A series of directional microwave paths carrying common information to be relayed between remote points; engineered to allow insertion of signals, dropping off of signals and switching of signals along its length at designated relay points.
In an amplifier or other device that draws current, there is always some noise output in addition to the desired signal.
A terrestrial communications channel linking an earth station to a local switching network or population center. [Sat07] Backoff
The process of reducing the input and output power levels of a traveling wave tube (TWT) to obtain more linear operation. [Sat07] Backreflection (BR)
A term applied to any process in the cable plant that causes light to change directions in a fiber and return to the source. Occurs most often at connector interfaces where a glass-air interface causes a reflection. [Fib111]
The return of a portion of scattered light to the input end of a fiber; the scattering of light in the direction opposite to its original propagation. [Fib111]
Backus Naur Form (BNF)
A formal notation used to define the syntax of a language. BNF was the first metalanguage to define programming languages. Introduced by John Backus in 1959 to describe the ALGOL 58 language, it was enhanced by Peter Naur and used to define ALGOL 60. A formal metasyntax used to express context-free grammars. Backus Normal Form was renamed Backus-Naur Form at the suggestion of Donald Knuth. [Fre11] Balun
A transformer used to match 75 ohm coaxial cable to a 300 ohm input on older televisions. This acronym is derived from combining the two words, BALanced and UNbalanced.[Arr11] Bandpass Filter
A circuit or device that allows only a specified range of frequencies to pass through a circuit. Bandwidth (BW)
(1) Analog Bandwidth: A measure of spectrum (frequency) use or capacity. For instance, an analog voice transmission by telephone requires a bandwidth of about 3000 hertz (3KHz). A TV channel occupies a bandwidth of 6 million hertz (6MHz) of radio frequency (RF) bandwidth. Cable system bandwidth occupies 50 to 300 MHz on the electromagnetic spectrum. (2) Measure of the frequency width of a transmission channel, or the difference between the highest and lowest frequency levels. Information-carrying capacity of a communication channel. The amount of transmission capacity possessed by a system or a specific location in a system. (3) Digital Bandwidth: The data rate of a digital signal carried in a data transmission channel. Digital bandwidth is commonly stated in units of bits-per-second (bps) and bytes-per-second (Bps) where 8 bits equals one byte. For example, DOCSIS 2.0 is capable of an upstream digital bandwidth of 27 Mbps in an analog channel bandwidth of 6.4 MHz using the 64 quadrature amplitude modulation (64 QAM).
Bandwidth Allocation Map
The DOCSIS MAC Management Message that the cable modem termination system uses to allocate transmission opportunities to cable modems.
Of an optical fiber, under specified launching and cabling conditions, at a specified wavelength, a figure of merit equal to the product of the fiber’s length and the 3 dB bandwidth of the optical signal. The bandwidth•distance product is usually stated in megahertz • kilometer (MHz•km) or gigahertz•kilometer (GHz•km). It is a useful figure of merit (FoM) for predicting the effective fiber bandwidth for other lengths, and for concatenated fibers. [Fib111] Bandwidth-limited Operation
The condition in a fiber optic link when bandwidth, rather than received optical power, limits performance. This condition is reached when the signal becomes distorted, principally by dispersion, beyond specified limits. [Fib111] Base Station
Also called cell station. A radio transceiver (transmitter/receiver) that uses processing hardware/software and an antenna array to control and relay voice and data signals between the central office of a telephone network, or the internet transport provider, and the remote subscriber unit (fixed or mobile) or internet appliance; it connects wireless users to a phone network, or to an internet service provider. Baseband
A transmission scheme that does not employ carrier modulation. In digital baseband systems, data is sent by varying the voltage (pulse amplitude modulation—PAM) or the duration (pulse width modulation—PWM) of signal pulses to indicate different values.
Baseline Privacy Interface (BPI)
A set of extended services within the DOCSIS MAC sublayer. BPI gives subscribers data privacy across the RF network, encrypting traffic flows between the cable modem termination system and cable modem.
Baseline Privacy Interface+ (BPI+)
BPI+ strengthens service protection by adding digital-certificate-based cable modem authentication to its key exchange protocol. BPI+ provides a level of data privacy across the shared medium cable network equal to or better than that provided by dedicated line network access services (analog modems or digital subscriber lines).
The basic program services distributed by a cable system for a basic monthly fee. These include one or more local broadcast stations, distant broadcast stations, non-pay networks and local origination programming.
Basic Rate Interface (BRI)
An ISDN BRI is a basic ISDN telephone connection commonly used for small office, home, and ISDN voice telephone service. Each ISDN BRI has two 56 or 64Kbps B Channels and one 16Kbps D Channel.
The number of signal-level transitions per second in digital data. For some common coding schemes, this equals bits per second, but this is not true for more complex coding, where it is often misused. Telecommunications specialists prefer bits per second, which is less ambiguous.[Arr11] Baud Rate
The measure of the speed of transmission of a digital code.
Broadband Interactive services; the delivery of all types of interactive video, data, and voice services over a broadband communications network. [Fib111] Beacon
Low-power carrier transmitted by a satellite which supplies the controlling engineers on the ground with a means of monitoring telemetry data, tracking the satellite, or conducting propagation experiments. This tracking beacon is usually a horn or omni antenna. [Sat07] Beamsplitter
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. [Fib111]
Beamsplitter Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/b
A measure used to describe the width of vision of an antenna. It is measured between the 3 dB half power points in angles.[Arr11] Bel
The fundamental division of a logarithmic scale for expressing the ratio of two powers, which are in the ratio of one to ten. The Bel is an awkwardly large unit, so the "decibel" (one-tenth of a Bel) is used instead.[Arr11] Bend Radius
The smallest radius an optical fiber or fiber cable can bend before excessive attenuation or breakage occurs. [Fib111]
Bend Radius Illustration courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/b
Attenuation caused by high-order modes radiating from the outside of a fiber optic waveguide which occur when the fiber is bent around a small radius. See also macrobending, microbending. [Fib111]
BER Bit Error Rate; the fraction of bits transmitted that are received incorrectly. In a noisy channel, the BER is often expressed as a function of the normalized carrier-to-noise ratio measure denoted Eb/N0, (energy per bit to noise power spectral density ratio), or Es/N0 (energy per modulation symbol to noise spectral density). [Wik1110] BFS Broadcast File System
A fiber optic connector developed by AT&T. BID
Bi-directional, as in systems used with CATV services using pay-per-view or cable modems. BID is not for use with off air antennas. [Lin07] BIDI
Bidirectional transceiver, a device that sends information in one direction and receives information from the opposite direction. [Fib111]
BIDI Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/b
BIDI 1Gbps Module Photo courtesy of SFPlus, http://www.sfplustransceiver.com/alcatel-lucent-3he00868ab