Subject: [AVTCORE] RTP Internal Multiplexing of RTP sessions

From: Magnus Westerlund <[email-masked]>
Date: Tue, 19 Jul 2011 17:35:12 +0200

WG,

As Individual contributor.

I don't know if people in the WG are aware of the discussion ongoing in
RTCWEB around multiplexing of protocols over the same underlying
transport flow, like UDP flow. That include RTP sessions.

There is a proposal:
"Multiplexing of Real-Time Transport Protocol (RTP) Traffic for Browser
                  based Real-Time Communications (RTC)"
https://datatracker.ietf.org/doc/draft-rosenberg-rtcweb-rtpmux/?include_text=1

This proposal is criticized by the following draft.
https://datatracker.ietf.org/doc/draft-perkins-rtcweb-rtp-usage/?include_text=1

There is an ongoing discussion on several aspects of these proposals on
the RTCWEB WG. You are welcome to go join the discussion of the other
questions raised on that mailing list.

Here I primarily want to raise the issue I see with multiplexing several
RTP sessions onto the same lower layer transport without something
explicitly identifying these separate sessions. And in particular the
RTP SSRC semantics changes that is proposed by the Rosenberg draft.

Personally I think it is time we tackle the issue of how to efficiently
run multiple RTP sessions over one lower layer transport. This as there
are several wanting to have that functionality. However, I think this
must be done in a very careful way. As we don't want to create an
alternative version of RTP which is what the Rosenberg proposal in fact
does. I do want us to gather the requirements on this and think of how
we can accomplish this.

I think there is a clear risk that we will not be able to accomplish it
without either adding some type of shim header which has it sets of
drawback or in fact fork or change the RTP protocol in such a way that
it will not be fully compatible with what exist today. But if that is to
be done, we should have a very clear consensus on that and ensure that
we then develop future extensions to RTP within a single version of the
protocol, not two.

As WG chair:

We are considering re-arranging the agenda to facilitate a debate of
this topic in Quebec.

So please indicate both your view of the topic in general and if you
think we should re-prioritize the agenda.

cheers

Magnus Westerlund

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From: David R Oran <[email-masked]>
Date: Tue, 19 Jul 2011 15:52:27 -0400

I'm very interested in this work and willing to help.

On Jul 19, 2011, at 11:35 AM, Magnus Westerlund wrote:

> _______________________________________________
> Audio/Video Transport Core Maintenance
> [email-masked]
> https://www.ietf.org/mailman/listinfo/avt

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From: "Ali C. Begen (abegen)" <[email-masked]>
Date: Tue, 19 Jul 2011 13:49:33 -0700

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of Magnus Westerlund
> Sent: Tuesday, July 19, 2011 5:35 PM
> To: IETF AVTCore WG
> Subject: [AVTCORE] RTP Internal Multiplexing of RTP sessions
> 
> WG,
> 

If that would help, I can donate some minutes from my presentations ;)

-acbegen

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From: "Elwell, John" <[email-masked]>
Date: Wed, 20 Jul 2011 11:30:46 +0200

I think this is an important topic and should receive some agenda time in Quebec.

John 

> Sent: 19 July 2011 16:35

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From: Colin Perkins <[email-masked]>
Date: Wed, 20 Jul 2011 23:51:58 +0100

I agree that there is a clear perception of a requirement here, and that we should discuss the issue in Quebec to determine if it's a real issue, and if so, how we should address the requirement.

Colin

-- 
Colin Perkins
http://csperkins.org/

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From: Harald Alvestrand <[email-masked]>
Date: Thu, 21 Jul 2011 16:33:11 +0200

Speaking as RTCWEB contributor....

I think the discussion in RTCWEB has shown clearly that there isn't a 
clear consensus in the community on what an RTP session is, what the 
existence of RTP sessions requires from the applications, and what the 
RTP session is an useful tool for.

The debate has been framed in terms of the cost (in both complexity and 
network resources) of running multiple transports when no difference in 
treatment is desired from the network - but I think the confusion goes 
deeper than that; in the discussions in the W3C WEBRTC WG, which deals 
with the API requirements for the same thing, there doesn't seem to be 
any sign that anyone sees the need to represent an "RTP session" at the 
API offered to the Web applications using RTCWEB.

I'm looking forward to the discussion, both inside and outside the 
AVTCORE session, in Quebec.

                      Harald