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New Member

No call from PSTN in SRST fall back mode


We are experiencing an issue with SRST fallback. When in fall back mode we can not receive any DID calls from the PSTN (PRI). When we use the num-exp

command this fixes the issue, But when we do this we do not receive calls via the PSTN when we are NOT in SRST mode.

Thanks in advance


Re: No call from PSTN in SRST fall back mode

I would suggest you modify your Call Manager configuration to match the incoming numbers after number-expansion.

Create a dial-peer that matches the post expanded numbers and point it at call manager, then create a translation pattern on CM to convert the numbers back to your extension numbers. This way calls should be succesful when in SRST or not.


New Member

Re: No call from PSTN in SRST fall back mode

Im not sure I follow. num-exp 6104583378 3502

so I should creat a dial peer like this

dial-peer voice 4 voip

preference 1

destination-pattern 3502

voice-class codec 1

session target ipv4:

dtmf-relay h245-alphanumeric

Re: No call from PSTN in SRST fall back mode


You stated that when you are not in SRST mode and you are using number expansion the calls are not going through to the extensions. When you are in SRST mode it works, this is because the post expanded number matches the SRST extension number.

I'm assuming that your extension numbers in SRST mode and Call Manager mode are the same, therefore the number being sent to call manager isn't being matched if you num-expand it.

So looking at your 2nd posting my guess is that you currently send the whole incoming number (6104583378) to call manager using something like

dial-peer voice 123 voip

destination pattern 6104583...

session target ipv4:

Call manager understand the whole incoming number, but this then doesn't match when you drop to SRST because you only have 4 digit extensions and the numbers do not match.

so by using number expansion ALL the time and matching the expanded number (3502) in call manager (as per your config in your 2nd posting) instead of the DID number, when SRST kicks in the same number is matched on the router, that call manager is using.

In effect you are trying to make Call manager and SRST proccess the same digit strings and not different strings. Your suggested dial-peer looks correct, you then just needs to make sure call manager matches those digits.


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