MGCP G729 SDP error

Unanswered Question
Feb 20th, 2007


In the following trace the call-agent request a g729AnnexA voice channel, but I cannot have the AS54000 MGCP gw to reply and build it. It only support AnnexB.

//create connection

CRCX 4202 s6/ds1-0/[email protected] MGCP 1.0

C: 45d83404

M: inactive


o=- 45544201 1070946003 IN IP4


c=IN IP4

t=0 0

m=audio 12178 RTP/AVP 18

a=rtpmap:18 G729/8000

a=fmtp:18 annexb=no




I: A6


o=- 166 0 IN IP4

s=Cisco SDP 0

c=IN IP4

t=0 0

m=audio 17702 RTP/AVP 18 101 100

a=rtpmap:101 telephone-event/8000

a=fmtp:101 0-15

a=rtpmap:100 X-NSE/8000

a=fmtp:100 200-202


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

Because fmtp line is missing from the desc. of G729 codec, the default is Annex B. Since it is an MGCP gw all control is from call-agent, so there is no any codec related configuration on it.

Any suggestion?



I have this problem too.
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vkapoor5 Mon, 02/26/2007 - 07:24

Try reset of CCM services. It should work.

OR Set the gateway to use G729R8. The Cisco CallManager will let G.729 calls through even in G.711 regions. You might be able to install a Media Transfer Agent on the CallManager server. You also might be able to use a gateway that supports MGCP, Skinny or H323v2.

wormhole Mon, 02/26/2007 - 08:01

This scennario consist a cisco gateway (with fxs port) connected to a 3rd party call agent and after an AS5400 gateway that is the egress to PSTN. So: 1st GW-CA-AS5400-PSTN. The 1st gateway communicates with CA with SIP or H.323. Between the CA and the AS5400 MGCP works. There is no CCM. The gateway try to build up a voice channel based on G.729 Annex A but the mgcp stack of the AS5400 give a wrong response.


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