Any ATC Expert here to clarify CPDLC Process?

[arvindasija]

1. Yes, if your operator forgets to update the ATC centers with an updated FPL, especially the REG and CODE( Airframe ID), the CPDLC connection is never successful. This happens when there is a change of airplane prior to departure.
2. A level change message goes directly to the controller as a CR ( clearance request)
3. Well, when the controller gets the CR, he evaluates the request and the feasibility of acceptance. If traffic permits, he triggers a response containing clear instructions , else UAB ( Unable).