1.2.1. H.323 Entities

The H.323 specification defines the entity types in an H.323 network including:

• Terminal - An endpoint on an IP network, that supports the real-time, two-way communication with another H.323 entity. A terminal supports multimedia coders/decoders (codecs) and setup and control signaling.
• Gateway - Provides the interface between a packet-based network (for example, an IP network) and a circuit-switched network (for example, the PSTN). A gateway translates communication procedures and formats between networks. It handles call setup and teardown and the compression and packetization of voice information.
• Gatekeeper - Manages a collection of H.323 entities in an H.323 zone controlling access to the network for H.323 terminals, Gateways and MCUs and providing address translation. A zone can span a wide geographical area and include multiple networks connected by routers and switches. Typically there is only one gatekeeper per zone, but there may be an alternate gatekeeper for backup and load balancing. Typically, endpoints, such as terminals, gateways and other gatekeepers register with the gatekeeper.
• Multipoint Control Unit (MCU) - An endpoint that support conferences between three or more endpoints. An MCU can be a stand-alone unit or integrated into a terminal, gateway, or gatekeeper. An MCU consists of:
  • Multipoint Controller (MC) - Handles control and signaling for conferencing support.
  • Multipoint Processor (MP) - Receives streams from endpoints, processes them, and returns them to the endpoints in the conference.

Figure 1 shows the entities in a typical H.323 network.

Figure 1. Typical H.323 Network

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