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Outgoing calls to a PSTN or PBX network through a MGCP gateway fail with symptoms like dead air or re-order tone


Core Issue

Calls to a Public Switched Telephone Network (PSTN) or PBX network through a Media Gateway Control Protocol (MGCP) gateway could fail with these symptoms:

Note: For call connection issues through an H.323 gateway, refer the document Outgoing calls to PSTN/PBX network through an H.323 gateway fail with a reorder tone after all the digits are dialed


If the re-order tone is heard after the complete number is dialed, digit manipulation could occur at the route pattern, route list or by use of translation patterns.

To address the issue, perform these steps:

  1. When using translation patterns for digit manipulation, ensure that the called party is reachable by the calling party. To address calling search space partition issues, refer to Understanding and Using Partitions and Calling Search Spaces With Cisco CallManager, and ensure the transformation masks match valid Distinguished Names (DNs) or route patterns. Refer to Translation Pattern to understand how translation patterns work in Cisco CallManager.

  2. If any digit manipulation is done on the route pattern, route list, or translation patterns, verify that the final result is a valid number. Adjust the digits being discarded or prepended to present a valid called party number to the PSTN. Issue the debug mgcp command on the gateway to verify the digits being sent to it. The observed event O: D/xxxxx (where x is the digit string) will show the digits collected by the gateway packet
  3. 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.

  4. 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

  5. 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.
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