Internet DRAFT - draft-pthatcher-avtext-esid
draft-pthatcher-avtext-esid
Network Working Group P. Thatcher
Internet-Draft Google
Intended status: Standards Track March 9, 2015
Expires: September 10, 2015
Encoded Stream ID Header Extension
draft-pthatcher-avtext-esid-00
Abstract
This document defines a new RTP Header Extension and SDES item for an
Encoded Stream ID or "ESID" which can be used for either identifying
Encoded Streams or for extending RTP Payload Types.
Status of This Memo
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This Internet-Draft will expire on September 10, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. RTP/RTCP extensions for ESID value transport . . . . . . . . 2
3.1. RTP ESID Header Extension . . . . . . . . . . . . . . . . 3
3.2. RTP ESID SDES Item . . . . . . . . . . . . . . . . . . . 3
4. Representation as a fmt value . . . . . . . . . . . . . . . . 4
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Change log . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
SDP Offerers and Answerers [RFC3264] can assign fmt values to SDP
Media Descriptions (m= lines) within SDP Offers and Answers, using
the procedures in [RFC4566]. Each fmt uniquely identifies a media
format, which is typically an RTP payload type.
fmt values are also used to identity an Encoded Stream, where each
combination of (Media Format, Encoded Stream) is represented as a
unique fmt value. For large numbers of Media Formats and Encoded
Streams, the number of fmts then can exceed what can typically fit in
an RTP payload type.
This specification defines a new RTP Header Extension and SDES item
for an Encoded Stream ID or "ESID" which can be used for either
identifying Encoded Streams or extending RTP Payload Types. It also
defines how these map to fmt values.
2. Terminology
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].
3. RTP/RTCP extensions for ESID value transport
This section defines a new RTP SDES item [RFC3264], 'ESID', which is
used to carry IDs for Encoded Streams values within RTCP SDES
packets. This section also defines a new RTP header extension
[RFC5285], which can be used to carry the ESID value in RTP packets.
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The SDES item and RTP header extension makes is possible for a
receiver to associate received RTCP- and RTP packets with a specific
Encoded Stream.
The RTP MID SDES item SHOULD be sent in the first few RTCP packets
sent on joining the session, and SHOULD be sent regularly thereafter.
The exact number of RTCP packets in which this SDES item is sent is
intentionally not specified here, as it will depend on the expected
packet loss rate, the RTCP reporting interval, and the allowable
overhead.
The RTP ESID header extension SHOULD be included in some RTP packets
at the start of the session and whenever the SSRC changes. It might
also be useful to include the header extension in RTP packets that
comprise random access points in the media (e.g., with video
I-frames). The exact number of RTP packets in which this header
extension is sent is intentionally not specified here, as it will
depend on expected packet loss rate and loss patterns, the overhead
the application can tolerate, and the importance of immediate receipt
of the ESID value.
For robustness purpose, endpoints need to be prepared for situations
where the ESID value is delayed, and SHOULD NOT terminate sessions in
such cases, as the ESID value is likely to arrive soon.
3.1. RTP ESID Header Extension
The payload, containing the ESID value, of the RTP ESID header
extension element can be encoded using either the one-byte or two-
byte header [RFC5285].
3.2. RTP ESID SDES Item
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ESID=TBD | length | ESID value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[RFC EDITOR NOTE: Please replace TBD with the assigned SDES
identifier value.]
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4. Representation as a fmt value
NOTE: The usage of other signalling protocols for carrying the ESID
value is not prevented, but the usage of such protocols is outside
the scope of this document.
fmt values typically do not exceed 127, the limit of the value that
can be reprsented by an RTP payload type. The ESID allows for values
for fmt larger than 127, calculated from the ESID and the RTP payload
type in the following way.
The value of the ESID is treated as a big-endian integer, which is
then shifted left 7 bits and added to the value of the RTP payload
type. This integer value is then used as the fmt value in the SDP.
5. Examples
For an ESID value of 1 and 2 and a Payload Type of 97, the fmt values
of (1 << 7) + 97 = 225 and (2 << 7) + 97 = 353 would be used:
v=0
o=alice 2890844526 2890844526 IN IP4 atlanta.example.com
s=
c=IN IP4 atlanta.example.com
t=0 0
m=video 10002 RTP/AVP 225 353
a=rtpmap:225 VP8/90000
a=rtpmap:353 VP8/90000
6. Security Considerations
TODO
7. IANA Considerations
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
[RFC EDITOR NOTE: Please replace TBD with the assigned SDES
identifier value.]
This document adds the MID SDES item to the IANA "RTP SDES item
types" registry as follows:
Value: TBD
Abbrev.: ESID
Name: Encoded Stream Identification
Reference: RFCXXXX
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8. Acknowledgements
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, June
2002.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP
Header Extensions", RFC 5285, July 2008.
Appendix A. Change log
Author's Address
Peter Thatcher
Google
747 6th Ave S
Kirkland, WA 98033
USA
Email: pthatcher@webrtc.org
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