somesh s wrote:
Hi All,
I have the following doubt in SDP.
UA1 ========================> UA2
Invite(SDP) ------------------>
From UA1:SDP has both audio & video capabilities.
At UA2:
UA2 doesn't have audio capability & so it doesn't know any codec. But according to RFC 3264, it MUST
reply something for audio. We have two choices -
1) Reply with port = 0 --> But we don't know the codecs?
2) Reply with inactive --> But we don't know the codecs?
Is it feasible to use either of the approach?
If UA2 doesn't support audio at all, then it makes more sense to respond with port=0 than inactive.
Please correct me if I am wrong?
is it valid to construct m= lines in SDP without any codec?
Unfortunately the syntax of SDP doesn't permit an m-line with no codec, even in the case of port=0 where the codec makes no sense.
To comply with offer/answer it is necessary to reply with some non-empty subset of the codecs offered in the request, even though they won't be used. It doesn't matter that you don't understand any of the codecs. All that is needed is to copy one from the offer into the answer. It may also be necessary to copy an a=rtpmap line as well.
Paul
With regards Somesh S. Shanbhag
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