# Call control and gateway applications

Gateway applications perform call control for calls that must be switched between separate trunks. They perform a switch-like function, such as directing inbound calls from the PSTN to appropriate addresses on an internal network (the application may also be embedded in the PSTN itself). Typically, these applications receive inbound calls, analyze the incoming addresses, and then place calls to the specified addresses.

Accepting and rejecting calls with gateway applications can pose problems because the decision to accept or reject an incoming call depends on the status of the associated outbound call. However, the time available in the incoming call protocol to accept the call can be shorter than the setup time for the corresponding outgoing call. For more information about gateway call control, refer to Accepting calls through gateway applications and Rejecting calls through gateway applications.