Good afternoon. We've run into something as we're migrating a client from CUCM to a 3CX environment. We have an Adtran 924 running as an SBC, this handles the PRI calling and sends the calls in to 3CX or Call Manager as needed as we transition. The CUCM server and 3CX are trunked together so userse on each system can communicate What we experience is that even though a call from CUCM shows up at 3CX with the 4 digit extension pver the trunk, the call never rings properly until an inbound rule is also created that matches that 4 digit extension and routes it to the extension in 3cx. I guess my question is, is this normal behavior? If a SIP call shows up at the PBX with a host part matching an extension on the system, why is an inbound rule also required?