H.323 is a protocol group defined by ITU-T for transmitting voice on the Internet (VoIP). In addition to voice applications, the H.323 combines ITU-T T.120 series standards also provides voice communication and data collaboration mechanisms. Based on Megaco and SIP standards, H.323 is one of the main VoIP standards.
H.323 is a framework structure specification because it includes various other ITU standards. H.323 defines four major components for network-based communication systems: terminal Terminal, gateway Gageway, Gagekeeper, multi-point control unit MCU.
Terminal Terminal is a node device that provides real-time, bidirectional communication in a packet network, is also an end user equipment, can communicate with a gateway, multi-point access control unit. All terminals must support voice communication, voice and data communication, video and data communication, or communication with voice, data, and video.
The gateway provides a connection between the H.323 network and network terminals belonging to different protocol stacks. Such as traditional PSTN networks, SIP, Megaco endpoint.
Guan Gu is primarily responsible for the conversion between telephone numbers and IP addresses. They are also responsible for managing bandwidth and providing terminal registration and authentication mechanisms. At the same time, Guankee also provides services such as call transmission, call forwarding.
MCU establishes a multi-point meeting. The MCU is composed of forced multi-point control, providing call signaling, conference control, and an optional multipoint processor. The processor can be used for the exchange / mixing of the medium stream, and sometimes it can also be used to perform real-time code conversion processes for video and audio streams.
There are five types of information exchange of H.323 structures:
Audio (digitized) voice; video (digitized); data (file or image); communication control (function supports exchange, logic control channel, etc.); Control connection and session (installation and removal).
H.323 was first released in 1996, completed the latest version V5 in 2003.
Protocol structure
The protocols in the H.323 protocol group include:
Call control and signaling
H.225.0: Call Signaling Protocol and Media Stream Packetization (a sub-protocol using Q.931 Signaling Protocol) H.225.0 / Ras: Registration, License, and Status H.245: Multi-communication Control Protocol Audio Processing
G.711: Pulse code modulation of sound frequencies G.722: 7 kHz audio decoding (64 kb / s) G.723.1: Dual rate speech coding under multimedia communication of 5.3 and 6.3 kb / s. G.728: Voice decoding of 16 kb / s through low-time delay excitation linear prediction coding. G.729: Voice decoding of 8 kb / s is achieved by a co-challation structure-generation excitation linear prediction code. Video processing
H.261: Video codec for audiovisual services is provided under PX64 KPS. H.263: Low-bit rate communication video decoded data conference
T.120: This is a protocol group for data transfer between endpoints. It can be used to collaborate various applications, such as white writing boards, applications sharing, and common document management. T.120 uses a hierarchical structure similar to an OSI model. The top layer (T.126, T.127) is based on a low-level service (T.121, T.125). Media transmission
RTP: Real-Time Transfer Protocol RTCP: RTP Control Protocol Security
H.235: Security, encrypting auxiliary service for H series multimedia terminals
