Out bound route from CUCM to PSTN trough Asterisk

I have an outbound route on my CUCM so I can call out side, when I call the range of ext for asterisk they work correctly however if I try to dial an external number form cucm it is ringing my ring group that I have configure for inbound. how can I configure a route so when a call comes from ext 1xxx with a dial number xxxxxxxxx and routes it to the pstn