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IP call to Unity does not disconnect if Unity fails

If Unity fails while an IPT user is leaving a message for another user, the call remains up and user does not know that Unity is down. The user will continue to talk and think the VM message has been left. Is this normal? Should the call be dropped by CCM?

Cisco Employee

Re: IP call to Unity does not disconnect if Unity fails

Hi Julie

Yes this is normal. Unity ports are as good as an IP phone. So let us say if IP phone A is talking to IP phone B and suddenly you plug the plug for phone B. Phone A nor the CallManager at this time with come to know that Phone B is plugged out.

There are two reasons for this problem. One is - the nature of voice transmission on IP (this is irrespective of PBX maker) and the second one is done purposefully (for survivability)

One: Phone A and B transmits voice using UDP/RTP packets that provide no acknowledgement to the other device hence there is no way to find receipt of voice assuming one of them went down.

Two: Again the CallManager and the phone maintain a keepalive timer that is sent every 30 seconds by default. After the failure of the 3rd keep alive the CallManager would unregister the disconnected phone from its DB.

But there is a catch with the second point. The callmanager also gives as a feature the capability for the devices to continue conversation in the event the CallManager went down in the middle of the conversation. Hence, if the CM finds the device to be unavailable after the timer expires it unregisters the device but does not send any signal for the device to disconnect.

The result is what you see.

I will let others pour in.

Hope this helps.

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