Verify the registration status of the MGCP gateway with the Cisco CallManager. In Cisco CallManager 3.1 and later, the gateway configuration screen indicates whether the device is registered. With Cisco CallManager 3.0, you must look at the performance monitor or the Cisco CallManager traces to show the status of the gateway.
If the exit port to PSTN or PBX is an Foreign Exchange Office (FXO) port, ensure that the port direction is set to either Outbound or Both ways
If the gateway is Cisco IOS -based, refer to Sample of Debug MGCP Packets. If the gateway is not Cisco IOS-based, the Signaling Connection Control Part (SCCP) controlled gateways utilize Primary Rate Interface (PRI) back haul. Use the Q.931 translator that ships with the Cisco CallManager to address the failed call. The Q931 translator is found at C:\Program Files\Cisco\Bin.