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New Member

Multiple site CallManager design question

I have a design question for CallManager in a multi-site environment.

The customer has 2 CallManagers, one at each location. The 2 locations are connected via gigabit with QoS so bandwidth is not a major issue. The question is whether to set the CallManagers up as a cluster, or to make them separate clusters and trunk between them.

Each site has a PBX that is connected to a 3725 router as a voice gateway. Each site has a separate connection to the PSTN on the voice gateway as well.

The kicker is that certain users want to be able to take their phones to either site and have the same extension.

Issues (as I can see them):


1) Call routing based on location is out, as the phone will always be in the same location no matter which CM it associates with. This leads to call routing and 911 problems.

2) Route Patterns on the voice gateways will be fairly crazy depending on which CM the phone is associated with.


1) No redundancy/failover if one CM fails.

2) duplicate configuration have to be maintained for each phone that wants to be at both sites.

3) This will not scale well if sites are added.

Any thoughts, suggestions, corrections would be greatly appreciated.

Thank you,



Re: Multiple site CallManager design question

If both sites are seperated via gigabit delay is not an issue. I would definately keep both CM's in the same cluster. As far as each site having their own PSTN connection and to take care of 911 issues that is no problem. All you will be doing is placing the phones in each building in a separate partition. Just make your route patterns (Route Patterns would not be that crazy. Personally I use Route Filters so I have many route patterns. But if you have a simple dial plan you would just have a 9.@ Route Pattern for each site) for each partition and assign it the correct gateway. As for location based routing (bandwidth shouldn't be an issue with Gigabit) you are ok as well. The phones in each building will have their own location configured in CM.

New Member

Re: Multiple site CallManager design question

That design is solid and would work well for the customer, except that they want the ability to take their phones with them when they are working at either facility and have the extensions follow them, etc. Extension Mobility is not an option as they are carrying wireless phones back and forth, and want those phones to work at either location.

New Member

Re: Multiple site CallManager design question

You need to ensure you use Cisco Emergency Responder so you can track those phones when they are in transit and when 911 is required, the system wil be able to send the 911 call out the correct gateway to the PSAP (you have a gateway at each location, I assume). Other than that, this should work considering you have the correct WAN link between the two sites.

New Member

Re: Multiple site CallManager design question

The ER will work for 911 calls, but my regular call routing becomes difficult. Phones with a location setting for site "A" that are temporarily in site "B" will still want to use site "A"s gateways for outgoing calls. I haven't found a way to filter or route on the CallManager that a phone is associated with.

The number of phones that will be at both locations is not large, but I don't want to waste the customer's bandwidth by routing across the WAN link just to go out to the PSTN at the other site.

Any thoughts?

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