User`s guide

They analysed several live debate/interview television programmes, and came up with a system
that automatically changed the camera view depending on a simple transition table. A limited
amount of feedback has been obtained so far, but users seem more comfortable with the system
than with a static camera angle.
The solutions to various human interface concerns are mostly yet to find their way into commercial
systems, but features such as AMX control are available for remotely controlling cameras (PictureTel
2000, First Virtual 2000), allowing users some camera interactivity.
2.3 Features of Videoconferencing Systems
Currently, only 10-15% of enterprise networks use video over IP (Perey 2000), but most who do
use it for streaming video, not for videoconferencing. For interactive videoconferencing, a network
bandwidth of 600 Kbit/sec is required, although 800 Kbit/sec or greater is ideal (Perey 2000).
ATM (Asynchronous Transfer Mode) combines the best of packet switching (like Ethernet) and
circuit switching (like ISDN) and for this reason is generally considered well-suited for videoconfer-
encing (Fish 1994), because it can handle sustained high-data rates in the presence of both voice
traffic and data bursts.
Many commercial systems have now been developed. First Virtual Corporation (FVC) have a
range of videoconferencing products, including the Video Access Node (VAN), and the VAN II, used
by Monash University.
The VAN (First Virtual 2000) provides high-quality videoconferencing, using MPEG-2 codecs
(compressor-decompressor). First Virtual claims that its video is comparable to that of VHS or
laserdisk systems. The VAN uses the H.310 standard. The VAN implements encoding and transfer
over ATM networks, including “long haul” ATM networks for wide area access. The VAN has a low
latency (delay between transmission and reception). This is an important feature because it allows
for use in business conferences, distance learning and medical applications. It supports both NTSC
and PAL television formats. The VAN uses integrated software running under Microsoft Windows
NT or IBM OS/2.
The VAN allows full-duplex audio, so that sound is received and transmitted simultaneously. This
can cause audio feedback, so an echo canceller is required. The VAN includes an echo canceller. Echo
cancellation is important for all videoconferencing systems (and also audioconferencing systems) that
allow full-duplex audio, and this is easily handled by hardware systems (First Virtual 2000).
Comparable commercial systems to First Virtual’s VAN include PictureTel’s Concorde series and
VTEL’s room systems. These are both commercial systems which use televisions or other video
output that accepts RGB or S-Video input, such as a projector. There are intended to be used as
group systems.
There are many videoconferencing standards (Cool 1992). The most commonly used are the
ITU’s Series H standards H.320 (for ISDN), H.321 or H.310 (for ATM), and H.323 (for IP), as well
as MPEG-2. H.323 is used mainly for software-based videoconferencing products, especially two-way
conferencing on PCs. The other standards are mainly used for hardware-based products. The VAN
uses H.310 for MPEG over ATM. Monash University’s ATM network runs at 155 Mbps.
IP videoconferencing has some advantages over hardware-based videoconferencing, such as lower
cost, use of existing network infrastructure, and the ability for users to use videoconferencing sys-
tems from their personal computers. However, hardware systems offer higher frame rates, better
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