Protocol Action: 'RTP Payload Format for Generic Forward Error Correction' to Proposed Standard

The IESG <> Wed, 10 October 2007 14:45 UTC

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Subject: Protocol Action: 'RTP Payload Format for Generic Forward Error Correction' to Proposed Standard
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The IESG has approved the following document:

- 'RTP Payload Format for Generic Forward Error Correction '
   <draft-ietf-avt-ulp-23.txt> as a Proposed Standard

This document is the product of the Audio/Video Transport Working Group. 

The IESG contact persons are Cullen Jennings and Jon Peterson.

A URL of this Internet-Draft is:

Technical Summary

This document specifies a payload format for generic Forward
Error Correction (FEC) for media data encapsulated in RTP. It is
based on the exclusive-or (parity) operation. The payload format
described in this draft allows end systems to apply protection
using various protection lengths and levels, in addition to
using various protection group sizes to adapt to different media
and channel characteristic. It enables complete recovery of the
protected packets or partial recovery of the critical parts of
the payload depending on the packet loss situation. This scheme
is completely compatible with non-FEC capable hosts, so the
receivers in a multicast group that do not implement FEC can
still work by simply ignoring the protection data. This
specification obsoletes RFC 2733 and RFC 3009. The FEC specified
in this document is not backward compatible with RFC 2733 and
RFC 3009.

Working Group Summary

This document has been under discussion in the AVT working group 
since the 48th IETF meeting, having been brought to AVT along with a 
competing draft (draft-lnt-avt-uxp-00.txt) from the ITU-T SG16. 
Considering their relative merits, AVT eventually decided to adopt 
both drafts, this draft being simpler and conceptually backwards 
compatible with RFC 2733, the UXP work being more complex (based on 
Reed Solomon coding, rather than simple parity coding) but with 
potentially better performance in some scenarios. Work on the UXP 
draft was abandoned in 2004, and the ULP draft progressed to completion.

More recently, there has been some discussion of the merits of the 
ULP work, compared to the schemes employed by 3GPP, and the ongoing 
work in FECFRAME. We believe the FECFRAME proposals will likely form 
the basis of future FEC work for RTP. Despite this, we believe it 
necessary to publish the ULP draft all the same, since it contains an 
important bug fix to RFC 2733, and since the layered extensions can 
potentially offer improved performance in a manner that is 
conceptually compatible with to RFC 2733.

Document Quality

Media type review on the -14 took place starting in December 2005, 
with no objection (there have been no changes in the draft that would 
change that consensus since then). Jonathan Rosenberg and Mark Watson 
provided extensive last call comments and review.


Colin Perkins is the document shepherd. Cullen Jennings is the 
responsible AD. David McGrew and Eric Rescorla review the interaction
of SRTP encryption and FEC.

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