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New Member

SRST - partial phones belong to SRST

I have a remote site using 2821 router and this site has more than 48+ phones. I have configured some phones to be on SRST and some don't. When in SRST mode, what will happen when the registered phone calling the unregistered phone? We see the calls get routed out to the PSTN gateway and the Telco rerouted back into the PSTN gateway which causing a loop. How can we prevent the loop in this case?

New Member

Re: SRST - partial phones belong to SRST


Here is a link about SRST licensing.

The 2821 max is 48 phones.

Also check the router config for max ephones 48. You can see twhat is configured by using the SHOW CALL-MANAGER FALLBACK command



Re: SRST - partial phones belong to SRST

Hi Julie, either with H323 or when the default H.323 application takes over with MGCP fallback, internal calls will not get automatically re-routed over the PSTN.

The only way this could possibly happen is if you have a destination-pattern on your outgoing POTs dial-peer which matches the called extension number.

A translation-rule or profile will then have to be applied to the same POTs dial-peer inorder for your 4-digit called extension number to be a translated to a number that the Telco accepts.

If none of this is configured, then when a registered SRST Phone calls a non-registered number you should simply hear fast-busy, which indicates the call could not be routed.

If you run a 'show dial-peer voice summary', you will see the registered ephone destination-patterns. If the phone is unable to register then you should not see this number in the output. Thus the call could not be routed, unless the number is configured on an outgoing POTs dial-peer as I have already mentioned.

Hope this helps.


New Member

Re: SRST - partial phones belong to SRST

Hi Allan,

I forgot to mention that we are 10 digits shop and we do not use access code. User dials 10 digits from their IP phone to another IP phone and 10 digits from their IP phone to an external local #. Also, our DIDs are not contiguous. We defined the following dial peer:

dial-peer voice 3 pots

description Local ten digit calls

preference 1

destination-pattern [2-9]..[2-9]......

port 0/0/0:23

forward-digits 10

So, when a user calls from their ip phone to an internal # which is not registerd to the SRST router, the call will then be forwarded out to the PRI as it matches the above dial peer. Since the # is asscoiated to this PRI, Telco then sends the call inbound into the PRI which creates a loop.

Not sure if there is any other way to get around this problem.


Re: SRST - partial phones belong to SRST

first the user dail howmany digits to get to the internal phone?

seconde u may try to make number translation in SRST mode that translate spicfic called numbers in SRST mode to numbers that never match the PSTN dial-peer


translation-profile incoming [ur translation profile]

good luck

hope this helps