SIP line forwarding issue

[JADF]

We are migrating our lines from E1 to SIP.

We encountered a specific scenario where the SIP line on the gateway is translated to a CUCM extension that has Call Forward All enabled to an external mobile number. In this case, when an external caller dials the SIP line, he hears a message stating that the number does not exist. If Call Forward All is deactivated, the call rings directly at the extension without any problems.

At present, both the E1 and SIP lines are active, and in this scenario, the forwarded outgoing call uses the E1 line instead of the SIP line.

I’ve attached the config file and a file containing the outputs of ccsip all, voip ccapi inout, and ISDN q931 for your reference. (original caller: xxxxxxx086, Sip line number on the router: xxxxxxx551 translates to 7014 which is forwarded to the external mobile number: xxxxxxx032)

Could you kindly help me identify the root cause of this issue?

[JADF]

I contacted the ITSP, and they said that we cannot receive a call and forward this same call over the same sip trunk.

Is this possibly true?

[Roger Kallberg]

I would push back to the SP on that. It’s quite common to do what you do. Often you’ll need to send either Diversion header or PAI header to the SP in the SIP dialogue to be able to do what you’ve outlined.

[JADF]

Thanks for the response Roger. 

I wanted to make sure that I understood your point.

You mean that I should send the diversion header or the pai header explicitly? Or what I'm doing here should be fine?

[Roger Kallberg · Accepted solution]

Service providers often require that a Diversion or P-Asserted-Identity header is sent with a number that belongs to your assigned DID numbers to allow calls from a number that doesn’t belong to your own number range.

[JADF]

Thanks Roger, this was really helpful