[Freeswitch-users] No Ringing tone when call is forwarded to PSTN

[Peter P GMX]

Hello,

we have the following scenario:
A PSTN call (A) is coming in to Freeswitch through a Patton gateway. For
the called FS user, call forwarding has been enabled to another PSTN
extension (B) .
Result: The calling party does not hear any ringing tone. Here an
Abstract of the SIP protocol we traced (PSTN(A) and PSTN(B) is in fact
the same Patton Gateway):

PSTN(A)====INVITE===>FS
PSTN(A)<===TRYING===>FS
                     FS===INVITE==>PSTN(B)
                     FS<==TRYING===PSTN(B)
                     FS<==RINGING==PSTN(B)
PSTN(A)<==PROGRESS===FS
                     FS<===OK======PSTN(B)
                     FS====ACK====>PSTN(B)
PSTN(A)<===OK========FS
PSTN(A)====ACK======>FS

I would expect that FS answers RINGING back to PSTN(A). Instead it only
answers SESSION PROGRESS.
When PSTN(B) answers, they can hear each other, but there was no ringing
tone to PSTN(A) before.

Are there any hints to overcome this, besides playing early media to
PSTN(A)?

Best regards
Peter