ATM - high-speed networking in the future

Today's networking environments can be described in terms of many facets: different topologies and geographies, equipment, interfaces, and physical media. Asynchronous Transfer Mode (ATM) will bring new meaning to the high-speed networking over great distances. It marks a new era of LAN/WAN integration and performance.

ATM is a transport protocol - a way of transmitting data, voice and video. It is an international standard for cell relay, a fast packet switching technology. It divides all of the information into very small cell units and transfers and switches these units at super high speeds. One of the important new technologies that ATM networks will provide is Broadband ISDN. Future transfer speed will reach up to 155.5 or 622 Mb per second. Narrowband ISDN (current) can transmit data at rates of 64 Kb per second.

ATM allows different types of information to be mixed up, or interleaved. In a multimedia application a single link into a workstation, or the home, can deliver voice, data, images and video all at the same time. This is the kind of flexibility needed for future applications, such as video on demand and online interactive shopping. For any PC user, whether mobile or not, this kind of performance will revolutionise many current computing fields.

Satellites - connectivity anywhere on this planet

The dream of connectivity anywhere, anytime, regardless of the service you require moves a step nearer reality with satellite connectivity. Imagine telephone, fax, web-browsing, e-mail, or even video conferencing wherever you are. No need to look for a connection, no compatibility problems and one "telephone" number wherever you are in the world. This is the vision of those companies now investing in satellite communications systems for the next century.

Four systems are currently proposed: Iridium, Globalstar, Astrolink and Teledesic. All except Astrolink envisage a large number of satellites in Low Earth Orbit (LEO). Astrolink plans to use just nine satellites in five slots at the geostationary orbit level. Individual throughput levels could be as high as 9.6 Mbps depending on user requirements. Astrolink users require a dish to access the system. Standard low-cost terminals of 16 to 384 Kbps are planned.

Of the three LEO systems, Iridium is the closest to launch. The first satellites should have gone up in January this year but there have been delays. Services are planned from 1998 using 66 satellites, 420 nautical miles high, capable of communicating with hand-held equipment. Globalstar is also planning to have services running within 1998. It uses 56 satellites in eight orbital planes 750 nautical miles high. To keep costs down, Globalstar plans to direct traffic from satellites through fixed earth links, only using satellites for the first and final stages.

Teledesic is a highly advanced system, but services are not planned until 2002. 840 satellites will offer variable channels from 16 Kbps up to 2 Mbps according to individual needs. The system will use packet-based networks employing ATM technology. Hand-held and mobile PC terminals are specifically foreseen. For the computer industry, it of interest that Bill Gates is a major backer of the Teledesic consortium. For mobile computer users, all satellite systems emphasise the real benefits of mobility: freedom to do what you want, when you want. Mobile connectivity has an exciting future.