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278 Glossary

Data communications channels OAM&P channels in SONET
that enable communications between intelligent controllers and
individual network nodes as well as inter-node communications.
Data rate The number of bits of information in a transmission
system, expressed in bits per second (bps), and which may or
may not be equal to the signal or baud rate.
DB Decibel.
DBc Decibel relative to a carrier level.

DBu Decibels relative to microwatt.
DBm Decibels relative to milliwatt.
Defect A limited interruption in the capability of an item to per-
form a required function.
Demultiplexer A module that separates two or more signals
previously combined by compatible multiplexing equipment.
Demultiplexing A process applied to a multiplex signal for
recovering signals combined within it and for restoring the dis-
tinct individual channels of the signals.
Dense Wave Division Multiplexing (DWDM) An optical mul-
tiplexing technique used to increase the carrying capacity of a
fiber network beyond what can currently be accomplished by
time division multiplexing (TDM) techniques. Different wave-
lengths of light are used to transmit multiple streams of infor-
mation along a single fiber with minimal interference. DWDM
has been mainly deployed as a point-to-point, static overlay to
the optical TDM network to create “virtual fiber.” As such,
DWDM is the precursor to optical networking. DWDM has dras-
tically reduced the cost of transport by reducing the number of
electrical regenerators required and sharing a single optical
amplifier over multiple signals through the use of EDFAs.
Dielectric A material with both conductive and insulating elec-
tromagnetic properties. A dielectric thin-film material exhibits
far more transmission than absorption at the wavelength of
interest.
Digital cross-connect (DCS) An electronic cross-connect that
has access to lower-rate channels in higher-rate multiplexed sig-