Life Cycle of a Call
The routing state looks in the dial plan module. It then builds a to-do list with name value pairs.
The execute state does the stuff found in the routing stage. The name value pairs are parsed and executed.
The hangup stage either transfers the call back to the routing stage, if there is a name value pair that requests it. Else it will hang up the call.
A separate page describes each of the the channel states.