AT&T SIP Trunk in USA - Setting for Redirected Calls

[TONY SMITH]

Hi,

Just wondering if anyone uses an AT&T SIP service in the US, and can confirm what settings or headers are needed for redirected calls (such as CFA) to work while presenting the original calling number. 

When I first looked at the system they were sending the original calling party number in the From and Contact headers, without PAI or Diversion headers.   These were being rejected with "403 Forbidden".

As a quick test I set a rule to re-write the calling number to one of their inbound DDIs and with that bodge in place the calls work.

So something is needed but in my experience there's no consistency between ITSP as to how they want this handled.  So it would be pure guesswork unless I either get an answer out of AT&T (an issue in itself!) or if someone has already been through this.

Thanks, Tony S

[TONY SMITH]

I may have found the answer to my own question.  No sign of any response or assistance from AT&T, which doesn't bode well if the customer ever has a more serious fault.  However I found a Cisco document from a few years back indicating that AT&T are looking for a Diversion header containing the full diverting number in 10 digit format. 

This particular customer has a pile of DDI ranges and four digit extensions so doing exactly would be pretty fiddly so I'm going to suggest a compromise of using the main billing number.  That way I can use a single static rule in the profile.   This might mess up itemised billing, but I can't think of any other downside.  I think I saw in previous discussion that there's no way to make CUCM apply the external number mask to the Diversion header.