WE had an issue where when trying to do a trunk to trunk on Talk Talk SIP trunks the call would fail.
From the trace we could see the outgoing leg of the call was being denied.
I Wireshark trace shows error code 630 denied
We found if we made these changes the Trunk to Trunk worked fine
On the SIP peer profile set
Use diverting party number as calling party number to YES
and
Use original calling party number if available to NO
To me this sounds like Talk Talk wont allow the original callers cli to be presented to the final destination.
Does the forum agree?
Thanks for any imput
MY blog with pictures of changes
http://phonesystemhelp.info/fix-trunk-to-trunk-calls-fail-on-talk-talk-sip-trunks-error-630/