Subject: [AVT] I-D ACTION:draft-ietf-avt-rtp-and-rtcp-mux-06.txt

From: [email-masked]
Date: Wed, 25 Jul 2007 13:15:01 -0400

A New Internet-Draft is available from the on-line Internet-Drafts 
directories.
This draft is a work item of the Audio/Video Transport Working Group of the IETF.

	Title		: Multiplexing RTP Data and Control Packets on a Single Port
	Author(s)	: C. Perkins, M. Westerlund
	Filename	: draft-ietf-avt-rtp-and-rtcp-mux-06.txt
	Pages		: 15
	Date		: 2007-7-25
	
This memo discusses issues that arise when multiplexing RTP data
   packets and RTP control protocol (RTCP) packets on a single UDP port.
   It updates RFC 3550 to describe when such multiplexing is, and is
   not, appropriate, and explains how the Session Description Protocol
   (SDP) can be used to signal multiplexed sessions.

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From: Randell Jesup <[email-masked]>
Date: Thu, 26 Jul 2007 14:54:53 -0400

>      Note: since all RTCP packets MUST be sent as compound packets
>      beginning with an SR or an RR packet ([1] Section 6.1), one might
>      wonder why RTP payload types other than 72 and 73 are prohibited
>      when multiplexing RTP and RTCP.  This is done to ensure robustness
>      against broken nodes which send non-compliant RTCP packets, which
>      might otherwise be confused with multiplexed RTP packets.

This should mention that relaxing that restriction is under consideration,
(I forget the exact draft name) and that by including the PT restrictions
in this draft we avoid a potential conflict with the other draft (i.e. it
may not be only "broken nodes").  I also would remove the word "broken",
it's misleading.  They are non-compliant with 3261 (until that draft is
approved).

>   When the Session Description Protocol (SDP) [8] is used to negotiate
>   RTP sessions following the offer/answer model [9], the "a=rtcp-mux"
>   attribute (see Section 8) indicates the desire to multiplex RTP and
>   RTCP onto a single port.

We should also discuss interaction with offering both "a=rtcp-mux" and
"a=rtcp <port>".  I can see an endpoint wanting (or needing) to include
both.  The answer selects between rtcp-mux and "normal" rtcp handling
(including a=rtcp, though there's no direct way to know if the answerer
supports it).

-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
[email-masked]
"The fetters imposed on liberty at home have ever been forged out of the weapons
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