[MMUSIC] Offer/Answer PT Questions

["DOLLY, MARTIN C" <[e-mail]>]

Hello O/A lovers,

Section 8.3.2 of RFC 3264 says the following:

   "However, in the case of RTP, the mapping from a particular dynamic payload type
   number to a particular codec within that media stream MUST NOT change
   for the duration of a session.  For example, if A generates an offer
   with G.711 assigned to dynamic payload type number 46, payload type
   number 46 MUST refer to G.711 from that point forward in any offers
   or answers for that media stream within the session."

Now, assume the following case:


1.      Alice sends an Offer, with the following PT values:

PT 100: AMR-WB(mode-set=2)
PT 111: AMR-WB(mode-set=2, OA)
PT 0: PCMU


2.      Bob sends the associated Answer:

PT 100: AMR-WB (mode-set=2)
PT 0: PCMU


3.      Later Bob sends the following subsequent Offer:

PT 111: AMR(mode-set=0,2,5,7)


QUESTION 1: Is it allowed for Bob to offer PT 111 for AMR in the subsequent Offer, as Alice used PT 111 for AMR-WG in the initial Offer? In other words, does the pt-value-must-only-refer-to-a-specific-payload-for-the-stream-within-the-session text in section 8.3.2 apply to user A only, or to *all* users within the session?

QUESTION 2:   Assuming the text applies to all users, is it allowed to re-use a PT value for the same codec, but for a different CODEC CONFIGURATION? The text only talks about codec.

Now, I agree that the easiest way to avoid trouble is simply to make sure PT values aren't re-used by any party. But, the text still needs to be clear, because this is causing problems in real deployments.

Regards,

Martin