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Thursday, February 3, 2011

What tells the call to move on and use the alternate trunk at another 2811 ISR?

At each site we have setup two route groups in a route list. Each route group has a SIP trunk to a 2811 ISR which in turn has a SIP trunk to our voice carrier. It is setup this way so that if the trunk to the carrier at this site fails - the call should be re-routed to a trunk at another site with an alternate path to the carrier. What we don't understand is the fail over mechanism.With IP routing of course if a route falls out of the table or becomes less desirable then the alternate path is taken. But in this scenario what causes a specific call to go to the backup route group/trunk in the event that the trunk to the carrier is broken at the primary 2811 ISR? Is it reorder tone? Other?

Perhaps an ASCII diagram will help explain.

[7965G]---SCCP-->[UCM7]--SIP-->[2811]--SIP-->{Telephony Provider/PSTN}

To make an external call the call will cross two SIP trunks: from UCM to 2811 ISR, and 2811 ISR to Provider. Now let's say the trunk to the provider fails.

[7965G]---SCCP-->[UCM7]--SIP-->[2811]--fail.SIP-->{Telephony Provider/PSTN}

What tells the call to move on and use the alternate trunk at another 2811 ISR?

[7965G]---SCCP-->[UCM7]--SIP-->[alternate.2811]--SIP-->{Telephony Provider/PSTN}

Tips:

This is what you are looking for Out-of-dialog OPTIONS Ping for Specified SIP Servers or Endpoints .This will busy-out the dial-peer incase the SIP provider doesn't respond. Click here for further information.

You should also look at how you can tweak the replies send to the CUCM if the heartbeat is missed .

Configure the SIP error code response, perform the following tasks:

"Configuring an Error Response Code upon an Out-of-Dialog OPTIONS Ping Failure at the Global Level" section (required).

Configuring an Error Response Code upon an Out-of-Dialog OPTIONS Ping Failure at the Dial Peer Level (required). For further details available here

Citation - This blog post does not reflect original content from the author. Rather it summarizes content that are relevant to the topic from different sources in the web. The sources might include any online discussion boards, forums, websites and others.

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