Glossary

BABT

British Approvals Board for Telecommunications

BASIC ACCESS

With ISDN basic access, the customer is presented with two B channels and one 16 kbit/s D channel; hence the designation "2B+D".

B-CHANNEL

A channel with a bit rate of 64 kbit/s which conveys user information.

BEARER SERVICE

A service providing transmission of user data between network interfaces without altering it.

BIT RATE

Number of bits transmitted per second. Expressed in bit/s or kbit/s (thousands of bits per second).

CCITT

Committee Consultative International Telegraphe et Telephone, the senior telecommunications body of the United Nations International Telecommunications Union. Its major work on ISDN was published in the CCITT blue (1988) and red (1984) books.

CODEC

A unit that codes and decodes digital signals from analogue audio.

D CHANNEL

A channel used to transport packetised signalling information between the user and the local exchange.

ETSI

European Telecommunications Standard Institute.

Euro-ISDN

A common European standard implementation based on the specification drawn up by the ETSI. According to the Memorandum of Understanding signed by representatives from 17 European countries, a core set of Euro-ISDN services were implemented in all countries from December 1993.

Inverse Multiplexer

A device allowing a single application to use a number of aggregated B channels when a higher bandwidth than 64 k/bits is required.

ISDN

Integrated Services Digital Network.

PRIMARY ACCESS

With ISDN primary access, the customer is presented with 30 B-channels and one 64 kbit/s D-channel; hence the designation "30B+D".

PSTN

Public switched telephone network.

TERMINAL ADAPTER (TA)

The TA is an external device which handles the interface between the ISDN line and any ISDN compatible digital equipment.