Re: [MMUSIC] [rtcweb] Text proposal for Bundle regarding Associating RTP/RTCP With Correct SDP Media Description

Assuming the collision is detected and B sends a BYE then once the SSRC latch is removed then A's packets will match on PT, a new SSRC latch is put in place and everything works.

> On Feb 2, 2017, at 2:19 PM, Cullen Jennings <fluffy@iii.ca> wrote:
> 
> 
>> On Jan 31, 2017, at 10:43 AM, Jonathan Lennox <jonathan@vidyo.com> wrote:
>> 
>> In general, this looks good.
>> 
>> I have one question, however.  What should happen if an RTP packet (without a MID) is received for a stream that has an existing mapping to an m= line, but whose PT is not valid for that m= line?
>> 
>> Should it
>> 1. Cause the stream’s mapping to be moved to another m= line, if the received PT is in the payload type table for some other m= line?
>> or 
>> 2. Be an error?
> 
> 
> Imagine a case where we have two sends call A and B and they each use one PT that is unique and go to different m lines on receiver C via a SFU.  Initially C get a packet from B with a given SSRC and the PT and creates a mapping for it. But imagine that A and B had an SSRC collision which they sort that out and A ends up having the SSRC that B initially used. If you don't have the PT override the SSRC, the packets are going to go to the wrong m-line because the PT points at the m-line A is using but the old SSRC incorrectly points at the m-line B is using. 
> 
> To put this a different way, if the packet has a mid, I think it is very clear the mid has to override the PT. Same for the PT. The mid is effectively just an extended PT. 
> 
> I'm not thinking to much about the case where SSRC is signalled in SDP but ignoring that case for a second, I think the really easy thing to specify, implement, and understand works is simply a priority order where roughly 
> 
> 1) if you have mid, use that and latch the SSRC
> 2) if you have a unique pt, use that and latch the SSRC 
> 3) if you have a latched SSRC use that 
> 
> If you had signaled SSRC, guess I would insert that as step 1.5 of use that 
> 
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