[SIPForum-discussion] Codecs in 200 OK response

[Waqas Arshad]

Hi,

Can someone please confirm if the SDP of 200 OK (in response to an INVITE) can contain multiple codecs in m-line or it should have only one codec at which B party has responded to establish the connection. e.g.

INVITE SDP:
m=audio 39838 RTP/AVP 0 8 18 101
a=rtpmap:0 pcmu/8000
a=rtpmap:8 pcma/8000
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=sendrecv

200 OK SDP:
m=audio 18238 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=X-sqn: 0
a=X-cap: 1 audio RTP/AVP 100
a=X-cpar: a=rtpmap:100 X-NSE/8000
a=X-cpar: a=fmtp:100 200-202
a=X-cap: 2 image udptl t38 

So can 200 OK SDP contain m-line as below too or just one codec at which call is going to be established???

m=audio 18238 RTP/AVP 0 8 18 101


Secondly, can someone please suggest the meaning of a=X-sqn in above 200OK?

Thanks in advance.
Waqas
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