We have a problem where no ringback is generated to the PSTN when our SIP outbound provider sends a "183 session progress". Another SIP carrier we use sends "180 ringing" and ringback is generated.
The problem manifests itself when an IP phone is set to call forward to a mobile.
Call flow would be as follows;
PSTN--->H323 gateway---> CCM --->SIP
We are using CCM 6.1.3, the H.323 gateway is a 5300 running 12.3.15a, SIP is our outbound provider
We have tried settings outlined in below links but to no avail
Has anyone experienced a similar issue? Any help appreciated