I have a Global Crossing SIP Trunk and CUBE connected to a CM 6.1.2 via a SIP Trunk, SIP_SIP CUBE.
With voice-class sip rel1xx system command and voice-class early-offer forced command both set on the outbound dial-peer, I am able to change order of preferred codecs in voice-class codec 1 and the provider sends me the codec I want, this part works fine.
The first issue is this, when an outbound fax machine places a call (G711 for faxing and in a G711 RE), it matches the one outbound dialpeer with voice-class codec 1 preferred g729/g711, the provider detects fax tone and sends me a re-invite for g711, we send back a 100 trying, bye and disconnect. How do we configure cube/cm to respond to the reinvite properly and send codec at g711 for the fax call? G711 only T38 not configured.
Issue 2, for inbound calls, provider sends an early-offer with g711/g729, we only respond with g711 and all calls go g711 inbound. I assume this is because I only have one sip trunk in CM and its in a G711RE? I have a voice-class codec 2 command on the inbound dial-peer but the order of preferred codecs has no affect. Is the fix for this to add a second SIP Trunk with the same destination IP or perhaps a different IP on another loopback on the same CUBE?
I attached a sip trace for the outbound fax issue.
Thanks for any help or suggested resources, I have searched the wiki and Cisco with no real help found for these issues.
Codec transparent may work for your incoming codec problem.
Generally the problems like that are restricted only when an MTP is required - the MTP cannot change codecs mid-call.