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By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79.
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This Internet-Draft will expire on March 8, 2009.
This memo discusses benefits and issues that arise when allowing RTCP packets to be transmitted with reduced size. The size can be reduced if the rules on how to create compound packets outlined in RFC3550 are removed or changed. Based on that analysis this memo defines certain changes to the rules to allow feedback messages to be sent as reduced-size RTCP packets under certain conditions when using the RTP AVPF profile (RFC 4585). This document updates [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.), [RFC3711] (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) and [RFC4585] (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.).
1.
Introduction
2.
Terminology
3.
Use Cases and Design Rationale
3.1.
RTCP Compound Packets (Background)
3.2.
Use Cases for Reduced-Size RTCP
3.3.
Benefits of Reduced-Size RTCP
3.4.
Issues with Reduced-Size RTCP
3.4.1.
Middle Boxes
3.4.2.
Packet Validation
3.4.3.
Encryption/authentication
3.4.4.
RTP and RTCP Multiplex on the Same Port
3.4.5.
Header Compression
4.
Use of Reduced-size RTCP with AVPF
4.1.
Definition of Reduced-Size RTCP
4.2.
Algorithm Considerations
4.2.1.
Verification of Delivery
4.2.2.
Single vs Multiple RTCP in a Reduced-Size RTCP
4.2.3.
Enforcing Compound RTCP
4.2.4.
Immediate Mode
5.
Signaling
6.
Security Considerations
7.
IANA Considerations
8.
Acknowledgements
9.
References
9.1.
Normative References
9.2.
Informative References
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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In RTP (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) [RFC3550] it is currently mandatory to send RTP Control Protocol (RTCP) packets as compound packets containing at least a Sender Report (SR) or Receiver Report (RR), followed by a Source Description (SDES) packet containing at least the CNAME item. There are good reasons for this, as discussed below (see Section 3.1 (RTCP Compound Packets (Background))), however it does result in the minimal RTCP packets being quite large.
The RTP profile AVPF (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.) [RFC4585] specifies new RTCP packet types for feedback messages. Some of these feedback messages would benefit from being transmitted with minimal delay. AVPF does provide some mechanisms to support this, however for environments with low- bitrate links these messages can still consume a large amount of resources, and can introduce extra delay in the time it takes to completely send the compound packet in the network. It is therefore desirable to send just the feedback, without the other parts of a compound RTCP packet. This memo proposes such a mechanism, for this, and other use cases, as discussed in Section 3.2 (Use Cases for Reduced-Size RTCP).
There are a number of benefits with reduced-size RTCP, these are discussed in Section 3.3 (Benefits of Reduced-Size RTCP).
The use of reduced-size RTCP is not without issues. This is discussed in Section 3.4 (Issues with Reduced-Size RTCP). These issues need to be considered and are part of the motivation for this document.
Finally this document defines how AVPF is updated to allow for the transmission of reduced-size RTCP in a way that would not substantially affect the mechanisms that compound packets provide, see Section 4 (Use of Reduced-size RTCP with AVPF) for more details. The connection to AVPF (or SAVPF) is motivated by the fact that reduced-size RTCP is mainly beneficial for event driven feedback purposes and that the AVPF early and immediate modes make this possible.
This document updates [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.), [RFC3711] (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) and [RFC4585] (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.).
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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.).
The naming convention for RTCP is often confusing. Below a list of RTCP terms and what they mean. See also section 6.1 in [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) and section 3.1 in [RFC4585] (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.) for details.
- RTCP packet:
- Can be of different types, contains a fixed header part followed by structured elements depending on RTCP packet type.
- Lower layer datagram:
- Can be interpreted as the UDP payload. It may however, depending on the transport, be TCP or DCCP payload or something else. Synonymous to "underlying protocol" defined in section 3 in [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.).
- Compound RTCP packet:
- A collection of two or more RTCP packets. A compound RTCP packet is transmitted in a lower layer datagram. It must contain at least an RTCP RR or SR packet and a SDES packet with the CNAME item. Often "compound" is left out, the interpretation of RTCP packet is therefore dependent on the context.
- Minimal compound RTCP packet:
- A compound RTCP packet that contains the RTCP RR or SR packets and the SDES packet with the CNAME item with a specified ordering.
- (Full) compound RTCP packet:
- A compound RTCP packet that conforms to the requirements on minimal compound RTCP packets and contains more RTCP packets.
- Reduced-size RTCP packet:
- May contain one or more RTCP packets but does not follow the compound RTCP rules defined in section 6.1 in [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) and are thus neither a minimal or a full compound RTCP. See Section 4.1 (Definition of Reduced-Size RTCP) for a full definition.
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Section 6.1 in [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) specifies that an RTCP packet must be sent as a compound RTCP packet consisting of at least two individual RTCP packets, first an Sender Report (SR) or Receiver Report (RR), followed by additional packets including a mandatory SDES packet containing a CNAME item for the transmitting source identifier (SSRC). Below is a short description what these RTCP packet types are used for.
Reviewing the above it is obvious that both SR/RR and the CNAME are very important for new session participants to be able to utilize any received media and to avoid flooding the network with RTCP reports. In addition, if not sent regularly the dynamic nature of the information provided would make it less useful.
The following sections will describe the cases when reduced-size RTCP is beneficial and also show the possible issues that must be considered.
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Below are listed a few use cases for reduced-size RTCP.
- Control Plane Signaling:
- Open Mobile Alliance (OMA) Push-to-talk over Cellular (PoC) [OMA‑PoC] (Open Mobile Alliance, “Specification : Push to talk Over Cellular User Plane, http://www.openmobilealliance.org/release_program/docs/PoC/V1_0_1-20061128-A/OMA-TS-PoC-UserPlane-V1_0_1-20061128-A.pdf,” November 2006.) makes use of reduced-size RTCP when transmitting certain events. The OMA POC service is primarily used over cellular links capable of IP transport, such as the GSM GPRS.
- Codec Control Signaling:
- An example that can be used with reduced-size RTCP is e.g TMMBR messages as specified in [RFC5104] (Wenger, S., Chandra, U., Westerlund, M., and B. Burman, “Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF),” February 2008.) which signal a request for a change in codec bitrate. The benefit of its use for these messages is in bad channel conditions as reduced-size RTCP are much more likely to be successfully transmitted than larger compound RTCP. This is critical as these messages are likely to occur when channel conditions are poor. Other examples of codec control usage for reduced-size RTCP are found in [MTSI‑3GPP] (3GPP, “Specification : 3GPP TS 26.114 (v7.4.0), http://www.3gpp.org/ftp/Specs/archive/26_series/26.114/26114-740.zip,” March 2007.)
- Feedback:
- An example of a feedback scenario that would benefit from reduced-size RTCP is Video streams with generic NACK. In cases where the RTT is shorter than the receiver buffer depth, generic NACK can be used to request retransmission of missing packets, thus improving playout quality considerably. If the generic NACK packets are transmitted as reduced-size RTCP, the bandwidth requirement for RTCP will be minimal, enabling more frequent feedback. Like in the codec control case it is important that these packets can be transmitted with as little delay as possible. Another interesting use for reduced-size RTCP is in cases when regular feedback is needed, as described in Section 3.3 (Benefits of Reduced-Size RTCP)
- Status Reports:
- One proposed idea is to transmit small measurement or status reports in reduced-size RTCP, and to be able to split the minimal compound RTCP and transmit the individual RTCP separately. The status reports can be used either by the endpoints or by other network monitoring boxes in the network. The benefit is that with some radio access technologies small packets are more robust to poor radio conditions than large packets. Additionally, with small (report) packets there is a smaller risk that the report packets will affect the channel that they report upon. Another benefit is that it is, with reduced-size RTCP, possible to allow e.g anonymous status reporting to be transmitted unencrypted. Something that may be beneficial for e.g network monitoring purposes.
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As mentioned in the introduction, most advantages of using reduced-size RTCP packets exists in cases when the available RTCP bitrate is limited. This because they can become substantially smaller than compound packets. A compound packet is forced to contain both an RR or an SR and the CNAME SDES item. The RR containing a report block for a single source is 32 bytes, an SR is 52 bytes. Both may be larger if they contain report blocks for multiple sources. The SDES packet containing a CNAME item will be 10 bytes plus the CNAME string length. Here it is reasonable that the CNAME string is at least 10 bytes to get a decent collision resistance. If the recommended form of user@host is used, then most strings will be longer than 20 characters. Thus a reduced-size RTCP can become at least 70-80 bytes smaller than the compound packet.
For low bitrate links the benefits of this reduction in size are as follows:
In cases when reduced-size RTCP carry important and time sensitive feedback, both shorter serialization time and the lower loss probability are important to enable the best possible functionality. Having a packet loss rate that is much higher for the feedback packets compared to media packets hurts when trying to perform media adaptation, to for example handle the changed performance present at the cell border in a cellular system.
For high bitrate applications there is usually no problem to supply RTCP with sufficient bitrates. When using AVPF one can use the "trr-int" parameter to restrict the regular reporting interval to approximately once per RTT or less often. As in most cases there is little reason to provide with regular reports of higher density than this. Any additional bandwidth can then be used for feedback messages. The benefit of reduced-size RTCP in this case is limited, but exists. One typical example is video using generic NACK in cases where the RTT is low. Using reduced-size RTCP would reduce the total amount of bits used for RTCP. This is primarily applicable if the number of reports is large. This would also result in lower processing delay and less complexity for the feedback packets as they do not need to query the RTCP database to construct the right messages.
As message size is generally a smaller issue at higher bitrates, it is also possible to transmit multiple RTCP in each lower layer datagram in these cases. The motivation behind reduced-size RTCP in this case is not size, rather it is to avoid the extra overhead caused by inclusion of the SR/RR and SDES CNAME items in each transmitted RTCP.
Independently of the link type there are additional benefits with sending feedback in small reduced-size RTCP. Applications that use RTCP AVPF in early or immediate mode to send frequent event driven feedback. Under these circumstances, the risk that the RTCP bandwidth becomes too high during periods of heavy feedback signaling is reduced.
In cases when regular feedback is needed, such as the profile under development for TCP friendly rate control (TFRC) for RTP [I‑D.ietf‑avt‑tfrc‑profile] (Gharai, L., “RTP with TCP Friendly Rate Control,” July 2007.), the size of compound RTCP can result in very high bandwidth requirements if the round trip time is short. For this particular application reduced-size RTCP gives a very substantial improvement.
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This section describes the known issues with reduced-size RTCP and also a brief analysis.
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Middle boxes in the network may discard RTCP that do not follow the rules outlined in section 6.1 of RFC3550. Newer report types may be interpreted as unknown by the middle box. For instance if the payload type number is 207 instead of 200 or 201 it may be treated as unknown. The effect of this might for instance be that compound RTCP would get through while the reduced-size RTCP would be lost.
Verification of the delivery of reduced-size RTCP is discussed in Section 4.2.1 (Verification of Delivery).
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A reduced-size RTCP packet will be discarded by the packet validation code in Appendix A of [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.). This has several impacts:
- Weakened Packet Validation:
- The packet validation code needs to be rewritten to accept reduced-size RTCP. This in particular affects section 9.1 in [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) in the sense that the header verification must take into account that the payload type numbers for the (first) RTCP in the lower layer datagram may differ from 200 or 201 (SR or RR). One potential effect of this change is much weaker validation that received packets actually are RTCP, and not packets of some other type being wrongly delivered. Thus some consideration should be done to ensure the best possible validation is available. For example restricting reduced-size RTCP to contain only some specific RTCP packet types, that is preferably signalled on a per-session basis. However, the application of a security mechanisms for source authentication on the packets will provide much stronger protection.
- Old RTP Receivers:
- Any RTCP receiver without updated packet validation code will discard the reduced-size RTCP which means that the receiver will not see e.g the contained feedback messages. The effect of this depends on the type of feedback message and the role of the receiver. For example this may cause complete function loss in the case of attempting to use a reduced size NACK message (see Section 6.2.1 of [RFC4585] (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.)) to non updated media sender in a session using the retransmission scheme defined by [RFC4588] (Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, “RTP Retransmission Payload Format,” July 2006.). This type of discarding would also effect the feedback suppression defined in AVPF. The result would be a partitioning of the receivers within the session between old ones only seeing the compound RTCP feedback messages and the newer ones seeing both. Where the old ones may send feedback messages for events already reported on in reduced-size RTCP.
- Bandwidth Considerations:
- The discarding of reduced-size RTCP would effect the RTCP transmission calculation in the following way: the avg_rtcp_size value would become larger than for RTP receivers that exclude the reduced-size RTCP in this calculation (assuming that reduced-size RTCP are smaller than compound ones). Therefore these senders would under-utilize the available bitrate and send with a longer interval than updated receivers. For most sessions this should not be an issue. However for sessions with a large portion of reduced-size RTCP may result in that the updated receivers time out non-updated senders prematurely. This is however not likely to occur as the time between RTCP transmission needs to become 5 times that used by the reduced-sized RTCP senders when sending compound RTCP.
- Computation of avg_rtcp_size:
- Long intervals between compound RTCP and many reduced-size RTCP in between may lead to a computation of a value for avg_rtcp_size that varies greatly over time. Investigation shows that although it varies this is not enough of a problem to warrant further changes or complexities to the RTCP scheduling algorithm.
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SRTP presents a problem for reduced-size RTCP. Section 3.4 in [RFC3711] (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) states "SRTCP MUST be given packets according to that requirement in the sense that the first part MUST be a sender report or a receiver report".
Upon examination of how SRTP process packets it becomes obvious
that SRTP has no real dependency on that the first packet is either
an SR or an RR packet. What is needed is the common RTCP packet
header, which is present in all the packet types, with a source
SSRC. The conclusion is therefore that it is possible to use
reduced-size RTCP with SRTP.
Nevertheless, as this implies
a change to the rules in [RFC3711] (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) changes in
SRTP implementations MAY become necessary.
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In applications which multiplex RTP and RTCP on the same port, as defined in [I‑D.ietf‑avt‑rtp‑and‑rtcp‑mux] (Perkins, C. and M. Westerlund, “Multiplexing RTP Data and Control Packets on a Single Port,” August 2007.), care must be taken to ensure that the de-multiplexing is done properly even though RTCP are reduced size. The downside of reduced size RTCP is that more values representing RTCP packets exist, reducing the available RTP payload type space. However, section 4 in [I‑D.ietf‑avt‑rtp‑and‑rtcp‑mux] (Perkins, C. and M. Westerlund, “Multiplexing RTP Data and Control Packets on a Single Port,” August 2007.) already requires the corresponding RTP payload type range not be used when performing this multiplexing.
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Two issues are related to header compression, possible changes are left for future work:
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Based on the above analysis it seems feasible to allow transmission of reduced-size RTCP under some restrictions:
This implies that the regular transmission of compound RTCP MUST be maintained throughout an RTP session. Reduced-size RTCP should be restricted to be used as extra RTCP (e.g feedback) sent in cases when a regular compound RTCP packet would not otherwise have been sent.
The usage of reduced-size RTCP SHALL only be done in RTP sessions
operating in AVPF (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.) [RFC4585] or SAVPF (Ott, J. and E. Carrara, “Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF),” February 2008.) [RFC5124] Early or Immediate mode.
Reduced-size RTCP SHALL NOT be sent until at least one
compound RTCP has been sent. In Immediate mode all feedback messages MAY
be sent as reduced-size RTCP. In early mode a feedback message scheduled
for transmission as an Early RTCP, i.e not a Regular RTCP, MAY be sent
as reduced-size RTCP. All RTCP that are scheduled for transmission as
Regular RTCP SHALL be sent as compound RTCP as indicated by AVPF (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.) [RFC4585].
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A reduced-size RTCP packet is an RTCP packet with the following properties that makes it deviate from the compound RTCP packet definition given in section 6.1 in [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.):
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If an application is to use reduced-size RTCP it is important to verify that the reduced-size RTCP packets actually reach the session participants. As outlined above in Section 3.4.1 (Middle Boxes) and Section 3.4.2 (Packet Validation) packets may be discarded along the path or in the end-point.
A few verification rules are RECOMMENDED to ensure robust RTCP transmission and reception and to solve the identified issues when reduced-size RTCP is used:
If the verification fails it is strongly RECOMMENDED that only compound RTCP according to the rules outlined in RFC3550 is transmitted.
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The result of the definition in Section 4.1 (Definition of Reduced-Size RTCP) may be that the resulting size of reduced-size RTCP can become larger than a regularly scheduled compound RTCP packet. For applications that use access types that are sensitive to packet size (see Paragraph 2 in Section 3.3 (Benefits of Reduced-Size RTCP)) it is strongly RECOMMENDED that the use of reduced-size RTCP is limited to the transmission of single RTCP in each lower layer datagram. The methods to determine the need for this is outside the scope of this draft.
In general, as the benefit with large sized reduced-size RTCP packets is very limited, it is strongly RECOMMENDED to transmit large reduced-size RTCP packets as compound RTCP packets instead.
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As discussed earlier it is important that the transmission of compound RTCP occurs at regular intervals. However, this will occur as long as the RTCP senders follow the AVPF scheduling algorithm defined in Section 3.5 in [RFC4585] (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.). This as all regular RTCP MUST be full compound RTCP. Note that also in immediate mode is there a requirement on sending regular RTCP.
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Section 3.3 in RFC4585 gives the option to use AVPF Immediate mode as long as the groupsize is below a certain limit. As transmission using reduced-size RTCP may reduce the bandwidth demand it opens up for a more liberal use of immediate mode.
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This document defines the "a=rtcp-rsize" SDP (Handley, M., Jacobson, V., and C. Perkins, “SDP: Session Description Protocol,” July 2006.) [RFC4566] attribute to indicate if the session participant is capable of supporting reduced-size RTCP for applications that uses SDP for configuration of RTP sessions. It is required that a participant that proposes the use of reduced-size RTCP itself supports the reception of reduced-size RTCP.
An offering client that wish to use reduced-size RTCP MUST include the attribute "a=rtcp-rsize" in the SDP offer. If "a=rtcp-rsize" is present in the offer SDP, the answerer that supports reduced-size RTCP and wish to use it SHALL include the "a=rtcp-rsize" attribute in the answer.
In declarative usage such as RTSP (Schulzrinne, H., Rao, A., and R. Lanphier, “Real Time Streaming Protocol (RTSP),” April 1998.) [RFC2326] and SAP (Handley, M., Perkins, C., and E. Whelan, “Session Announcement Protocol,” October 2000.) [RFC2974] of SDP the presence of the attribute indicates that the session participant MAY use reduced size RTCP packets in its RTCP transmissions.
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The security considerations of RTP (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) [RFC3550] and AVPF (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.) [RFC4585] will apply also to reduced-size RTCP. The reduction in validation strength for received packets on the RTCP port may result in a higher degree of acceptance of spurious data as real RTCP. This vulnerability can mostly be addressed by usage of any security mechanism that provide authentication, one example such mechanism is SRTP [RFC3711] (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.).
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Following the guidelines in [RFC4566] (Handley, M., Jacobson, V., and C. Perkins, “SDP: Session Description Protocol,” July 2006.), the IANA is requested to register one new SDP attribute:
This attribute defines the support for reduced-size RTCP, i.e the possibility to transmit RTCP that does not conform to the rules for compound RTCP defined in RFC3550. It is a property attribute, which does not take a value.
Note to RFC Editor: please replace "RFC XXXX" above with the RFC number of this memo, and remove this note.
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The authors would like to thank all the people who gave feedback on this document. Special thanks go to Colin Perkins.
This document also contain some text copied from [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.), (Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” July 2006.) [RFC4585]and (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) [RFC3711]. We take the opportunity to thank the authors of said documents.
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| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
| [RFC3550] | Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” STD 64, RFC 3550, July 2003 (TXT, PS, PDF). |
| [RFC3551] | Schulzrinne, H. and S. Casner, “RTP Profile for Audio and Video Conferences with Minimal Control,” STD 65, RFC 3551, July 2003 (TXT, PS, PDF). |
| [RFC4585] | Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, “Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF),” RFC 4585, July 2006 (TXT). |
| [RFC5124] | Ott, J. and E. Carrara, “Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF),” RFC 5124, February 2008 (TXT). |
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| [I-D.ietf-avt-rtp-and-rtcp-mux] | Perkins, C. and M. Westerlund, “Multiplexing RTP Data and Control Packets on a Single Port,” draft-ietf-avt-rtp-and-rtcp-mux-07 (work in progress), August 2007 (TXT). |
| [I-D.ietf-avt-tfrc-profile] | Gharai, L., “RTP with TCP Friendly Rate Control,” draft-ietf-avt-tfrc-profile-10 (work in progress), July 2007 (TXT). |
| [MTSI-3GPP] | 3GPP, “Specification : 3GPP TS 26.114 (v7.4.0), http://www.3gpp.org/ftp/Specs/archive/26_series/26.114/26114-740.zip,” March 2007. |
| [OMA-PoC] | Open Mobile Alliance, “Specification : Push to talk Over Cellular User Plane, http://www.openmobilealliance.org/release_program/docs/PoC/V1_0_1-20061128-A/OMA-TS-PoC-UserPlane-V1_0_1-20061128-A.pdf,” November 2006. |
| [RFC2326] | Schulzrinne, H., Rao, A., and R. Lanphier, “Real Time Streaming Protocol (RTSP),” RFC 2326, April 1998 (TXT). |
| [RFC2974] | Handley, M., Perkins, C., and E. Whelan, “Session Announcement Protocol,” RFC 2974, October 2000 (TXT). |
| [RFC3095] | Bormann, C., Burmeister, C., Degermark, M., Fukushima, H., Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le, K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K., Wiebke, T., Yoshimura, T., and H. Zheng, “RObust Header Compression (ROHC): Framework and four profiles: RTP, UDP, ESP, and uncompressed,” RFC 3095, July 2001 (TXT). |
| [RFC3711] | Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” RFC 3711, March 2004 (TXT). |
| [RFC4566] | Handley, M., Jacobson, V., and C. Perkins, “SDP: Session Description Protocol,” RFC 4566, July 2006 (TXT). |
| [RFC4588] | Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, “RTP Retransmission Payload Format,” RFC 4588, July 2006 (TXT). |
| [RFC5104] | Wenger, S., Chandra, U., Westerlund, M., and B. Burman, “Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF),” RFC 5104, February 2008 (TXT). |
| TOC |
| Ingemar Johansson | |
| Ericsson AB | |
| Laboratoriegrand 11 | |
| SE-971 28 Lulea | |
| SWEDEN | |
| Phone: | +46 73 0783289 |
| Email: | ingemar.s.johansson@ericsson.com |
| Magnus Westerlund | |
| Ericsson AB | |
| Färögatan 6 | |
| SE-164 80 Stockholm | |
| SWEDEN | |
| Phone: | +46 8 7190000 |
| Email: | magnus.westerlund@ericsson.com |
| TOC |
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