Backbone - A cable connection between telecommunication or wiring closets, floor distribution terminals, entrance facilities, and equipment rooms either within or between buildings. In star networks, the backbone cable interconnects hubsand similar devices, as opposed to cables running between hub and station. In a bus network, the bus cable.

Back reflection - The light reflected back towards the source from the fiber optic ends and deformations.

Backscattering - Refers to light diffraction at microscopic non-uniformities in the index of refraction of the optical fiber causing back reflection of optical power towards the source. Used in OTDRs.
Balanced Cable, Balanced Line - A cable having two identical conductors that carry voltages of opposite polarities and equal magnitude with respect to ground. The conductors are twisted to maintain balance over a distance.

Balanced Transmission - A mode of signal transmission in which each conductor carries the signal of equal magnitude, but opposite polarity. A 5 volt signal for example, appears as a +2.5 Volts on one conductor and -2.5 Volts on the other.

Balun - An impedance matching transformer that converts the impedance of one interface to the impedance of another interface. Generally used to connect balanced twisted pair cabling with unbalanced coaxial cabling. The term is derived from "balanced / unbalanced".

Bandpass - A range of frequencies or wavelengths within which a component operates.

Baseband - A transmission method 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 is simpler, cheaper and less sophisticated than Broadband.

Bandwidth - The range of frequencies required for proper transmission of a signal. Expressed in Hertz (cycles per second). The higher the bandwidth, the more information that can be carried. A continuous range starting from zero is said to be "baseband", while a range starting substantially above zero is "broadband".

Baud - The number of changes in signal per second. A given baud rate does not necessarily transmit an equal number of bits/sec. For example, a signal with four voltage levels may be used to transfer two bits of information for every baud.

Beacon -A special frame in Token-Ring systems indicating a serious problem with the ring such as a break.

Bel - A unit that represents the logarithm of the ratio of two levels.

Bend Loss - A form of increased attenuation in an optical fiber caused by an excessively small bend radius. The attenuation may be permanent if micro-fractures caused by the bend continue to affect transmission of the light signal.

Bend Radius - Radius of curvature that a fiber optic or metallic cable can bend before the risk of breakage or increased attenuation occurs.

BER - see Bit Error Rate

BICSI - Building Industry Consulting Service International.

Binder - A tape or thread used to hold assembled cable components in place.

BISDN - Broadband ISDN

Bit - One binary digit.

Bit Error Rate - A measure of data integrity, expressed as the ratio of received bits that are in error, relative to the amount of bits received. Often expressed as a negative power of ten.

Bit Stream - A continuous transfer of bits over some medium.

Bit Stuffing - A method of breaking up continuous strings of 1 bits by inserting a 0 bit. The 0 bit is removed at the receiver.

Bit Time - The length of time required to transmit one bit of information.

BL - Blue.

BNC - A coaxial connector that uses a "bayonet" style turn and lock mating method. Used with RG-58 or smaller coaxial cable. Used with 10Base2 Ethernet thin coaxial cable. BNC is an acronym for Bayonet-Neill-Concelman.

Bonding - A method used to produce good electrical contact between metallic parts. Also refers to the grounding bars and straps used in buildings to bond equipment to an approved ground.

BPS - Bits per second.

BR - Brown.

Braid - Fine wires interwoven to form a tubular flexible structure that may be applied over one or more wires for the purpose of shielding. May also be formed into a flattened conductor to be used as a grounding strap.

BRI - ISDN Basic Rate Interface

Bridged Tap - Multiple appearances of the same cable pair at several distribution points.

Broadband - A transmission facility having a bandwidth sufficient to carry multiple voice, video or data channels simultaneously. Each channel occupies (is modulated to) a different frequency bandwidth on the transmission medium and is demodulated to its original frequency at the receiving end. Channels are separated by "guardbands" (empty spaces) to ensure that each channel will not interfere with its neighboring channels. This technique is used to provide many CATV channels on one coaxial cable.

Broadcast - Sending data to more than one receiving device at a time.

Buffer - A protective coating over a strand of optical fiber.

Bus Topology - 1. In general, a physical layout of network devices in which all devices must share a common medium to transfer data, and no two devices may transmit simultaneously. With LANs, a linear network topology in which all computers are connected to a single cable.

Butyl Rubber -A synthetic rubber with good electrical insulating properties.

Byte - A group of 8 bits.