After an upgrade from Cisco IOS Software Release 12.3.8(T5) to Cisco IOS Software Release 12.3(11)T8 on a Media Gateway Control Protocol (MGCP) voice gateway, random analog foreign exchange office (FXO) ports unregister from Cisco CallManager after it is accessed one to two times. Approximately once or twice a day all incoming calls fail on one of the ports. The ports get re-registered for a couple of hours by either issuing the no mgcp/mgcp command on the gateway or by resetting the gateway on the Cisco CallManager. However, it unregisters with the Cisco CallManager again. The Cisco CallManager traces show that the gateway sends an on-hook message to CallManager, then the CallManager replies with a 200 OK. A request notify is then sent but the gateway responds with a endpoint is busied out 501 error.
Cisco bug ID CSCej50165 documents this issue. This issue occurs in Cisco IOS Software Release 12.3(11)T8 which causes problems with the FXO ports failing to respond after a period of time.
This issue is fixed in Cisco IOS Software Release 12.3(11)T9. Upgrade to either Cisco IOS Software Release 12.3(11)T9 or 12.3(14)T4 to solve this issue. You can download the relevant Cisco IOS software release from Software Center (Downloads) - Cisco IOS Software.
Refer to these documents for more information:
CallManager 3.x, CallManager 4.x