[SIPForum-discussion] Codecs in 200 OK response

[Pramod Kumar]

Hi Waqas,

Yes, 200 OK can have more than one codec in SDP answer. It is based to
support the codec negotiation functionality. However it is implementation
dependent how to select the final codec like select first codec from the
SDP answer for that call.

Regards,
Pramod



On Mon, Oct 7, 2013 at 1:09 PM, Waqas Arshad <waqas.arshad000 at yahoo.com>wrote:

> 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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