Page 289 - Optical Switching And Networking Handbook

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274 Glossary

and an information field. The transfer mode is asynchronous in
the sense that the use of the cells depends on the required or
instantaneous bit rate.
Attenuation The reduction of signal magnitude or signal loss
usually expressed in decibels.
Automatic Protection Switching (APS) The capability of a
network element to detect a failed working line and switch the
service to a spare (protection) line. 1 1 APS pairs a protection
line with each working line. 1:n APS provides one protection line
for every n working lines.

Bandwidth The carrying capacity or size of a communications
channel; usually expressed in hertz (cycles per second) for analog
circuits (the original meaning of the term) and in bits per second
(bps) for digital circuits (newer meaning).
Baseband A method of communication in which a signal is
transmitted at its original frequency without being impressed on
a carrier.
Baud A unit of signaling speed equal to the number of signal
symbols per second, which may or may not be equal to the data
rate in bits per second.

Beamsplitter An optical device, such as a partially reflecting
mirror, that splits a beam of light into two or more beams. Used
in fiber optics for directional couplers.
Bending loss Attenuation caused by high-order modes radiating
from the outside of a fiber optic waveguide, which occur when
the fiber is bent around a small radius.
Bend radius The smallest radius an optical fiber or fiber cable
can bend before increased attenuation or breakage occurs.
Bi-directional Operating in both directions. Bi-directional APS
enables protection switching to be initiated by either end of the
line.
Broadband Integrated Services Digital Network (BISDN)
A single ISDN network that can handle voice, data, and eventu-
ally video services.