we are experiencing the following problem:
we have a SIP trunk from our Call Manager (ver 5.1.3) to our IPT provider. When a call comes over this trunk to an IP phone and then gets transfered, there is music on hold, but no ringback tone after that.
This scenario works fine when calls go over GSM gateway and not over that SIP trunk. If the call is internal it also works fine.
I've tried setting 'Send H225 User Info Message' parameter but that doesnt help.
I also tried different trunk settings, but nothing seems to help. Does anyone know of any solution to this problem?
Or could it be that this has something to do with the IPT provider?