How it H.323 Works

An H.323 terminal is an endpoint in a LAN that participates in real-time two-way communications with another H.323 terminal, gateway, or multipoint control unit (MCU). H.323 endpoints are grouped together in zones, and each zone has one gatekeeper that manages all the endpoints in that zone. Each terminal must support audio communication, but they also can support audio with video, audio with data, or a combination of these capabilities.

H.323 can be referred to as “intelligent endpoint protocol,” which means that all the intelligence required to locate the remote endpoint and to establish media streams between the local and the remote device is an integral part of this protocol. “Device control protocols” are complementary to H.323, and those current protocols are H.248 and MGCP.


Basic Usage
To understand how H.323 is used, it helps to understand how the gateway works. In VoIP, the gateway usually is a device that offers an IP interface on one side and some sort of legacy telephone interface on the other side.gateways were viewed as monolithic devices that had call control provided by H.323 (or SIP) and hardware required to control the PSTN interface.

The H.323 gateway can provide an interface between H.323 and a PSTN, but it also can provide an interface between H.320, V.70, H.324 and other speech terminals. H.323 uses CODECs to convert between circuit-switched and packet formats, and works with the gatekeeper through RAS protocols to route signals from voice and fax through the network.