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Datacommunications Definitions


Attenuation

A reduction is strength or deterioration of an electrical signal as it passes through a transmission medium. Attenuation generally increases with frequency, cable length and the number of connections in a circuit. Attenuation is measured in decibels (dB). In optical fiber, a diminution of the signal is only a function of length traveled.

Backbone

Generally, the more permanent part of a communications network which carries the heaviest traffic. Usually a vertical arrangement that connects floors in a multi-story building. however, the same function may be served by a lateral backbone for horizontal distribution in a low, wide building.

Bend Radius

The radius a cable can bend before the risk of breakage or increase in attenuation occurs.

Bus

1)A data path shared by many devices. 2)A linear network topology in which all workstations are connected to a single cable. On a bus network, such as Ethernet, all workstations receive all transmissions; only the workstation that the information is addressed to will use the information. Contrast with ring and star.

Crossover

A conductor which connects to a different pin number at each end.

Crosstalk

The phenomenon in which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel, generally related to wire placement, shielding, and transmission techniques.

Ethernet

A baseband LAN used for connecting computers and terminals within the same building.

Home Runs

A pathway or cable between two locations without a point of access in between.

Impedance

A unit of measure, expressed in Ohms, of the total opposition (resistance, capacitance and inductance) offered to the flow of an alternating current.

Jumper

An assembly of twisted pairs without connectors, used to join telecommunications circuits/links at the cross-connect.

Local Area Network (LAN)

A non-public data communications network confined to a limited geographic area (usually within a few miles), used to provide communication between computers and peripherals. The area served may consist of a single building, a cluster of buildings, or a campus-type arrangement. It is owned by its user, includes some type of switching technology and does not use common carrier circuits - although it may have gateways or bridges to other public or private networks.

Patch Panel

A cross-connect system of matable connectors that facilitates administration.

Token

A unique combination of bits used in LANs to grant permission to a station to transmit. In a ring network, the token circulates continuously; in a bus it must be addressed.

Twisted Pair Cable

A type of communications transmission cable in which two individually insulated wires are twisted around each other to reduce induction (thus interference) from one wire to the other. The pair may be surrounded by a shield, insulating jacket or additional pairs of wires.