Hi Atilla,
> Then, given that the draft says
> (end of section "6.1 Unicast Streams"):
> "In the case of RTP, it MUST use the payload type numbers
> from the offer, even if they differ from those in the
> answer."
>
> I believe "it" is referring to the answerer.
True. I believe so too :)
> So, therefore, from the example scenario, endpoint B
> (the answerer) must send to port 10036 using an RTP payload
> of 119.
>
> And, though not explicitly stated, I believe endpoint A
> (the offerer) must send to port 10022 using an RTP payload
> of 97.
Right about the ports, incorrect about the RTP payload I feel.
As per the draft:
* offer SDP -
> m=audio 10036 RTP/AVP 8 119
> a=rtpmap:8 PCMA/8000
> a=rtpmap:119 telephone-event/8000
* a proper SDP answer SHOULD be -
> m=audio 10022 RTP/AVP 8 119
> a=rtpmap:8 pcma/8000
> a=rtpmap:119 telephone-event/8000
* It MAY (if the endpoint B does not form the SDP
correctly) be -
> m=audio 10022 RTP/AVP 8 97
> a=rtpmap:8 pcma/8000
> a=rtpmap:97 telephone-event/8000
*However* both parties must use 119 as the RTP payload
(and port numbers as you said).
Let me elaborate a bit. Again, there's one slight
misunderstanding here. What each party considers as
the SDP "offer" is the same SDP description:
The SDP sent by endpoint A to endpoint B.
So if both endpoints obey the snippet you sent in your mail,
"it (answerer) MUST use the payload type numbers
from the offer, even if they differ from those in the
answer."
Even if the answerer sends payload "97" in the SDP answer,
the RTP payload MUST use 119 as that was the payload number
in the offer SDP. Please correct me if I missed something
here as this is my understanding as of now.
Regards,
Siddharth.
------------------
Siddharth Toshniwal @ Hughes Software Systems
http://www.hssworld.com
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