[SIPForum-discussion] Is "fmtp" line needed in 200 OK answer?

[Donald Lee]

# the "g" and "G" have no difference. and the offer indicate that it's not
G729B codec.
# I don't think the lack of fmtp in answer is the reason for issue. Maybe
the ip phone should reply only one codec in its SDP. Maybe the multi codec
in answer make the offer confused.


On 12/11/07, Andrea Puddu <androjoker at hotmail.com> wrote:
>
>  Hello guys,
>
> I'm facing an issue when a mobile (common mobile 3G phone) tries to call
> an internal SIP phone through its geographical number.
> The issue is that when the SBC sends the INVITE to the IP phone,  in the
> SDP  enclosure it  suggests these codecs:
>
> m=audio 19570 RTP/AVP 18 8 0
> a=rtpmap:18 G729/8000
> a=fmtp:18 annexb=no
> a=rtpmap:8 PCMA/8000
> a=rtpmap:0 PCMU/8000
>
> The 200 OK of the phone (SDP part only) is:
>
> m=audio 57956 RTP/AVP 18 8 0
> a=rtpmap:18 g729/8000
> a=rtpmap:8 pcma/8000
> a=rtpmap:0 pcmu/8000
> a=sendrecv
>
> So the IP phone start to talk with G729 and SBC replies with G711A!!! So I
> can't hear the voice coming from mobile phone!!!!
>
> I have two questions:
>
> - Can the difference between the offer (G729) and the answer (g729) be
> significant? I mean the difference because the "g" is not capital in the
> answer
> - Can the lack of the "fmtp" line in the answer cause troubles?
>
>
> Thanks 1000,
>
> Andrea
>
>
>
>
>
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-- 
BR
Donald
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