I have some problem, I use CUCM7.01 create a sip trunk to my GW2811. GW2811 connection PSTN use ISDN PRI. When I make a call to my cellphone, after finish dial the number, I hear the ringback immediately. but my cellphone not ringing, because connection don't establish. I think the ringback is GW2811 provide. For testing, I change GW mode to H.323, and make call, that call will normal, I can hear ringback until my cellphone ringing, that ringback is music provide form ISP, SIP trunk did not hear that. The real problem is use sip trunk call cellphone, cellphone ringing but hang up the call, This time IPphone still listen normal ringback! not busy or disconnect.
My English is bed, hope everyone can understanding and help me to resolve that problem. THX
You should go to the Cisco CallManager Service Parameter Configuration page. In Clusterwide Parameters (Device - SIP) make sure SIP Rel1XX Enabled is set to Send PRACK for all 1xx Messages.
Also check if you are using a IOS release later than 12.4(20)T on your VGW.