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Outgoing calls from IP phones to a PSTN through a T1, E1, or PRI link on a H.323 or MGCP gateway are never completed or give a fast busy tone


Core Issue

Outgoing calls to a Public Switched Telephone Network (PSTN) network through a H.323 gateway can fail with these symptoms:

To address other issues concerning outgoing calls through a Media Gateway Control Protocol (MGCP) gateway, refer to Outgoing calls to a PSTN or PBX network through a MGCP gateway fail with symptoms like dead air or re-order tone.


Before you perform the steps identified, verify that the PRI line is operational by issuing a show controller T1 command.

If the circuit is not up, fix the circuit by referring to T1 PRI Troubleshooting.

To resolve this issue, perform these steps:

  1. Issue the debug voip ccapi inout command on the Cisco IOS  gateway. Issue the terminal monitor command if you are not on the console of the gateway.
  2. Place a test call out the gateway, and save the debugs. If no debug messages are displayed, the call setup messages may not have arrived at the gateway. The problem could be with Cisco CallManager. In this case, perform the procedure for setting up traces in Setting up Cisco CallManager Traces for the TAC. Check the results against the information in Troubleshooting Cisco IP Phone-to-Cisco IOS Gateway Calls for Cisco CallManager release 4.0.

    For other versions of Cisco CallManager, refer to the CallManager Troubleshooting Guides index. Select the appropriate troubleshooting guide, and navigate to the relevant chapter. You can also present these traces to the Cisco Technical Support web site for further analysis.

  3. From the debug outputs, verify that the called party and calling party numbers are correct. If there is any mismatch, check the dialed number and the digits being prepended or discarded at the Cisco CallManager. Look at the route patterns, the route list and the gateway configuration. Also check the Plain Old Telephone Service (POTS) dial-peer to ensure the correct digits are being discarded.
  4. Verify from the debug outputs that the correct dial-peer on Cisco IOS gateway is matched for this call. To understand how Cisco IOS matches the dial-peer, refer to Understanding How Inbound and Outbound Dial Peers are Matched on Cisco IOS Platforms.
  5. If steps four and five do not resolve the issue, refer to VoIP with Channel Associated Signaling (CAS) or Troubleshooting and Debugging VoIP Call Basic(PRI), based on the signalling or network used in your case.
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