Last weekend, I had a weird issue. My client setup is as below -
CUCM ---- SIP Trunk ----> CUBE ---- SIP Trunk ----> SIP Proxy
Client is having 1800 users spread across 100+ sites.
When one site dialing internal extensions of some other site, everything is working fine. But when anyone dials Full National Number of some other site, there is no voice or one way voice. Weird thing is if any of the caller or receiver puts a call on hold and then resume the call, everything started working sometimes.
Run few debugs on the CUBE -
1. "debug ccsip messages"
2. debug voice ccapi inout"
After capturing the debugs, I found that the initial invite messages from CUCM to CUBE doesn't have any SDP Information in it, which is normal as CUCM is using Delayed Offer. SIP Invite messages between CUBE and SIP Proxy is having right SDP Information in it as they are expecting to use SIP Early Offer. As per cisco, this is absolutely normal.
But I have got 1800 users impacted.
I had to change SIP Profile being used in the SIP Trunks between CUCM and Cube to support SIP Early Offer as below -
Everything started working fine after this. Please note that I am not using any MTP for any calls or any devices.
