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Term Main definition
A method of communication in which the entire bandwidth of the transmission medium is used to transmit a single digital signal. The signal is driven directly onto the transmission medium without modulation of any kind. Baseband uses the entire bandwidth of the carrier, whereas broadband only uses part of the bandwidth. Baseband is simpler, cheaper, and less sophisticated than broadband.
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Basic rate interface (BRI)
As defined by ISDN, consists of two 64Kbps B-channels used for data and one 16Kbps D-channel (used primarily for signaling). Thus, a basic rate user can have up to 128Kbps service.
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Battery distribution fuse bay (BDFB)

A type of DC

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The number of signal level transitions per second. Commonly confused with bits per second, the baud rate does not necessarily transmit an equal number of bits per second. In some encoding schemes, baud will equal bits per second, but in others it will not. For example, a signal with four voltage levels may be used to transfer two bits of information for every baud.
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A special frame in Token Ring systems indicating a serious problem with the ring such as a break. Any station on the ring can detect a problem and begin beaconing.
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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.
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For a round light beam, the diameter of a beam, measured across the width of the beam. Often specified in nanometers (nm) or millimeters (mm).
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Bearer channel (B-channel)
On an ISDN network, carries the data. Each bearer channel typically has a bandwidth of 64Kbps.
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Named for Alexander Graham Bell, this unit represents the logarithm of the ratio of two levels. See Chapter 1 for an explanation of bel and decibels.
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Bend loss
A form of increased attenuation in a fiber where light is escaping from bent fiber. Bend loss is caused by bending a fiber around a restrictive curvature (a macrobend) or from minute distortions in the fiber (microbend). The attenuation may be permanent if fractures caused by the bend continue to affect transmission of the light signal.
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Bend radius (minimum)

The smallest bend a cable can withstand before the transmission is affected. UTP copper cabling usually has a bend radius that is four times the diameter of the cable; optical fiber is usually 10 times the diameter of the cable. Bending a cable any more than this can cause transmission problems or cable damage. Also referred to as cable bend radius.

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Biconic connector

A fiber-optic termination connector that is cone-shaped and designed for multiple connects and disconnects. The biconic connector was developed by AT&T but is not commonly used.

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Bidirectional attenuation testing

Refers to measuring the attenuation of a link using an OTDR in each direction.

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Bidirectional couplers

Couplers that operate in both directions and function in the same way in both directions.

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Bifurcated contact prongs

Contacts in a 66- or 110-block that are split in two so that the wire can be held better.

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