In H.323-compliant networks, a central point of control in a zone. Endpoints may communicate directly, in either a unicast or a multicast environment, if no gatekeeper is present. If a gatekeeper is present, all endpoints in its zone must register with it.The gatekeeper performs the function of admission control, determining if devices are authorized to connect and if there is sufficient bandwidth to support the call. Gatekeepers serve to translate LAN addresses into IP or IPX addresses, as defined in the Registration/Admission/Status (RAS) specification. Gatekeepers also can act to route H.323 calls through gateways, if necessary, and monitor the network bit rate capacity, with the ability to deny access to a session if programmable bandwidth thresholds have been reached or exceeded. Gatekeepers also can perform certain administrative functions, such as accounting, billing, directory, and collecting network usage data. Gatekeepers may be distinct network elements (NEs), or gatekeeper functionality can be incorporated into multipoint control units (MCUs). See also bit rate, endpoint, H.323, IP, IPX, LAN, MCU, multicast, NE, RAS, and unicast.