I previously wrote about how CM determines proper inbound call delivery (inc-call-handling-trmt), but might loosely be considered the DID -> Extension association. But… the inc-call-handling-trmt tables only tell CM how to figure out which extension to which a call should be delivered; they don’t actually associate DIDs with extensions. So how does CM determine the outbound calling party number when a station/extension makes an outgoing call? Enter public-unknown-numbering.
Incoming call handling treatment is the administrative function used to instruct CM how to route incoming calls traversing specific trunks.