These are not different channels but different uses of the control channel. Let's clear up this terminology confusion by looking at call processing. We'll look at the way AMPS sets up calls. We'll also touch on a number of new terms along the way. The control channel and the voice channel, paired frequencies upon which information flows.
Paths indicate direction of flow.
Actually, I can't think of a case where it would not be. But we don't think of it that way in the business. We have a set-up channel and we have voice channels. If you ask an engineer in an AMPS system what channels he has on a cell, he'll automatically give you the voice channels. Set up channel is a separate question.