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H.323 Protocol Overview

Protocol Standard

The H.323 protocol is an International Telecommunication Union (ITU-T) standard that describes transmission for packet-based video, audio, and data conferencing. The current ITU-T recommendation, known as Version 2.0, was ratified by Study Group 16 of the Telecommunications Sector. H.323 is an umbrella standard that refers to these other standards:

• The H.225.0 standard includes the following:

• Q.931 for call signaling (setup, teardown)

• RAS for Registration, Admission, and Status

• RTP/RTCP for media stream packetization and synchronization

• H.235 for security

• H.245 for call control (capabilities, master/slave, logical channel)

• H.261 and H.263 video codecs

• H.450 for supplementary services

• G.711, G.728, G.729, G.723 audio codecs

Allows Multimedia

The H.323 protocol is used for multimedia (audio, video, and data) conferencing over packet networks. The goal of H.323 is to allow multimedia communication devices to interoperate regardless of the type of network those devices are connected to.

H.323 in Packet Networks

H.323 can be used on top of any packet network transport layer, such as Ethernet, IP/TCP/UDP, ATM, and Frame Relay. H.323 uses the Internet Protocol (IP) for internetwork conferencing.

ITU-T standard defines a set of call control, channel setup, and codec specifications for transmitting real-time voice and video over networks that do not offer guaranteed service or quality of service.
International Telecommunications Union (UN)
International Telephone Union – Telecommunications sector (UN)
Call signaling protocol for setup and termination of calls.
The Registration, Admission, and Status messages communicated between two H.323 entities for example between an Endpoint and a Gatekeeper.
Real-Time Transport Protocol. Supports transport of real-time data like interactive voice and video over packet-switched networks.
Real-Time Transport Control Protocol.
The protocol used in most local area PC networks. Typically, most Ethernet networks support data transmission speeds up to 10 Mbps, but 100 Mbps is also possible.
Internet Protocol. Part of the TCP/IP family of protocols used to route messages and tracks the addresses of nodes.
Asynchronous Transfer Mode
A group of data bits in a specific format, with a flag at each end to indicate the beginning and the end of the frame.