Fig. 2 shows a simplified, yet common H.323 architecture.

The gatekeeper functions as the H.323 manager, provides

required services to registered clients (such as address

translation, admission control, signaling, authorization,

etc.), and is the central control point for all calls within

its zone. Like an SIP gateway, the H.323 gateway acts as a

call endpoint to provide connectivity to other networks.

When required, the multipoint control unit (MCU) acts as

an endpoint to provide a capability for three or more UAs.

The MCU consists of the multipoint controller (MC) and

an optional multipoint processor (MP). The MC controls

conference resources and determines the common capabil-

ities and functions of the call agents. The MP is controlled

by the MC and performs codec conversions when neces-

sary, multiplexes and demultiplexes the media streams,

and distributes the media.