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New Member

Basic question on SRST and inbound calls

Imagine I have Cisco 2911 - SRST with 4FXO ports, CME licenses and 4 POTS lines at my disposal. Sites connected via MPLS backbone, main hub processes calls via SIP Trunking (Cisco CUBE). CUCM 8.5 and Cisco Unity Conn 8.5 on main hub.

Let's say Branch1 phone number is 408-111-1111.


Let's say MPLS circuit for the remote office goes down hard.

I totally understand people from the branch office could happily make phones calls from the branch to 911 and outbound calls to anyone on the PSTN.

Now a stupid question:

Is it possible an external user, on the PSTN, call the branch office using still that 408-111-1111 phone number? Or  because the POTS lines have a different DID now inbound calls now has to be made using the respective DID for those POTS lines?

If it is possible to still reach Branch1 using 408-111-1111, which type of configuration is required on CME or CUCM to make this work?

Hall of Fame Super Silver

Re: Basic question on SRST and inbound calls

Where does 408-111-1111 normally arrive to? CUBE?

If so then you would need to have forwarded to the pots line at branch site.

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New Member

Re: Basic question on SRST and inbound calls

Yes, it would be delivered via SIP trunking to the CUBEs in the main hub first.

So should I plan to put a configuraton in the CUBE to make it forward automatically to the respective POTS line DID in the branch office? Is that thought correct?

But then how do I that logic to see if the target remote site is down, then if it is, forward it to the POTS_Line_backup_phone...?

Thanks for your patience.

New Member

Re: Basic question on SRST and inbound calls


You are looking for Call Forward Unregistered (CFUR).  Communication between the IP Phone and CUCM will be lost and CUCM will call the phone as "unregistered".  Under the call forward settings of the phone you need to specify the DID of the POTS number including your outbound dialling prefix (9 or 0) and a CSS which will allow all calls out the SIP trunk (No COR). When a call from the SIP trunk hits the CUCM the call is forward once the phone becomes unregistered.


Hope this helps

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