Hi we have a cucm system (v8.X) with a sip trunk to a SIP pbx and H323 gateway to the PSTN. All works fine regarding calls in/out between PSTN and both the cucm and SIP PBX. However if we receive an external call to an extension on the SIP PBX and then try to transfer it to another PSTN number, the call fails with fast busy tone when the far end answers. we have G711 codec throughout and have tried HW conference and transcoder resources local on the gateway with no luck.
Any Ideas? Will changing the gateway to MGCP help?