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Umbrella Standards

The H.320 ITU-T recommendation regulates the basics of video communication on the circuit-switched narrowband ISDN network. The bandwidth ranges between 64 kbps and 1920 kbps and is provided in the form of individual channels, up to 64 kbps each.
In the current language the channel type H12 with 1920 kbps is called S0-connection.

In this standard the requirements for audio and data processing are defined and formats are specified for the media transmission. Furthermore, additional protocols for call signalling are displayed as well as the synchronisation of the communication links.

H.323 is an international ITU standard for the communication of speech, data and video on package-based networks which determines specific abilities of end devices in the IP area. This standard derives from the H.320 standard and defines gateways to ISDN and ATM. A further function is to guarantee the interoperability between the manufacturers products as well as to describe four main groups and its communication among one another: Terminals, Gateways, Gatekeeper und MCUs (Multipoint Control Units).

The standard defines the multimedia communication on LANs which do not provide a guarantee of service. This standard tries to minimize the negative effects thereby caused, like package loss, jitter or other delays during multimedial real-time services.

H.323 updates constantly and is available in version 7.0 since December 2009. The original title 'Visual telephone systems and equipment for local area networks which provide a non-guaranteed quality of service' has already been changed in the version 2.0 in 1998 into "Packet-based multimedia communications systems".

H.323 is a so-called umbrella standard which sums up also other standards. It defines e.g.

The data transmission is specified by means of H.239. This protocol isn't a component of H.323 but is closely linked in content.

Further standards

The standards H.310/H.321/ H.322/ H.324 don't have any practical importance for today's video conferences (IP respectively ISDN conferences). However, for the sake of completeness, they are listed below:

Standard H.310 enables an adaptation of the MPEG-2 standard for the communication via broadband networks, by means of H.262 and H.222.0. It's closely linked in content with H.322.

Standard H.321 is the adaptation of H.320 for broadband networks. The underlying infrastructure didn't change, but the cooperation between narrow and broadband networks has improved.

Standard H.322 is the basis of video communication on reliable and package-oriented networks. The physical basis is formed by a network, where beside of a 10 Mbps channel, also an isochronal (special form of the asynchronous transmission with time-stamping) 6 Mbps channel is provided for multimedia with a guaranteed bandwidth (QoS, Quality of Service). The signalization runs by H.242 unlike the H.310.

Standard H.324 defines necessary techniques for audiovisual communication via analogue modem connections. The modem standard V.34 defines the network interface with 33.600 kbps. Thus, using highly compressed Codecs like H.263 (video) and G.723.1 (audio) is compulsory.