draft-ietf-avtcore-multi-media-rtp-session-05.txt   draft-ietf-avtcore-multi-media-rtp-session-06.txt 
AVTCORE WG M. Westerlund AVTCORE WG M. Westerlund
Internet-Draft Ericsson Internet-Draft Ericsson
Updates: 3550, 3551 (if approved) C. Perkins Updates: 3550, 3551 (if approved) C. Perkins
Intended status: Standards Track University of Glasgow Intended status: Standards Track University of Glasgow
Expires: August 18, 2014 J. Lennox Expires: April 11, 2015 J. Lennox
Vidyo Vidyo
February 14, 2014 October 08, 2014
Sending Multiple Types of Media in a Single RTP Session Sending Multiple Types of Media in a Single RTP Session
draft-ietf-avtcore-multi-media-rtp-session-05 draft-ietf-avtcore-multi-media-rtp-session-06
Abstract Abstract
This document specifies how an RTP session can contain media streams This document specifies how an RTP session can contain media streams
with media from multiple media types such as audio, video, and text. with media from multiple media types such as audio, video, and text.
This has been restricted by the RTP Specification, and thus this This has been restricted by the RTP Specification, and thus this
document updates RFC 3550 and RFC 3551 to enable this behaviour for document updates RFC 3550 and RFC 3551 to enable this behaviour for
applications that satisfy the applicability for using multiple media applications that satisfy the applicability for using multiple media
types in a single RTP session. types in a single RTP session.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 18, 2014. This Internet-Draft will expire on April 11, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview of Solution . . . . . . . . . . . . . . . . . . . . 5 4. Overview of Solution . . . . . . . . . . . . . . . . . . . . 5
5. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Usage of the RTP session . . . . . . . . . . . . . . . . 6 5.1. Usage of the RTP session . . . . . . . . . . . . . . . . 6
5.2. Signalled Support . . . . . . . . . . . . . . . . . . . . 6 5.2. Signalled Support . . . . . . . . . . . . . . . . . . . . 7
5.3. Homogeneous Multi-party . . . . . . . . . . . . . . . . . 7 5.3. Homogeneous Multi-party . . . . . . . . . . . . . . . . . 7
5.4. Reduced number of Payload Types . . . . . . . . . . . . . 8 5.4. Reduced number of Payload Types . . . . . . . . . . . . . 8
5.5. Stream Differentiation . . . . . . . . . . . . . . . . . 8 5.5. Stream Differentiation . . . . . . . . . . . . . . . . . 8
5.6. Non-compatible Extensions . . . . . . . . . . . . . . . . 8 5.6. Non-compatible Extensions . . . . . . . . . . . . . . . . 8
6. RTP Session Specification . . . . . . . . . . . . . . . . . . 9 6. RTP Session Specification . . . . . . . . . . . . . . . . . . 9
6.1. RTP Session . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. RTP Session . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. Sender Source Restrictions . . . . . . . . . . . . . . . 11 6.2. Sender Source Restrictions . . . . . . . . . . . . . . . 12
6.3. Payload Type Applicability . . . . . . . . . . . . . . . 12 6.3. Payload Type Applicability . . . . . . . . . . . . . . . 12
6.4. RTCP Considerations . . . . . . . . . . . . . . . . . . . 12 6.4. RTCP Considerations . . . . . . . . . . . . . . . . . . . 12
7. Extension Considerations . . . . . . . . . . . . . . . . . . 12 7. Extension Considerations . . . . . . . . . . . . . . . . . . 13
7.1. RTP Retransmission . . . . . . . . . . . . . . . . . . . 13 7.1. RTP Retransmission . . . . . . . . . . . . . . . . . . . 13
7.2. Generic FEC . . . . . . . . . . . . . . . . . . . . . . . 13 7.2. Generic FEC . . . . . . . . . . . . . . . . . . . . . . . 13
8. Signalling . . . . . . . . . . . . . . . . . . . . . . . . . 14 8. Signalling . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. SDP-Based Signalling . . . . . . . . . . . . . . . . . . 14 8.1. SDP-Based Signalling . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
10. Security Considerations . . . . . . . . . . . . . . . . . . . 15 10. Security Considerations . . . . . . . . . . . . . . . . . . . 15
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
12.1. Normative References . . . . . . . . . . . . . . . . . . 15 12.1. Normative References . . . . . . . . . . . . . . . . . . 15
12.2. Informative References . . . . . . . . . . . . . . . . . 16 12.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
When the Real-time Transport Protocol (RTP) [RFC3550] was designed, When the Real-time Transport Protocol (RTP) [RFC3550] was designed,
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behaves as a single RTP stack entity it is classified as a single behaves as a single RTP stack entity it is classified as a single
endpoint. endpoint.
Media Stream: A sequence of RTP packets using a single SSRC that Media Stream: A sequence of RTP packets using a single SSRC that
together carries part or all of the content of a specific Media together carries part or all of the content of a specific Media
Type from a specific sender source within a given RTP session. Type from a specific sender source within a given RTP session.
Media Type: Audio, video, text or application whose form and meaning Media Type: Audio, video, text or application whose form and meaning
are defined by a specific real-time application. are defined by a specific real-time application.
QoS: Quality of Service, i.e. network mechanisms that intended to QoS: Quality of Service, i.e. network mechanisms that intended to
ensure that the packets within a flow or with a specific marking ensure that the packets within a flow or with a specific marking
are transported with certain properties. are transported with certain properties.
RTP Session: As defined by [RFC3550], the endpoints belonging to the RTP Session: As defined by [RFC3550], the endpoints belonging to the
same RTP Session are those that share a single SSRC space. That same RTP Session are those that share a single SSRC space. That
is, those endpoints can see an SSRC identifier transmitted by any is, those endpoints can see an SSRC identifier transmitted by any
one of the other endpoints. An endpoint can receive an SSRC one of the other endpoints. An endpoint can receive an SSRC
either as SSRC or as CSRC in RTP and RTCP packets. Thus, the RTP either as SSRC or as CSRC in RTP and RTCP packets. Thus, the RTP
Session scope is decided by the endpoints' network interconnection Session scope is decided by the endpoints' network interconnection
topology, in combination with RTP and RTCP forwarding strategies topology, in combination with RTP and RTCP forwarding strategies
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each SSRC will be associated with a specific media type, communicated each SSRC will be associated with a specific media type, communicated
through the RTP payload type, allowing a middlebox to do media type through the RTP payload type, allowing a middlebox to do media type
specific operations. The second argument is that in many contexts specific operations. The second argument is that in many contexts
blind combining without additional contexts are anyway not suitable. blind combining without additional contexts are anyway not suitable.
Regarding bullet 5 this is a understood and explicitly stated Regarding bullet 5 this is a understood and explicitly stated
applicability limitations for the method described in this document. applicability limitations for the method described in this document.
6.2. Sender Source Restrictions 6.2. Sender Source Restrictions
A SSRC in the RTP session MUST only send one media type (audio, A SSRC in the RTP session MUST only send one media type (audio,
video, text etc.) during the SSRC's lifetime. The main motivation is video, text etc.) during the SSRC's lifetime. The main motivation
that a given SSRC has its own RTP timestamp and sequence number is that a given SSRC has its own RTP timestamp and sequence number
spaces. The same way that you can't send two streams of encoded spaces. The same way that you can't send two streams of encoded
audio on the same SSRC, you can't send one audio and one video audio on the same SSRC, you can't send one audio and one video
encoding on the same SSRC. Each media encoding when made into an RTP encoding on the same SSRC. Each media encoding when made into an RTP
stream needs to have the sole control over the sequence number and stream needs to have the sole control over the sequence number and
timestamp space. If not, one would not be able to detect packet loss timestamp space. If not, one would not be able to detect packet loss
for that particular stream. Nor can one easily determine which clock for that particular stream. Nor can one easily determine which clock
rate a particular SSRCs timestamp will increase with. For additional rate a particular SSRCs timestamp will increase with. For additional
arguments why RTP payload type based multiplexing of multiple media arguments why RTP payload type based multiplexing of multiple media
streams doesn't work see Appendix A in streams doesn't work see Appendix A in
[I-D.ietf-avtcore-multiplex-guidelines]. [I-D.ietf-avtcore-multiplex-guidelines].
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types. In fact this document (Section 7.2) suggest that for usage of types. In fact this document (Section 7.2) suggest that for usage of
Generic FEC (XOR-based) as defined in RFC 5109 can actually use a Generic FEC (XOR-based) as defined in RFC 5109 can actually use a
single media type when used with independent RTP sessions for source single media type when used with independent RTP sessions for source
and repair data. and repair data.
Note a particular SSRC carrying Generic FEC will clearly only Note a particular SSRC carrying Generic FEC will clearly only
protect a specific SSRC and thus that instance is bound to the protect a specific SSRC and thus that instance is bound to the
SSRC's media type. For this specific case, it is possible to have SSRC's media type. For this specific case, it is possible to have
one be applicable to both. However, in cases when the signalling one be applicable to both. However, in cases when the signalling
is setup to enable fall back to using separate RTP sessions, then is setup to enable fall back to using separate RTP sessions, then
using a different media type, e.g. application, than the media using a different media type, e.g. application, than the media
being protected can create issues. being protected can create issues.
6.4. RTCP Considerations 6.4. RTCP Considerations
Guidelines for handling RTCP when sending multiple media streams with Guidelines for handling RTCP when sending multiple media streams with
disparate rates in a single RTP session are outlined in disparate rates in a single RTP session are outlined in
[I-D.ietf-avtcore-rtp-multi-stream]. These guidelines apply when [I-D.ietf-avtcore-rtp-multi-stream]. These guidelines apply when
sending multiple types of media in a single RTP session if the sending multiple types of media in a single RTP session if the
different types of media have different rates. different types of media have different rates.
7. Extension Considerations 7. Extension Considerations
This section discusses the impact on some RTP/RTCP extensions due to This section discusses the impact on some RTP/RTCP extensions due to
usage of multiple media types in on RTP session. Only extensions usage of multiple media types in on RTP session. Only extensions
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contradict both the FID semantics [RFC5888] and an assumption in the contradict both the FID semantics [RFC5888] and an assumption in the
RTP retransmission specification [RFC4588]. RTP retransmission specification [RFC4588].
7.2. Generic FEC 7.2. Generic FEC
The RTP Payload Format for Generic Forward Error Correction The RTP Payload Format for Generic Forward Error Correction
[RFC5109], and also its predecessor [RFC2733], requires some [RFC5109], and also its predecessor [RFC2733], requires some
considerations, and they are different depending on what type of considerations, and they are different depending on what type of
configuration of usage one has. configuration of usage one has.
Independent RTP Sessions, i.e. where source and repair data are sent Independent RTP Sessions, i.e. where source and repair data are sent
in different RTP sessions. As this mode of configuration requires in different RTP sessions. As this mode of configuration requires
different RTP session, there has to be at least one RTP session for different RTP session, there has to be at least one RTP session for
source data, this session can be one using multiple media types. The source data, this session can be one using multiple media types. The
repair session only needs one RTP Payload type indicating repair repair session only needs one RTP Payload type indicating repair
data, i.e. x/ulpfec or x/parityfec depending if RFC 5109 or RFC 2733 data, i.e. x/ulpfec or x/parityfec depending if RFC 5109 or RFC 2733
is used. The media type in this session is not relevant and can in is used. The media type in this session is not relevant and can in
theory be any of the defined ones. It is RECOMMENDED that one uses theory be any of the defined ones. It is RECOMMENDED that one uses
"Application". "Application".
In stream, using RTP Payload for Redundant Audio Data [RFC2198] In stream, using RTP Payload for Redundant Audio Data [RFC2198]
combining repair and source data in the same packets. This is combining repair and source data in the same packets. This is
possible to use within a single RTP session. However, the usage and possible to use within a single RTP session. However, the usage and
configuration of the payload types can create an issue. First of all configuration of the payload types can create an issue. First of all
it might be necessary to have one payload type per media type for the it might be necessary to have one payload type per media type for the
FEC repair data payload format, i.e. one for audio/ulpfec and one for FEC repair data payload format, i.e. one for audio/ulpfec and one
text/ulpfec if audio and text are combined in an RTP session. for text/ulpfec if audio and text are combined in an RTP session.
Secondly each combination of source payload and its FEC repair data Secondly each combination of source payload and its FEC repair data
has to be an explicit configured payload type. This has potential has to be an explicit configured payload type. This has potential
for making the limitation of RTP payload types available into a real for making the limitation of RTP payload types available into a real
issue. issue.
8. Signalling 8. Signalling
The Signalling requirements The Signalling requirements
Establishing an RTP session with multiple media types requires Establishing an RTP session with multiple media types requires
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The authors would like to thank Christer Holmberg, Gunnar Hellstroem, The authors would like to thank Christer Holmberg, Gunnar Hellstroem,
and Charles Eckel for the feedback on the document. and Charles Eckel for the feedback on the document.
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-avtcore-rtp-multi-stream] [I-D.ietf-avtcore-rtp-multi-stream]
Lennox, J., Westerlund, M., Wu, W., and C. Perkins, Lennox, J., Westerlund, M., Wu, W., and C. Perkins,
"Sending Multiple Media Streams in a Single RTP Session", "Sending Multiple Media Streams in a Single RTP Session",
draft-ietf-avtcore-rtp-multi-stream-02 (work in progress), draft-ietf-avtcore-rtp-multi-stream-05 (work in progress),
January 2014. July 2014.
[I-D.ietf-mmusic-sdp-bundle-negotiation] [I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings, Holmberg, C., Alvestrand, H., and C. Jennings,
"Multiplexing Negotiation Using Session Description "Negotiating Media Multiplexing Using the Session
Protocol (SDP) Port Numbers", draft-ietf-mmusic-sdp- Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
bundle-negotiation-05 (work in progress), October 2013. negotiation-11 (work in progress), September 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551, Video Conferences with Minimal Control", STD 65, RFC 3551,
 End of changes. 17 change blocks. 
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