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GLOSSARY GL-7
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CSU The terms channel service unit and customer service unit are both
abbreviated to CSU and are both synonymous with network channel-
terminating equipment. See network channel-terminating equipment.
customer provided
(premises) equipment
(CPE)
Customer owned equipment that is not provided as part of the system but
is to be connected to it.
customer service unit
(CSU)
See network channel-terminating equipment.
D4 framing format A format containing 12 frames. See also extended frame and frame.
D-channel The 16-kbps or 64-kbps packet-switched channel on an Integrated
Services Digital Network basic rate interface (ISDN-BRI) or 64-kbps on
an Integrated Services Digital Network primary rate interface (ISDN-PRI)
packet-switched channel that carries signaling messages and packet-
switched user data. A D-channel is the (IDSN-PRI) Q.931 signaling
channel. (A D-channel can also carry data, but this capability is not used
on a DEFINITY Communications System Generic 2.) See also B-
channel, and Q.930 and Q.931.
data-carrier detect (DCD) A data communications equipment (DCE) signal that shows whether the
received data-channel line signal is within appropriate limits as defined by
the DCE. See also data circuit-terminating equipment.
data channel The means of transmission for and the intervening equipment used in the
transfer of information in a given direction.
data-circuit terminating
equipment (DCE)
See data communications equipment.
Data-Communications
Access (DCA)
On a System 85 and Generic 2, a feature that uses a unique analog data
port to provide access to on-premises host computers for data endpoints
with an analog interface (modem). These endpoints include analog
telephones and attendant consoles. On a System 75 and Generic 1, the
equivalent functionality is provided by using the same analog-line port
circuit used to interface with analog telephones.
data communications
equipment (DCE)
The equipment — usually a modem, data module, or packet
assembler/disassembler — used for terminating the circuit that provides
the connection between terminal endpoints. The circuit itself is not
considered part of the DCE. Also called data circuit-terminating. See
also data-carrier detect.