[RTW] RTP Session Multiplexing (Re: Fwd: I-D Action:draft-perkins-rtcweb-rtp-usage-00.txt)

[Magnus Westerlund]

Harald Alvestrand skrev 2011-03-08 13:10:
> Short summary, to see if I understand Magnus correctly:
> 
> If we want to use RTP over UDP as it currently stands, we have to 
> multiplex on port number. If one sender sends two media streams to one 
> recipients, at least one part of the <sender ip:port>:<recipient 
> ip:port> 4-tuple has to be different.

Not strictly, I would say that both using unique 5-tuples and an
explicit multiplexing layer is fine from RTP perspective. Explicit
multiplexing layer is already used, for example when sending RTP over
RTSP's signalling TCP connection [RFC2326].

> 
> The alternatives involve modifying protocols that are not otherwise 
> within the scope of this working group.

Well, the charter isn't approved yet. And I think there will be need for
a RTC-WEB WG to in some cases agree that some work is needed. Then the
question of where can be raised, within the WG, in some other WG or in a
new WG. Sure, this must be weighted against the time it takes to
complete the work.

An explicit multiplexing layer needs not be complex if one keeps the
requirements simple. Thus if it is considered necessary then I think it
can be developed in the RTC-web WG. If using different UDP flows are the
preferred way, then that comes at a different set of trade-offs. Airing
these trade-offs and gaols are likely the right way of achieving at
least rough consensus going forward here.

I want to be clear that I have not yet any strong view on what the right
choice is here. Except that I don't want to redesign RTP now and for
this. Secondly, I want to ensure that RTP sessions can be used, but that
is just of question of ensuring that there some explicit indicator of
what RTP session a particular packet belongs to.

Cheers

Magnus Westerlund

----------------------------------------------------------------------
Multimedia Technologies, Ericsson Research EAB/TVM
----------------------------------------------------------------------
Ericsson AB                | Phone  +46 10 7148287
Färögatan 6                | Mobile +46 73 0949079
SE-164 80 Stockholm, Sweden| mailto: magnus.westerlund at ericsson.com
----------------------------------------------------------------------