Core Issue
This problem occurs when MGCP is being used and a caller is leaving a voice message.
The Media Gateway Control Protocol (MGCP) gateway initiates a disconnect after a period of silence in one direction, such as when the mute button is pressed, or when a voicemail message is being left.
This issue is documented in Cisco bug ID CSCdv05532.
Resolution
For a workaround, issue the no mgcp timer receive-rtcp command.
For more information, refer to these documents: