Glossary of Terms and acronyms

ADSL:
Asymmetrical Digital Subscriber Loop. Technology currently under development and testing which allows the local loop in a public telephone network to be upgraded to provide broadband services along side (and at the same time as) telephony. Uses computer servers at the local telephone exchange to store such information as films which can be downloaded at a customer's request. Downstream data rate is between 1.5 MBit/s and 9 MBit/s.

Amplifier:
A device used to boost the strength of an electronic signal.

Analogue:
A form of transmitting information characterised by continuously variable quantities, as opposed to digital transmission, which is characterised by discrete bits of information in numerical steps. An analogue signal is responsive to changes in light, sound, heat and pressure.

Antenna:
A device for transmitting and receiving radio waves. Depending on their use and operating frequency, antennas can take the form of a single piece of wire, a di-pole a grid such as a yagi array, a horn, a helix, a sophisticated parabolic-shaped dish, or a phase array of active electronic elements of virtually any flat or convoluted surface.

ATM:
Asynchronous Transfer Mode. This is an emerging high speed digital packet switch technology which many believe will become the de facto standard for interactive and multimedia services. Unlike conventional packet switching, ATM divides information up into standard length packets of 53 bits for transmission. This makes it easier to reassemble the signal at the destination point and thus allow for full interactive services such as video telephony, video-conferencing and two-way voice. It is a platform for a wide variety of digital services which use standard protocols, such as IP/TCP, Frame Relay and X25.

Attenuation:
The loss in power of electromagnetic signals between transmission and reception points.

Attitude Control:
The orientation of the satellite in relationship to the earth and the sun.