OS = Redhat FC 10
Fpbx version = FreePBX 2.7.0.5
Asterisk 1.4.36
Recording is on (mixmonitor)
Issue: Just recently any calls going to specific numbers through our SIP provider via “from-internal” are not showing a SIP 183 in stream. This causes the ringback to be missing entirely.
I should note the provider has stated they are forcing the 183. Typically I expect 100,180,200 (and 183 when requested.)
I created a custom dial out context exten => _X.,1,Dial(SIP/${EXTEN}@Excel,40,)
and assigned it to my specific extension for testing. Oddly when that specific context is used to dial a problematic number, the issue does not happen. Both “from-internal” and my custom context use the same peer entry in sip_additional.conf, as entered by the free pbx interface.
I am assuming this is (more or less) an issue with the provider’s media gateway that is manifesting itself through the different contexts.
I have a full (core + sip + verbose) dump of the two calls, as well as wireshark of both (see links below).
working: http://min.us/mveVeIA and http://pastebin.com/hGkKtfaq
vs
not working: http://min.us/mveQyTd and http://pastebin.com/SKZYMkst
The log dumps are a lot longer than I expected… 
I am working with the provider to figure this out, but ultimately the fact it signals two different ways based on the context used is perplexing.
Thanks in advance
Edit: see this third test. Works calling another number regardless of method or context. Odd.