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| D |
D Connector - see Subminiature D Connector
Data Connector - A four position connector for 150-ohm
STP used primarily with Token-Ring networks.
Data Grade - A term used for twisted-pair cable used
in networks to carrydata signals. Data grade media has a higher
frequency rating than voice grade media used in telephone wiring.
DAS - Dual Attachment Station. Term used with FDDI networks
to denote a station that attaches to both the primary and secondary
rings.
dB - Decibel. A unit for measuring the relative strength
of a signal. Usually expressed as the logarithmic ratio of the
strength of a transmitted signal to the strength of the original
signal. A decibel is one tenth of a "bel".
DB-9 - Nine pin D connector.
DB-15 - Fifteen pin D connector.
DB-25 - Twenty-five pin D connector.
DC - see Direct Current.
DCE - Data Communications Equipment. Any equipment that
connects to Data Terminal Equipment (DTE) to allow transmission
between DTEs.
DC Loop Resistance - The total DC resistance of a cable.
For twisted pair cable, it includes the round trip resistance,
down one wire of the pair and back up the other wire.
Demand Priority - A network access method used by 100VG-AnyLAN.
The hub arbitrates requests for network access received from
stations, assigning access based on priority and traffic loads.
Demarcation Point - A point where the operational control
or ownership changes, such as the point of interconnection between
telephone company facilities and a user's building or residence.
DGM - Data Grade Media (see Data Grade)
Dielectric - An insulating (non-conducting) material.
Dielectric Constant - The property of a dielectric which
determines the amount of electrostatic energy that can be stored
by the material when a given voltage is applied to it. Also
called permattivity.
Digital Signal - An electric signal which possesses two distinct
states (on/off, positive/negative, one/zero).
Direct Current - An electric current that flows in one
direction and does not reverse direction as with "alternating
current".
Dispersion - The phenomenon in an optical fiber whereby
light photons arrive at a distant point in different phase than
they entered the fiber. Dispersion causes receive signal distortion
that ultimately limits the bandwidth and usable length of the
fiber cable. The two major types of dispersion are 1) mode (or
modal) dispersion caused by differential optical path lengths
in a multimode fiber, and 2) material dispersion caused by differing
transmission times of different wavelengths of light in the
fiber optic material.
Distortion - Any undesired change in a wave for or signal.
Distribution Frame - A structure with terminations for
connecting the permanent cabling of a facility in a manner that
interconnections or cross connects may be readily made.
DIW -Direct Inside Wire. Twisted pair wire used inside a building,
usually two or four pair AWG 26.
Drain Wire - An uninsulated wire in contact with a shield
throughout its length. Used to terminate the shield.
Drop Cable - The cable which allows connection and access to
and from the trunk cables of a network such as the cables that
connect individual PCs to the bus on a bus LAN. In a CATV system,
the transmission cable from the distribution cable to a dwelling.
DS1/DS3 - see T1 and T3
DTE - Data Terminal Equipment. Any piece of equipment
at which a communications path begins or ends.
Duct - A single enclosed raceway for wires or cable or
an enclosure in which air is moved.
Duplex - A circuit used to transmit signals simultaneously
in both directions or two receptacles or jacks in a common housing
which accepts two plugs. |
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