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GLOSSARY GL-5
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BRI See basic rate interface.
BSC See binary synchronous communications.
BX.25 An AT&T version of the CCITT X.25 protocol for data communications.
BX.25 adds a fourth level to the standard X.25 interface. This uppermost
level combines levels 4, 5, and 6 of the International Standards
Organization (ISO) reference model. See also CCITT, Flexible
Assignment of BX.25 Signaling Ports, packet switching, and X.25.
bypass tie trunk A one-way, outgoing tie trunk from a tandem switch to a main switch in
an electronic tandem network (ETN).
byte A sequence of (usually eight) bits processed together.
Call Transfer into
AUDIX
A feature that enables a covering user to transfer a call to another
extension, typically AUDIX but possibly another covering user, with all
pertinent call-related information retained. See also AUDIX.
CCITT (Comite ’e Consultatif International Telephonique et Telegraphique) an
international body that sets universal standards for data communications,
including Integrated Services Digital Network (ISDN). CCITT members
are from telecommunications companies and organizations around the
world. See also BX.25 and Q recommendations.
central office (CO) The location of telephone switching equipment that provides local
telephone service and access to toll facilities for long-distance calling.
More than one CO can serve the same area.
central office (CO) trunk A telecommunications channel that provides access from a PBX to the
public network through the local central office.
central processing unit
(CPU)
The part of a computer that interprets and executes instructions. Also
called central processor.
channel A telecommunications transmission path for voice and/or data.
channel bank Terminal equipment for a transmission system used to multiplex
individual channels using frequency-division multiplexing (FDM) or
time-division multiplexing (TDM).
circuit 1. An arrangement of electrical elements through which electric current
flows, providing one or more specific functions. 2. A channel or
transmission path between two or more points.
class of restriction (COR) On a System 75 or Generic 1, a feature that allows definition of up to 64
classes of call-origination and call-termination restrictions for telephones,
telephone groups, data modules, and trunk groups. See also class of
service.