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Contents
Chapter 1
Standards
At present, most videoconferencing must take place between participants who are each using
the same videoconferencing software package since packages from different vendors tend to
use their own proprietary compression schemes and control protocols. This may be acceptable
for internal organisational communication where a de facto standard hardware/software policy
has been adopted but is obviously fairly prohibitive where different organisations, possibly
in different countries, or participants on different platforms, wish to conference.
The answer is, of course, an international standard for videoconferencing communication.
The
relevant standard in this area, which is currently being adopted by the computer industry, is
called H.320. It is a ITU-T (International Telecommunications Union - Telecommunications
Standards Section), formerly CCITT, standard which encompasses several subsidiary standards
for: communications protocol (H.242), audio/video synchronisation (H.221), video
compression (H261) and audio (G.728, G.722, G.711) transmissions. The H.261 standard was
developed to work over Px64 digital channels (64 Kbits/sec to 2.048 Megabits/sec). H.320
also includes standards to handle multi-way conferencing with ISDN (H.231 and H.243) and
will also eventually include a standard covering document sharing or whiteboard (T.120).
H320 is a relatively recent development and products which support it are only just beginning
to appear. In fact, at the time of writing, we have seen several glossy brochures claiming
support for it, but we have not seen a delivered product. If other new standards are anything
to go by it is probably premature to assume that H320 will provide a short-term answer to
cross-product and cross-platform videoconferencing.
In fact vendors have been developing their own 'standards' and it is possible that one or
more
of these could develop into a de facto standard if one of these vendors begins to dominate the
market. CELLB for video compression from SUN and Indeo from Intel are two such
candidates. We found in our study that video performance using Showme which uses CELLB
was noticeably better than that using the public domain item IVS which uses H261. This may
be an indication that the H320 group of standards could become outdated quickly and will
increase the likelihood that a dominant vendors product (likely to be in the Windows market)
will become a de facto standard.
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