asterisk users - Nov 2010 - Ringback problem. Order of "183 Session Progress" and "180 Ringing"

Chris Abel writes:
>Hello everyone!
>
>I've had this problem for a while and cant figure it out. When an
outside
>caller calls an extension on my asterisk system, they do not hear any
>sort of ringing. Inside extensions calling other extensions do hear
>ringing. We have 3 other asterisk systems that are configured the same
>way, but do not have this problem. We think it has something to do with
>asterisk 1.6. The other asterisk systems are using 1.4. I have played
>around with "progressinband" in sip.conf with now success.
Whatever I set
>progressinband to, it doesn't seem to change a thing. "183 Session
>Progress" never seems to be called when looking at sip debug. It is
only
>when I use the Progress application before my dial command that I get the
>"183 Session Progress" message in sip debug.
>
>We also have a Trixbox system using asterisk 1.6 that had the same
>problem. The way I fixed that was to set progressinband=yes in sip.conf.
>This did not work with this system (Yes I know Trixbox is completely
>different).
>
>The only thing that looks different is the order in which "183 Session
>Progress" and "180 Ringing" get sent in sip debug. On the
troubled
>Asterisk system 183 gets sent before 180. On the fixed Trixbox system 180
>gets sent before 183. Does this mean anything? We also have Polycom
>Phones which I heard are notorious with ringback issues.
>
>Thanks,
>Chris
I should also say that I tested moh instead of ringing and that works
fine. Very weird.

-Chris