Core Issue
After you restart the Cisco CallManager services, IP phones on a remote site cannot be called and the caller receives a fast busy tone. One-way call failure, on either the outbound call or inbound calls individually, can occur in an IOS Media Gateway Control Protocol (MGCP) gateway after an unexpected reset of the services.
Resolution
In order to resolve this issue, reconfigure the MGCP gateway. Generally, this involves reconfiguring the primary rate interfaces (PRIs) and/or Foreign Exchange Office (FXO) interfaces and then restarting MGCP on the gateway by issuing the IOS command no mgcp and then mgcp in global configuration mode.
For more information on restarting the MGCP and other issues, refer to Configuring Cisco CallManager with IOS MGCP Gateways (Analog FXO, FXS Ports).
