iPedia Free Information Center

Information about H.323

H.323 is an umbrella recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network. It is currently implemented by various Internet real-time applications such as NetMeeting and Ekiga (the latter using the OpenH323 implementation). It is a part of the H.32x series of protocols which also address communications over Integrated Services Digital Network (ISDN), Public switched telephone network (PSTN) or Signaling System 7 (SS7). H.323 is commonly used in Voice over IP (VoIP, Internet Telephony, or IP Telephony) and Internet Protocol (IP)-based videoconferencing. Its purpose is thus similar to that of the Session Initiation Protocol (SIP).

History

H.323 was originally created to provide a mechanism for transporting multimedia applications over LANs but it has rapidly evolved to address the growing needs of VoIP networks.

One strength of H.323 was the relatively early availability of a set of standards, not only defining the basic call model, but in addition the supplementary services, needed to address business communication expectations. H.323 was the first VoIP standard to adopt the Internet Engineering Task Force (IETF) standard Real-time Transport Protocol (RTP) to transport audio and video over IP networks.

H.323 is based on the ITU-T Recommendation Q.931 protocol and is suited for transmitting calls across networks using a mixture of Internet Protocol and QSIG over ISDN. A call model, similar to the ISDN call model, eases the introduction of IP telephony into existing networks of ISDN-based PBX systems, including transitions to IP-based Private Branch eXchanges (PBXs).

Within the context of H.323, an IP-based PBX is a H.323 Gatekeeper, as well as a provider of supplementary services.

Protocols

H.323 references many other ITU-T protocols like:
  • H.225.0 protocol is used to describe call signaling, the media (audio and video), the stream packetization, media stream synchronization and control message formats.
  • H.245 control protocol for multimedia communication, describes the messages and procedures used for opening and closing logical channels for audio, video and data, capability exchange, control and indications.
  • H.450 describes the Supplementary Services
  • H.235 describes security in H.323
  • H.239 describes dual stream use in videoconferencing, usually one for live video, the other for presentation
  • H.460.17-19 describes firewall traversal in H.323
  • H.261 H.263 H.264 describes video encoding

External links

General Information Papers Projects
The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland.
..... Click the link for more information.
Microsoft NetMeeting is a VoIP and multi-point videoconferencing client included in many versions of Microsoft Windows (from Windows 95 OSR2 to Windows XP). It uses the H.
..... Click the link for more information.
Ekiga (formerly called GnomeMeeting) is a free and open source VoIP and video conferencing application for GNOME and Windows. Ekiga supports both the SIP and H.323 (based on OpenH323) protocols and is fully interoperable with any other SIP compliant application and with
..... Click the link for more information.
The OpenH323 project goal is developing a full featured, open source (MPL) implementation of the H.323 Voice over IP protocol. The code is written in C++ and, through the development effort of numerous people around the world, fully supports the H.323 protocol.
..... Click the link for more information.
Integrated Services Digital Network (ISDN) is a circuit-switched telephone network system, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in better quality and higher data speeds than are available with analog.
..... Click the link for more information.
The public switched telephone network (PSTN) is the network of the world's public circuit-switched telephone networks, in much the same way that the Internet is the network of the world's public IP-based packet-switched networks.
..... Click the link for more information.
SS7 protocol suite
Layer Protocols
Application INAP, MAP, IS-41...
TCAP, CAP, ISUP, ...
Transport SCCP
Network MTP Level 3
Data link MTP Level 2 ...
Physical MTP Level 1 ...
..... Click the link for more information.
Voice over Internet Protocol, also called VoIP, IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of voice conversations over the Internet or through any other IP-based network.
..... Click the link for more information.
Internet protocol may refer to:
  • The Internet Protocol, a data-oriented protocol used for communicating data across a packet-switched internetwork
  • The Internet protocol suite, a set of communications protocols that implement the protocol stack on which the Internet runs

..... Click the link for more information.
A videoconference (also known as a videoteleconference) is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously.
..... Click the link for more information.
The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants.
..... Click the link for more information.
Voice over Internet Protocol, also called VoIP, IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of voice conversations over the Internet or through any other IP-based network.
..... Click the link for more information.
Internet Engineering Task Force (IETF) develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standard bodies; and dealing in particular with standards of the TCP/IP and Internet protocol suite.
..... Click the link for more information.
The Real-time Transport Protocol (or RTP) defines a standardized packet format for delivering audio and video over the Internet. It was developed by the Audio-Video Transport Working Group of the IETF and first published in 1996 as RFC 1889 which was made obsolete in 2003 by
..... Click the link for more information.
The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland.
..... Click the link for more information.
ITU-T Recommendation Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet Protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN
..... Click the link for more information.
Internet protocol may refer to:
  • The Internet Protocol, a data-oriented protocol used for communicating data across a packet-switched internetwork
  • The Internet protocol suite, a set of communications protocols that implement the protocol stack on which the Internet runs

..... Click the link for more information.
QSIG is an ISDN based signaling protocol for signaling between private branch exchanges (PBXs) in a Private Integrated Services Network (PISN). It makes use of the connection-level Q.931 protocol and the application-level ROSE protocol.
..... Click the link for more information.
Private Branch eXchange (PBX) is a telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company operates for many businesses or for the general public.
..... Click the link for more information.
Private Branch eXchange (PBX) is a telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company operates for many businesses or for the general public.
..... Click the link for more information.
An H.323 Gatekeeper serves the purpose of Call Admission Control and translation services from E.164 IDs (commonly a phone number) to IP addresses in an H.323 telephony network. Gatekeepers can be combined with a gateway function to proxy H.
..... Click the link for more information.
The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland.
..... Click the link for more information.
H.225.0 is a member of the H.323 family of protocols.

The main objective of H.225.0 is the definition of messages:
  • Call Signaling: establish, control and end an H.323 call. The call signaling of H.225.

..... Click the link for more information.
H.245 is a control channel protocol used with[in] H.323 communication sessions, and involves the line transmission of non-telephone signals. It also offers the possibility to be tunneled within H.225.0 call signaling messages. This eases firewall traversing.

H.
..... Click the link for more information.
H.450 refers to a set of standards created by the International Telecommunications Union (ITU) to define several Supplementary Services of the packet based telecommunication protocol known as H.323.
..... Click the link for more information.
H.235 covers security and encryption for H.323 and other H.245 based terminals.

The standard addresses authentication by means of several algorithms, including Diffie-Hellman methods, and privacy. Privacy allows for encryption, also of the media streams.
..... Click the link for more information.
H.239 is an ITU-T recommendation from the H.32x Multimedia Communications' macrofamily of standards for multimedia communications over various networks.

The H.239 recommendation is titled "Role management and additional media channels for H.
..... Click the link for more information.
A videoconference (also known as a videoteleconference) is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously.
..... Click the link for more information.
H.261 is a 1990 ITU-T video coding standard originally designed for transmission over ISDN lines on which data rates are multiples of 64 kbit/s. It is one member of the H.26x family of video coding standards in the domain of the ITU-T Video Coding Experts Group (VCEG).
..... Click the link for more information.
H.263 is a video codec standard originally designed by the ITU-T in a project ending in 1995/1996 as a low-bitrate compressed format for videoconferencing. It is one member of the H.26x family of video coding standards in the domain of the ITU-T Video Coding Experts Group (VCEG).
..... Click the link for more information.


This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus


page counter