H.323是由ITU制定的通信控制协议，用于在分组交换网中提供多媒体业务。呼叫控制是其中的重要组成部分，它可用来建立点到点的媒体会话和多点间媒体会议。H.323定义了介于电路交换网和分组交换网之间的H.323网关（GateWay）、用于地址翻译和访问控制的网守（GateKeeper）、提供多点控制的多点会议控制器（MC）、提供多点会议媒体流混合的多点处理器（MP），以及多点会议控制单元（MCU）等实体-Developed by the ITU H.323 is a communication control protocol is used to provide multimedia services in the packet switched network. Call control is an important part of it, it can be used to establish media sessions between point-to-point and multi-media conference. H.323 defines the range of circuit-switched networks and packet switching network between H.323 gateways (GateWay), used for address translation and access control gatekeeper (GateKeeper), provides multi-point control of the multipoint controller ( MC), providing mixed multipoint multi-media stream processor (MP), and a multipoint control unit (MCU) and other entities