[SIPForum-discussion] Is "fmtp" line needed in 200 OK answer?
Andrea Puddu
androjoker at hotmail.com
Tue Dec 11 15:28:21 UTC 2007
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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