Page 292 - Optical Switching And Networking Handbook

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Glossary 277

CEPT European Conference of Postal and Telecommunications
Administrations. The CEPT format defines the 2.048-Mbps
European E1 signal made up of 32 voice-frequency channels.
Channel A generic term for a communications path on a given
medium; multiplexing techniques enable providers to put multi-
ple channels over a single medium.
Circuit A communications path or network; usually a pair of
channels providing bi-directional communication.
Circuit switching A switching system that establishes a dedi-
cated physical communications connection between end points,
through the network, for the duration of the communications
session; this is most often contrasted with packet switching in
data communications transmissions.
Cladding Material that surrounds the core of an optical fiber. Its
lower index of refraction, compared to that of the core, causes the
transmitted light to travel down the core.
Concatenate The linking together of various data structures,
such as two bandwidths joined to form a single bandwidth.
Concatenated VT A virtual tributary (VT Nc) which is com-
posed of N VTs combined. Its payload is transported as a sin-
gle entity rather than separate signals.
Connection-oriented A term applied to network architectures
and services that require the establishment of an end-to-end,
predefined circuit prior to the start of a communications session.
Frame Relay circuits are examples of connection-oriented ses-
sions.
Core The light-conducting central portion of an optical fiber, com-
posed of material with a higher index of refraction than the
cladding. The portion of the fiber that transmits light.
Cyclic Redundancy Check (CRC) A technique for using over-
head bits to detect transmission errors.
Dark fiber Fiber-optic cables that have been laid but have no
illuminating signals in them.