[RESOLVED]Conferencing on Cisco 7940/7960 using g729 Codec

Hi ,

I have working asterisk seutp. Recently observed that i am unable to use conference facitliy though the “conf” button available on my Cisco 7940. I am getting following error. I am not sure what configuration i am missing here. Please help me.

[May 3 10:11:09] NOTICE[5637]: chan_sip.c:5098 process_sdp: No compatible codecs, not accepting this offer!

[May 3 10:11:12] NOTICE[5637]: chan_sip.c:5098 process_sdp: No compatible codecs, not accepting this offer!

I have 60 - g729 licenses which i purchased.

asterisk-pbx*CLI> show g729
1/1 encoders/decoders of 60 licensed channels are currently in use

my sip.conf is:


After enabling ‘sip debug’ i found below.

— (18 headers 11 lines) —
Sending to : 5060 (no NAT)
Using INVITE request as basis request - 0008210f-8377000f-51d6b3c0-03a525be@
Found user '7900’
Found RTP audio format 0
Found RTP audio format 8
Found RTP audio format 101
Peer audio RTP is at port
Found description format PCMU for ID 0
Found description format PCMA for ID 8
Found description format telephone-event for ID 101
Capabilities: us - 0x102 (gsm|g729), peer - audio=0xc (ulaw|alaw)/video=0x0 (nothing), combined - 0x0 (nothing)
Non-codec capabilities (dtmf): us - 0x1 (telephone-event), peer - 0x1 (telephone-event), combined - 0x1 (telephone-event)
[May 3 14:21:54] NOTICE[5637]: chan_sip.c:5098 process_sdp: No compatible codecs, not accepting this offer!

i am wondering why “peer - audio=0xc (ulaw|alaw)” has to be ulaw|alaw ?

i purchased g729 license to save my bandwidth. Please suggest.


I have not used the describe Cisco phone, so I can’t say exactly. But i’ll make a guess at what is going on.

Your sip.conf file only allows the peer to use the g729 codec. So my guess is that when you press the ‘conf’ button on your phone it (the phone) is programmed to use a different set of codecs (ulaw / alaw).

My suggestion would be to add an ‘allow’ in the sip.conf for either ulaw or alaw, and see if that fixes the issue. If that does then take a closer look at the phone to see why it uses different settings for the ‘conf’ button. Possibly there is an additional option you need to configure to make the ‘conf’ button use the g729 codec.

Just a suggestion, can’t say if it will work for sure because I’ve never used that phone.


Honestly, I do not know why it does so. I have only one idea (probably wrong) - cisco does not have enough CPU power to decode/encode multiple g729 streams simultaneously. (g729 is very CPU intensive). That is why as soon as you start conference, it decides to switch to more lightweight codecs.

If I were you, I would just add allow = alaw, allow = ulaw below allow = g729

Thanks for the replies.

I changed my sip.conf to below:


my conf. option is working fine, BUT my phone is not using g729 even for normal calls. by default it is going with ulaw codec. i dont have sufficient WAN bandwidth and that was the reason i purchased g729 licenses. Any help would be highly appreciated.

If some one has Cisco 7940/7960 with conference option enabled, please send me the phone setting (.cnf) file for me.


Hi everyone,
got a work around by adding “preferred_codec: g729a” option to my SIPDefault.cnf.