The half-call model processes a call request in two phases:
Origination: The feature server applies services to the originator of the call.
Termination: The feature server applies services to the recipient of the call.
The origination phase and the termination phase are separate operations that different feature servers perform.
The half-call model supports full application sequencing. The number of originating sequenced applications can be different from the number of terminating sequenced applications.
