[rtcweb] Does RID require the same ext id for all the m= sections?

[Iñaki Baz Castillo <[e-mail]>]

Hi,

Let's assume I send two videos over a BUNDLEd transport, both of them
with simulcast enabled. So I get a local SDP offer with two m=video
sections, having each one 2 or 3 a=rid lines.


1) First question:

Should N in "a=extmap:N urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id"
be the same value in both m=sections?

Let's assume that they are different and that MID is not in use. How
would the receiving transport discover which m= section the RTP packet
belongs to? Note that, upon receipt of the RTP packet, the transport
should read the RID extension header to get the associated m= section.
Which ID should it use to read the packet RID? Unfortunately (DUE THE
ENDLESS SDP MESS) RTP header extensions that are required for the
transport (such as MID, RID, ABS, etc) are placed within m= sections
rather than "globally". So sometimes they must match, sometimes not,
and workarounds like that. Is that the case when using RID? should all
the m= sections use he same ID mapping for the RID extension?


2) Second question:

Should the values of RID be different in the first m=video and the
second m=video? If they were the same then bullet 1) above gets
invalidated because the RID value in RTP packets wouldn't be useful to
find the corresponding m= section. In that case MID would be mandatory
in order to also use RID. Is this correct?


Thanks a lot.


-- 
Iñaki Baz Castillo
<[e-mail]>