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Glossary
100 ISU 512 User Manual 61202.086L1-1
CCITT
Consultative Committee on International Telephony and Telegraphy. A body of
the International Telegraph Union (ITU) which prepares recommendations, com-
monly referred to as international standards, to resolve technical telegraph and
telephone problems.
central office (CO)
In telephony, the phone company switching facility or center, usually a Class 5 end
office, at which subscriber's local loops terminate. Handles a specific geographic
area, identified by the first three digits of the local telephone number. Usually the
facilities of the local BOC.
channel bank
Equipment in a telephone central office that performs multiplexing of lower speed
digital channels into a higher speed composite channel. The channel bank also de-
tects and transmits signaling information for each channel, transmitting framing
information so that time slots allocated to each channel can be identified by the re-
ceiver.
clear channel
A channel in which all the 64 kbps are used for transmission. To achieve this bit
robbing signaling must be eliminated.
CPE
Customer premises equipment. A generic term for communications terminal gear
owned by the customer, residing on customer premises.
CSU
Channel service unit. A component of CPE used to terminate a digital circuit, such
as DDS or T1 at the customer site. Performs certain line-conditioning functions,
ensures network compliance per FCC rules, and responds to loopback commands
from the central office. Also ensures proper 1s density in transmitted bit stream
and performs bipolar violation correction. See DSU.
D-channel
The ISDN channel that carries signaling information to control the call setup, tear-
down, or invocation of supplementary services. The D-Channel may also be used
to provide Packet Mode Data Service.
DCE
Data communications equipment. The portion of a data terminal that provides the
interface to the network.