we are experiencing random phones that unregister with following error in log:
089919: Aug 5 15:31:18 EDT: %IPPHONE-6-UNREGISTER_ABNORMAL: ephone-60:SEP0026CBCXXXX IP:X,X.X.X Socket:168 DeviceType:Phone has unregistered abnormally.
we have been chasing our tails on this. network is saying its the router , CME team is saying its a network issue.
i did find this bug but its on a 3825 router with same IOS and CME version
http://www.ciscosystems.com/en/US/docs/ios/15_1/release/notes/151TCAVS.html
CSCth28007
Symptoms: Cisco IP phone users may experience dropped calls, resetting phones, and one-way audio.
Conditions: These symptoms are observed on a Cisco 3825 router that is running Cisco IOS Release 15.1(1)T and CME 8.0 when there are 4 or more active calls. The symptoms occur with the following topology:
Router/ PBX ---pri---- CISCO3825 ----sccp---- ip phone.
It is a normal external call: PSTN <-----> IP phone calls.
Workaround: Install Cisco IOS Release 12.4(15)XZ2 or another release earlier than Release 15.n.