[VoiceOps] Strange Call Flow

[Tim Donahue]

I'm seeing a strange call flow from a client with a Cisco CUBE setup.
This is happening when they attempt to forward a call from their system
to a PSTN line.

SBC                          CUBE
 | ----------INVITE---------> |
 | <------100 Trying--------- |
 | <------180 Trying--------- |
 | <--183 Session Progress--- |
 | <--------200 OK----------- |

I've never seen a call setup that switched from a 180 Ringing to a 183
Session Progress mid-setup before, and it seems to be doing funny things
to the media transport through our SBC (we see audio come in from one of
the call legs but it doesn't get forwarded to the other call leg).  Is
this a legal call flow that we should add to our tests when evaluating
new hardware?

Has anyone seen problems like this before?

Tim