Re: [rtcweb] Clarification on simulcast and RID and RepairedRtpStreamId

[Magnus Westerlund <[e-mail]>]

On 2018-12-04 11:01, Sergio Garcia Murillo wrote:
>> However, an RTP middlebox has the freedom to introduce those header
>> extensions when switching. They do not need to be sent end-to-end all
>> the time. So after the initial establishment of them, I see it as the
>> central middlebox responsibility to ensure that they are included in the
>> down stream legs towards the conference participants. Also at least for
>> video introducing them only on reception of a FIR also makes sense.
> Same could be said about changing the ssrc to avoid collisions and we 
> would have avoided our selves to introduced all this new ids.

I think you are significantly misrepresenting the reasons why RID's are
needed. The fact that we have multiple models for how RTP middleboxes
works is a significant contributing factor. The next is in RTP ancestry
as a non-centralized multi-party protocol, i.e. intended to work over
any source multicast. And as simulcast do implies a selection by the
middlebox that aspect do needs to be handled. A clean-slate approach
could possibly select another set of constraints and maybe be somewhat
simpler but not a lot.

I do note that also the MIDs and RIDs only have per signalling context
and may require translation between the various legs of the conference
in a multi-party one.

Cheers 

Magnus Westerlund 

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