Notes:  This glossary provides brief explanations of technical terms used in this Report. It is not intended as a general guide to all technical terms employed in discussions of converging technologies. Where a word appears in a definition in bold, it is explained elsewhere in the glossary.

ADSL

See DSL.

Analogue signal

A method of conveying voice, image or video information by a signal that varies continuously in amplitude with the information being transmitted (ie, the direct representation of a waveform) and is re-converted into sound and pictures by receiving equipment.

Bandwidth

The effective frequency range occupied by a signal.

Bit-rate

The rate at which digital information is transmitted, usually measured in Mbits/s.

Broadband

General term which implies the ability to carry enormous quantities of information at high speed, the capacity for two-way communication and the ability to deliver any media, including video, text, audio and images.

Compression

Reduction of the bit-rate required for the transmission of a particular digital signal, achieved by the identification and elimination of redundant information, such as repetition of information contained in a previous signal.

Conditional access

System used by broadcasters of pay TV services to ensure that only authorised viewers are able to receive the service; usually achieved by encryption.

Digital signal

A discrete or discontinuous electrical signal composed of a series of on and off pulses, representing binary digits (ones and zeros).

DSL

Digital Subscriber Loop (or Line). DSL technology makes use of a pair of modems at each end of a normal telephone access line to create a digital line that makes greater use of the bandwidth available. xDSL is sometimes used as a generic phrase, where x is the relevant form of DSL. ADSL (Asymmetric DSL) offers a transmission bit-rate of about 2 Mbits/s from network to user, but a more limited transmission capacity from the user to the network. HDSL (High Data Rate DSL) offers symmetric data transfer at up to 2 Mbits/s.

Electronic Programme Guides

Software in a receiver which takes data on programmes and displays these in the form of an on-screen guide. The guide displays information about current and future programmes on each channel. Viewers may also be able to use the on-screen menu to order pay-per-view services or to access interactive services.

Encryption

The transformation of data by the use of cryptography (hiding data information content) to produce unintelligible data (encrypted data) to ensure its confidentiality.

Fibre Optic Cable

A fibre optic (glass) cable can carry very pure (coherent) light, provided by a laser, over considerable distances without degeneration. The light can be modulated to carry many television and radio signals, without interference, and because the fibres are so thin, one cable can contain many fibres. Optical fibre is a broadband medium which can easily provide capacity for a large number of channels.

HDSL

See DSL.

ISDN

Integrated Services Digital Network: provides for higher speed transmission of voice and data applications, including the Internet, with existing copper wire; in the case of ISDN2, provides speeds up to four times that of a normal modem.

Mbits/s

Megabits per second. A measure of the speed of transfer of digital information.

Multiplex

Describes a frequency band capable of carrying digital programme services as well as additional services. Each digital terrestrial multiplex in the United Kingdom (of which there will initially be six) will carry typically between three and six individual programme services at any one time. Multiplexing refers to the process of combining together different digital signals into a single stream of binary digits.

MVDS

Multi-point Video Distribution System (MVDS) involves the use of very high frequency transmissions for video signals or other services; suitable for transmission in small areas; requires a direct line of sight between the transmitter and a roof-top dish aerial.

Near Video on Demand (NVOD)

A service which relays into homes several channels on which the same programme starts at intervals. A viewer selects the programme and then chooses from one of several starting times.

Teletext

Generic name for systems, such as the BBC's Ceefax, which use 'spare' lines in the television signal to transmit information pages for home viewing. This word has been registered, and is now being used, as the trade name for the information service on ITV and Channel 4/S4C.

Video on Demand (VOD)

A service which enables viewers to call up a programme or film from a selected list via a cable or telephone network. The signal is then sent individually to that home.

UMTS

Universal Mobile Telephone Service (UMTS) will enable transmission of broadband interactive multi-media material by terrestrial radio; to be made possible by spectrum auction expected in 1999 with services to be launched from about 2002.

x-DSL

See DSL.