Call security system

Abstract

An access-control module (22) is used in connection with a conventional private branch exchange (12) to control direct inward service access (DISA), by which callers calling in on one trunk are afforded access to an outgoing trunk or other destination within the PBX environment. The access-control module (22) is simply plugged into an existing extension, and the PBX (12) initially directs to that extension all calls from the incoming trunk. The access-control module (22) receives the users' authorization code and desired destination and then signals the PBX in the normal manner to transfer the call to an outgoing trunk or other destination within the PBX environment if the incoming call meets certain criteria imposed by the access-control module (22). Specifically, the access-control module (22) compares the current level of traffic for the user with that user's historical norms and either denies access to the outgoing line or requests further identification if deviation from the norms exceeds predetermined limits.

Dependencies are inferred from the claim text.