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Video conferencing and the Integrated Services Digital Network

Ross Davies and Kevin Harding
Corporate Customer Division
Telecom Australia


Initially, we want to make some distinctions between the various types of video services available. Until recently, video services were mainly used by television stations to distribute programme material. Two important characteristics of these services are that they are one way, and they are of TV broadcast quality.

Broadcast quality is also commonly referred to as full motion or full bandwidth video. Technically, the bandwidth of such video services is approximately 5.5 MHz. The actual value is not so important. What is important is to think of broadcast quality services as requiring a very large communications pipe, such as optical fibre, to provide the service, which is usually expensive. Two way video conference services based on broadcast quality services are therefore usually only cost effective in a metropolitan area.

Video conferencing services, which have become available recently, aim to reduce the bandwidth, that is the size of the communications pipe, in order to reduce the cost of the service. Video conferencing services, as the name suggests, are inherently two way in nature.

Video conferencing and codecs

Coder-decoders (codecs) are used in video conferencing services to reduce the bandwidth required. They take the full bandwidth analogue video signals, for example from a video camera, and convert them to a digital signal which they then process. Video conference services are therefore provided only using digital transmission systems.

The bandwidths used for video conferencing services are typically in the range 56 kbit/s to 2 Mbit/s. This compares to approximately 100 Mbit/s for broadcast quality video. More significantly it can be compared with a normal (voice) telephone call through the Telecom network which uses a 64 kbit/s transmission channel.

The codecs use compression algorithms to reduce the bandwidth required. For example they will only transmit information about what has changed from one frame to another. Of course there is a trade off in the loss of ability to accurately display fast movement. Again, as the name suggests, video conferencing is suitable for conference style meetings or seminars where participants are seated, or other activities such as lectures where there is reduced movement.

Telecom uses codecs from Compression Laboratories Incorporated (USA) which is the world's biggest codec manufacturer. Importantly, Telecom purchases its codecs with a prepaid upgrade from the manufacturer to the proposed international CCITT standard H261.

Telecom networks for video conferencing

As mentioned, video conferencing codecs work on digital transmission systems. Some alternative network options for video conferencing include

ISDN and video conferencing

The ISDN is a digital switched network (see Figure 1 for a schematic represent-ation). Setting up a digital connection for a video conference is therefore the same as dialling up a telephone call (or multiple calls). ISDN is available throughout the Perth metropolitan area and most major regional centres.

Figure 1

Figure 1: Integrated Services Digital Network

The initial video conferencing service on ISDN from Telecom (Figure 2) consists of

Figure 2

Figure 2: ISDN and video conferencing

Initially, conferencing is at 384 kbit/s, obtained from 6 x 64 kbit/s channels, or six telephone calls established, with further developments to allow the user to select the number of channels to be used. The spare capacity on the ISDN Macrolink service is available for other applications, which may include

Ideas and new opportunities

The following points are aimed at stimulating thought on the benefits and applications of video conferencing. Ideas include


The following figures provide budget information for video conferencing services (the prices are indicative and include sales tax).

ISDN access$10,000p.a. rental
Codec and multiplexor$100,000purchase
Room equipment (cameras, etc)$30-100,000purchase
Usage examples (per hour at 384 kbit/s, business hours rates):
Perth - Kalgoorlie
Perth - Sydney

Important issues

Some important issues when considering the establishment of a video conferencing network include the following.


There are a number of network options for video conferencing services. ISDN provides a network that can be used for a whole range of digital services including video conferencing. Video conferences are established under user control, and provide flexibility in relation to trade offs between bandwidth and call cost.

Telecom can provide a complete video conferencing service, including video conferencing room design and fit out. When establishing a video conference service it is vitally important that new users see a service that is easy to operate, and one that performs well. First impressions when exposed to new technology are critical to the acceptance of the technology.

Should you wish to know more about Telecom video conferencing in WA, or would like a tour of Telecom's video conferencing facilities, please contact Ross Davies, Communications Consultant (09 420 9256) or Kevin Harding, Account Executive Education (09 420 9288), at the Corporate Customer Division, Telecom Australia, in Markalinga House, 251 St Georges Terrace, Perth.

Please cite as: Davies, R. and Harding, K. (1990). Video conferencing and the Integrated Services Digital Network. In R. Atkinson and C. McBeath (Eds.), Open Learning and New Technology: Conference proceedings, 88-92. Perth: Australian Society for Educational Technology WA Chapter.

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