Re: [MMUSIC] RTSP: Usage of RTP and RTCP Muxing with RTSP media sessions

[RÃmi Denis-Courmont <rem at videolan.org>]

Le Tuesday 11 September 2007 17:22:45 Magnus Westerlund, vous avez ÃcritÂ:
> Hi,
>
> draft-ietf-avt-rtp-and-rtcp-mux-07 is currently in the RFC-editor queue.
> If we allow for RTP and RTCP muxing with RTSP we can half the port
> consumption for a RTSP based streaming server. Or at least avoid RTCP
> using additional ports which has been a major complaint from vendors of
> high capacity servers.

And possibly leverage RTCP-RR as a way to keep the firewall binding open. I 
have not checked if the maximum interval between RTCP-RR is short enough 
though.

> As I can see this can be introduced in the 
> following ways:
>
> A. Mandate that RTCP MUX shall be supported by RTSP 2.0 servers and
> clients supporting RTP transport. A flag indicate may be used to
> indicate if RTCP is to be used or not instead of the extra port.
>
> B. Allow RTP and RTCP muxing to be optional to support. Include a flag
> to negotiate this usage. Only when both side indicate support is muxing
> performed.
>
> I think A is easier and more interoperable in the long run. However it
> increase the burden in the transition period from RTSP 1.0 to 2.0.

Actually, I see no problems with B. The server can simply put "a=rtcp-mux" in 
the SDP if it supports it. Then (and only then) the client can specify 
a "port range" of a single port in the SETUP client_port, and the server 
replies accordingly.

A would indeed make clients implementation slightly easier - no need to check 
for server support. However, I would expect implementors to do implement 
various even more complicated tricks as a result of the lack of RTCP mux in 
RTSP/1.0. As such, I would prefer B.

-- 
RÃmi Denis-Courmont
http://www.remlab.net/

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