Electronic surveillance in a public switched telephone network

Abstract

Telephone network surveillance is provided for targeting subscriber terminals that receive service through an office lacking a switch with surveillance capability. A foreign exchange line is relied upon to connect the target's line to an office having that capability. Advanced Intelligent Network (AIN) functionality controls routing and billing of incoming and outgoing calls, so that the telephone network operations appear completely normal during the surveillance. In the office normally serving the target's line, a terminating attempt trigger causes that office to obtain instructions from a service control point (SCP), to route the call to the foreign exchange line terminated in the office with the surveillance capability. The instructions also prevent billing of the redirection through the surveillance office to either the called party or the calling party. An off-hook delay trigger set against the foreign exchange line in the surveillance office causes that office to obtain instructions from the SCP, to facilitate billing for the call as if initiated from the target's normal telephone line connection.