RADVision VIU-323, Руководство пользователя

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Overview
2-4
An Introduction to H.323
H.323 is the globally accepted standard for audio/video/data communications over IP-based
networks. It specifically describes how multimedia communications occur between user
terminals, network equipment, and assorted services on Local and Wide Area Internet
Protocol (IP) networks.
What is the H.323 Standard
H.323 is an umbrella recommendation from the International Telecommunications Union
(
ITU ) that specifies real-time multimedia communications over Internet Protocol-compliant
networks. It defines new models of interaction for both point-to-point and multipoint
conferences. For example, H.323 specifies how gatekeepers can provide address translation
and bandwidth management and how gateways can connect terminals on the LAN to those
on the WAN.
H.323 Network Components
The H.323 specification defines a number of new network components that interoperate
with other standards-compliant endpoints and networks by virtue of an H.323/H.32X
gateway.
Following are the network components defined by the H.323 standard:
Terminals
are the endpoints on the LAN which provide for real-time, two-way
communications. Most H.323 terminals are desktop computers running H.323 compliant
software. All terminals must support voice communications while video and data are
optional. However, if these other media are supported, H.323 specifies what modes of
operation are required so that all terminals supporting video and/or data can work
seamlessly together.
Gateways
are the devices that provide the needed translation services between H.323
conferencing endpoints on the IP network and other ITU-compliant terminals (for example,
H.320 room systems) on other circuit switched networks.
Gatekeepers
perform crucial control and administration tasks for H.323 entities while
providing network administrators the ability to incorporate management and security
policies into the network. Although the H.323 recommendation describes the gatekeeper as
an optional component of a functional H.323 system in practice the gatekeeper is essential.
The H.323 gatekeeper is responsible for providing address translation between LAN aliases
and IP addresses, call control and routing, basic telephony services such as directory
services and PBX functions, H.323 traffic bandwidth usage control and total network usage
control and the implementation of overall system management and security policies.