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New Member

IP Centrex solution and CME


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.

Cisco Employee

Re: IP Centrex solution and CME

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



New Member

Re: IP Centrex solution and CME


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.

Cisco Employee

Re: IP Centrex solution and CME

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.

New Member

Re: IP Centrex solution and CME

You need SRST to do this

You need an SRST license for the 2821