Problem: After configuring SIP-based CUCME, I noticed that my SIP phones would intermittently re-register. The phone would also be non-responsive when I tried to initiate outbound calls. Ironically, though, was that the SIP phones could receive calls. During the troubleshooting phase, I tried everything I could think of. I even made sure that the firmware on the SIP phone was the version explicitly stated in the CUCME Admin Guide.
Debugs: I ran the following debugs to gather logs: debug voice register events, debug voice register errors, debug ccsip message, debug ccsip info. Based on the debugs, this is what I was seeing:
Resolution: Based on the logs, the phone was never receiving the 401 challenge to the register refresh request. To correct this issue, I bound the SIP signaling to the interface used as the source address under voice register global. In my case, this was Vlan400:
Voice service voip
Bind control source-interface VLAN400
Bind media source-interface VLAN400
The phone has been stable and the registration refreshes successfully.
It seemed the phone was not receiving the 401 challenge to the register refresh. Due to this the phone was resending the register without authentication information and the CUCME would again reject the request. This process would repeat until registration timed out and the CUCME closed the TCP connection. At this point the phone would reset and would successfully register.