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This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79.
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The specified IETF emergency services architecture puts a strong emphasis on emergency call and emergency messaging via the Voice Service Provider (VSP) / Application Service Provider (ASP). There are two reasons for this design decision: The call routing via the VSP/ASP is more natural as it follows the standard communication pattern and transition deployments assume non-updated end hosts.
As the deployment of the Location-to-Service Translation protocol progresses there are possibilities for upgraded end devices to directly communicate with the IP-based emergency services network without the need to interact with a VSP/ASP, which simplifies the task of regulators as the involved parties are within the same jurisdiction.
This memo describes the procedures and operations of a generic emergency calling client utilizing the available building blocks.
1.
Introduction
2.
Terminology
3.
The Jurisdictional Problem
4.
ESRP Route Determination
5.
Emergency Client Registration
6.
Emergency Client Call Intitiation
7.
Call Termination Control
8.
SIP Feature Restrictions
9.
Testing
9.1.
Test Registration
9.2.
Format
10.
PSAP Callback
11.
Security Considerations
12.
IANA Considerations
13.
Acknowledgements
14.
References
14.1.
Normative References
14.2.
Informative References
§
Authors' Addresses
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The description of the IETF emergency services architecture, found in [I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.) and in [I‑D.ietf‑ecrit‑framework] (Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, “Framework for Emergency Calling using Internet Multimedia,” July 2009.), focuses on devices where emergency calls are routed primarily through the subscriber's home VSP and the direct signaling communication between the end host and the Public Safety Answering Point (PSAP) that contains the IP-based PSAP is only an exception. This is a convenient assumption if one considers the regular communication patterns of the device and the potential proprietary protocol implementations used between the end host and the VSP and the ability to move the interoperability challenges away from the end device and closer to VSPs. There are, however, challenges for regulators to enforce emergency services functionality when the VSP is located in a different jurisdiction. Inclusion of a VSP introduces unnecessary elements into the emergency call path making the overall solution more cumbersome.
With the help of the Location-to-Service Translation protocol a PSAP URI is discovered that allows the end device to directly send SIP communication requests towards the PSAP.
Note that the information returned by LoST may not necessarily be the address of the PSAP itself but might rather be an entity that gets the emergency call closer to the PSAP by returning the address of an Emergency Services Routing Proxy (ESRP).
The intent of this client is that it will be able to use the available ECRIT building blocks to allow any IP enabled device with access to the Internet to make an emergency call without requiring the signaling interaction with the VSP. In fact, there is no assumption or requirement for a VSP subscription to exist. The interacting entities are shown in Figure 1 (Network Configuration).
.... ....
,' ',' ',
; ;
+--------+ ; ; +------+
| Device |--->: ISP :----->| ESRP |
+--------+ ; ; +------+
`, ,', ,'
, , , ,
```` ````
| Figure 1: Network Configuration |
Furthermore, a means for call-back in the event of a dropped call is also described.
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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 [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).
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The jurisdictional problem is illustrated with Figure 2 (Jurisdictional Boundaries in Internet Emergency Calling) that highlights that provided the data in the Location Information Server (LIS) and the LoST server are correct, that the caller and the PSAP are assured of being in the same regulatory jurisdiction. This is important, because it shows that it is the access component of the network and not the service component against which reguatory obligations can be imposed with any hope of enforcement. Regulation without the possibility of enforcement is challenging as there is very little coordination between regulators world wide in this area, consequently any emergency calling procedure should ensure that all nodes against which the procedures apply fall within the same regulatory boundary.
+-----+
| VSP |
| # |
+-----+
o-------------o----------------------o-------------o
/ \
/ +---------+ +--------+ \
/ | Access \ / ESINet \ \
o | Network \ / \ o
| + + + O + |
| / O | / <P\ | |
| + <C\ o REGULATORY + /'\ + |
| | /'\ / | PSAP / o
o + Caller + JURISDICTION + +-------+ + /
\ \ __________| \ / \/ /
\ /
o--------------o----------------------o---------------o
| Figure 2: Jurisdictional Boundaries in Internet Emergency Calling |
| TOC |
The ESRP is discovered by the emergency client obtaing its location from a LIS, for example, using HELD, and then using LoST to resolve the location and 'urn:services.sos' Service URN to the ESRP URI.
When the emergency client is started the device needs to perform LIS and LoST server discovery, as described in Section 7 of [I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.).
The emergency client MUST support location acquisition and the LCPs described in Section 6.5 of [I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.). The description in Section 6.5 and 6.6 of [I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.) regarding the interaction between the device and the LIS applies to this document.
The emergency client MUST use LoST [RFC5222] (Hardie, T., Newton, A., Schulzrinne, H., and H. Tschofenig, “LoST: A Location-to-Service Translation Protocol,” August 2008.) to obtain an ESRP URI. The exact timing of individual LoST lookups may vary based on a number of factors, including the design of the user interface. For example, a hypothetical user interface may offer an emergency call button that triggers a <listServicesByLocation> interaction to learn about the available emergency services (potentially using the serviceListBoundary extension defined in [I‑D.ietf‑ecrit‑lost‑servicelistboundary] (Wolf, K., “LoST Service List Boundary Extension,” February 2010.)). The service options may be presented to the emergency caller in a graphical fashion and once a specific service is selected a LoST query would be initiated (unless a cached mapping is available that makes this request obsolete). The LoST <findService> query to obtain the ESRP URI for the selected service is in this example initiated at the time the emergency call setup is performed. It is recommended that ESRP discovery occurs at call time.
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Emergency registration is only necessary when an emergency call procedure is initiated. Immediately prior to making an emergency call, the emergency client performs a SIP emergency registration with the registrar in the ESRP, the ESRP-registrar. The emergency registration is a SIP registration with specific options and headers which are required in order to guard the emergency network and ensure callback should it be required.
Each emergency client MUST provide an instance-id, as defined in [I‑D.ietf‑sip‑outbound] (Jennings, C., “Managing Client Initiated Connections in the Session Initiation Protocol (SIP),” June 2009.), this allows the ESRP-registrar to generate a GRUU [RFC5627] (Rosenberg, J., “Obtaining and Using Globally Routable User Agent URIs (GRUUs) in the Session Initiation Protocol (SIP),” October 2009.) that can be used as a callback identifier. A GRUU is necessary as the callback identifier because the emergency client does not provide a longer-term contact address to the ESRP-registrar prior to registration, and the GRUU provides a handle by which the PSAP can identify the calling emergency client. To simplify the emergency client and ESRP-registrar implementations, only public GRUUs are provided by the ESRP-registrar. The public GRUU is guaranteed to be the same for a device regardless of re-registration with a different call-id, which may occur if the device unexpectedly reboots. This is not true for temporary GRUUs, which makes temporary GRUUs undesriable in the scope of this application space.
The PSAP is able to define and mandate the time over which callback is possible. This needs to be a reasonable period of time, nominally 10s of minutes, as the device may well be transient with regards to network attachment. The ESRP-registrar reflects the regulatory callback period in the expiry value of emergency registration responses. Emergency clients claiming compliance to this specification MUST honour the value in the registration response from the ESRP-registrar, up to a maximum of 60 minutes. An emergency client SHOULD respect a registration expiry of longer than 60 minutes, but MAY terminate its registration with and ESRP-registrar at 60 minutes if the expiry value provided by the ESRP-registrar was longer.
In the event that a registration is lost by the emergency client prior to reaching registration expiry then the emergency client MUST re-register with the ESRP-registrar and SHOULD use the same call-id. In this circumstance the ESRP-registrar SHOULD match the instance-id and the call-id to recognize that it is a re-registration for a dropped connection, and expiry time in the registration response SHOULD be set to the time remaining when the original registration occurred.
[I‑D.ietf‑sip‑outbound] (Jennings, C., “Managing Client Initiated Connections in the Session Initiation Protocol (SIP),” June 2009.) requires a device to support at least 2 registrations to different proxies. The emergency client requirements in this memo relax this requirement down to one registration, but more than one is allowed. There are several reasons for relaxing the connection redundancy requirement. Firstly, ESRPs are expected to have inbuilt redundancy, so if a connection is dropped due to a failed proxy in the ESRP, then a new connection or registration will automatically be directed to an active proxy in the ESRP cluster. If the connection dropped because of some other failure along the path from the emergency client to the ESRP, then multiple SIP registrations are unlikely to provide any measurable reliability improvements since single points of failure in this path are inherently likely. Secondly, re-registrations only occur immediately prior to call placement, so any outbound failure will also likely result in the call dropping. If this occurs then the emergency client MUST re-register with the ESRP-registrar, and since instance-id and public GRUU will remain unchanged as a result of this, the emergency client can either receive a callback from the PSAP, or it can initiate a new call to the emergency network.
Location information is critical to emergency calling. Providing location information to the calling-entity with sufficient granularity to allow ESRP route determination is crucial. Since this must occur prior to the emergency client registering with the ESRP-registrar, the emergency client must have access to a certain amount of location information (and the amount varies depending on the specific emergency services deployment architecture).
The device SHOULD include all the location information it has when registering with the ERSP-registrar. Inclusion of location information in SIP REGISTER messages is specified in [I‑D.ietf‑sipcore‑location‑conveyance] (Polk, J. and B. Rosen, “Location Conveyance for the Session Initiation Protocol,” February 2010.). There are three possible execution paths for the ESRP-registrar when receiving a REGISTER message:
Where location conveyance is used confidentiality protection SHOULD be provided using Transport Layer Security (TLS).
Figure 3 (Example Registration Message Flow) show the registration message exchange graphically.
+--------+ +-----+ +------+ +------+
| Device | | LIS | | LoST | | ESRP |
+--------+ +-----+ +------+ +------+
| | | |
+<----LIS Discovery---->+ | |
| | | |
+----locationRequest--->+ | |
| | | |
+<---locationResponse---| | |
| | | |
+------------------findService------------->+ |
| | | |
+<--------------findServiceResponse---------+ |
| | | |
+------------------------REGISTER------------------------>+
| | | |
| +<------locationRequest-----------+
| | | |
| +-------locationResponse--------->+
| | | |
+<-------------------------200 OK ------------------------+
| | | |
| Figure 3: Example Registration Message Flow |
REGISTER sip:sos.example.com SIP/2.0
Via: SIP/2.0/TCP 192.0.2.2;branch=z9hG4bKnashds7
Max-Forwards: 70
From: anon <sip:anon@sos.example.com>;tag=7F94778B653B
To: anon <sip:anon@sos.example.com>
Call-ID: 16CB75F21C70
CSeq: 1 REGISTER
Geolocation: <https://lis.access.example.com:9192/suXweu838737d72>
;inserted-by="anon@192.0.2.2"
;routing-allowed=yes
Geolocation: <cid:target123@192.0.2.2>
;inserted-by="anon@192.0.2.2"
;routing-allowed=no
Require: gruu, geolocation
Supported: outbound, gruu
Contact: <sip:anon@192.0.2.2;transport=tcp>
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
| Figure 4: Sample REGISTER message |
Since the emergency client does not have a domain, it MUST register in the same domain as the ESRP. This is illustrated in the example REGISTER message show in Figure 4 (Sample REGISTER message).
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Immediately subsequent to the registration a SIP INVITE request is sent to the ESRP in the following form:
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The description in [I‑D.rosen‑ecrit‑premature‑disconnect‑rqmts] (Rosen, B., “Requirements for handling abandoned calls and premature disconnects in emergency calls on the Internet,” January 2009.) is relevant for this document.
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The functionality defined in Section 9.3 in [I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.) regarding disabling of certain features is relevant for this document and an emergency client MUST NOT implement the the features listed in ED-70, and ED-71.
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The description in Section 15 of [I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.) regarding emergency call testing is used by this specification. Since this specification mandates a registration with the ESRP-registrar a similar tagging URI to that described in [I‑D.patel‑ecrit‑sos‑parameter] (Patel, M., “SOS Uniform Resource Identifier (URI) Parameter for Marking of Session Initiation Protocol (SIP) Requests related to Emergency Services,” February 2010.) is used to indicate a test registration.
Test registrations SHALL be of short durations, but MUST be long enough to allow completion of a "test call" as described in [I‑D.ietf‑ecrit‑phonebcp] (Rosen, B. and J. Polk, “Best Current Practice for Communications Services in support of Emergency Calling,” January 2010.).
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When the emergency client sends a REGISTER request for emergency test registration, the "sos.test" URI parameter MUST be appended to the URI in the Contact header. This indicates to the ESRP-registrar that the request is for emergency test registration.
...
Contact: <sip:anon@192.0.2.2;transport=tcp;sos.test>
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
| Figure 5: Test REGISTER Message Fragment |
Only one Contact header field SHOULD be included in the emergency REGISTER test request. If more than one Contact header is included then the presence of the "sos.test" URI in any of the Contact fields SHALL result in the ESRP-registrar treating the registration as a test registration.
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The following syntax specification uses the augmented Backus-Naur Form (BNF) as described in [RFC5234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” January 2008.).
The "sos.test" URI parameter is a "uri-parameter", as defined by [RFC3261] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.).
uri-parameter =/ sos-param-test
sos-param-test = "sos.test"
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PSAP callback occurs as described in [I‑D.schulzrinne‑ecrit‑psap‑callback] (Schulzrinne, H., Tschofenig, H., and M. Patel, “Public Safety Answering Point (PSAP) Callbacks,” March 2010.).
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TBD
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This specification defines one new SIP URI parameter, as per the registry created by [RFC3969] (Camarillo, G., “The Internet Assigned Number Authority (IANA) Uniform Resource Identifier (URI) Parameter Registry for the Session Initiation Protocol (SIP),” December 2004.).
Parameter Name: sos.test
Predefined Values: none
Reference: [RFCXXXX]
[NOTE TO IANA: Please replace XXXX with the RFC number of this specification.]
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Thanks to Elaine Quah for being a sounding board.
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| [I-D.ietf-ecrit-framework] | Rosen, B., Schulzrinne, H., Polk, J., and A. Newton, “Framework for Emergency Calling using Internet Multimedia,” draft-ietf-ecrit-framework-10 (work in progress), July 2009 (TXT). |
| [I-D.ietf-ecrit-lost-servicelistboundary] | Wolf, K., “LoST Service List Boundary Extension,” draft-ietf-ecrit-lost-servicelistboundary-03 (work in progress), February 2010 (TXT). |
| [I-D.patel-ecrit-sos-parameter] | Patel, M., “SOS Uniform Resource Identifier (URI) Parameter for Marking of Session Initiation Protocol (SIP) Requests related to Emergency Services,” draft-patel-ecrit-sos-parameter-08 (work in progress), February 2010 (TXT). |
| [I-D.rosen-ecrit-premature-disconnect-rqmts] | Rosen, B., “Requirements for handling abandoned calls and premature disconnects in emergency calls on the Internet,” draft-rosen-ecrit-premature-disconnect-rqmts-02 (work in progress), January 2009 (TXT). |
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| James Winterbottom | |
| Andrew Corporation | |
| Andrew Building (39) | |
| University of Wollongong, NSW 2500 | |
| AU | |
| Email: | james.winterbottom@andrew.com |
| Martin Thomson | |
| Andrew Corporation | |
| Andrew Building (39) | |
| University of Wollongong, NSW 2500 | |
| AU | |
| Email: | martin.thomson@andrew.com |
| Hannes Tschofenig | |
| Nokia Siemens Networks | |
| Linnoitustie 6 | |
| Espoo, 02 600 | |
| Finland | |
| Email: | Hannes.Tschofenig@gmx.net |
| Henning Schulzrinne | |
| Columbia University | |
| Department of Computer Science | |
| 450 Computer Science Building | |
| New York, NY 10027 | |
| US | |
| Phone: | +1 212 939 7004 |
| Email: | hgs+ecrit@cs.columbia.edu |
| URI: | http://www.cs.columbia.edu |