entication is a one-way form of authentication that is used only by Gatekeepers. It requires no prior contact between endpoints. The Gatekeeper uses this form of authentication to validate subsequent Gatekeeper directed requests and to verify that the requests are from a registered node. Symmetric Encryption-based Authentication does not provide a mechanism for the endpoints to validate the Gatekeeper's identity. Subscription-based Authentication requires prior contact or information exchange between the endpoints-usually through passwords or signed digital certificates. Each endpoint identifies itself with a well-known text string identifier. Subscription- based Authentication allows both endpoints to be authenticated and is, therefore, bi- directional. The Q.931 protocol uses a reliable IP transport-based mechanism to establish the first leg in a point-to-point session between two endpoints. The H.245 protocol is responsible for capability exchange communication and mode switching. H.235 integrity protection can enhance security by preventing tampering with the Q.931 and H.245 packets, by enabling complete encryption of the Q.931 streams, and by facilitating user authentication to verify end-points during the transmission of the call setup packets. H.450 H.450 comprises three recommendations for implementation of supplementary services to H.323. The formal names of those standards are, "H.450.1 - Generic Functional Protocol For The Support Of Supplementary Services In H.323," "H.450.2 - Call Transfer Supplementary Service For H.323," and "H.450.3 - Call Diversion Supplementary Service For H.323." All were approved in February 1998. These supplementary services are designed to enable IP networks to provide the telephony features that users have come to expect in conventional circuit-switched Standards for Videoconferencing networks and, conversely, to enable conventional circuit-switched networks to provide non-conventional services that are offered on IP networks. H.450 enables hybrid IP/circuit-switched networ