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Community Member

IOS telephony services

Does anyone know where I can find some good information on ITS and how it could be used in conjuction with a call manager. We are deploying a call manager in the near future and I'm being told I should also run ITS on my routers in conjuction with the call manager to provide failover should the call manager fail. I'm looking for information containing the pro's and con's of ITS and also how to configure it on the routers. Thanks in advance for your assistance.

Cisco Employee

Re: IOS telephony services


Normally if you have ITS you have a router to which all your phones are registered and there is no real failback mechanism to callmanager. You can off course configure it so that we can call eachother.

However if you use a feature called SRST then your phones that are eg at a remote site connect to the CCM when the WAN is up but when that has an outage the phones will failover to the router and register to that one.

Are you talking about scenario A or B?

Kind Regards


Community Member

Re: IOS telephony services

Here's my senario.

site A will contain a CCM and we'll say sites B-E will be connecting to Site A's CCM. If for some reason the CCM goes down at Site A, I still want sites B-E to be able to call each other.

Correct me if I'm wrong, but from what you are saying, if I run ITS on the routers then theres no need for a call manager because all the phones are registered to the router??? If I run SRST, then I'm provided with failover capability should the CCM fail for some reason. Sounds to me like I should look into SRST rather than ITS????

Thanks for your comments....

Cisco Employee

Re: IOS telephony services


Have a look at the following URL's they provide more info on this:



If you want your phones in general to be subscribed to your main CCM then you will have to use the SRST option.

Kind Regards

Ullie Versavel


Re: IOS telephony services

If you are running ITS then there is no need for your phones at site B-E to register to the call manager. However interoperability with call manager and ITS is not complete yet and some of the features are limited. So you are better off registering everything with CCM right now. You can use the SRST feature to fall back on if the CCM or the WAN between sites goes down.


Re: IOS telephony services

ITS 2.1 has a lot of features, compared to the older versions.

In case you need sites B and E to call when the CCM is down, you ll need to enable SRST, so that the gateway will route the calls through the PSTN, for the time, the CCM is down, and revert back to CCM, when it comes back up.

ITS can offload the need for a call manager, but all features of a call manager are not yet available for the ITS. I have tested the ITS 2.1, IT has a web GUI, you can use a CLI also. Upto 48 phones are supported. Its a good solution, if you want only limited features and want it to be cost effective.

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