What is the difference between service and channel?

What is the difference between service and channel?
Channel is a path that can be physical or virtual.Service is a set of transparant (not visable) jobs that give a preset outcome.Example: Telephone service. You pick up the phone and dial a number. The phone on the other end will ring.
Example: Ask a waiter for coffee and donut. The waiter will do that task for you. You however will not know all the tasks he will have to perform.