents information automatically extracted from a user's utterances by a semantic interpretation component, where "utterance" is to be taken in the general sense of a meaningful user input in any modality supported by the MRCPv2 implementation.
MRCPv2 recognition resources employ the Natural Language Semantics Markup Language (NLSML) to interpret natural language speech input and to format the interpretation for consumption by an MRCPv2 client.
The elements of the markup fall into the following general functional categories: Interpretation, Side Information, and Multi-Modal Integration.
Elements and attributes represent the semantics of a user's utterance, including the <result>, <interpretation>, and <instance> elements. The <result> element contains the full result of processing one utterance. It may contain multiple <interpretation> elements if the interpretation of the utterance results in multiple alternative meanings due to uncertainty in speech recognition or natural language understanding. There are at least two reasons for providing multiple interpretations:
These are elements and attributes representing additional information about the interpretation, over and above the interpretation itself. Side information includes:
When more than one modality is available for input, the interpretation of the inputs need to be coordinated. The "mode" attribute of <input> supports this by indicating whether the utterance was input by speech, dtmf, pointing, etc. The "timestamp_start" and "timestamp_end" attributes of <interpretation> also provide for temporal coordination by indicating when inputs occurred.
The recognizer elements in NLSML fall into two categories:
Next to each element are its attributes. In addition, some elements can contain multiple instances of other elements. For example, a <result> can contain multiple <interpretations>, each of which is taken to be an alternative. Similarly, <input> can contain multiple child <input> elements which are taken to be cumulative. To illustrate the basic usage of these elements, as a simple example, consider the utterance "ok" (interpreted as "yes"). The example illustrates how that utterance and its interpretation would be represented in the NLSML markup.
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="http://www.example.com/theYesNoGrammar">
<interpretation>
<instance>
<ex:response>yes</ex:response>
</instance>
<input>ok</input>
</interpretation>
</result>
This example includes only the minimum required information. There is an overall <result> element which includes one interpretation and an input element. The interpretation contains the application-specific element "<response>" which is the semantically interpreted result.
The root element of the markup is <result>. The <result> element includes one or more <interpretation> elements. Multiple interpretations can result from ambiguities in the input or in the semantic interpretation. If the "grammar" attribute does not apply to all of the interpretations in the result it can be overridden for individual interpretations at the <interpretation> level.
Attributes:
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
grammar="http://www.example.com/grammar">
<interpretation>
....
</interpretation>
</result>
An <interpretation> element contains a single semantic interpretation.
Attributes:
Interpretations MUST be sorted best-first by some measure of "goodness". The goodness measure is "confidence" if present, otherwise, it is some implementation-specific indication of quality.
The grammar is expected to be specified most frequently at the <result> level. However, it can be overridden at the <interpretation> level because it is possible that different interpretations may match different grammar rules.
The <interpretation> element includes an optional <input> element which contains the input being analyzed, and an <instance> element containing the interpretation of the utterance.
<interpretation confidence="0.75"
grammar="http://www.example.com/grammar">
...
</interpretation>
The <instance> element contains the interpretation of the utterance. When the Semantic Interpretation for Speech Recognition format is used, the <instance> element contains the XML serialization of the result using the approach defined in that specification. When there is semantic markup in the grammar that does not create semantic objects, but instead only does a semantic translation of a portion of the input, such as translating "coke" to "coca-cola", the instance contains the whole input but with the translation applied. The NLSML looks like the markup in Figure 132 below. If there are no semantic objects created, nor any semantic translation the instance value is the same as the input value.
Attributes:
<instance>
<nameAddress>
<street confidence="0.75">123 Maple Street</street>
<city>Mill Valley</city>
<state>CA</state>
<zip>90952</zip>
</nameAddress>
</instance>
<input>
My address is 123 Maple Street,
Mill Valley, California, 90952
</input>
<instance>
I would like to buy a coca-cola
</instance>
<input>
I would like to buy a coke
</input>
The <input> element is the text representation of a user's input. It includes an optional "confidence" attribute which indicates the recognizer's confidence in the recognition result (as opposed to the confidence in the interpretation, which is indicated by the "confidence" attribute of <interpretation>). Optional "timestamp-start" and "timestamp-end" attributes indicate the start and end times of a spoken utterance, in ISO 8601 format [ISO.8601.1988].
Attributes:
Note that it may not make sense for temporally overlapping inputs to have the same mode; however, this constraint is not expected to be enforced by implementations.
When there is no time zone designator, ISO 8601 time representations default to local time.
<input>onions</input>
<input>
<input mode="speech" confidence="0.5"
timestamp-start="2000-04-03T0:00:00"
timestamp-end="2000-04-03T0:00:00.2">fried</input>
<input mode="speech" confidence="1.0"
timestamp-start="2000-04-03T0:00:00.25"
timestamp-end="2000-04-03T0:00:00.6">onions</input>
</input>
There are three possible formats for the <input> element.
The <nomatch> element under <input> is used to indicate that the semantic interpreter was unable to successfully match any input with confidence above the threshold. It can optionally contain the text of the best of the (rejected) matches.
<interpretation>
<instance/>
<input confidence="0.1">
<nomatch/>
</input>
</interpretation>
<interpretation>
<instance/>
<input mode="speech" confidence="0.1">
<nomatch>I want to go to New York</nomatch>
</input>
</interpretation>
<noinput> indicates that there was no input - a timeout occurred in the speech recognizer due to silence.
<interpretation>
<instance/>
<input>
<noinput/>
</input>
</interpretation>
If there are multiple levels of inputs, the most natural place for <nomatch> and <noinput> elements to appear is under the highest level of <input> for <noinput>, and under the appropriate level of <interpretation> for <nomatch>. So <noinput> means "no input at all" and <nomatch> means "no match in speech modality" or "no match in dtmf modality". For example, to represent garbled speech combined with dtmf "1 2 3 4", the markup would be:
<input> <input mode="speech"><nomatch/></input> <input mode="dtmf">1 2 3 4</input> </input>
Note: while <noinput> could be represented as an attribute of input, <nomatch> cannot, since it could potentially include PCDATA content with the best match. For parallelism, <noinput> is also an element.
All enrollment elements are contained within a single <enrollment-result> element under <result>. The elements are described below and have the schema defined in Section 16.2. The following elements are defined:
The <num-clashes> element contains the number of clashes that this pronunciation has with other pronunciations in an active enrollment session. The associated Clash-Threshold header field determines the sensitivity of the clash measurement. Note that clash testing can be turned off completely by setting the Clash-Threshold header field value to 0.
The <num-good-repetitions> element contains the number of consistent pronunciations obtained so far in an active enrollment session.
The <num-repetitions-still-needed> element contains the number of consistent pronunciations that must still be obtained before the new phrase can be added to the enrollment grammar. The number of consistent pronunciations required is specified by the client in the request header field Num-Min-Consistent-Pronunciations. The returned value must be 0 before the client can successfully commit a phrase to the grammar by ending the enrollment session.
The <consistency-status> element is used to indicate how consistent the repetitions are when learning a new phrase. It can have the values of consistent, inconsistent, and undecided.
The <clash-phrase-ids> element contains the phrase ids of clashing pronunciation(s), if any. This element is absent if there are no clashes.
The <transcriptions> element contains the transcriptions returned in the last repetition of the phrase being enrolled.
The <confusable-phrases> element contains a list of phrases from a command grammar that are confusable with the phrase being added to the personal grammar. This element may be absent if there are no confusable phrases.
The DEFINE-GRAMMAR method, from the client to the server, provides one or more grammars and requests the server to access, fetch, and compile the grammars as needed. The DEFINE-GRAMMAR method implementation MUST do a fetch of all external URIs that are part of that operation. If caching is implemented, this URI fetching MUST conform to the cache control hints and parameter header fields associated with the method in deciding whether it should be fetched from cache or from the external server. If these hints/parameters are not specified in the method, the values set for the session using SET-PARAMS/GET-PARAMS apply. If it was not set for the session their default values apply.
If the server resource is in the recognition state, the DEFINE-GRAMMAR request MUST respond with a failure status.
If the resource is in the idle state and is able to successfully process the supplied grammars, the server MUST return a success code status and the request-state MUST be COMPLETE.
If the recognizer resource could not define the grammar for some reason, for example if the download failed, the grammar failed to compile, or the grammar was in an unsupported form, the MRCPv2 response for the DEFINE-GRAMMAR method MUST contain a failure status-code of 407, and contain a Completion-Cause header field describing the failure reason.
C->S:MRCP/2.0 ... DEFINE-GRAMMAR 543257
Channel-Identifier:32AECB23433801@speechrecog
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C:MRCP/2.0 ... 543257 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
C->S:MRCP/2.0 ... DEFINE-GRAMMAR 543258
Channel-Identifier:32AECB23433801@speechrecog
Content-Type:application/srgs+xml
Content-ID:<helpgrammar@root-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0">
<rule id="request">
I need help
</rule>
S->C:MRCP/2.0 ... 543258 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
C->S:MRCP/2.0 ... DEFINE-GRAMMAR 543259
Channel-Identifier:32AECB23433801@speechrecog
Content-Type:application/srgs+xml
Content-ID:<request2@field-level.store>
Content-Length:...
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE grammar PUBLIC "-//W3C//DTD GRAMMAR 1.0//EN"
"http://www.w3.org/TR/speech-grammar/grammar.dtd">
<grammar xmlns="http://www.w3.org/2001/06/grammar" xml:lang="en"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/06/grammar
http://www.w3.org/TR/speech-grammar/grammar.xsd"
version="1.0" mode="voice" root="basicCmd">
<meta name="author" content="Stephanie Williams"/>
<rule id="basicCmd" scope="public">
<example> please move the window </example>
<example> open a file </example>
<ruleref
uri="http://grammar.example.com/politeness.grxml#startPolite"/>
<ruleref uri="#command"/>
<ruleref
uri="http://grammar.example.com/politeness.grxml#endPolite"/>
</rule>
<rule id="command">
<ruleref uri="#action"/> <ruleref uri="#object"/>
</rule>
<rule id="action">
<one-of>
<item weight="10"> open <tag>open</tag> </item>
<item weight="2"> close <tag>close</tag> </item>
<item weight="1"> delete <tag>delete</tag> </item>
<item weight="1"> move <tag>move</tag> </item>
</one-of>
</rule>
<rule id="object">
<item repeat="0-1">
<one-of>
<item> the </item>
<item> a </item>
</one-of>
</item>
<one-of>
<item> window </item>
<item> file </item>
<item> menu </item>
</one-of>
</rule>
</grammar>
S->C:MRCP/2.0 ... 543259 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
C->S:MRCP/2.0 ... RECOGNIZE 543260
Channel-Identifier:32AECB23433801@speechrecog
N-Best-List-Length:2
Content-Type:text/uri-list
Content-Length:...
session:request1@form-level.store
session:request2@field-level.store
session:helpgramar@root-level.store
S->C:MRCP/2.0 ... 543260 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C:MRCP/2.0 ... START-OF-INPUT 543260 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C:MRCP/2.0 ... RECOGNITION-COMPLETE 543260 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Waveform-URI:<http://web.media.com/session123/audio.wav>;
size=124535;duration=2340
Content-Type:application/x-nlsml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
The RECOGNIZE method from the client to the server requests the recognizer to start recognition and provides it with one or more grammar references for grammars to match against the input media. The RECOGNIZE method can carry header fields to control the sensitivity, confidence level and the level of detail in results provided by the recognizer. These header field values override the current values set by a previous SET-PARAMS method.
The RECOGNIZE method can request the recognizer resource to operate in normal or hotword mode as specified by the Recognition-Mode header field. The default value is "normal". If the resource could not start a recognition, the server MUST respond with a failure status-code of 407 and a Completion-Cause header field in the response describing the cause of failure.
The RECOGNIZE request uses the message body to specify the grammars applicable to the request. The active grammar(s) for the request can be specified in one of 3 ways. If the client needs to explicitly control grammar weights for the recognition operation, it MUST employ method 3 below. The order of these grammars specifies the precedence of the grammars which is used when more than one grammar in the list matches the speech; in this case, the grammar with the higher precedence is returned as a match. This precedence capability is useful in applications like VoiceXML browsers to order grammars specified at the dialog, document and root level of a VoiceXML application.Section 13.6).
In addition to performing recognition on the input, the recognizer MUST also enroll the collected utterance in a personal grammar if the Enroll-Utterance header field is set to true and an Enrollment is active (via an earlier execution of the START-PHRASE-ENROLLMENT method). If so, and if the RECOGNIZE request contains a Content-ID header field, then the resulting grammar (which includes the personal grammar as a sub-grammar) can be referenced through the "session" URI scheme (see
If the resource was able to successfully start the recognition, the server MUST return a success status-code and a request-state of IN-PROGRESS. This means that the recognizer is active and that the client MUST be prepared to receive further events with this request-id.
If the resource was able to queue the request the server MUST return a success code and request-state of PENDING. This means that the recognizer is currently active with another request and that this request has been queued for processing.
If the resource could not start a recognition, the server MUST respond with a failure status-code of 407 and a Completion-Cause header field in the response describing the cause of failure.
For the recognizer resource, RECOGNIZE and INTERPRET are the only requests that returns a request-state of IN-PROGRESS, meaning that recognition is in progress. When the recognition completes by matching one of the grammar alternatives or by a time-out without a match or for some other reason, the recognizer resource MUST send the client a RECOGNITION-COMPLETE event (or INTERPRETATION-COMPLETE, if INTERPRET was the request) with the result of the recognition and a request-state of COMPLETE.
Large grammars can take a long time for the server to compile. For grammars which are used repeatedly, the client can improve server performance by issuing a DEFINE-GRAMMAR request with the grammar ahead of time. In such a case the client can issue the RECOGNIZE request and reference the grammar through the session: URI scheme (see Section 13.6). This also applies in general if the client wants to repeat recognition with a previous inline grammar.
The RECOGNIZE method implementation MUST do a fetch of all external URIs that are part of that operation. If caching is implemented, this URI fetching MUST conform to the cache control hints and parameter header fields associated with the method in deciding whether it should be fetched from cache or from the external server. If these hints/parameters are not specified in the method, the values set for the session using SET-PARAMS/GET-PARAMS apply. If it was not set for the session their default values apply.
Note that since the audio and the messages are carried over separate communication paths there may be a race condition between the start of the flow of audio and the receipt of the RECOGNIZE method. For example, if an audio flow is started by the client at the same time as the RECOGNIZE method is sent, either the audio or the RECOGNIZE can arrive at the recognizer first. As another example, the client may choose to continuously send audio to the Server and signal the Server to recognize using the RECOGNIZE method. Mechanisms to resolve this condition are outside the scope of this specification. The recognizer can expect the media to start flowing when it receives the recognize request, but MUST NOT buffer anything it receives beforehand in order to preserve the semantics that application authors expect with respect to the input timers.
When a RECOGNIZE method has been received the recognition is initiated on the stream. The No-Input-Timer MUST be started at this time if the Start-Input-Timers header field is specified as "true". If this header field is set to "false", the No-Input-Timer MUST be started when it receives the START-INPUT-TIMERS method from the client. The Recognition-Timer MUST be started when the recognition resource detects speech or a DTMF digit in the media stream.
Non-Hotword mode recognition:
When the recognition resource detects speech or a DTMF digit in the media stream it MUST send the START-OF-INPUT event. When enough speech has been collected for the server to process, the recognizer can try to match the collected speech with the active grammars. If the speech collected at this point fully matches with any of the active grammars, the Speech-Complete-Timer is started. If it matches partially with one or more of the active grammars, with more speech needed before a full match is achieved, then the Speech-Incomplete-Timer is started.
1. When the No-Input-Timer expires, the recognizer MUST complete with a Completion-Cause code of "no-input-timeout".
2. The recognizer MUST support detecting a no-match condition upon detecting end of speech. The recognizer MAY support detecting a no-match condition before waiting for end-of-speech. If this is supported, this capability is enabled by setting the "Early-No-Match" header field to "true". Upon detecting a no-match condition the RECOGNIZE MUST return with "no-match".
3. When the Speech-Incomplete-Timer expires the recognizer SHOULD complete with a Completion-Cause code of "partial-match", unless the recognizer cannot differentiate a partial-match in which case it MUST return a Completion-Cause code of "no-match". The recognizer MAY return results for the partially matched grammar.
4. When the Speech-Complete-Timer expires the recognizer MUST complete with a Completion-Cause code of "success".
5. When the Recognition-Timer expires one of the following MUST happen:
5.1 If there was a partial-match the recognizer SHOULD complete with a Completion-Cause code of "partial-match-maxtime", unless the recognizer cannot differentiate a partial-match in which case it MUST complete with a Completion-Cause code of "no-match-maxtime". The recognizer MAY return results for the partially matched grammar.
5.2 If there was a full-match the recognizer MUST complete with a Completion-Cause code of "success-maxtime".
5.3 If there was a no match the recognizer MUST complete with a Completion-Cause code of "no-match-maxtime".
For the Hotword mode recognition:
Note that for Hotword mode recognition the START-OF-INPUT event is not generated when speech or a DTMF digit is detected.
1. When the No-Input-Timer expires, the recognizer MUST complete with a Completion-Cause code of "no-input-timeout".
2. If at any point a match occurs, the RECOGNIZE MUST complete with a Completion-Cause code of "success".
3. When the Recognition-Timer expires and there is not a match, the RECOGNIZE MUST complete with a Completion-Cause code of "hotword-maxtime".
4. When the Recognition-Timer expires and there is a match, the RECOGNIZE MUST complete with a Completion-Cause code of "success-maxtime".
5. When the Recognition-Timer is running but the detected speech/DTMF has not resulted in a match, the Recognition-Timer MUST be stopped and reset. It MUST then be restarted when speech/DTMF is again detected.
C->S:MRCP/2.0 ... RECOGNIZE 543257
Channel-Identifier:32AECB23433801@speechrecog
Confidence-Threshold:0.9
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C: MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C:MRCP/2.0 ... START-OF-INPUT 543257 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C:MRCP/2.0 ... RECOGNITION-COMPLETE 543257 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Waveform-URI:<http://web.media.com/session123/audio.wav>;
size=424252;duration=2543
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
C->S: MRCP/2.0 ... RECOGNIZE 543257
Channel-Identifier:32AECB23433801@speechrecog
Confidence-Threshold:0.9
Fetch-Timeout:20
Content-Type:application/srgs+xml
Content-Length:...
<?xml version="1.0"? Version="1.0" mode="voice"
root="Basic md">
<rule id="rule_list" scope="public">
<one-of>
<item weight=10>
<ruleref uri=
"http://grammar.example.com/world-cities.grxml#canada"/>
</item>
<item weight=1.5>
<ruleref uri=
"http://grammar.example.com/world-cities.grxml#america"/>
</item>
<item weight=0.5>
<ruleref uri=
"http://grammar.example.com/world-cities.grxml#india"/>
</item>
</one-of>
</rule>
The STOP method from the client to the server tells the resource to stop recognition if a request is active. If a RECOGNIZE request is active and the STOP request successfully terminated it, then the response header section contains an active-request-id-list header field containing the request-id of the RECOGNIZE request that was terminated. In this case, no RECOGNITION-COMPLETE event is sent for the terminated request. If there was no recognition active, then the response MUST NOT contain an active-request-id-list header field. Either way the response MUST contain a status-code of 200 (Success).
C->S: MRCP/2.0 ... RECOGNIZE 543257
Channel-Identifier:32AECB23433801@speechrecog
Confidence-Threshold:0.9
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C: MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
C->S: MRCP/2.0 ... STOP 543258 200
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 ... 543258 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Active-Request-Id-List:543257
The GET-RESULT method from the client to the server may be issued when the recognizer resource is in the recognized state. This request allows the client to retrieve results for a completed recognition. This is useful if the client decides it wants more alternatives or more information. When the server receives this request it re-computes and returns the results according to the recognition constraints provided in the GET-RESULT request.
The GET-RESULT request can specify constraints such as a different confidence-threshold, or n-best-list-length. This capability is optional for MRCPv2 servers and the automatic speech recognition engine in the server MAY return a status of unsupported feature.
C->S: MRCP/2.0 ... GET-RESULT 543257
Channel-Identifier:32AECB23433801@speechrecog
Confidence-Threshold:0.9
S->C: MRCP/2.0 ... 543257 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
This is an event from the server to the client indicating that the recognition resource has detected speech or a DTMF digit in the media stream. This event is useful in implementing kill-on-barge-in scenarios when a synthesizer resource is in a different session from the recognizer resource and hence is not aware of an incoming audio source (see Section 8.4.2). In these cases, it is up to the client to act as a intermediary and respond to this event by issuing a BARGE-IN-OCCURRED event to the synthesizer resource. The recognizer resource also MUST send a Proxy-Sync-Id header field with a unique value for this event.
This event MUST be generated by the server irrespective of whether the synthesizer and recognizer are on the same server or not.
This request is sent from the client to the recognition resource when it knows that a kill-on-barge-in prompt has finished playing (see Section 8.4.2). This is useful in the scenario when the recognition and synthesizer engines are not in the same session. When a kill-on-barge-in prompt is being played, the client may want a RECOGNIZE request to be simultaneously active so that it can detect and implement kill on barge-in. But at the same time the client doesn't want the recognizer to start the no-input timers until the prompt is finished. The Start-Input-Timers header field in the RECOGNIZE request allows the client to say whether the timers should be started immediately or not. If not, the recognizer resource MUST NOT start the timers until the client sends a START-INPUT-TIMERS method to the recognizer.
This is an Event from the recognizer resource to the client indicating that the recognition completed. The recognition result is sent in the body of the MRCPv2 message. The request-state field MUST be COMPLETE indicating that this is the last event with that request-id, and that the request with that request-id is now complete. The server MUST maintain the recognizer context containing the results and the audio waveform input of that recognition until the next RECOGNIZE request is issued for that resource or the session terminates. A URI to the audio waveform MAY be returned to the client in a Waveform-URI header field in the RECOGNITION-COMPLETE event. The client can use this URI to retrieve or playback the audio.
Note if an enrollment session was active, the RECOGNITION-COMPLETE event can contain either recognition or enrollment results depending on what was spoken. The following example shows a complete exchange with a recognition result.
C->S: MRCP/2.0 ... RECOGNIZE 543257
Channel-Identifier:32AECB23433801@speechrecog
Confidence-Threshold:0.9
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C: MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 ... START-OF-INPUT 543257 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 ... RECOGNITION-COMPLETE 543257 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Waveform-URI:<http://web.media.com/session123/audio.wav>;
size=342456;duration=25435
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
If the result were instead an enrollment result, the final message from the server above could have instead been:
S->C: MRCP/2.0 ... RECOGNITION-COMPLETE 543257 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version= "1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
grammar="Personal-Grammar-URI">
<enrollment-result>
<num-clashes> 2 </num-clashes>
<num-good-repetitions> 1 </num-good-repetitions>
<num-repetitions-still-needed>
1
</num-repetitions-still-needed>
<consistency-status> consistent </consistency-status>
<clash-phrase-ids>
<item> Jeff </item> <item> Andre </item>
</clash-phrase-ids>
<transcriptions>
<item> m ay b r ow k er </item>
<item> m ax r aa k ah </item>
</transcriptions>
<confusable-phrases>
<item>
<phrase> call </phrase>
<confusion-level> 10 </confusion-level>
</item>
</confusable-phrases>
</enrollment-result>
</result>
The START-PHRASE-ENROLLMENT method from the client to the server starts a new phrase enrollment session during which the client may call RECOGNIZE multiple times to enroll a new utterance in a grammar. An enrollment session consists of a set of calls to RECOGNIZE in which the caller speaks a phrase several times so the system can "learn" it. The phrase is then added to a personal grammar (speaker-trained grammar), so that the system can recognize it later.
Only one phrase enrollment session may be active at a time for a resource. The Personal-Grammar-URI identifies the grammar that is used during enrollment to store the personal list of phrases. Once RECOGNIZE is called, the result is returned in a RECOGNITION-COMPLETE event and may contain either an enrollment result OR a recognition result for a regular recognition.
Calling END-PHRASE-ENROLLMENT ends the ongoing phrase enrollment session, which is typically done after a sequence of successful calls to RECOGNIZE. This method can be called to commit the new phrase to the personal grammar or to abort the phrase enrollment session.
The grammar to contain the new enrolled phrase, specified by Personal-Grammar-URI, is created if it does not exist. Also, the personal grammar may ONLY contain phrases added via a phrase enrollment session.
The Phrase-ID passed to this method is used to identify this phrase in the grammar and will be returned as the speech input when doing a RECOGNIZE on the grammar. The Phrase-NL similarly is returned in a RECOGNITION-COMPLETE event in the same manner as other Natural Language (NL) in a grammar. The tag-format of this NL is implementation specific.
If the client has specified Save-Best-Waveform as true, then the response after ending the phrase enrollment session MUST contain the location/URI of a recording of the best repetition of the learned phrase.
C->S: MRCP/2.0 ... START-PHRASE-ENROLLMENT 543258
Channel-Identifier:32AECB23433801@speechrecog
Num-Min-Consistent-Pronunciations:2
Consistency-Threshold:30
Clash-Threshold:12
Personal-Grammar-URI:<personal grammar uri>
Phrase-Id:<phrase id>
Phrase-NL:<NL phrase>
Weight:1
Save-Best-Waveform:true
S->C: MRCP/2.0 ... 543258 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
The ENROLLMENT-ROLLBACK method discards the last live utterance from the RECOGNIZE operation. The client can invoke this method when the caller provides undesirable input such as non-speech noises, side-speech, commands, utterance from the RECOGNIZE grammar, etc. Note that this method does not provide a stack of rollback states. Executing ENROLLMENT-ROLLBACK twice in succession without an intervening recognition operation has no effect the second time.
C->S: MRCP/2.0 ... ENROLLMENT-ROLLBACK 543261
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 ... 543261 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
The client MAY call the END-PHRASE-ENROLLMENT method ONLY during an active phrase enrollment session. It MUST NOT be called during an ongoing RECOGNIZE operation. To commit the new phrase in the grammar, the client MAY call this method once successive calls to RECOGNIZE have succeeded and Num-Repetitions-Still-Needed has been returned as 0 in the RECOGNITION-COMPLETE event. Alternatively, the client MAY abort the phrase enrollment session by calling this method with the Abort-Phrase-Enrollment header field.
If the client has specified Save-Best-Waveform as true in the START-PHRASE-ENROLLMENT request, then the response MUST contain a Waveform-URI header whose value is the location/URI of a recording of the best repetition of the learned phrase.
C->S: MRCP/2.0 ... END-PHRASE-ENROLLMENT 543262
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 ... 543262 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Waveform-URI:<http://mediaserver.com/recordings/file1324.wav>;
size=242453;duration=25432
The MODIFY-PHRASE method sent from the client to the server is used to change the phrase ID, NL phrase and/or weight for a given phrase in a personal grammar.
If no fields are supplied then calling this method has no effect.
C->S: MRCP/2.0 ... MODIFY-PHRASE 543265
Channel-Identifier:32AECB23433801@speechrecog
Personal-Grammar-URI:<personal grammar uri>
Phrase-Id:<phrase id>
New-Phrase-Id:<new phrase id>
Phrase-NL:<NL phrase>
Weight:1
S->C: MRCP/2.0 ... 543265 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
The DELETE-PHRASE method sent from the client to the server is used to delete a phase in a personal grammar added through voice enrollment or text enrollment. If the specified phrase does not exist, this method has no effect.
C->S: MRCP/2.0 ... DELETE-PHRASE 543266
Channel-Identifier:32AECB23433801@speechrecog
Personal-Grammar-URI:<personal grammar uri>
Phrase-Id:<phrase id>
S->C: MRCP/2.0 ... 543266 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
The INTERPRET method from the client to the server takes as input an interpret-text header field containing the text for which the semantic interpretation is desired, and returns, via the INTERPRETATION-COMPLETE event, an interpretation result which is very similar to the one returned from a RECOGNIZE method invocation. Only portions of the result relevant to acoustic matching are excluded from the result. The interpret-text header field MUST be included in the INTERPRET request.
Recognizer grammar data is treated in the same way as it is when issuing a RECOGNIZE method call.
If a RECOGNIZE, RECORD or another INTERPRET operation is already in progress for the resource, the server MUST reject the request with a response having a status-code of 402 "Method not valid in this state", and a COMPLETE request state.
C->S: MRCP/2.0 ... INTERPRET 543266
Channel-Identifier:32AECB23433801@speechrecog
Interpret-Text:may I speak to Andre Roy
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C: MRCP/2.0 ... 543266 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 ... INTERPRETATION-COMPLETE 543266 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
This event from the recognition resource to the client indicates that the INTERPRET operation is complete. The interpretation result is sent in the body of the MRCP message. The request state MUST be set to COMPLETE.
The Completion-Cause header field MUST be included in this event and MUST be set to an appropriate value from the list of cause codes.
C->S: MRCP/2.0 ... INTERPRET 543266
Channel-Identifier:32AECB23433801@speechrecog
Interpret-Text:may I speak to Andre Roy
Content-Type:application/srgs+xml
Content-ID:<request1@form-level.store>
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to tokens -->
<rule id="yes">
<one-of>
<item xml:lang="fr-CA">oui</item>
<item xml:lang="en-US">yes</item>
</one-of>
</rule>
<!-- single language attachment to a rule expansion -->
<rule id="request">
may I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C: MRCP/2.0 ... 543266 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
S->C: MRCP/2.0 ... INTERPRETATION-COMPLETE 543266 200 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
Digits received as DTMF tones are delivered to the recognition resource in the MRCPv2 server in the RTP stream according to RFC4733 [RFC4733]. The automatic speech recognizer (ASR) MUST support RFC4733 to recognize digits and it MAY support recognizing DTMF tones [Q.23] in the audio.
This resource captures received audio and video and stores it as content pointed to by a URI. The main usages of recorders areRTSP [RFC2326]. This includes Audio endpointing (i.e. detecting speech or silence). The support for video is optional and is mainly capturing video mails that may require the speech or audio processing mentioned above.
Both these applications require functionality above and beyond those specified by protocols such as
A recorder MUST provide some endpointing capabilities for suppressing silence at the beginning and end of a recording, and MAY also suppress silence in the middle of a recording. If such suppression is done, the recorder MUST maintain timing metadata to indicate the actual time stamps of the recorded media.
See the discussion on the sensitivity of saved waveforms in Section 12.
Idle Recording State State | | |---------RECORD------->| | | |<------STOP------------| | | |<--RECORD-COMPLETE-----| | | | |--------| | START-OF-INPUT | | |------->| | | | |--------| | START-INPUT-TIMERS | | |------->| | |
The recorder resource supports the following methods.
recorder-method = "RECORD"
/ "STOP"
/ "START-INPUT-TIMERS"
The recorder resource may generate the following events.
recorder-event = "START-OF-INPUT"
/ "RECORD-COMPLETE"
Method invocations for the recorder resource may contain resource-specific header fields containing request options and information to augment the Method, Response or Event message it is associated with.
recorder-header = sensitivity-level
/ no-input-timeout
/ completion-cause
/ completion-reason
/ failed-uri
/ failed-uri-cause
/ record-uri
/ media-type
/ max-time
/ trim-length
/ final-silence
/ capture-on-speech
/ ver-buffer-utterance
/ start-input-timers
/ new-audio-channel
To filter out background noise and not mistake it for speech, the recorder may support a variable level of sound sensitivity. The sensitivity-level header field is a float value between 0.0 and 1.0 and allows the client to set the sensitivity level for the recorder. This header field MAY occur in RECORD, SET-PARAMS or GET-PARAMS. A higher value for this header field means higher sensitivity. The default value for this header field is implementation specific.
sensitivity-level = "Sensitivity-Level" ":" FLOAT CRLF
When recording is started and there is no speech detected for a certain period of time, the recorder can send a RECORD-COMPLETE event to the client and terminate the record operation. The no-input-timeout header field can set this timeout value. The value is in milliseconds. This header field MAY occur in RECORD, SET-PARAMS or GET-PARAMS. The value for this header field ranges from 0 to an implementation specific maximum value. The default value for this header field is implementation specific.
no-input-timeout = "No-Input-Timeout" ":" 1*19DIGIT CRLF
This header field MUST be part of a RECORD-COMPLETE event from the recorder resource to the client. This indicates the reason behind the RECORD method completion. This header field MUST be sent in the RECORD responses if they return with a failure status and a COMPLETE state. In the ABNF below, the 'cause-code' contains a numerical value selected from the Cause-Code column of the following table. The 'cause-name' contains the corresponding token selected from the Cause-Name column.
completion-cause = "Completion-Cause" ":" cause-code SP
cause-name CRLF
cause-code = 3DIGIT
cause-name = *VCHAR
| Cause-Code | Cause-Name | Description |
|---|---|---|
| 000 | success-silence | RECORD completed with a silence at the end |
| 001 | success-maxtime | RECORD completed after reaching maximum recording time specified in record method. |
| 002 | noinput-timeout | RECORD failed due to no input |
| 003 | uri-failure | Failure accessing the record URI. |
| 004 | error | RECORD request terminated prematurely due to a recorder error. |
This header field MAY be present in a RECORD-COMPLETE event coming from the recorder resource to the client. It contains the reason text behind the RECORD request completion. This header field communicates text describing the reason for the failure.
The completion reason text is provided for client use in logs and for debugging and instrumentation purposes. Clients MUST NOT interpret the completion reason text.
completion-reason = "Completion-Reason" ":"
quoted-string CRLF
When a recorder method needs to post the audio to a URI and access to the URI fails, the server MUST provide the failed URI in this header field in the method response.
failed-uri = "Failed-URI" ":" absoluteURI CRLF
When a recorder method needs to post the audio to a URI and access to the URI fails, the server MAY provide the URI specific or protocol specific response code through this header field in the method response. The value encoding is UTF-8 (RFC3629 [RFC3629]) to accommodate any access protocol, some of which might have a response string instead of a numeric response code.
failed-uri-cause = "Failed-URI-Cause" ":" 1*UTFCHAR
CRLF
When a recorder method contains this header field the server MUST capture the audio and store it. If the header field is present but specified with no value, the server MUST store the content locally and generate a URI that points to it. This URI is then returned in either the STOP response or the RECORD-COMPLETE event. If the header field in the RECORD method specifies a URI, the server MUST attempt to capture and store the audio at that location. If this header field is not specified in the RECORD request, the server MUST capture the audio, MUST encode it, and MUST send it in the STOP response or the RECORD-COMPLETE event as a message body. In this case, the response carrying the audio content MUST include a Content ID (cid) [RFC2392] value in this header pointing to the Content-ID in the message body.
The server MUST also return the size in octets and the duration in milliseconds of the recorded audio wave-form as parameters associated with the header field.
Implementations MUST support 'http', 'https' [RFC2616], 'file' [RFC3986], and 'cid' [RFC2392] schemes in the URI. Note that implementations already exist that support other schemes.
record-uri = "Record-URI" ":" ["<" uri ">"
";" "size" "=" 1*19DIGIT
";" "duration" "=" 1*19DIGIT] CRLF
A RECORD method MUST contain this header field, which specifies to the server the Media Type of the captured audio or video.
media-type = "Media-Type" ":" media-type-value
CRLF
When recording is started this specifies the maximum length of the recording in milliseconds, calculated from the time the actual capture and store begins and is not necessarily the time the RECORD method is received. It specifies the duration before silence suppression, if any, has been applied by the recorder resource. After this time, the recording stops and the server MUST return a RECORD-COMPLETE event to the client having a request-state of "COMPLETE". This header field MAY occur in RECORD, SET-PARAMS or GET-PARAMS. The value for this header field ranges from 0 to an implementation specific maximum value. A value of zero means infinity and hence the recording continues until one or more of the other stop conditions are met. The default value for this header field is 0.
max-time = "Max-Time" ":" 1*19DIGIT CRLF
This header field MAY be sent on a STOP method and specifies the length of audio to be trimmed from the end of the recording after the stop. The length is interpreted to be in milliseconds. The default value for this header field is 0.
trim-length = "Trim-Length" ":" 1*19DIGIT CRLF
When recorder is started and the actual capture begins, this header field specifies the length of silence in the audio that is to be interpreted as the end of the recording. This header field MAY occur in RECORD, SET-PARAMS or GET-PARAMS. The value for this header field ranges from 0 to an implementation specific maximum value and is interpreted to be in milliseconds. A value of zero means infinity and hence the recording will continue until one of the other stop conditions are met. The default value for this header field is implementation specific.
final-silence = "Final-Silence" ":" 1*19DIGIT CRLF
If false, the recorder MUST start capturing immediately when started. If true, the recorder MUST wait for the endpointing functionality to detect speech before it starts capturing. This header field MAY occur in the RECORD, SET-PARAMS or GET-PARAMS. The value for this header field is a Boolean. The default value for this header field is false.
capture-on-speech = "Capture-On-Speech " ":" BOOLEAN CRLF
This header field is the same as the one described for the verifier resource (see Section 11.4.14). This tells the server to buffer the utterance associated with this recording request into the verification buffer. Sending this header field is permitted only if the verification buffer is for the session. This buffer is shared across resources within a session. It gets instantiated when a verifier resource is added to this session and is released when the verifier resource is released from the session.
This header field MAY be sent as part of the RECORD request. A value of false tells the recorder resource to start the operation, but not to start the no-input timer until the client sends a START-INPUT-TIMERS request to the recorder resource. This is useful in the scenario when the recorder and synthesizer resources are not part of the same session. When a kill-on-barge-in prompt is being played, the client may want the RECORD request to be simultaneously active so that it can detect and implement kill-on-barge-in (see Section 8.4.2). But at the same time the client doesn't want the recorder resource to start the no-input timers until the prompt is finished. The default value is "true".
start-input-timers = "Start-Input-Timers" ":"
BOOLEAN CRLF
This header field is the same as the one described for the Recognizer resource (see Section 9.4.23).
If the RECORD request did not have a Record-Uri header field, the STOP response or the RECORD-COMPLETE event MUST contain a message body carrying the captured audio. In this case, the message carrying the audio content has a Record-Uri header field with a Content ID value pointing to the message body entity that contains the recorded audio. See Section 10.4.7 for details.
The RECORD request places the recorder resource in the Recording state. Depending on the header fields specified in the RECORD method, the resource may start recording the audio immediately or wait for the end pointing functionality to detect speech in the audio. The audio is then made available to the client either in the message body or as specified by Record-URI.
The server MUST support the HTTPS URI scheme and MAY support other schemes. Note that due to the sensitive nature of voice recordings, any protocols used for dereferencing SHOULD employ integrity and confidentiality, unless other means, such as physical security, are employed.
If a RECORD operation is already in progress, invoking this method causes the server to issue a response having a status code of 402, "Method not valid in this state", and a COMPLETE request state.
If the recording-uri is not valid, a status code of 404, "Illegal Value for Header Field", is returned in the response. If it is impossible for the server to create the requested stored content, a status code of 407, "Method or Operation Failed", is returned.
If the type specified in the Media-Type header field is not supported, the server MUST respond with a status code of 409, "Unsupported Header Field Value", with the Media-Type header field in its response.
When the recording operation is initiated, the response indicates an IN-PROGRESS request state. The server MAY generate a subsequent START-OF-INPUT event when speech is detected. Upon completion of the recording operation, the server generates a RECORD-COMPLETE event.
C->S: MRCP/2.0 ... RECORD 543257
Channel-Identifier:32AECB23433802@recorder
Record-URI:<file://mediaserver/recordings/myfile.wav>
Media-Type:audio/wav
Capture-On-Speech:true
Final-Silence:300
Max-Time:6000
S->C: MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@recorder
S->C: MRCP/2.0 ... START-OF-INPUT 543257 IN-PROGRESS
Channel-Identifier:32AECB23433802@recorder
S->C: MRCP/2.0 ... RECORD-COMPLETE 543257 COMPLETE
Channel-Identifier:32AECB23433802@recorder
Completion-Cause:000 success-silence
Record-URI:<file://mediaserver/recordings/myfile.wav>;
size=242552;duration=25645
The STOP method moves the recorder from the recording state back to the idle state. If a RECORD request is active and the STOP request successfully terminated it, then the STOP response MUST contain an active-request-id-list header field containing the RECORD request-id that was terminated. In this case, no RECORD-COMPLETE event is sent for the terminated request. If there was no recording active, then the response MUST NOT contain an active-request-id-list header field. If the recording was a success the STOP response MUST contain a Record-URI header field pointing to the recorded audio content or to an typed entity in the body of the STOP response containing the recorded audio. The STOP method may have a Trim-Length header field, in which case the specified length of audio is trimmed from the end of the recording after the stop. In any case, the response MUST contain a status-code of 200 (Success).
C->S: MRCP/2.0 ... RECORD 543257
Channel-Identifier:32AECB23433802@recorder
Record-URI:<file://mediaserver/recordings/myfile.wav>
Capture-On-Speech:true
Final-Silence:300
Max-Time:6000
S->C: MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@recorder
S->C: MRCP/2.0 ... START-OF-INPUT 543257 IN-PROGRESS
Channel-Identifier:32AECB23433802@recorder
C->S: MRCP/2.0 ... STOP 543257
Channel-Identifier:32AECB23433802@recorder
Trim-Length:200
S->C: MRCP/2.0 ... 543257 200 COMPLETE
Channel-Identifier:32AECB23433802@recorder
Record-URI:<file://mediaserver/recordings/myfile.wav>;
size=324253;duration=24561
Active-Request-Id-List:543257
If the recording completes due to no-input, silence after speech, or max-time, the server MUST generate the RECORD-COMPLETE event to the client with a request-state of "COMPLETE". If the recording was a success the RECORD-COMPLETE event contains a Record-URI header field pointing to the recorded audio file on the server or to a typed entity in the message body containing the recorded audio.
C->S: MRCP/2.0 ... RECORD 543257
Channel-Identifier:32AECB23433802@recorder
Record-URI:<file://mediaserver/recordings/myfile.wav>
Capture-On-Speech:true
Final-Silence:300
Max-Time:6000
S->C: MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433802@recorder
S->C: MRCP/2.0 ... START-OF-INPUT 543257 IN-PROGRESS
Channel-Identifier:32AECB23433802@recorder
S->C: MRCP/2.0 ... RECORD-COMPLETE 543257 COMPLETE
Channel-Identifier:32AECB23433802@recorder
Completion-Cause:000 success
Record-URI:<file://mediaserver/recordings/myfile.wav>;
size=325325;duration=24652
This request is sent from the client to the recorder resource when it discovers that a kill-on-barge-in prompt has finished playing (see Section 8.4.2). This is useful in the scenario when the recorder and synthesizer resources are not in the same MRCPv2 session. When a kill-on-barge-in prompt is being played, the client wants the RECORD request to be simultaneously active so that it can detect and implement kill on barge-in. But at the same time the client doesn't want the recorder resource to start the no-input timers until the prompt is finished. The Start-Input-Timers header field in the RECORD request allows the client to say if the timers should be started or not. In the above case the recorder resource does not start the timers until the client sends a START-INPUT-TIMERS method to the recorder.
The START-OF-INPUT event is returned from the server to the client once the server has detected speech. This event is always returned by the recording resource when speech has been detected. The recorder resource also MUST send a Proxy-Sync-Id header field with a unique value for this event.
S->C: MRCP/2.0 ... START-OF-INPUT 543259 IN-PROGRESS
Channel-Identifier:32AECB23433801@recorder
Proxy-Sync-Id:987654321
This section describes the methods, responses and events employed by MRCPv2 for doing Speaker Verification / Identification.
Speaker verification is a voice authentication methodology that can be used to identify the speaker in order to grant the user access to sensitive information and transactions. Because speech is a biometric, a number of essential security considerations related to biometric authentication technologies apply to its implementation and usage. Implementers should carefully read Section 12 in this document and the corresponding section of Speechsc Requirements [RFC4313].
In speaker verification, a recorded utterance is compared to a previously stored voiceprint which is in turn associated with a claimed identity for that user. Verification typically consists of two phases: a designation phase to establish the claimed identity of the caller and an execution phase in which a voiceprint is either created (training) or used to authenticate the claimed identity (verification).
Speaker identification is the process of associating an unknown speaker with a member in a population. It does not employ a claim of identity. When an individual claims to belong to a group (e.g., one of the owners of a joint bank account) a group authentication is performed. This is generally implemented as a kind of verification involving comparison with more than one voice model. It is sometimes called 'multi-verification'. If the individual speaker can be identified from the group, this may be useful for applications where multiple users share the same access privileges to some data or application. Speaker identification and group authentication are also done in two phases, a designation phase and an execution phase. Note that from a functionality standpoint identification can be thought of as a special case of group authentication (if the individual is identified) where the group is the entire population, although the implementation of speaker identification may be different from the way group authentication is performed. To accommodate single-voiceprint verification, verification against multiple voiceprints, group authentication, and identification, this specification provides a single set of methods that can take a list of identifiers, called “voiceprint identifiers”, and return a list of identifiers, with a score for each representing how well the input speech matched each identifier. The input and output lists of identifiers do not have to match, allowing a vendor-specific group identifier to be used as input to indicate that identification is to be performed. In this specification, the terms “Identification” and “Multi-verification” are used to indicate that the input represents a group (potentially the entire population) and that results for multiple voiceprints may be returned.
It is possible for a verifier resource to share the same session with a recognizer resource or to operate independently. In order to share the same session, the verifier and recognizer resources MUST be allocated from within the same SIP dialog. Otherwise, an independent verifier resource, running on the same physical server or a separate one, will be set up. Note that in addition to allowing both resources to be allocated in the same INVITE, it is possible to allocate one initially and the other later via a re-INVITE.
Some of the speaker verification methods, described below, apply only to a specific mode of operation.
The verifier resource has a verification buffer associated with it (see Section 11.4.14). This allows the storage of speech utterances for the purposes of verification, identification or training from the buffered speech. This buffer is owned by the verifier resource but other input resources such as the recognition resource or recorder resource may write to it. This allows the speech received as part of a recognition or recording operation to be later used for verification, identification or training. Access to the buffer is limited to one operation at time. Hence when the resource is doing read, write or delete operation such as a RECOGNIZE with ver-buffer-utterance turned on, another operation involving the buffer fails with a status-code of 402. The verification buffer can be cleared by a CLEAR-BUFFER request from the client and is freed when the verifier resource is deallocated or the session with the server terminates.
The verification buffer is different from collecting waveforms and processing them using either the real time audio stream or stored audio, because this buffering mechanism does not simply accumulate speech to a buffer. The verification buffer may contain additional information gathered by the recognition resource that serves to improve verification performance.
Speaker verification may operate in a training or a verification session. Starting one of these sessions does not change the state of the verifier resource, i.e. it remains idle. Once a verification or training session is started, then utterances are trained or verified by calling the VERIFY or VERIFY-FROM-BUFFER method. The state of the verifier resources goes from IDLE to VERIFYING state each time VERIFY or VERIFY-FROM-BUFFER is called.
Idle Session Opened Verifying/Training State State State | | | |--START-SESSION--->| | | | | | |----------| | | | START-SESSION | | |<---------| | | | | |<--END-SESSION-----| | | | | | |---------VERIFY--------->| | | | | |---VERIFY-FROM-BUFFER--->| | | | | |----------| | | | VERIFY-ROLLBACK | | |<---------| | | | | | | |--------| | | GET-INTERMEDIATE-RESULT | | | |------->| | | | | | |--------| | | START-INPUT-TIMERS | | | |------->| | | | | | |--------| | | START-OF-INPUT | | | |------->| | | | | |<-VERIFICATION-COMPLETE--| | | | | |<--------STOP------------| | | | | |----------| | | | STOP | | |<---------| | | | | |----------| | | | STOP | | |<---------| | | | |----------| | | | CLEAR-BUFFER | | |<---------| | | | | |----------| | | | CLEAR-BUFFER | | |<---------| | | | | | | |----------| | | | QUERY-VOICEPRINT | | |<---------| | | | | |----------| | | | QUERY-VOICEPRINT | | |<---------| | | | | | | |----------| | | | DELETE-VOICEPRINT | | |<---------| | | | | |----------| | | | DELETE-VOICEPRINT | | |<---------| | |
The verifier resource supports the following methods.
verifier-method = "START-SESSION"
/ "END-SESSION"
/ "QUERY-VOICEPRINT"
/ "DELETE-VOICEPRINT"
/ "VERIFY"
/ "VERIFY-FROM-BUFFER"
/ "VERIFY-ROLLBACK"
/ "STOP"
/ "CLEAR-BUFFER"
/ "START-INPUT-TIMERS"
/ "GET-INTERMEDIATE-RESULT"
These methods allow the client to control the mode and target of verification or identification operations within the context of a session. All the verification input operations that occur within a session may be used to create, update, or validate against the voiceprint specified during the session. At the beginning of each session the verifier resource is reset to the state it had prior to any previous verification session.
Verification/identification operations can be executed against live or buffered audio. The verifier resource provides methods for collecting and evaluating live audio data, and methods for controlling the verifier resource and adjusting its configured behavior.
There are no dedicated methods for collecting buffered audio data. This is accomplished by calling VERIFY, RECOGNIZE or RECORD as appropriate for the resource, with the header field Ver-Buffer-Utterance. Then, when the following method is called verification is performed using the set of buffered audio.
The following methods are used for verification of live audio utterances :
The following methods are used for configuring the verifier resource and for establishing resource states :
The following method allows the polling a Verification in progress for intermediate results.
The verifier resource generates the following events.
verifier-event = "VERIFICATION-COMPLETE"
/ "START-OF-INPUT"
A verifier resource message may contain header fields containing request options and information to augment the Request, Response or Event message it is associated with.
verification-header = repository-uri
/ voiceprint-identifier
/ verification-mode
/ adapt-model
/ abort-model
/ min-verification-score
/ num-min-verification-phrases
/ num-max-verification-phrases
/ no-input-timeout
/ save-waveform
/ media-type
/ waveform-uri
/ voiceprint-exists
/ ver-buffer-utterance
/ input-waveform-uri
/ completion-cause
/ completion-reason
/ speech-complete-timeout
/ new-audio-channel
/ abort-verification
/ start-input-timers
This header field specifies the voiceprint repository to be used or referenced during speaker verification or identification operations. This header field is required in the START-SESSION, QUERY-VOICEPRINT and DELETE-VOICEPRINT methods.
repository-uri = "Repository-URI" ":" uri CRLF
This header field specifies the claimed identity for verification applications. The claimed identity MAY be used to specify an existing voiceprint or to establish a new voiceprint. This header field MUST be present in the QUERY-VOICEPRINT and DELETE-VOICEPRINT methods. The Voiceprint-Identifier MUST be present in the START-SESSION method for verification operations. For Identification or Multi-Verification operations this header field MAY contain a list of voiceprint identifiers separated by semi-colons. For identification operations the client MAY also specify a voiceprint group identifier instead of a list of voiceprint identifiers.
voiceprint-identifier = "Voiceprint-Identifier" ":"
vid *[";" vid] CRLF
vid = 1*VCHAR ["." 1*VCHAR]
This header field specifies the mode of the verifier resource and is set by the START-SESSION method. Acceptable values indicate whether the verification session will train a voiceprint ("train") or verify/identify using an existing voiceprint ("verify").
Training and verification sessions both require the voiceprint Repository-URI to be specified in the START-SESSION. In many usage scenarios, however, the system does not know the speaker's claimed identity until a recognition operation has, for example, recognized an account number to which the user desires access. In order to allow the first few utterances of a dialog to be both recognized and verified, the verifier resource on the MRCPv2 server retains a buffer. In this buffer, the MRCPv2 server accumulates recognized utterances. The client can later execute a verification method and apply the buffered utterances to the current verification session.
Some voice user interfaces may require additional user input that should not be subject to verification. For example, the user's input may have been recognized with low confidence and thus require a confirmation cycle. In such cases, the client should not execute the VERIFY or VERIFY-FROM-BUFFER methods to collect and analyze the caller's input. A separate recognizer resource can analyze the caller's response without any participation by the verifier resource.
Once the following conditions have been met:
the verifier resource may begin providing verification information during verification operations. If the verifier resource does not reach one of the two major states ("train" or "verify") , it MUST report an error condition in the MRCPv2 status code to indicate why the verifier resource is not ready for the corresponding usage.
The value of verification-mode is persistent within a verification session. If the client attempts to change the mode during a verification session, the verifier resource reports an error and the mode retains its current value.
verification-mode = "Verification-Mode" ":"
verification-mode-string
verification-mode-string = "train"
/ "verify"
This header field indicates the desired behavior of the verifier resource after a successful verification operation. If the value of this header field is "true", the sever SHOULD use audio collected during the verification session to update the voiceprint to account for ongoing changes in a speaker's incoming speech characteristics, unless local policy prohibits updating the voiceprint. If the value is "false" (the default), the server MUST NOT update the voiceprint. This header field MAY occur in the START-SESSION method.
adapt-model = "Adapt-Model" ":" BOOLEAN CRLF
The Abort-Model header field indicates the desired behavior of the verifier resource upon session termination. If the value of this header field is "true", the server MUST discard any pending changes to a voiceprint due to verification training or verification adaptation. If the value is "false" (the default), the server MUST commit any pending changes for a training session or a successful verification session to the voiceprint repository. A value of "true" for Abort-Model overrides a value of "true" for the Adapt-Model header field. This header field MAY occur in the END-SESSION method.
abort-model = "Abort-Model" ":" BOOLEAN CRLF
The Min-Verification-Score header field, when used with a verifier resource through a SET-PARAMS, GET-PARAMS or START-SESSION method, determines the minimum verification score for which a verification decision of "accepted" may be declared by the server. This is a float value between -1.0 and 1.0 that determines the minimum verification score for which a verification decision of "accepted" may be declared by the server. The default value for this header field is implementation specific.
min-verification-score = "Min-Verification-Score" ":"
[ %x2D ] FLOAT CRLF
The Num-Min-Verification-Phrases header field is used to specify the minimum number of valid utterances before a positive decision is given for verification. The value for this header field is an integer and the default value is 1. The verifier resource MUST NOT declare a verification 'accepted' unless Num-Min-Verification-Phrases valid utterances have been received. The minimum value is 1. This header field MAY occur in START-SESSION, SET-PARAMS or GET-PARAMS.
num-min-verification-phrases = "Num-Min-Verification-Phrases" ":"
1*19DIGIT CRLF
The Num-Max-Verification-Phrases header field is used to specify the number of valid utterances required before a decision is forced for verification. The verifier resource MUST NOT return a decision of 'undecided' once Num-Max-Verification-Phrases have been collected and used to determine a verification score. The value for this header field is an integer and the minimum value is 1. The default value is implementation-specific. This header field MAY occur in START-SESSION, SET-PARAMS or GET-PARAMS.
num-max-verification-phrases = "Num-Max-Verification-Phrases" ":"
1*19DIGIT CRLF
The No-Input-Timeout header field sets the length of time from the start of the verification timers (see START-INPUT-TIMERS) until the declaration of a no-input event in the VERIFICATION-COMPLETE server event message. The value is in milliseconds. This header field MAY occur in VERIFY, SET-PARAMS or GET-PARAMS. The value for this header field ranges from 0 to an implementation specific maximum value. The default value for this header field is implementation specific.
no-input-timeout = "No-Input-Timeout" ":" 1*19DIGIT CRLF
This header field allows the client to request that the verifier resource save the audio stream that was used for verification/identification. The verifier resource MUST attempt to record the audio and make it available to the client in the form of a URI returned in the Waveform-URI header field in the VERIFICATION-COMPLETE event. If there was an error in recording the stream or the audio content is otherwise not available, the verifier resource MUST return an empty Waveform-URI header field. The default value for this header field is "false". This header field MAY appear in the VERIFY method. Note that this header field does not appear in the VERIFY-FROM-BUFFER method since it only controls whether or not to save the waveform for live verification / identification operations.
save-waveform = "Save-Waveform" ":" BOOLEAN CRLF
This header field MAY be specified in the SET-PARAMS, GET-PARAMS or the VERIFY methods and tells the server resource the Media Type of the captured audio or video such as the one captured and returned by the Waveform-URI header field.
media-type = "Media-Type" ":" media-type-value
CRLF
If the Save-Waveform header field is set to true, the verifier resource MUST attempt to record the incoming audio stream of the verification into a file and provide a URI for the client to access it. This header field MUST be present in the VERIFICATION-COMPLETE event if the Save-Waveform header field was set to true by the client. The value of the header field MUST be empty if there was some error condition preventing the server from recording. Otherwise, the URI generated by the server MUST be globally unique across the server and all its verification sessions. The content MUST be available via the URI until the verification session ends. Since the Save-Waveform header field applies only to live verification / identification operations, the server can return the Waveform-URI only in the VERIFICATION-COMPLETE event for live verification / identification operations.
The server MUST also return the size in octets and the duration in milliseconds of the recorded audio wave-form as parameters associated with the header field.
waveform-uri = "Waveform-URI" ":" ["<" uri ">"
";" "size" "=" 1*19DIGIT
";" "duration" "=" 1*19DIGIT] CRLF
This header field MUST be returned in QUERY-VOICEPRINT and DELETE-VOICEPRINT responses. This is the status of the voiceprint specified in the QUERY-VOICEPRINT method. For the DELETE-VOICEPRINT method this header field indicates the status of the voiceprint at the moment the method execution started.
voiceprint-exists = "Voiceprint-Exists" ":" BOOLEAN CRLF
This header field is used to indicate that this utterance could be later considered for Speaker Verification. This way, a client can request the server to buffer utterances while doing regular recognition or verification activities and speaker verification can later be requested on the buffered utterances. This header field is OPTIONAL in the RECOGNIZE, VERIFY and RECORD methods. The default value for this header field is "false".
ver-buffer-utterance = "Ver-Buffer-Utterance" ":" BOOLEAN
CRLF
This header field specifies stored audio content that the client requests the server to fetch and process according to the current verification mode, either to train the voiceprint or verify a claimed identity. This header field enables the client to implement the buffering use case where the recognizer and verifier resources are in different sessions and the verification buffer technique cannot be used. It MAY be specified on the VERIFY request.
input-waveform-uri = "Input-Waveform-URI" ":" uri CRLF
This header field MUST be part of a VERIFICATION-COMPLETE event from the verifier resource to the client. This indicates the cause of VERIFY or VERIFY-FROM-BUFFER method completion. This header field MUST be sent in the VERIFY, VERIFY-FROM-BUFFER, and QUERY-VOICEPRINT responses, if they return with a failure status and a COMPLETE state. In the ABNF below, the 'cause-code' contains a numerical value selected from the Cause-Code column of the following table. The 'cause-name' contains the corresponding token selected from the Cause-Name column.
completion-cause = "Completion-Cause" ":" cause-code SP
cause-name CRLF
cause-code = 3DIGIT
cause-name = *VCHAR
| Cause-Code | Cause-Name | Description |
|---|---|---|
| 000 | success | VERIFY or VERIFY-FROM-BUFFER request completed successfully. The verify decision can be "accepted", "rejected", or "undecided". |
| 001 | error | VERIFY or VERIFY-FROM-BUFFER request terminated prematurely due to a verifier resource or system error. |
| 002 | no-input-timeout | VERIFY request completed with no result due to a no-input-timeout. |
| 003 | too-much-speech-timeout | VERIFY request completed with no result due to too much speech. |
| 004 | speech-too-early | VERIFY request completed with no result due to spoke too soon. |
| 005 | buffer-empty | VERIFY-FROM-BUFFER request completed with no result due to empty buffer. |
| 006 | out-of-sequence | Verification operation failed due to out-of-sequence method invocations. For example calling VERIFY before QUERY-VOICEPRINT. |
| 007 | repository-uri-failure | Failure accessing Repository URI. |
| 008 | repository-uri-missing | Repository-uri is not specified. |
| 009 | voiceprint-id-missing | Voiceprint-identification is not specified. |
| 010 | voiceprint-id-not-exist | Voiceprint-identification does not exist in the voiceprint repository. |
| 011 | speech-not-usable | VERIFY request completed with no result because the speech was not usable (too noisy, too short, etc.) |
This header field MAY be specified in a VERIFICATION-COMPLETE event coming from the verifier resource to the client. It contains the reason text behind the VERIFY request completion. This header field communicates text describing the reason for the failure.
The completion reason text is provided for client use in logs and for debugging and instrumentation purposes. Clients MUST NOT interpret the completion reason text.
completion-reason = "Completion-Reason" ":"
quoted-string CRLF
This header field is the same as the one described for the Recognizer resource. See Section 9.4.15. This header field MAY occur in VERIFY, SET-PARAMS, or GET-PARAMS.
This header field is the same as the one described for the Recognizer resource. See Section 9.4.23. This header field MAY be specified in a VERIFY request.
This header field MUST be sent in a STOP request to indicate whether or not to abort a VERIFY method in progress. A value of "true" requests the server to discard the results. A value of "false" requests the server to return in the STOP response the verification results obtained up to the point it received the STOP request.
Abort-verification = "Abort-Verification " ":" BOOLEAN CRLF
This header field MAY be sent as part of a VERIFY request. A value of false tells the verifier resource to start the VERIFY operation, but not to start the no-input timer yet. The verifier resource MUST NOT start the timers until the client sends a START-INPUT-TIMERS request to the resource. This is useful in the scenario when the verifier and synthesizer resources are not part of the same session. In this scenario, when a kill-on-barge-in prompt is being played, the client may want the VERIFY request to be simultaneously active so that it can detect and implement kill-on-barge-in (see Section 8.4.2). But at the same time the client doesn't want the verifier resource to start the no-input timers until the prompt is finished. The default value is "true".
start-input-timers = "Start-Input-Timers" ":"
BOOLEAN CRLF
A verification response or event message may carry additional data as described in the following subsection.
Verification results are returned to the client in the message body of the VERIFICATION-COMPLETE event or the GET-INTERMEDIATE-RESULT response message as described in Section 6.3. Element and attribute descriptions for the verification portion of the NLSML format are provided in Section 11.5.2 with a normative definition of the schema in Section 16.3.
All verification elements are contained within a single <verification-result> element under <result>. The elements are described below and have the schema defined in Section 16.2. The following elements are defined:
This element in the verification results provides information on how the speech data matched a single voiceprint. The result data returned may have more than one such entity in the case of Identification or Multi-Verification. Each <voiceprint> element and the XML data within the element describe verification result information for how well the speech data matched that particular voiceprint. The list of voiceprint element data are ordered according to their cumulative verification match scores, with the highest score first.
Within each <voiceprint> element there MUST be a <cumulative> element with the cumulative scores of how well multiple utterances matched the voiceprint.
The first <voiceprint> element MAY contain an <incremental> element with the incremental scores of how well the last utterance matched the voiceprint.
This element is found within the <incremental> or <cumulative> element within the verification results. Its value indicates the verification decision. It can have the values of "accepted", "rejected" or "undecided".
This element MAY occur within either the <incremental> or <cumulative> elements within the first <voiceprint> element. Its value indicates the size in milliseconds, respectively, of the last utterance or the cumulated set of utterances.
This element is found within the incremental or cumulative element within the verification results. Its value indicates the apparent type of device used by the caller as determined by the verifier resource. It can have the values of "cellular-phone", "electret-phone", "carbon-button-phone", or "unknown".
This element is found within the incremental or cumulative element within the verification results. Its value indicates the apparent gender of the speaker as determined by the verifier resource. It can have the values of "male", "female" or "unknown".
This element is found within the first <voiceprint> element within the verification results. When verification is trying to confirm the voiceprint, this indicates if the voiceprint has been adapted as a consequence of analyzing the source utterances. It is not returned during verification training. The value can be "true" or "false".
This element is found within the incremental or cumulative element within the verification results. Its value indicates the score of the last utterance as determined by verification.
During verification, the higher the score the more likely it is that the speaker is the same one as the one who spoke the voiceprint utterances. During training, the higher the score the more likely the speaker is to have spoken all of the analyzed utterances. The value is a floating point between -1.0 and 1.0. If there are no such utterances the score is -1. Note that the verification score is not a probability value.
MRCPv2 servers MAY send verification results that contain implementation specific data which augment the information provided by the MRCPv2-defined elements. Such data might be useful to clients who have private knowledge of how to interpret these schema extensions. Implementation specific additions to the verification results schema MUST belong to the vendor's own namespace. In the result structure, either they MUST be indicated by a namespace prefix declared within the result, or they MUST be children of an element identified as belonging to the respective namespace.
The following example shows the results of three voiceprints. Note that the first one has crossed the verification score threshold, and the speaker has been accepted. The voiceprint was also adapted with the most recent utterance.
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
grammar="What-Grammar-URI">
<verification-result>
<voiceprint id="johnsmith">
<adapted> true </adapted>
<incremental>
<utterance-length> 500 </utterance-length>
<device> cellular-phone </device>
<gender> male </gender>
<decision> accepted </decision>
<verification-score> 0.98514 </verification-score>
</incremental>
<cumulative>
<utterance-length> 10000 </utterance-length>
<device> cellular-phone </device>
<gender> male </gender>
<decision> accepted </decision>
<verification-score> 0.96725</verification-score>
</cumulative>
</voiceprint>
<voiceprint id="marysmith">
<cumulative>
<verification-score> 0.93410 </verification-score>
</cumulative>
</voiceprint>
<voiceprint uri="juniorsmith">
<cumulative>
<verification-score> 0.74209 </verification-score>
</cumulative>
</voiceprint>
</verification-result>
</result>
In this next example, the verifier has enough information to decide to reject the speaker.
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:xmpl="http://www.example.org/2003/12/mrcpv2"
grammar="What-Grammar-URI">
<verification-result>
<voiceprint id="johnsmith">
<incremental>
<utterance-length> 500 </utterance-length>
<device> cellular-phone </device>
<gender> male </gender>
<verification-score> 0.88514 </verification-score>
<xmpl:raspiness> high </xmpl:raspiness>
<xmpl:emotion> sadness </xmpl:emotion>
</incremental>
<cumulative>
<utterance-length> 10000 </utterance-length>
<device> cellular-phone </device>
<gender> male </gender>
<decision> rejected </decision>
<verification-score> 0.9345 </verification-score>
</cumulative>
</voiceprint>
</verification-result>
</result>
The START-SESSION method starts a Speaker Verification or Identification session. Execution of this method places the verifier resource into its initial state. If this method is called during an ongoing verification session, the previous session is implicitly aborted. If this method is invoked when VERIFY or VERIFY-FROM-BUFFER is active, the method fails and the server returns a status code of 402.
Upon completion of the START-SESSION method, the verifier resource MUST have terminated any ongoing verification session, and cleared any voiceprint designation.
A verification session is associated with the voiceprint repository to be used during the session. This is specified through the "Repository-URI" header field (see Section 11.4.1).
The START-SESSION method also establishes, through the Voiceprint-Identifier header field, which voiceprints are to be matched or trained during the verification session. If this is an Identification session or if the client wants to do Multi-Verification, the Voiceprint-Identifier header field contains a list of semi-colon separated voiceprint identifiers.
The Adapt-Model header field may also be present in the START-SESSION request to indicate whether or not to adapt a voiceprint based on data collected during the session (if the voiceprint verification phase succeeds). By default, the voiceprint model MUST NOT be adapted with data from a verification session.
The START-SESSION also determines whether the session is for a train or verify of a voiceprint. Hence the Verification-Mode header field MUST be sent in every START-SESSION request. The value of the Verification-Mode header field MUST be one of either "train" or "verify".
Before a verification/identification session is started, the client MAY only request that VERIFY-ROLLBACK and generic SET-PARAMS and GET-PARAMS operations be performed on the verifier resource. The server MUST return status-code 402 "Method not valid in this state" for all other verification operations.
A verifier resource MUST NOT have more than a single session active at one time.
C->S: MRCP/2.0 ... START-SESSION 314161
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/voiceprintdbase/
Voiceprint-Mode:verify
Voiceprint-Identifier:johnsmith.voiceprint
Adapt-Model:true
S->C: MRCP/2.0 ... 314161 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
The END-SESSION method terminates an ongoing verification session and releases the verification voiceprint resources. The session may terminate in one of three ways:
The Abort-Model header field MAY be included in the END-SESSION to control whether or not to abort any pending changes to the voiceprint. The default behavior is to commit (not abort) any pending changes to the designated voiceprint.
The END-SESSION method may be safely executed multiple times without first executing the START-SESSION method. Any additional executions of this method without an intervening use of the START-SESSION method have no effect on the verifier resource.
The following example assumes there is either a training session or a verification session in progress.
C->S: MRCP/2.0 ... END-SESSION 314174
Channel-Identifier:32AECB23433801@speakverify
Abort-Model:true
S->C: MRCP/2.0 ... 314174 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
The QUERY-VOICEPRINT method is used to get status information on a particular voiceprint and can be used by the client to ascertain if a voiceprint or repository exists and if it contains trained voiceprints.
The response to the QUERY-VOICEPRINT request contains an indication of the status of the designated voiceprint in the Voiceprint-Exists header field, allowing the client to determine whether to use the current voiceprint for verification, train a new voiceprint, or choose a different voiceprint.
A voiceprint is completely specified by providing a repository location and a voiceprint identifier. The particular voiceprint or identity within the repository is specified by a string identifier that is unique within the repository. The Voiceprint-Identifier header field carries this unique voiceprint identifier within a given repository.
The following example assumes a verification session is in progress and the voiceprint exists in the voiceprint repository.
C->S: MRCP/2.0 ... QUERY-VOICEPRINT 314168
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/voiceprints/
Voiceprint-Identifier:johnsmith.voiceprint
S->C: MRCP/2.0 ... 314168 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/voiceprints/
Voiceprint-Identifier:johnsmith.voiceprint
Voiceprint-Exists:true
The following example assumes that the URI provided in the Repository-URI header field is a bad URI.
C->S: MRCP/2.0 ... QUERY-VOICEPRINT 314168
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/bad-uri/
Voiceprint-Identifier:johnsmith.voiceprint
S->C: MRCP/2.0 ... 314168 405 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/bad-uri/
Voiceprint-Identifier:johnsmith.voiceprint
Completion-Cause:007 repository-uri-failure
The DELETE-VOICEPRINT method removes a voiceprint from a repository. This method MUST carry the Repository-URI and Voiceprint-Identifier header fields.
If the corresponding voiceprint does not exist, the DELETE-VOICEPRINT method MUST return a 200 status code.
The following example demonstrates a DELETE-VOICEPRINT operation to remove a specific voiceprint.
C->S: MRCP/2.0 ... DELETE-VOICEPRINT 314168
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/bad-uri/
Voiceprint-Identifier:johnsmith.voiceprint
S->C: MRCP/2.0 ... 314168 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
The VERIFY method is used to request that the verifier resource either train/adapt the voiceprint or verify/identify a claimed identity. If the voiceprint is new or was deleted by a previous DELETE-VOICEPRINT method, the VERIFY method trains the voiceprint. If the voiceprint already exits, it is adapted and not retrained by the VERIFY command.
C->S: MRCP/2.0 ... VERIFY 543260
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 543260 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speakverify
When the VERIFY request is completes, the MRCPv2 server MUST send a VERIFICATION-COMPLETE event to the client.
The VERIFY-FROM-BUFFER method directs the verifier resource to verify buffered audio against a voiceprint. Only one VERIFY or VERIFY-FROM-BUFFER method may be active for a verifier resource at a time.
The buffered audio is not consumed by this method and thus VERIFY-FROM-BUFFER may be invoked multiple times by the client to attempt verification against different voiceprints.
For the VERIFY-FROM-BUFFER method, the server MAY optionally return an IN-PROGRESS response before the VERIFICATION-COMPLETE event.
When the VERIFY-FROM-BUFFER method is invoked and the verification buffer is in use by another resource sharing it, the server MUST return an IN-PROGRESS response and wait until the buffer is available to it. The verification buffer is owned by the verifier resource but is shared with write access from other input resources on the same session. Hence, it is considered to be in use if there is a read or write operation such as a RECORD or RECOGNIZE with the Ver-Buffer-Utterance header field set to "true" on a resource that shares this buffer. Note that if a RECORD or RECOGNIZE method returns with a failure cause code, the VERIFY-FROM-BUFFER request waiting to process that buffer MUST also fail with a Completion-Cause of 005 (buffer-empty).
The following example illustrates the usage of some buffering methods. In this scenario the client first performed a live verification, but the utterance had been rejected. In the meantime, the utterance is also saved to the audio buffer. Then, another voiceprint is used to do verification against the audio buffer and the utterance is accepted. For the example, we assume both Num-Min-Verification-Phrases and Num-Max-Verification-Phrases are 1.
C->S: MRCP/2.0 ... START-SESSION 314161
Channel-Identifier:32AECB23433801@speakverify
Verification-Mode:verify
Adapt-Model:true
Repository-URI:http://www.example.com/voiceprints
Voiceprint-Identifier:johnsmith.voiceprint
S->C: MRCP/2.0 ... 314161 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
C->S: MRCP/2.0 ... VERIFY 314162
Channel-Identifier:32AECB23433801@speakverify
Ver-buffer-utterance:true
S->C: MRCP/2.0 ... 314162 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... VERIFICATION-COMPLETE 314162 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
Completion-Cause:000 success
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
grammar="What-Grammar-URI">
<verification-result>
<voiceprint id="johnsmith">
<incremental>
<utterance-length> 500 </utterance-length>
<device> cellular-phone </device>
<gender> female </gender>
<decision> rejected </decision>
<verification-score> 0.05465 </verification-score>
</incremental>
<cumulative>
<utterance-length> 500 </utterance-length>
<device> cellular-phone </device>
<gender> female </gender>
<decision> rejected </decision>
<verification-score> 0.05465 </verification-score>
</cumulative>
</voiceprint>
</verification-result>
</result>
C->S: MRCP/2.0 ... QUERY-VOICEPRINT 314163
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/voiceprints/
Voiceprint-Identifier:johnsmith
S->C: MRCP/2.0 ... 314163 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
Repository-URI:http://www.example.com/voiceprints/
Voiceprint-Identifier:johnsmith.voiceprint
Voiceprint-Exists:true
C->S: MRCP/2.0 ... START-SESSION 314164
Channel-Identifier:32AECB23433801@speakverify
Verification-Mode:verify
Adapt-Model:true
Repository-URI:http://www.example.com/voiceprints
Voiceprint-Identifier:marysmith.voiceprint
S->C: MRCP/2.0 ... 314164 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
C->S: MRCP/2.0 ... VERIFY-FROM-BUFFER 314165
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 314165 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... VERIFICATION-COMPLETE 314165 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
Completion-Cause:000 success
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
grammar="What-Grammar-URI">
<verification-result>
<voiceprint id="marysmith">
<incremental>
<utterance-length> 1000 </utterance-length>
<device> cellular-phone </device>
<gender> female </gender>
<decision> accepted </decision>
<verification-score> 0.98 </verification-score>
</incremental>
<cumulative>
<utterance-length> 1000 </utterance-length>
<device> cellular-phone </device>
<gender> female </gender>
<decision> accepted </decision>
<verification-score> 0.98 </verification-score>
</cumulative>
</voiceprint>
</verification-result>
</result>
C->S: MRCP/2.0 ... END-SESSION 314166
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 314166 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
The VERIFY-ROLLBACK method discards the last buffered utterance or discards the last live utterances (when the mode is "train" or "verify"). The client should invoke this method when the user provides undesirable input such as non-speech noises, side-speech, out-of-grammar utterances, commands, etc. Note that this method does not provide a stack of rollback states. Executing VERIFY-ROLLBACK twice in succession without an intervening recognition operation has no effect on the second attempt.
C->S: MRCP/2.0 ... VERIFY-ROLLBACK 314165
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 314165 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
The STOP method from the client to the server tells the verifier resource to stop the VERIFY or VERIFY-FROM-BUFFER request if one is active. If such a request is active and the STOP request successfully terminated it, then the response header section contains an active-request-id-list header field containing the request-id of the VERIFY or VERIFY-FROM-BUFFER request that was terminated. In this case, no VERIFICATION-COMPLETE event is sent for the terminated request. If there was no verify request active, then the response MUST NOT contain an active-request-id-list header field. Either way the response MUST contain a status-code of 200 (Success).
The STOP method can carry a Abort-Verification header field which specifies if the verification result until that point should be discarded or returned. If this header field is not present or if the value is "true", the verification result is discarded and the STOP response does not contain any result data. If the header field is present and its value is "false", the STOP response MUST contain a Completion-Cause header field and carry the Verification result data in its body.
An aborted VERIFY request does an automatic roll-back and hence does not affect the cumulative score. A VERIFY request that was stopped with no Abort-Verification header field or with the Abort-Verification header field set to "false" does affect cumulative scores and would need to be explicitly rolled-back if the client does not want the verification result considered in the cumulative scores.
The following example assumes a voiceprint identity has already been established.
C->S: MRCP/2.0 ... VERIFY 314177
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 314177 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speakverify
C->S: MRCP/2.0 ... STOP 314178
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 314178 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
Active-Request-Id-List:314177
This request is sent from the client to the verifier resource to start the no-input timer, usually once the client has ascertained that any audio prompts to the user have played to completion.
C->S: MRCP/2.0 ... START-INPUT-TIMERS 543260
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 543260 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
The VERIFICATION-COMPLETE event follows a call to VERIFY or VERIFY-FROM-BUFFER and is used to communicate the verification results to the client. The event message body contains only verification results.
S->C: MRCP/2.0 ... VERIFICATION-COMPLETE 543259 COMPLETE
Completion-Cause:000 success
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
grammar="What-Grammar-URI">
<verification-result>
<voiceprint id="johnsmith">
<incremental>
<utterance-length> 500 </utterance-length>
<device> cellular-phone </device>
<gender> male </gender>
<decision> accepted </decision>
<verification-score> 0.85 </verification-score>
</incremental>
<cumulative>
<utterance-length> 1500 </utterance-length>
<device> cellular-phone </device>
<gender> male </gender>
<decision> accepted </decision>
<verification-score> 0.75 </verification-score>
</cumulative>
</voiceprint>
</verification-result>
</result>
The START-OF-INPUT event is returned from the server to the client once the server has detected speech. This event is always returned by the verifier resource when speech has been detected, irrespective of whether the recognizer and verifier resources share the same session or not.
S->C: MRCP/2.0 ... START-OF-INPUT 543259 IN-PROGRESS
Channel-Identifier:32AECB23433801@speakverify
The CLEAR-BUFFER method can be used to clear the verification buffer. This buffer is used to buffer speech during a recognition, record or verification operations that may later be used by VERIFY-FROM-BUFFER. As noted before, the buffer associated with the verifier resource is shared by other input resources like recognizers and recorders. Hence, a CLEAR-BUFFER request fails if the verification buffer is in use. This can happen when any one of the input resources that shares this buffer has an active read or write operation such as RECORD, RECOGNIZE or VERIFY with the Ver-Buffer-Utterance header field set to "true".
C->S: MRCP/2.0 ... CLEAR-BUFFER 543260
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 543260 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
A client can use the GET-INTERMEDIATE-RESULT method to poll for intermediate results of a verification request that is in progress. Invoking this method does not change the state of the resource. The verifier resource collects the accumulated verification results and returns the information in the method response. The message body in the response to a GET-INTERMEDIATE-RESULT REQUEST contains only verification results. The method response MUST NOT contain a Completion-Cause header field as the request is not yet complete. If the resource does not have a verification in progress the response has a 402 failure status-code and no result in the body.
C->S: MRCP/2.0 ... GET-INTERMEDIATE-RESULT 543260
Channel-Identifier:32AECB23433801@speakverify
S->C: MRCP/2.0 ... 543260 200 COMPLETE
Channel-Identifier:32AECB23433801@speakverify
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
grammar="What-Grammar-URI">
<verification-result>
<voiceprint id="marysmith">
<incremental>
<utterance-length> 50 </utterance-length>
<device> cellular-phone </device>
<gender> female </gender>
<decision> undecided </decision>
<verification-score> 0.85 </verification-score>
</incremental>
<cumulative>
<utterance-length> 150 </utterance-length>
<device> cellular-phone </device>
<gender> female </gender>
<decision> undecided </decision>
<verification-score> 0.65 </verification-score>
</cumulative>
</voiceprint>
</verification-result>
</result>
MRCPv2 is designed to comply with the security-related requirements documented in SpeechSC Requirements [RFC4313]. Implementers and users of MRCPv2 are strongly encouraged to read the Security Considerations section of [RFC4313], because that document contains discussion of a number of important security issues associated with the utilization of speech as biometric authentication technology, and on the threats against systems which store recorded speech, contain large corpora of voiceprints, and send and receive sensitive information based on voice input to a recognizer or speech output from a synthesizer. Specific security measures employed by MRCPv2 are summarized in the following subsections. See the corresponding sections of this specification for how the security-related machinery is invoked by individual protocol operations.
MRCPv2 control sessions are established as media sessions described by SDP within the context of a SIP dialog. In order to ensure secure rendezvous between MRCPv2 clients and servers, the following are required:
Sensitive data is carried over the MRCPv2 control channel. This includes things like the output of speech recognition operations, speaker verification results, input to text-to-speech conversion, personally-identifying grammars, etc. For this reason MRCPv2 servers must be properly authenticated and the control channel must permit the use of both confidentiality and integrity for the data. To ensure control channel protection, MRCPv2 clients and servers MUST support TLS and SHOULD utilize it by default unless alternative control channel protection is used. When TLS is used, the client MUST verify the identity of the server to which it connects, following the rules and guidelines defined in [RFC4572]. If there are multiple TLS-protected channels between the client and the server, the server MUST NOT send a response to the client over a channel for which the TLS identities of the server or client differ from the channel over which the server received the corresponding request. Alternative control channel protection MAY be used if desired (e.g. Security Architecture for the Internet Protocol (IPsec) [RFC4301]).
Sensitive data is also carried on media sessions terminating on MRCPv2 servers (the other end of a media channel may or may not be on the MRCPv2 client). This data includes the user's spoken utterances and the output of text-to-speech operations. MRCPv2 servers MUST support a security mechanism for protection of audio media sessions. MRCPv2 clients that originate or consume audio similarly MUST support a security mechanism for protection of the audio. If appropriate, usage of the Secure Real-time Transport Protocol (SRTP) [RFC3711] is RECOMMENDED.
MCRPv2 employs content indirection extensively. Content may be fetched and/or stored based on URI-addressing on systems other than the MRCPv2 client or server. Not all of the stored content is necessarily sensitive (e.g. XML schemas), but the majority generally needs protection, and some indirect content, such as voice recordings and voiceprints, are extremely sensitive and must always be protected. MRCPv2 clients and servers MUST implement HTTPS for indirect content access, and SHOULD employ secure access for all sensitive indirect content. Other secure URI-schemes such as Secure FTP (FTPS) [RFC4217] MAY also be used. See Section 6.2.15 for the header fields used to transfer cookie information between the MRCPv2 client and server if needed for authentication.
MRCPv2 makes no inherent assumptions about the lifetime and access controls associated with a URI. For example, if neither authentication nor scheme-specific access controls are used, a leak of the URI is equivalent to a leak of the content. Moreover, MRCPv2 makes no specific demands on the lifetime of a URI. If a server offers a URI and the client takes a long, long time to access that URI, the server may have removed the resource in the interim time period. MRCPv2 deals with this case by using the URI access scheme's resource not found error, such as 404 for HTTPS. How long a server should keep a dynamic resource available is highly application and context dependent. However, the server SHOULD keep the resource available for a reasonable amount of time to make it likely the client will have the resource available when the client needs the resource. Conversely, to mitigate state exhaustion attacks, MRCPv2 servers are not obligated to keep resources and resource state in perpetuity. The server SHOULD delete dynamically-generated resources associated with an MRCPv2 session when the session ends.
One method to avoid resource leakage is for the server to use one-time resource URIs. In this instance, there can be only a single access to the underlying resource using the given URI. A downside to this approach is if an attacker uses the URI before the client uses the URI, then the client is denied the resource. Other methods would be to adopt a mechanism similar to the URLAUTH IMAP extension [RFC4467], where the server sets cryptographic checks on URI usage, as well as capabilities for expiration, revocation, and so on. Specifying such a mechanism is beyond the scope of this document.
MRCPv2 applications often require the use of stored media. Voice recordings are both stored (e.g. for diagnosis and system tuning), and fetched (for replaying utterances into multiple MRCPv2 resources). Voiceprints are fundamental to the speaker identification and verification functions. This data can be extremely sensitive and can present substantial privacy and impersonation risks if stolen. Systems employing MRCPv2 should be deployed in ways that minimize these risks. The SpeechSC Requirements [RFC4313] contains a more extensive discussion of these risks and ways they may be mitigated.
DTMF buffers and recognition buffers may grow large enough to exceed the capabilities of a server, and the server MUST be prepared to gracefully handle resource consumption. A server MAY respond with the appropriate recognition incomplete if the server is in danger of running out of resources.
This section describes the name spaces (registries) for MRCPv2 that IANA is requested to create and maintain. Assignment/registration policies are described in RFC5226 [RFC5226].
IANA SHALL create a new name space of "MRCPv2 resource types". All maintenance within and additions to the contents of this name space MUST be according to the "Standards Action" registration policy. The initial contents of the registry, defined in Section 4.2, are given below:
Resource type Resource description Reference ------------- -------------------- --------- speechrecog Speech Recognizer [RFCXXXX] dtmfrecog DTMF Recognizer [RFCXXXX] speechsynth Speech Synthesizer [RFCXXXX] basicsynth Basic Synthesizer [RFCXXXX] speakverify Speaker Verifier [RFCXXXX] recorder Speech Recorder [RFCXXXX]
IANA SHALL create a new name space of "MRCPv2 methods and events". All maintenance within and additions to the contents of this name space MUST be according to the "Standards Action" registration policy. The initial contents of the registry, defined by the "method-name" and "event-name" BNF in Section 15 and explained in Section 5.2 and Section 5.5, are given below.
Name Resource type Method/Event Reference ---- ------------- ------------ --------- SET-PARAMS Generic Method [RFCXXXX] GET-PARAMS Generic Method [RFCXXXX] SPEAK Synthesizer Method [RFCXXXX] STOP Synthesizer Method [RFCXXXX] PAUSE Synthesizer Method [RFCXXXX] RESUME Synthesizer Method [RFCXXXX] BARGE-IN-OCCURRED Synthesizer Method [RFCXXXX] CONTROL Synthesizer Method [RFCXXXX] DEFINE-LEXICON Synthesizer Method [RFCXXXX] DEFINE-GRAMMAR Recognizer Method [RFCXXXX] RECOGNIZE Recognizer Method [RFCXXXX] INTERPRET Recognizer Method [RFCXXXX] GET-RESULT Recognizer Method [RFCXXXX] START-INPUT-TIMERS Recognizer Method [RFCXXXX] STOP Recognizer Method [RFCXXXX] START-PHRASE-ENROLLMENT Recognizer Method [RFCXXXX] ENROLLMENT-ROLLBACK Recognizer Method [RFCXXXX] END-PHRASE-ENROLLMENT Recognizer Method [RFCXXXX] MODIFY-PHRASE Recognizer Method [RFCXXXX] DELETE-PHRASE Recognizer Method [RFCXXXX] RECORD Recorder Method [RFCXXXX] STOP Recorder Method [RFCXXXX] START-INPUT-TIMERS Recorder Method [RFCXXXX] START-SESSION Verifier Method [RFCXXXX] END-SESSION Verifier Method [RFCXXXX] QUERY-VOICEPRINT Verifier Method [RFCXXXX] DELETE-VOICEPRINT Verifier Method [RFCXXXX] VERIFY Verifier Method [RFCXXXX] VERIFY-FROM-BUFFER Verifier Method [RFCXXXX] VERIFY-ROLLBACK Verifier Method [RFCXXXX] STOP Verifier Method [RFCXXXX] START-INPUT-TIMERS Verifier Method [RFCXXXX] GET-INTERMEDIATE-RESULT Verifier Method [RFCXXXX] SPEECH-MARKER Synthesizer Event [RFCXXXX] SPEAK-COMPLETE Synthesizer Event [RFCXXXX] START-OF-INPUT Recognizer Event [RFCXXXX] RECOGNITION-COMPLETE Recognizer Event [RFCXXXX] INTERPRETATION-COMPLETE Recognizer Event [RFCXXXX] START-OF-INPUT Recorder Event [RFCXXXX] RECORD-COMPLETE Recorder Event [RFCXXXX] VERIFICATION-COMPLETE Verifier Event [RFCXXXX] START-OF-INPUT Verifier Event [RFCXXXX]
IANA SHALL create a new name space of "MRCPv2 header fields". All maintenance within and additions to the contents of this name space MUST be according to the "Standards Action" registration policy. The initial contents of the registry, defined by the "message-header" BNF in Section 15 and explained in Section 5.1, are given below. Note that the values permitted for the "Vendor-Specific-Parameters" parameter are managed according to a different policy. See Section 13.1.6.
Name Resource type Reference ---- ------------- --------- channel-identifier Generic [RFCXXXX] accept Generic [RFC2616] active-request-id-list Generic [RFCXXXX] proxy-sync-id Generic [RFCXXXX] accept-charset Generic [RFC2616] content-type Generic [RFCXXXX] content-id Generic [RFC2392, RFC2046, and RFC5322] content-base Generic [RFCXXXX] content-encoding Generic [RFCXXXX] content-location Generic [RFCXXXX] content-length Generic [RFCXXXX] fetch-timeout Generic [RFCXXXX] cache-control Generic [RFCXXXX] logging-tag Generic [RFCXXXX] set-cookie Generic [RFCXXXX] set-cookie2 Generic [RFCXXXX] vendor-specific Generic [RFCXXXX] jump-size Synthesizer [RFCXXXX] kill-on-barge-in Synthesizer [RFCXXXX] speaker-profile Synthesizer [RFCXXXX] completion-cause Synthesizer [RFCXXXX] completion-reason Synthesizer [RFCXXXX] voice-parameter Synthesizer [RFCXXXX] prosody-parameter Synthesizer [RFCXXXX] speech-marker Synthesizer [RFCXXXX] speech-language Synthesizer [RFCXXXX] fetch-hint Synthesizer [RFCXXXX] audio-fetch-hint Synthesizer [RFCXXXX] failed-uri Synthesizer [RFCXXXX] failed-uri-cause Synthesizer [RFCXXXX] speak-restart Synthesizer [RFCXXXX] speak-length Synthesizer [RFCXXXX] load-lexicon Synthesizer [RFCXXXX] lexicon-search-order Synthesizer [RFCXXXX] confidence-threshold Recognizer [RFCXXXX] sensitivity-level Recognizer [RFCXXXX] speed-vs-accuracy Recognizer [RFCXXXX] n-best-list-length Recognizer [RFCXXXX] input-type Recognizer [RFCXXXX] no-input-timeout Recognizer [RFCXXXX] recognition-timeout Recognizer [RFCXXXX] waveform-uri Recognizer [RFCXXXX] input-waveform-uri Recognizer [RFCXXXX] completion-cause Recognizer [RFCXXXX] completion-reason Recognizer [RFCXXXX] recognizer-context-block Recognizer [RFCXXXX] start-input-timers Recognizer [RFCXXXX] speech-complete-timeout Recognizer [RFCXXXX] speech-incomplete-timeout Recognizer [RFCXXXX] dtmf-interdigit-timeout Recognizer [RFCXXXX] dtmf-term-timeout Recognizer [RFCXXXX] dtmf-term-char Recognizer [RFCXXXX] failed-uri Recognizer [RFCXXXX] failed-uri-cause Recognizer [RFCXXXX] save-waveform Recognizer [RFCXXXX] media-type Recognizer [RFCXXXX] new-audio-channel Recognizer [RFCXXXX] speech-language Recognizer [RFCXXXX] ver-buffer-utterance Recognizer [RFCXXXX] recognition-mode Recognizer [RFCXXXX] cancel-if-queue Recognizer [RFCXXXX] hotword-max-duration Recognizer [RFCXXXX] hotword-min-duration Recognizer [RFCXXXX] interpret-text Recognizer [RFCXXXX] dtmf-buffer-time Recognizer [RFCXXXX] clear-dtmf-buffer Recognizer [RFCXXXX] early-no-match Recognizer [RFCXXXX] num-min-consistent-pronunciations Recognizer [RFCXXXX] consistency-threshold Recognizer [RFCXXXX] clash-threshold Recognizer [RFCXXXX] personal-grammar-uri Recognizer [RFCXXXX] enroll-utterance Recognizer [RFCXXXX] phrase-id Recognizer [RFCXXXX] phrase-nl Recognizer [RFCXXXX] weight Recognizer [RFCXXXX] save-best-waveform Recognizer [RFCXXXX] new-phrase-id Recognizer [RFCXXXX] confusable-phrases-uri Recognizer [RFCXXXX] abort-phrase-enrollment Recognizer [RFCXXXX] sensitivity-level Recorder [RFCXXXX] no-input-timeout Recorder [RFCXXXX] completion-cause Recorder [RFCXXXX] completion-reason Recorder [RFCXXXX] failed-uri Recorder [RFCXXXX] failed-uri-cause Recorder [RFCXXXX] record-uri Recorder [RFCXXXX] media-type Recorder [RFCXXXX] max-time Recorder [RFCXXXX] trim-length Recorder [RFCXXXX] final-silence Recorder [RFCXXXX] capture-on-speech Recorder [RFCXXXX] ver-buffer-utterance Recorder [RFCXXXX] start-input-timers Recorder [RFCXXXX] new-audio-channel Recorder [RFCXXXX] repository-uri Verifier [RFCXXXX] voiceprint-identifier Verifier [RFCXXXX] verification-mode Verifier [RFCXXXX] adapt-model Verifier [RFCXXXX] abort-model Verifier [RFCXXXX] min-verification-score Verifier [RFCXXXX] num-min-verification-phrases Verifier [RFCXXXX] num-max-verification-phrases Verifier [RFCXXXX] no-input-timeout Verifier [RFCXXXX] save-waveform Verifier [RFCXXXX] media-type Verifier [RFCXXXX] waveform-uri Verifier [RFCXXXX] voiceprint-exists Verifier [RFCXXXX] ver-buffer-utterance Verifier [RFCXXXX] input-waveform-uri Verifier [RFCXXXX] completion-cause Verifier [RFCXXXX] completion-reason Verifier [RFCXXXX] speech-complete-timeout Verifier [RFCXXXX] new-audio-channel Verifier [RFCXXXX] abort-verification Verifier [RFCXXXX] start-input-timers Verifier [RFCXXXX] input-type Verifier [RFCXXXX]
IANA SHALL create a new name space of "MRCPv2 status codes" with the initial values that are defined in Section 5.4 All maintenance within and additions to the contents of this name space MUST be according to the "Specification Required with Expert Review" registration policy.
IANA SHALL create a new name space of "Grammar Reference List Parameters". All maintenance within and additions to the contents of this name space MUST be according to the "Specification Required with Expert Review" registration policy. There is only one initial parameter, "weight", which is defined in Section 13.5.1 and Section 9.9.
IANA SHALL create a new name space of "MRCPv2 vendor-specific parameters". All maintenance within and additions to the contents of this name space MUST be according to the "Hierarchical Allocation" registration policy as follows. Each name (corresponding to the "vendor-av-pair-name" ABNF production) MUST satisfy the syntax requirements of Internet Domain Names as described in section 2.3.1 of RFC 1035 [RFC1035] (and as updated or obsoleted by successive RFCs), with one exception, the order of the domain names is reversed. For example, a vendor-specific parameter "foo" by example.com would have the form "com.example.foo". The first, or top-level domain, is restricted to exactly the set of Top-Level Internet Domains defined by IANA and will be updated by IANA when and only when that set changes. The second-level and all subdomains within the parameter name MUST be allocated according to the "Expert Review" policy. The Designated Expert MAY advise IANA to allow delegation of subdomains to the requester. As a general guideline, the Designated Expert is encouraged to manage the allocation of corporate, organizational, or institutional names and delegate all subdomains accordingly. For example, the Designated Expert MAY allocate "com.example" and delegate all subdomains of that name to the organization represented by the Internet domain name "example.com". For simplicity, the Designated Expert is encouraged to perform allocations according to the existing allocations of Internet domain names to organizations, institutions, corporations, etc.
The registry contains a list of vendor-registered parameters, where each defined parameter is associated with a reference to an RFC defining it. The registry is initially empty.
IANA is requested to register the following Media Type according to the process defined in RFC 4288 [RFC4288].
IANA is requested to register and maintain the following XML Schema. Information provided follows the template in RFC 3688 [RFC3688].
IANA is requested to register and maintain the following XML Name space. Information provided follows the template in RFC 3688 [RFC3688].
IANA is requested to register the following text Media Types according to the process defined in RFC 4288 [RFC4288].
IANA is requested to register the following new URI scheme. The information below follows the template given in RFC 4395 [RFC4395].
IANA is requested to register the following SDP parameter values. The information for each follows the template given in RFC 4566 [RFC4566], Appendix B.
"TCP/MRCPv2" value of the "proto" parameter
"TCP/TLS/MRCPv2" value of the "proto" parameter
"resource" value of the "att-field" parameter
"channel" value of the "att-field" parameter
"cmid" value of the "att-field" parameter
The following is an example of a typical MRCPv2 session of speech synthesis and recognition between a client and a server. Although the SDP "s" attribute in these examples has a text description value to assist in understanding the examples, please keep in mind that RFC 3264 [RFC3264] recommends that messages actually put on the wire use a space or a dash.
The figure below illustrates opening a session to the MRCPv2 server. This exchange does not allocate a resource or setup media. It simply establishes a SIP session with the MRCPv2 server.
C->S:
INVITE sip:mresources@example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg1
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323123 INVITE
Contact:<sip:sarvi@client.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=sarvi 2614933546 2614933546 IN IP4 192.0.2.12
s=Set up MRCPv2 control and audio
i=Initial contact
c=IN IP4 192.0.2.12
S->C:
SIP/2.0 200 OK
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg1;received=192.0.32.10
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323123 INVITE
Contact:<sip:mresources@server.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=- 3000000001 3000000001 IN IP4 192.0.2.11
s=Set up MRCPv2 control and audio
i=Initial contact
c=IN IP4 192.0.2.11
C->S:
ACK sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg2
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323123 ACK
Content-Length:0
The client requests the server to create a synthesizer resource control channel to do speech synthesis. This also adds a media stream to send the generated speech. Note that in this example, the client requests a new MRCPv2 TCP stream between the client and the server. In the following requests, the client will ask to use the existing connection.
C->S:
INVITE sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg3
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323124 INVITE
Contact:<sip:sarvi@client.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=sarvi 2614933546 2614933547 IN IP4 192.0.2.12
s=Set up MRCPv2 control and audio
i=Add TCP channel, synthesizer and one-way audio
c=IN IP4 192.0.2.12
t=0 0
m=application 9 TCP/MRCPv2 1
a=setup:active
a=connection:new
a=resource:speechsynth
a=cmid:1
m=audio 49170 RTP/AVP 0 96
a=rtpmap:0 pcmu/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=recvonly
a=mid:1
S->C:
SIP/2.0 200 OK
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg3;received=192.0.32.10
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323124 INVITE
Contact:<sip:mresources@server.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=- 3000000001 3000000002 IN IP4 192.0.2.11
s=Set up MRCPv2 control and audio
i=Add TCP channel, synthesizer and one-way audio
c=IN IP4 192.0.2.11
t=0 0
m=application 32416 TCP/MRCPv2 1
a=setup:passive
a=connection:new
a=channel:32AECB23433801@speechsynth
a=cmid:1
m=audio 48260 RTP/AVP 0
a=rtpmap:0 pcmu/8000
a=sendonly
a=mid:1
C->S:
ACK sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg4
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323124 ACK
Content-Length:0
This exchange allocates an additional resource control channel for a recognizer. Since a recognizer would need to receive an audio stream for recognition, this interaction also updates the audio stream to sendrecv, making it a 2-way audio stream.
C->S:
INVITE sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg5
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323125 INVITE
Contact:<sip:sarvi@client.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=sarvi 2614933546 2614933548 IN IP4 192.0.2.12
s=Set up MRCPv2 control and audio
i=Add recognizer and duplex the audio
c=IN IP4 192.0.2.12
t=0 0
m=application 9 TCP/MRCPv2 1
a=setup:active
a=connection:existing
a=resource:speechsynth
a=cmid:1
m=audio 49170 RTP/AVP 0 96
a=rtpmap:0 pcmu/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=recvonly
a=mid:1
m=application 9 TCP/MRCPv2 1
a=setup:active
a=connection:existing
a=resource:speechrecog
a=cmid:2
m=audio 49180 RTP/AVP 0 96
a=rtpmap:0 pcmu/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=sendonly
a=mid:2
S->C:
SIP/2.0 200 OK
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg5;received=192.0.32.10
To:MediaServer <sip:mresources@example.com>;tag=62784
From:sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323125 INVITE
Contact:<sip:mresources@server.example.com>
Content-Type:application/sdp
Content-Length:...
v=0
o=- 3000000001 3000000003 IN IP4 192.0.2.11
s=Set up MRCPv2 control and audio
i=Add recognizer and duplex the audio
c=IN IP4 192.0.2.11
t=0 0
m=application 32416 TCP/MRCPv2 1
a=channel:32AECB23433801@speechsynth
a=cmid:1
m=audio 48260 RTP/AVP 0
a=rtpmap:0 pcmu/8000
a=sendonly
a=mid:1
m=application 32416 TCP/MRCPv2 1
a=channel:32AECB23433801@speechrecog
a=cmid:2
m=audio 48260 RTP/AVP 0
a=rtpmap:0 pcmu/8000
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
a=recvonly
a=mid:2
C->S:
ACK sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg6
Max-Forwards:6
To:MediaServer <sip:mresources@example.com>;tag=62784
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
Call-ID:a84b4c76e66710
CSeq:323125 ACK
Content-Length:0
A MRCPv2 SPEAK request initiates speech.
C->S:
MRCP/2.0 ... SPEAK 543257
Channel-Identifier:32AECB23433801@speechsynth
Kill-On-Barge-In:false
Voice-gender:neutral
Voice-age:25
Prosody-volume:medium
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>You have 4 new messages.</s>
<s>The first is from Stephanie Williams
<mark name="Stephanie"/>
and arrived at <break/>
<say-as interpret-as="vxml:time">0345p</say-as>.</s>
<s>The subject is <prosody
rate="-20%">ski trip</prosody></s>
</p>
</speak>
S->C:
MRCP/2.0 ... 543257 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechsynth
Speech-Marker:timestamp=857205015059
The synthesizer hits the special marker in the message to be spoken and faithfully informs the client of the event.
S->C: MRCP/2.0 ... SPEECH-MARKER 543257 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechsynth
Speech-Marker:timestamp=857206027059;Stephanie
The synthesizer finishes with the SPEAK request.
S->C: MRCP/2.0 ... SPEAK-COMPLETE 543257 COMPLETE
Channel-Identifier:32AECB23433801@speechsynth
Speech-Marker:timestamp=857207685213;Stephanie
The recognizer is issued a request to listen for the customer choices.
C->S: MRCP/2.0 ... RECOGNIZE 543258
Channel-Identifier:32AECB23433801@speechrecog
Content-Type:application/srgs+xml
Content-Length:...
<?xml version="1.0"?>
<!-- the default grammar language is US English -->
<grammar xmlns="http://www.w3.org/2001/06/grammar"
xml:lang="en-US" version="1.0" root="request">
<!-- single language attachment to a rule expansion -->
<rule id="request">
Can I speak to
<one-of xml:lang="fr-CA">
<item>Michel Tremblay</item>
<item>Andre Roy</item>
</one-of>
</rule>
</grammar>
S->C: MRCP/2.0 ... 543258 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
The client issues the next MRCPv2 SPEAK method.
C->S: MRCP/2.0 ... SPEAK 543259
Channel-Identifier:32AECB23433801@speechsynth
Kill-On-Barge-In:true
Content-Type:application/ssml+xml
Content-Length:...
<?xml version="1.0"?>
<speak version="1.0"
xmlns="http://www.w3.org/2001/10/synthesis"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/10/synthesis
http://www.w3.org/TR/speech-synthesis/synthesis.xsd"
xml:lang="en-US">
<p>
<s>Welcome to ABC corporation.</s>
<s>Who would you like Talk to.</s>
</p>
</speak>
S->C: MRCP/2.0 ... 543259 200 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechsynth
Speech-Marker:timestamp=857207696314
This next section of this ongoing example demonstrates how kill-on-barge-in support works. Since this last SPEAK request had Kill-On-Barge-In set to "true", when the recognizer (the server) generated the START-OF-INPUT event while a SPEAK was active the client immediately issued a BARGE-IN-OCCURRED method to the synthesizer resource. The speech synthesizer then terminated playback and notified the client. The completion-cause code provided the indication that this was a kill-on-barge-in interruption rather than a normal completion.
Note that since the recognition and synthesizer resources are in the same session on the same server, to obtain a faster response the server might have internally relayed the start-of-input condition to the synthesizer directly, before receiving the expected BARGE-IN-OCCURRED event. However, any such communication is outside the scope of the MRCPv2 protocol.
S->C: MRCP/2.0 ... START-OF-INPUT 543258 IN-PROGRESS
Channel-Identifier:32AECB23433801@speechrecog
Proxy-Sync-Id:987654321
C->S: MRCP/2.0 ... BARGE-IN-OCCURRED 543259
Channel-Identifier:32AECB23433801@speechsynth
Proxy-Sync-Id:987654321
S->C: MRCP/2.0 ... 543259 200 COMPLETE
Channel-Identifier:32AECB23433801@speechsynth
Active-Request-Id-List:543258
Speech-Marker:timestamp=857206096314
S->C: MRCP/2.0 ... SPEAK-COMPLETE 543259 COMPLETE
Channel-Identifier:32AECB23433801@speechsynth
Completion-Cause:001 barge-in
Speech-Marker:timestamp=857207685213
The recognition resource matched the spoken stream to a grammar and generated results. The result of the recognition is returned by the server as part of the RECOGNITION-COMPLETE event.
S->C: MRCP/2.0 ... RECOGNITION-COMPLETE 543258 COMPLETE
Channel-Identifier:32AECB23433801@speechrecog
Completion-Cause:000 success
Waveform-URI:<http://web.media.com/session123/audio.wav>;
size=423523;duration=25432
Content-Type:application/nlsml+xml
Content-Length:...
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="session:request1@form-level.store">
<interpretation>
<instance name="Person">
<ex:Person>
<ex:Name> Andre Roy </ex:Name>
</ex:Person>
</instance>
<input> may I speak to Andre Roy </input>
</interpretation>
</result>
Since the client was now finished with the session, including all resources, it issued a SIP BYE request to close the SIP session. This caused all control channels and resources allocated under the session to be de-allocated.
C->S: BYE sip:mresources@server.example.com SIP/2.0
Via:SIP/2.0/TCP client.atlanta.example.com:5060;
branch=z9hG4bK74bg7
Max-Forwards:6
From:Sarvi <sip:sarvi@example.com>;tag=1928301774
To:MediaServer <sip:mresources@example.com>;tag=62784
Call-ID:a84b4c76e66710
CSeq:323126 BYE
Content-Length:0
System: To which city will you be traveling?
User: I want to go to Pittsburgh.
<?xml version="1.0"?>
<result xmlns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns:ex="http://www.example.com/example"
grammar="http://www.example.com/flight">
<interpretation confidence="0.6">
<instance>
<ex:airline>
<ex:to_city>Pittsburgh</ex:to_city>
<ex:airline>
<instance>
<input mode="speech">
I want to go to Pittsburgh
</input>
</interpretation>
<interpretation confidence="0.4"
<instance>
<ex:airline>
<ex:to_city>Stockholm</ex:to_city>
</ex:airline>
</instance>
<input>I want to go to Stockholm</input>
</interpretation>
</result>
System: What would you like?
User: I would like 2 pizzas, one with pepperoni and cheese,
one with sausage and a bottle of coke, to go.
This example includes an order object which in turn contains objects named "food_item", "drink_item" and "delivery_method". The representation assumes there are no ambiguities in the speech or natural language processing. Note that this representation also assumes some level of intra-sentential anaphora resolution, i.e., to resolve the two "one's" as "pizza".
<?xml version="1.0"?>
<nl:result xmlns:nl="http://www.ietf.org/xml/ns/mrcpv2"
xmlns="http://www.example.com/example"
grammar="http://www.example.com/foodorder">
<nl:interpretation confidence="1.0" >
<nl:instance>
<order>
<food_item confidence="1.0">
<pizza>
<ingredients confidence="1.0">
pepperoni
</ingredients>
<ingredients confidence="1.0">
cheese
</ingredients>
</pizza>
<pizza>
<ingredients>sausage</ingredients>
</pizza>
</food_item>
<drink_item confidence="1.0">
<size>2-liter</size>
</drink_item>
<delivery_method>to go</delivery_method>
</order>
</nl:instance>
<nl:input mode="speech">I would like 2 pizzas,
one with pepperoni and cheese, one with sausage
and a bottle of coke, to go.
</nl:input>
</nl:interpretation>
</nl:result>
A combination of DTMF input and speech is represented using nested input elements. For example:
User: My pin is (dtmf 1 2 3 4)
<input>
<input mode="speech" confidence ="1.0"
timestamp-start="2000-04-03T0:00:00"
timestamp-end="2000-04-03T0:00:01.5">My pin is
</input>
<input mode="dtmf" confidence ="1.0"
timestamp-start="2000-04-03T0:00:01.5"
timestamp-end="2000-04-03T0:00:02.0">1 2 3 4
</input>
</input>
Note that grammars that recognize mixtures of speech and DTMF are not currently possible in SRGS; however, this representation might be needed for other applications of NLSML, and this mixture capability might be introduced in future versions of SRGS.
Natural language communication makes use of meta-dialog and meta-task utterances. This specification is flexible enough so that meta utterances can be represented on an application-specific basis without requiring other standard markup.
Here are two examples of how meta-task and meta-dialog utterances might be represented.
System: What toppings do you want on your pizza?
User: What toppings do you have?
<interpretation grammar="http://www.example.com/toppings">
<instance>
<question>
<questioned_item>toppings<questioned_item>
<questioned_property>
availability
</questioned_property>
</question>
</instance>
<input mode="speech">
what toppings do you have?
</input>
</interpretation>
User: slow down.
<interpretation grammar="http://www.example.com/generalCommandsGrammar">
<instance>
<command>
<action>reduce speech rate</action>
<doer>system</doer>
</command>
</instance>
<input mode="speech">slow down</input>
</interpretation>
This specification can be used on an application-specific basis to represent utterances that contain unresolved anaphoric and deictic references. Anaphoric references, which include pronouns and definite noun phrases that refer to something that was mentioned in the preceding linguistic context, and deictic references, which refer to something that is present in the non-linguistic context, present similar problems in that there may not be sufficient unambiguous linguistic context to determine what their exact role in the interpretation should be. In order to represent unresolved anaphora and deixis using this specification, one strategy would be for the developer to define a more surface-oriented representation that leaves the specific details of the interpretation of the reference open. (This assumes that a later component is responsible for actually resolving the reference).
Example: (ignoring the issue of representing the input from the
pointing gesture.)
System: What do you want to drink?
User: I want this (clicks on picture of large root beer.)
<?xml version="1.0"?>
<nl:result xmlns:nl="http://www.ietf.org/xml/ns/mrcpv2"
xmlns="http://www.example.com/example"
grammar="http://www.example.com/beverages.grxml">
<nl:interpretation>
<nl:instance>
<doer>I</doer>
<action>want</action>
<object>this</object>
</nl:instance>
<nl:input mode="speech">I want this</nl:input>
</nl:interpretation>
</nl:result>
For programming convenience, it is useful to be able to distinguish between individual items and sets containing one item in the XML representation of semantic results. For example, a pizza order might consist of exactly one pizza, but a pizza might contain zero or more toppings. Since there is no standard way of marking this distinction directly in XML, in the current framework, the developer is free to adopt any conventions that would convey this information in the XML markup. One strategy would be for the developer to wrap the set of items in a grouping element, as in the following example.
<order>
<pizza>
<topping-group>
<topping>mushrooms</topping>
</topping-group>
</pizza>
<drink>coke</drink>
</order>
In this example, the programmer can assume that there is supposed to be exactly one pizza and one drink in the order, but the fact that there is only one topping is an accident of this particular pizza order.
Note that the client controls both the grammar and the semantics to be returned upon grammar matches, so the user of the MRCPv2 protocol is fully empowered to cause results to be returned in NLSML in such a way that the interpretation is clear to that user.
Extensibility in NLSML is provided via result content flexibility, as discussed in the discussions of meta utterances and anaphora. NLSML can easily be used in sophisticated systems to convey application-specific information that more basic systems would not make use of, for example defining speech acts.
The following productions make use of the core rules defined in Section 6.1 of RFC 5234 [RFC5234].
LWS = [*WSP CRLF] 1*WSP ; linear whitespace
SWS = [LWS] ; sep whitespace
UTF8-NONASCII = %xC0-DF 1UTF8-CONT
/ %xE0-EF 2UTF8-CONT
/ %xF0-F7 3UTF8-CONT
/ %xF8-FB 4UTF8-CONT
/ %xFC-FD 5UTF8-CONT
UTF8-CONT = %x80-BF
UTFCHAR = %x21-7E
/ UTF8-NONASCII
param = *pchar
quoted-string = SWS DQUOTE *(qdtext / quoted-pair )
DQUOTE
qdtext = LWS / %x21 / %x23-5B / %x5D-7E
/ UTF8-NONASCII
quoted-pair = "\" (%x00-09 / %x0B-0C / %x0E-7F)
token = 1*(alphanum / "-" / "." / "!" / "%" / "*"
/ "_" / "+" / "`" / "'" / "~" )
reserved = ";" / "/" / "?" / ":" / "@" / "&" / "="
/ "+" / "$" / ","
mark = "-" / "_" / "." / "!" / "~" / "*" / "'"
/ "(" / ")"
unreserved = alphanum / mark
pchar = unreserved / escaped
/ ":" / "@" / "&" / "=" / "+" / "$" / ","
alphanum = ALPHA / DIGIT
BOOLEAN = "true" / "false"
FLOAT = *DIGIT ["." *DIGIT]
escaped = "%" HEXDIG HEXDIG
fragment = *uric
uri = [ absoluteURI / relativeURI ]
[ "#" fragment ]
absoluteURI = scheme ":" ( hier-part / opaque-part )
relativeURI = ( net-path / abs-path / rel-path )
[ "?" query ]
hier-part = ( net-path / abs-path ) [ "?" query ]
net-path = "//" authority [ abs-path ]
abs-path = "/" path-segments
rel-path = rel-segment [ abs-path ]
rel-segment = 1*( unreserved / escaped / ";" / "@"
/ "&" / "=" / "+" / "$" / "," )
opaque-part = uric-no-slash *uric
uric = reserved / unreserved / escaped
uric-no-slash = unreserved / escaped / ";" / "?" / ":"
/ "@" / "&" / "=" / "+" / "$" / ","
path-segments = segment *( "/" segment )
segment = *pchar *( ";" param )
scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
authority = srvr / reg-name
srvr = [ [ userinfo "@" ] hostport ]
reg-name = 1*( unreserved / escaped / "$" / ","
/ ";" / ":" / "@" / "&" / "=" / "+" )
query = *uric
userinfo = ( user ) [ ":" password ] "@"
user = 1*( unreserved / escaped
/ user-unreserved )
user-unreserved = "&" / "=" / "+" / "$" / "," / ";"
/ "?" / "/"
password = *( unreserved / escaped
/ "&" / "=" / "+" / "$" / "," )
hostport = host [ ":" port ]
host = hostname / IPv4address / IPv6reference
hostname = *( domainlabel "." ) toplabel [ "." ]
domainlabel = alphanum / alphanum *( alphanum / "-" )
alphanum
toplabel = ALPHA / ALPHA *( alphanum / "-" )
alphanum
IPv4address = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "."
1*3DIGIT
IPv6reference = "[" IPv6address "]"
IPv6address = hexpart [ ":" IPv4address ]
hexpart = hexseq / hexseq "::" [ hexseq ] / "::"
[ hexseq ]
hexseq = hex4 *( ":" hex4)
hex4 = 1*4HEXDIG
port = 1*19DIGIT
; generic-message is the top-level rule
generic-message = start-line message-header CRLF
[ message-body ]
message-body = *OCTET
start-line = request-line / response-line / event-line
request-line = mrcp-version SP message-length SP method-name
SP request-id CRLF
response-line = mrcp-version SP message-length SP request-id
SP status-code SP request-state CRLF
event-line = mrcp-version SP message-length SP event-name
SP request-id SP request-state CRLF
method-name = generic-method
/ synthesizer-method
/ recognizer-method
/ recorder-method
/ verifier-method
generic-method = "SET-PARAMS"
/ "GET-PARAMS"
request-state = "COMPLETE"
/ "IN-PROGRESS"
/ "PENDING"
event-name = synthesizer-event
/ recognizer-event
/ recorder-event
/ verifier-event
message-header = 1*(generic-header / resource-header / generic-field)
generic-field = field-name ":" [ field-value ]
field-name = token
field-value = *LWS field-content *( CRLF 1*LWS field-content)
field-content = <the OCTETs making up the field-value
and consisting of either *TEXT or combinations
of token, separators, and quoted-string>
resource-header = synthesizer-header
/ recognizer-header
/ recorder-header
/ verifier-header
generic-header = channel-identifier
/ accept
/ active-request-id-list
/ proxy-sync-id
/ accept-charset
/ content-type
/ content-id
/ content-base
/ content-encoding
/ content-location
/ content-length
/ fetch-timeout
/ cache-control
/ logging-tag
/ set-cookie
/ set-cookie2
/ vendor-specific
; -- content-id is as defined in RFC2392, RFC2046 and RFC5322
; -- accept and accept-charset are as defined in RFC2616
mrcp-version = "MRCP" "/" 1*2DIGIT "." 1*2DIGIT
message-length = 1*19DIGIT
request-id = 1*10DIGIT
status-code = 3DIGIT
channel-identifier = "Channel-Identifier" ":"
channel-id CRLF
channel-id = 1*alphanum "@" 1*alphanum
active-request-id-list = "Active-Request-Id-List" ":"
request-id *("," request-id) CRLF
proxy-sync-id = "Proxy-Sync-Id" ":" 1*VCHAR CRLF
content-base = "Content-Base" ":" absoluteURI CRLF
content-length = "Content-Length" ":" 1*19DIGIT CRLF
content-type = "Content-Type" ":" media-type-value CRLF
media-type-value = type "/" subtype *( ";" parameter )
type = token
subtype = token
parameter = attribute "=" value
attribute = token
value = token / quoted-string
content-encoding = "Content-Encoding" ":"
*WSP content-coding
*(*WSP "," *WSP content-coding *WSP )
CRLF
content-coding = token
content-location = "Content-Location" ":"
( absoluteURI / relativeURI ) CRLF
cache-control = "Cache-Control" ":"
[*WSP cache-directive
*( *WSP "," *WSP cache-directive *WSP )]
CRLF
fetch-timeout = "Fetch-Timeout" ":" 1*19DIGIT CRLF
cache-directive = "max-age" "=" delta-seconds
/ "max-stale" ["=" delta-seconds ]
/ "min-fresh" "=" delta-seconds
delta-seconds = 1*19DIGIT
logging-tag = "Logging-Tag" ":" 1*UTFCHAR CRLF
vendor-specific = "Vendor-Specific-Parameters" ":"
[vendor-specific-av-pair
*(";" vendor-specific-av-pair)] CRLF
vendor-specific-av-pair = vendor-av-pair-name "="
value
vendor-av-pair-name = 1*UTFCHAR
set-cookie = "Set-Cookie:" cookies CRLF
cookies = cookie *("," *LWS cookie)
cookie = attribute "=" value *(";" cookie-av)
cookie-av = "Comment" "=" value
/ "Domain" "=" value
/ "Max-Age" "=" value
/ "Path" "=" value
/ "Secure"
/ "Version" "=" 1*19DIGIT
/ "Age" "=" delta-seconds
set-cookie2 = "Set-Cookie2:" cookies2 CRLF
cookies2 = cookie2 *("," *LWS cookie2)
cookie2 = attribute "=" value *(";" cookie-av2)
cookie-av2 = "Comment" "=" value
/ "CommentURL" "=" DQUOTE uri DQUOTE
/ "Discard"
/ "Domain" "=" value
/ "Max-Age" "=" value
/ "Path" "=" value
/ "Port" [ "=" DQUOTE portlist DQUOTE ]
/ "Secure"
/ "Version" "=" 1*19DIGIT
/ "Age" "=" delta-seconds
portlist = portnum *("," *LWS portnum)
portnum = 1*19DIGIT
; Synthesizer ABNF
synthesizer-method = "SPEAK"
/ "STOP"
/ "PAUSE"
/ "RESUME"
/ "BARGE-IN-OCCURRED"
/ "CONTROL"
/ "DEFINE-LEXICON"
synthesizer-event = "SPEECH-MARKER"
/ "SPEAK-COMPLETE"
synthesizer-header = jump-size
/ kill-on-barge-in
/ speaker-profile
/ completion-cause
/ completion-reason
/ voice-parameter
/ prosody-parameter
/ speech-marker
/ speech-language
/ fetch-hint
/ audio-fetch-hint
/ failed-uri
/ failed-uri-cause
/ speak-restart
/ speak-length
/ load-lexicon
/ lexicon-search-order
jump-size = "Jump-Size" ":" speech-length-value CRLF
speech-length-value = numeric-speech-length
/ text-speech-length
text-speech-length = 1*UTFCHAR SP "Tag"
numeric-speech-length = ("+" / "-") positive-speech-length
positive-speech-length = 1*19DIGIT SP numeric-speech-unit
numeric-speech-unit = "Second"
/ "Word"
/ "Sentence"
/ "Paragraph"
kill-on-barge-in = "Kill-On-Barge-In" ":" BOOLEAN
CRLF
speaker-profile = "Speaker-Profile" ":" uri CRLF
completion-cause = "Completion-Cause" ":" cause-code SP
cause-name CRLF
cause-code = 3DIGIT
cause-name = *VCHAR
completion-reason = "Completion-Reason" ":"
quoted-string CRLF
voice-parameter = voice-gender
/ voice-age
/ voice-variant
/ voice-name
voice-gender = "Voice-Gender:" voice-gender-value CRLF
voice-gender-value = "male"
/ "female"
/ "neutral"
voice-age = "Voice-Age:" 1*3DIGIT CRLF
voice-variant = "Voice-Variant:" 1*19DIGIT CRLF
voice-name = "Voice-Name:"
1*UTFCHAR *(1*WSP 1*UTFCHAR) CRLF
prosody-parameter = "Prosody-" prosody-param-name ":"
prosody-param-value CRLF
prosody-param-name = 1*VCHAR
prosody-param-value = 1*VCHAR
timestamp = "timestamp" "=" time-stamp-value
time-stamp-value = 1*20DIGIT
speech-marker = "Speech-Marker" ":"
timestamp
[";" 1*(UTFCHAR / %x20)] CRLF
speech-language = "Speech-Language" ":" 1*VCHAR CRLF
fetch-hint = "Fetch-Hint" ":" ("prefetch" / "safe") CRLF
audio-fetch-hint = "Audio-Fetch-Hint" ":"
("prefetch" / "safe" / "stream") CRLF
failed-uri = "Failed-URI" ":" absoluteURI CRLF
failed-uri-cause = "Failed-URI-Cause" ":" 1*UTFCHAR CRLF
speak-restart = "Speak-Restart" ":" BOOLEAN CRLF
speak-length = "Speak-Length" ":" positive-length-value
CRLF
positive-length-value = positive-speech-length
/ text-speech-length
load-lexicon = "Load-Lexicon" ":" BOOLEAN CRLF
lexicon-search-order = "Lexicon-Search-Order" ":"
"<" absoluteURI ">" *(" " "<" absoluteURI ">") CRLF
; Recognizer ABNF
recognizer-method = recog-only-method
/ enrollment-method
recog-only-method = "DEFINE-GRAMMAR"
/ "RECOGNIZE"
/ "INTERPRET"
/ "GET-RESULT"
/ "START-INPUT-TIMERS"
/ "STOP"
enrollment-method = "START-PHRASE-ENROLLMENT"
/ "ENROLLMENT-ROLLBACK"
/ "END-PHRASE-ENROLLMENT"
/ "MODIFY-PHRASE"
/ "DELETE-PHRASE"
recognizer-event = "START-OF-INPUT"
/ "RECOGNITION-COMPLETE"
/ "INTERPRETATION-COMPLETE"
recognizer-header = recog-only-header
/ enrollment-header
recog-only-header = confidence-threshold
/ sensitivity-level
/ speed-vs-accuracy
/ n-best-list-length
/ input-type
/ no-input-timeout
/ recognition-timeout
/ waveform-uri
/ input-waveform-uri
/ completion-cause
/ completion-reason
/ recognizer-context-block
/ start-input-timers
/ speech-complete-timeout
/ speech-incomplete-timeout
/ dtmf-interdigit-timeout
/ dtmf-term-timeout
/ dtmf-term-char
/ failed-uri
/ failed-uri-cause
/ save-waveform
/ media-type
/ new-audio-channel
/ speech-language
/ ver-buffer-utterance
/ recognition-mode
/ cancel-if-queue
/ hotword-max-duration
/ hotword-min-duration
/ interpret-text
/ dtmf-buffer-time
/ clear-dtmf-buffer
/ early-no-match
enrollment-header = num-min-consistent-pronunciations
/ consistency-threshold
/ clash-threshold
/ personal-grammar-uri
/ enroll-utterance
/ phrase-id
/ phrase-nl
/ weight
/ save-best-waveform
/ new-phrase-id
/ confusable-phrases-uri
/ abort-phrase-enrollment
confidence-threshold = "Confidence-Threshold" ":"
FLOAT CRLF
sensitivity-level = "Sensitivity-Level" ":" FLOAT
CRLF
speed-vs-accuracy = "Speed-Vs-Accuracy" ":" FLOAT
CRLF
n-best-list-length = "N-Best-List-Length" ":" 1*19DIGIT
CRLF
input-type = "Input-Type" ":" inputs CRLF
inputs = "speech" / "dtmf"
no-input-timeout = "No-Input-Timeout" ":" 1*19DIGIT
CRLF
recognition-timeout = "Recognition-Timeout" ":" 1*19DIGIT
CRLF
waveform-uri = "Waveform-URI" ":" ["<" uri ">"
";" "size" "=" 1*19DIGIT
";" "duration" "=" 1*19DIGIT] CRLF
recognizer-context-block = "Recognizer-Context-Block" ":"
[1*VCHAR] CRLF
start-input-timers = "Start-Input-Timers" ":"
BOOLEAN CRLF
speech-complete-timeout = "Speech-Complete-Timeout" ":"
1*19DIGIT CRLF
speech-incomplete-timeout = "Speech-Incomplete-Timeout" ":"
1*19DIGIT CRLF
dtmf-interdigit-timeout = "DTMF-Interdigit-Timeout" ":"
1*19DIGIT CRLF
dtmf-term-timeout = "DTMF-Term-Timeout" ":" 1*19DIGIT
CRLF
dtmf-term-char = "DTMF-Term-Char" ":" VCHAR CRLF
save-waveform = "Save-Waveform" ":" BOOLEAN CRLF
new-audio-channel = "New-Audio-Channel" ":"
BOOLEAN CRLF
recognition-mode = "Recognition-Mode" ":"
normal-value / hotword-value CRLF
normal-value = "normal"
hotword-value = "hotword"
cancel-if-queue = "Cancel-If-Queue" ":" BOOLEAN CRLF
hotword-max-duration = "Hotword-Max-Duration" ":"
1*19DIGIT CRLF
hotword-min-duration = "Hotword-Min-Duration" ":"
1*19DIGIT CRLF
interpret-text = "Interpret-Text" ":" 1*VCHAR CRLF
dtmf-buffer-time = "DTMF-Buffer-Time" ":" 1*19DIGIT CRLF
clear-dtmf-buffer = "Clear-DTMF-Buffer" ":" BOOLEAN CRLF
early-no-match = "Early-No-Match" ":" BOOLEAN CRLF
num-min-consistent-pronunciations =
"Num-Min-Consistent-Pronunciations" ":" 1*19DIGIT CRLF
consistency-threshold = "Consistency-Threshold" ":" FLOAT
CRLF
clash-threshold = "Clash-Threshold" ":" FLOAT CRLF
personal-grammar-uri = "Personal-Grammar-URI" ":" uri CRLF
enroll-utterance = "Enroll-Utterance" ":" BOOLEAN CRLF
phrase-id = "Phrase-ID" ":" 1*VCHAR CRLF
phrase-nl = "Phrase-NL" ":" 1*UTFCHAR CRLF
weight = "Weight" ":" weight-value CRLF
weight-value = FLOAT
save-best-waveform = "Save-Best-Waveform" ":"
BOOLEAN CRLF
new-phrase-id = "New-Phrase-ID" ":" 1*VCHAR CRLF
confusable-phrases-uri = "Confusable-Phrases-URI" ":"
uri CRLF
abort-phrase-enrollment = "Abort-Phrase-Enrollment" ":"
BOOLEAN CRLF
; Recorder ABNF
recorder-method = "RECORD"
/ "STOP"
/ "START-INPUT-TIMERS"
recorder-event = "START-OF-INPUT"
/ "RECORD-COMPLETE"
recorder-header = sensitivity-level
/ no-input-timeout
/ completion-cause
/ completion-reason
/ failed-uri
/ failed-uri-cause
/ record-uri
/ media-type
/ max-time
/ trim-length
/ final-silence
/ capture-on-speech
/ ver-buffer-utterance
/ start-input-timers
/ new-audio-channel
record-uri = "Record-URI" ":" [ "<" uri ">"
";" "size" "=" 1*19DIGIT
";" "duration" "=" 1*19DIGIT] CRLF
media-type = "Media-Type" ":" media-type-value CRLF
max-time = "Max-Time" ":" 1*19DIGIT CRLF
trim-length = "Trim-Length" ":" 1*19DIGIT CRLF
final-silence = "Final-Silence" ":" 1*19DIGIT CRLF
capture-on-speech = "Capture-On-Speech " ":"
BOOLEAN CRLF
; Verifier ABNF
verifier-method = "START-SESSION"
/ "END-SESSION"
/ "QUERY-VOICEPRINT"
/ "DELETE-VOICEPRINT"
/ "VERIFY"
/ "VERIFY-FROM-BUFFER"
/ "VERIFY-ROLLBACK"
/ "STOP"
/ "CLEAR-BUFFER"
/ "START-INPUT-TIMERS"
/ "GET-INTERMEDIATE-RESULT"
verifier-event = "VERIFICATION-COMPLETE"
/ "START-OF-INPUT"
verifier-header = repository-uri
/ voiceprint-identifier
/ verification-mode
/ adapt-model
/ abort-model
/ min-verification-score
/ num-min-verification-phrases
/ num-max-verification-phrases
/ no-input-timeout
/ save-waveform
/ media-type
/ waveform-uri
/ voiceprint-exists
/ ver-buffer-utterance
/ input-waveform-uri
/ completion-cause
/ completion-reason
/ speech-complete-timeout
/ new-audio-channel
/ abort-verification
/ start-input-timers
/ input-type
repository-uri = "Repository-URI" ":" uri CRLF
voiceprint-identifier = "Voiceprint-Identifier" ":"
vid *[";" vid] CRLF
vid = 1*VCHAR ["." 1*VCHAR]
verification-mode = "Verification-Mode" ":"
verification-mode-string
verification-mode-string = "train" / "verify"
adapt-model = "Adapt-Model" ":" BOOLEAN CRLF
abort-model = "Abort-Model" ":" BOOLEAN CRLF
min-verification-score = "Min-Verification-Score" ":"
[ %x2D ] FLOAT CRLF
num-min-verification-phrases = "Num-Min-Verification-Phrases"
":" 1*19DIGIT CRLF
num-max-verification-phrases = "Num-Max-Verification-Phrases"
":" 1*19DIGIT CRLF
voiceprint-exists = "Voiceprint-Exists" ":"
BOOLEAN CRLF
ver-buffer-utterance = "Ver-Buffer-Utterance" ":"
BOOLEAN CRLF
input-waveform-uri = "Input-Waveform-URI" ":" uri CRLF
abort-verification = "Abort-Verification " ":"
BOOLEAN CRLF
The following productions add a new SDP session-level attribute. See Section 13.7.2, Paragraph 5.
cmid-attribute = "a=cmid:" identification-tag identification-tag = token
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.ietf.org/xml/ns/mrcpv2"
xmlns="http://www.ietf.org/xml/ns/mrcpv2"
elementFormDefault="qualified"
attributeFormDefault="unqualified" >
<xs:annotation>
<xs:documentation> Natural Language Semantic Markup Schema
</xs:documentation>
</xs:annotation>
<xs:include schemaLocation="enrollment-schema.rng"/>
<xs:include schemaLocation="verification-schema.rng"/>
<xs:element name="result">
<xs:complexType>
<xs:sequence>
<xs:element name="interpretation" maxOccurs="unbounded">
<xs:complexType>
<xs:sequence>
<xs:element name="instance" minOccurs="0">
<xs:complexType mixed="true">
<xs:sequence minOccurs="0">
<xs:any namespace="##other" processContents="lax"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="input">
<xs:complexType mixed="true">
<xs:choice>
<xs:element name="noinput" minOccurs="0"/>
<xs:element name="nomatch" minOccurs="0"/>
<xs:element name="input" minOccurs="0"/>
</xs:choice>
<xs:attribute name="mode"
type="xs:string"
default="speech"/>
<xs:attribute name="confidence"
type="confidenceinfo"
default="1.0"/>
<xs:attribute name="timestamp-start"
type="xs:string"/>
<xs:attribute name="timestamp-end"
type="xs:string"/>
</xs:complexType>
</xs:element>
</xs:sequence>
<xs:attribute name="confidence" type="confidenceinfo"
default="1.0"/>
<xs:attribute name="grammar" type="xs:anyURI"
use="optional"/>
</xs:complexType>
</xs:element>
<xs:element name="enrollment-result"
type="enrollment-contents"/>
<xs:element name="verification-result"
type="verification-contents"/>
</xs:sequence>
<xs:attribute name="grammar" type="xs:anyURI"
use="optional"/>
</xs:complexType>
</xs:element>
<xs:simpleType name="confidenceinfo">
<xs:restriction base="xs:float">
<xs:minInclusive value="0.0"/>
<xs:maxInclusive value="1.0"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
<?xml version="1.0" encoding="UTF-8"?>
<!-- MRCP Enrollment Schema
(See http://www.oasis-open.org/committees/relax-ng/spec.html)
-->
<grammar datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"
ns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns="http://relaxng.org/ns/structure/1.0">
<start>
<element name="enrollment-result">
<ref name="enrollment-content"/>
</element>
</start>
<define name="enrollment-content">
<interleave>
<element name="num-clashes">
<data type="nonNegativeInteger"/>
</element>
<element name="num-good-repetitions">
<data type="nonNegativeInteger"/>
</element>
<element name="num-repetitions-still-needed">
<data type="nonNegativeInteger"/>
</element>
<element name="consistency-status">
<choice>
<value>consistent</value>
<value>inconsistent</value>
<value>undecided</value>
</choice>
</element>
<optional>
<element name="clash-phrase-ids">
<oneOrMore>
<element name="item">
<data type="token"/>
</element>
</oneOrMore>
</element>
</optional>
<optional>
<element name="transcriptions">
<oneOrMore>
<element name="item">
<text/>
</element>
</oneOrMore>
</element>
</optional>
<optional>
<element name="confusable-phrases">
<oneOrMore>
<element name="item">
<text/>
</element>
</oneOrMore>
</element>
</optional>
</interleave>
</define>
</grammar>
<?xml version="1.0" encoding="UTF-8"?>
<!-- MRCP Verification Results Schema
(See http://www.oasis-open.org/committees/relax-ng/spec.html)
-->
<grammar datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"
ns="http://www.ietf.org/xml/ns/mrcpv2"
xmlns="http://relaxng.org/ns/structure/1.0">
<start>
<element name="verification-result">
<ref name="verification-contents"/>
</element>
</start>
<define name="verification-contents">
<element name="voiceprint">
<ref name="firstVoiceprintContent"/>
</element>
<zeroOrMore>
<element name="voiceprint">
<ref name="restVoiceprintContent"/>
</element>
</zeroOrMore>
</define>
<define name="firstVoiceprintContent">
<attribute name="id">
<data type="string"/>
</attribute>
<interleave>
<optional>
<element name="adapted">
<data type="boolean"/>
</element>
</optional>
<optional>
<element name="needmoredata">
<ref name="needmoredataContent"/>
</element>
</optional>
<optional>
<element name="incremental">
<ref name="firstCommonContent"/>
</element>
</optional>
<element name="cumulative">
<ref name="firstCommonContent"/>
</element>
</interleave>
</define>
<define name="restVoiceprintContent">
<attribute name="id">
<data type="string"/>
</attribute>
<element name="cumulative">
<ref name="restCommonContent"/>
</element>
</define>
<define name="firstCommonContent">
<interleave>
<element name="decision">
<ref name="decisionContent"/>
</element>
<optional>
<element name="utterance-length">
<ref name="utterance-lengthContent"/>
</element>
</optional>
<optional>
<element name="device">
<ref name="deviceContent"/>
</element>
</optional>
<optional>
<element name="gender">
<ref name="genderContent"/>
</element>
</optional>
<zeroOrMore>
<element name="verification-score">
<ref name="verification-scoreContent"/>
</element>
</zeroOrMore>
</interleave>
</define>
<define name="restCommonContent">
<interleave>
<optional>
<element name="decision">
<ref name="decisionContent"/>
</element>
</optional>
<optional>
<element name="device">
<ref name="deviceContent"/>
</element>
</optional>
<optional>
<element name="gender">
<ref name="genderContent"/>
</element>
</optional>
<zeroOrMore>
<element name="verification-score">
<ref name="verification-scoreContent"/>
</element>
</zeroOrMore>
</interleave>
</define>
<define name="decisionContent">
<choice>
<value>accepted</value>
<value>rejected</value>
<value>undecided</value>
</choice>
</define>
<define name="needmoredataContent">
<data type="boolean"/>
</define>
<define name="utterance-lengthContent">
<data type="nonNegativeInteger"/>
</define>
<define name="deviceContent">
<choice>
<value>cellular-phone</value>
<value>electret-phone</value>
<value>carbon-button-phone</value>
<value>unknown</value>
</choice>
</define>
<define name="genderContent">
<choice>
<value>male</value>
<value>female</value>
<value>unknown</value>
</choice>
</define>
<define name="verification-scoreContent">
<data type="float">
<param name="minInclusive">-1</param>
<param name="maxInclusive">1</param>
</data>
</define>
</grammar>
Pierre Forgues
Nuance Communications Ltd.
1500 University Street
Suite 935
Montreal, Quebec
Canada H3A 3S7
Email: forgues@nuance.com
Charles Galles
Intervoice, Inc.
17811 Waterview Parkway
Dallas, Texas 75252
Email: charles.galles@intervoice.com
Klaus Reifenrath
Scansoft, Inc
Guldensporenpark 32
Building D
9820 Merelbeke
Belgium
Email: klaus.reifenrath@scansoft.com
Andre Gillet (Nuance Communications)
Andrew Hunt (ScanSoft)
Andrew Wahbe (Genesys)
Aaron Kneiss (ScanSoft)
Brian Eberman (ScanSoft)
Corey Stohs (Cisco Systems Inc)
Dave Burke (VoxPilot)
Jeff Kusnitz (IBM Corp)
Ganesh N Ramaswamy (IBM Corp)
Klaus Reifenrath (ScanSoft)
Kristian Finlator (ScanSoft)
Magnus Westerlund (Ericsson)
Martin Dragomirecky (Cisco Systems Inc)
Paolo Baggia (Loquendo)
Peter Monaco (Nuance Communications)
Pierre Forgues (Nuance Communications)
Ran Zilca (IBM Corp)
Suresh Kaliannan (Cisco Systems Inc.)
Skip Cave (Intervoice Inc)
Thomas Gal (LumenVox)
The chairs of the speechsc work group are Eric Burger (Georgetown University) and Dave Oran (Cisco Systems, Inc.).
Many thanks go in particular to Robert Sparks, Alex Agranovsky, and Henry Phan, who were there at the end to dot all the i's and cross all the t's.