Library items tagged: standards

The main standard in use for data sharing within videoconferencing is T.120 Equipment that is T.120 compliant interleaves the data sharing information within the pass band of the H.320, H.323 etc. conferencing channel. This is an asset as sound, vision and data are shared across a single channel, but it can also be a hindrance as with low bandwidth channels, e.g. ISDN2, the T.120 data exchange part can degrade the audio and video signals to an unacceptable degree. For further information, see the VTAS guide, Data Sharing within Videoconferencing.

Manufacturers may also choose to include proprietary enhancements, e.g. Polycom’s Siren Audio extends the audio bandwidth up to 14kHz to improve the sound quality. These proprietary enhancements are not international standards so only provide a benefit when used between products from the same manufacturer. Proprietary standards should not be confused with ‘options’ within the ITUT standards. The options are not mandatory but when incorporated will allow improved compatible communication between dissimilar equipment without problems.

Within each ITUT umbrella standard, minimum mandatory standards are defined that will guarantee compatibility, albeit at a basic level, e.g. within H.320 provision must be made for H.261 video coding, G.711 audio coding and H.221, H.230, H.242 communications protocols. Similarly for H.323, the corresponding mandatory standards are H.261, G.711 and H.225/H.245 communication protocols. These mandatory requirements will allow all compliant products to communicate easily and effectively.

Dr Syngen Brown of the University of London Computer Centre (ULCC) has made most helpful and detailed comments on the standards. Polycom® is a registered trademark of Polycom in the U.S. and various countries.  A videoconference link requires: