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H323 Gateway: PSTN side continue to ring after IP phone picks up



I have configured a H323 Gateway with a call manager 7.0. Th voice gateway have four fxo port, under all the voice ports i have configured a connection plar opx to the directory number of the opérator. I have an issue, when we call the PSTN Number from the outside, the opérator IP Phone ring, but when she picks up the call, they don't hear anything and the call continue to ring from the PSTN side.

Can you help me solve this issue.

Thanks in advance

1 Reply 1


When loop-start signaling is used, the FXO interface of a router looks like a phone to the switch, a private branch exchange (PBX), public switched telephone network (PSTN), Key-System, to which it connects. The FXO interface closes the loop in order to indicate off-hook. The switch always provides a battery so there is no disconnect supervision from the switch side. Since a switch expects a phone user, for example, an FXO interface, in order to hang up the phone when the call is terminated on either side, it also expects the FXO port on the router to hang-up. This human intervention is not built into the router. The FXO port expects the switch to tell it when to hang-up, or remove the battery in order to indicate on-hook. Because of this, there is no guarantee that a near-end or far-end FXO port disconnects the call once either end of the call hangs-up.

The most common symptoms of this problem are phones that continue to ring when the caller has cleared, or FXO ports that remain busy after the previous call should have been cleared.


Refer to these documents for workarounds and further background information:

Understanding FXO Disconnect Problem

Understanding Foreign Exchange Office (FXO) Voice Interface Cards
Hope this helps.

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