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Active calls get dropped after a consistent time period


Core Issue

Answer supervision is not being provided by the Public Switched Telephone Network (PSTN) switch or PBX.


The router is expecting some kind of M lead response after it has placed the call toward the PBX. If it does not get a change of state, it assumes the call failed or was never picked up (no answer signal came back) and it drops the call.

To resolve this issue, choose from one of these options:

To confirm that the M lead response is the problem, put a multimeter across the recEive and transMit (E&M) leads while a call is up. Refer to the Understanding and Troubleshooting Analog E&M Interface Types and Wiring Arrangements E&M debugging guide as a reference.

You will be able to see seizure from the router to PBX or PBX to router and confirm if you are getting end-to-end answer supervision.

If you do not see any return M response from the PBX after the user has answered the phone, this is most likely the problem.

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