H.323 (contd)
Terminals: All terminals must support voice; video and data are optional.
Gateway: an optional element which provides translation functions between H.323 conferencing endpoints (esp for ISDN, PSTN)
Gatekeeper: most important component which provides call control services
Multipoint Control Unit (MCU): supports conferences between three or more endpoints. Consists of a Multipoint Controller (MC) and Multipoint Processors (MP).