IPMA in SRST or backup mode

Unanswered Question
Sep 5th, 2008


Wondering how does IPMA proxy mode (with assistant and manager on Branch office) beahaves when:

- Branch office is in SRST mode (without connectivity to head office with CUCM4)? (IPMA stops working tottaly?)

- Branch office is connected to head office by backup isdn line? (IPMA works slowly, because of latency issues?)

Thanks for your help,


I have this problem too.
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mshavrov Fri, 09/05/2008 - 06:33

When your location goes to SRST mode, the "Manager phone" registers to the router, and works as an "standalone phone". All phones at the SRST location are at the same "partition" (unless you configured COR for phones and dial-peers). So, when someone calls the manager's phone, it will ring directly. Also, if you want to preserve 4-digits dialing, you must configure some kind of mechanism (for example, translation pattern) at your Main Location to reach phones at the SRST site.

Good luck,




CCIE Voice (in progress)


metalium2007 Fri, 09/05/2008 - 07:00

OK, no IPMA in SRST mode.

And about the isdn backup question? Any problems or will it work correctly? Latency counts, no?

mshavrov Fri, 09/05/2008 - 07:12

What you mean under the definition "isdn backup"? Is it another gateway/route group/route list?

Anyway, consider the router in SRST mode as a standalone router. It means you must configure dial plan manually (controller, voice ports, dial peers, COR, etc.). So, let's say if you have a primary T1 and backup ISDN, you will need to configure them separately, create dial peers for required dial patterns, and assign lower priority to ISDN dial-peers.

Good luck,



CCNP, CCDP, CCSP, CCVP, MCSE W2K, CCIE Voice (in progress)


metalium2007 Mon, 09/08/2008 - 01:01

The same router with connection to CCM via ISDN backup and not main circuit. Like ISDN-128k.

Will it impact negatively and noticeable the connection between the assistant and manager ip phone to cti/ccm ?



mshavrov Mon, 09/08/2008 - 04:17

If it is a regular WAN backup, then, when the IP connectivity between the Main Site and Remote Site established, the Remote Site should switchback from SRST mode to a regular mode. However you must carefully plan for CAC - basically you will be replacing your WAN link with a "128k WAN link" without informing CallManager about it, so, you can easily oversubscribe it with just a couple calls.


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