Re: [AVTCORE] SSRC multiplexing of RTP

[Magnus Westerlund <[e-mail]>]

Harald Alvestrand skrev 2011-03-11 11:51:
> On 03/09/11 16:40, Magnus Westerlund wrote:
>> Hi Gunnar,
>>
>> Gunnar Hellström skrev 2011-03-09 16:11:
>>> Cullen
>>>
>>> I agree. I have also got negative feedback on SSRC multiplexing.
>>>
>>> I had it described in the draft for multi-party handling of real-time
>>> text in draft-hellstrom-text-conference-02.txt
>>> in order to easily separate the streams from different sources and
>>> display them in a way that the receiver decides.
>>>
>>> But the feedback was that many RTP implementations would just regard it
>>> to be an error if a new SSRC appeared in the session and it would cause
>>> problems.
>> Well, this is how you are supposed to use cases when you have multiple
>> sources. And text chat is case when implementations can't really say
>> that they don't have the rendering capabilities for it. But I do
>> understand that most implementations sucks at handling multiple SSRCs
>> which is very bad.
>>
>> My hope is that we will see a bit of signalling support for handling
>> multiple SSRCs as part of the CLUE work. But, we do need to push that
>> support for multiple SSRCs, it needs to be in the stacks.

> Seems to me that since this isn't clear from current specs, there needs 
> to be a specification of what a new SSRC appearing in a session means, 
> possibly agreed to at call setup time, and if both renumbering and 
> multiple streams are to be supported:
> 
> - if it is a new stream, how to tell that it's a new stream
> - if it is an old stream, renumbered, how to tell what the old stream was

I don't think the specs are that unclear on what is what. You do need
the CNAME to determine which case it is. Sure it can be clarified. I
mostly think the issue is with the state of the implementations. They
haven't considered the implications and need for multiple SSRC support.

> 
> This will certainly be an RTCWEB discussion item, so I'm happy to see 
> AVTCORE pick it up to be worked on.

Lets figure out what is considered the issues here.

Cheers

Magnus Westerlund

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