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Community Member

SRST configuration issue

I have configured SRST on a cisco 2821 as follows


max-conferences 8 gain -6

ip source-address port 2000

max-ephones 45

max-dn 120

It is on a remote site. Now when i deleberately remove the route from the remote site edge router towards call manager, the phones are able to register in the SRST router. But when i call from a remote site to any of that registerd phone i get a fast busy tone.

In CCM there status is unable to register. The phones have get there IPs from local DHCP and are registering in the SRST router.

What abut TFTF ? My ccm is down in this case and it is the primary TFTP server. From where the phones will now get there config information ?

Much Thanks.


Re: SRST configuration issue

The SRST router should have the necessary phone config information stored locally in flash, and you should have tftp-server flash: statements in the gateway so that the phones can get their configuration files, etc.

As far as making calls from the remote site to phones that are registered in CCM, if you are using on-net dialing, you wouldnt be able to make those calls, as you have removed the link between the gateway and the CCM. You would have to dial the full E164 phone number and the call would go thru the PSTN. If you would like SRST to be transparent to your end users, you would have to configure some sort of digit-manipulation to transform say a 5 digit dialed extension into the full phone number and then have the call routed across the PSTN via your pots dial-peers.

Hope that made sense

Community Member

Re: SRST configuration issue

Thanks mohammed.

Now i am able to make the calls with in the office. I am understnading your point that whay i cant make a call from the remote office.Thanks much for the precise explanation.So, its decided that without using some thing like FXO cards etc etc and PSTN lines i cant make a call from the remote office (registerd with SRST router) to the phones in HQ (registerd with CCM) ???

Can u explain a little about TFTP server. Even if i want to maintain locally TFTP files of the phone how it can be configured.

Any link / document to read on SRST will be very helpful.

Thanks very much

Re: SRST configuration issue

You are correct, without PSTN connectivity of some sort(FXO, PRI, etc), you will not be able to make calls to the HQ (or anywhere else for that matter) when the router is in SRST mode. You will only be able to make intra-office calls.

The phones use TFTP to download files required during the registration process, such as the following:

SEPxxxxyyyyzzzz.cnf.xml flie

Phone firmware (if an upgrade or downgrade is necessary)

Network and user locale files

Language files

Basically, in the gateway,if you have them the TFTP server statements look something like this:

tftp-server flash:ATA030100SCCP040211A.zup

tftp-server flash:P00305000600.bin

tftp-server flash:P00305000600.sbn

tftp-server flash:cmterm_7936.3-3-9-0.bin

As far as configuring SRST, here is a good interactive link to show you exactly how it works:

also the SRST admin guide

Hope that helps, if so please rate the posts.


Re: SRST configuration issue

Hi munawar

This is the admin guide for SRST it should help you out.


Community Member

Re: SRST configuration issue

And what about IOS versions? Does every version of voice IOS support SRST? How can I test SRST function without going netlink down? Where I can find information about supporting SRST feature?

Re: SRST configuration issue

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