If the incoming circuit is a T1 or E1 PRI, ensure that the circuit is up by following the procedures in T1 PRI Troubleshooting. If the circuit is up, use the Q.931 translator that ships with Cisco CallManager to analyze the failure code. The tool can be found at C:\Program Files\Cisco\Bin. Compare the output with what is available in the debugs described in Troubleshooting and Debugging VoIP Call Basics.
If the incoming circuit is a T1 Channel Associated Signaling (CAS) circuit, refer to the debug voip ccapi inoutsection of Troubleshooting and Debugging VoIP Call Basics.
If the incoming circuit is an analog recEive and transMit (E&M) or analog Foreign Exchange Office (FXO) and Foreign Exchange Station (FXS) port, verify that those circuits are operational. For more information, refer to these Cisco TAC Case Collection cases: