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Emergence of IP telephony applications in recent years has opened numerous technical and legal problems. A particular problem in implementing IP telephony services is complying with legal requirements imposed on telephony service providers in many countries. Certain legal requirements are easy to fulfill in the conventional public circuit-switched telephone network, but present significant problems in IP telephony. One of these requirements is the possibility of electronic surveillance by authorized law enforcement agencies, i.e. wiretap service. Currently, there is no standard solution for call interception in IP telephony networks. We describe four proposed basic methods for implementing a call interception system in IP telephony networks based on the ITU-T H.323 standard. The proposed methods are Wiretap on Gateway, Wiretap Routing on the Gatekeeper, Fixed Route Wiretap, and Promiscuous Wiretap. We examine each of these four methods and show their basic advantages and disadvantages.

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