IP Centrex solution and CME

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Sep 14th, 2010
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Imagine customer accepted to buy Cisco IP phones and we have the following solution:

30 Cisco IP Phones----SwitchCisco(L2)----------CiscoRouter2821--WAN-----IP Centrex (Call Manager hosted here in Service Provider)

If WAN link goes down, customer wants to have ability to let internal staff communicate on Cisco IP Phones. I hope that no intervention (static phone configuration on router reconfiguration) is required in that event.

So if I run CME on Cisco Router2821 I could accomplish that, right?

If you can give me a hint on directions I need to take to configure that, or point me to documentation, that would be great. Let me know if that is something practical or perhaps cumbersome.

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dksingh Tue, 09/14/2010 - 10:22
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  • Cisco Employee,

Hi there,

Assuming those 30 IP phones at remote site are going to be registering with the CUCM

across the WAN and u want those phones to be able to call each other and perhaps

via a PSTN connection off local GW when WAN/CCM goes down ?

If yes, please take a look at Cisco SRST feature which will provide the




news2010a Tue, 09/14/2010 - 10:24
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In this case the customer does not want to pay to have SRST (additional PSTN connection).

As long as the internal people can call each other when the WAN goes down, he is happy with that.

Let me know.

dksingh Tue, 09/14/2010 - 10:28
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  • Cisco Employee,

SRST does not mean additional PSTN connection.

The feature you are looking at is SRST or CME-as-SRST

which would allow IP phones to register with local router

in case of WAN/CCM failure and able to call each other.

Hope this helps.

brendand05 Tue, 09/14/2010 - 16:53
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You need SRST to do this

You need an SRST license for the 2821


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