[VoiceOps] Ringback issues when calling T-Mobile?

[Hunter Fuller]

Is anyone else getting an eerie lack of ringback when originating
toward T-Mobile?

We get a 183 Session Progress with media, then a 180 Ringing a third
of a second later. So the result is a 1/3 second long burst of
ringback and then silence. We are seeing if we might be able to start
locally generating ringback when we see the 180, but to be honest,
that's just a weird sequence of messages and I would never expect to
receive them in that order. So we didn't exactly plan for it.

The relevant trunk is from Comcast, but I highly suspect they are just
passing through what they got from T-Mobile (or whoever they route
T-Mobile calls through). We are in the north Alabama area and we have
heard of other customers with various carriers having similar issues.

Just wondering if anyone had a technical reason/explanation or any
more information.

--
Hunter Fuller (they)
Router Jockey
VBH M-1A
+1 256 824 5331

Office of Information Technology
The University of Alabama in Huntsville
Network Engineering