Fiber Optics Illustrated Dictionary - Part 11 potx

designed to provide enhanced broadband phone fea- tures through CDMA technology. InterDigital is col- laborating with Siemens AG and Samsung Electron- ics Company, Ltd., in developing the proprietary B-CDMA technology. See COMA. B-DC, BDC broadband digital cross-connect. See broadband digital cross-connect system. B-DCS, BDCS See broadband digital cross-connect system. B-frame bidirectionally predictive-coded frame. In MPEG animations, a picture that has been encoded into a video frame according to information derived from both past or later frames in the sequence, using predicted motion compensation algorithms. This is a compression mechanism commonly used for storing large amounts of data on limited-space optical media. See I-frame, P-frame. B-ICI B-ISDN (Broadband-ISDN) InterCarrier In- terface. 1. A specification defined by The ATM F 0- rum for the connecting interface between public ATM networks, for the support of user services across multiple public carriers. 2. An lTU-Tstandard for protocols and procedures for broadband switched virtual connections (SVCs) between public networks. B-ICI SAAL Broadband Inter-Carrier Interface Sig- naling ATM Adaptation Layer. A signaling layer en- abling the transfer of connection control signaling and ensuring reliable delivery of the protocol message. See asynchronous transfer mode, SAAL, AAL5. B-ISDN Broadband ISDN. See ISDN for an intro- duction to ISDN concepts. B-ISDN was designed to meet some of the demands for increased speed and enhanced services on primary ISDN lines. It was geared to the needs of commercial users. It has since evolved into a strategy for delivery for many new telecommunications services including teleconferencing, remote banking, videoconferencing, interactive TV, audio, and text transmissions. Broadband ISDN is intended for services that require channel rates greater than single primary rate channels (i.e., voice at 64 kbps) and thus are offered over fiber optic-based telephone systems. B-ISDN services can be broadly or- ganized as follows: The essential characteristics ofB- ISDN services were approved in the I-series Recommendations by the messaging, data paging, electronic mail, data files (images, sound, formatted documents). Fiber Optics Illustrated Dictionary station, Fiber Distributed Data Interface, optical by- pass, port adaptor. See Aport for a diagram. B Series Recommendations A series of ITU -T recommendations providing guidelines for the various means of expression of information, including defi- nitions, symbols, and classification. These guidelines are available as publications from the lTU -T for purchase and some are downloadable without charge from the Net. Since lTV -T specifications and recommendations are widely followed by vendors in the telecommunications industry, those wanting to maximize interoperability with other systems need to be aware of the information disseminated by the ITV- T. A full list of general categories is listed in the Ap- pendix and specific series topics are listed under individual entries in this dictionary, e.g., A Series Rec- ommendations. :.· ·.r Rae. Date. 'PeIPrintinn BJ ·1988 ';~~llIi~i~ml~~~ns B.3 1988 U~oftheinterna.tional systemlofunits (~I) ••. '.' •· • i. B."lQ 1988 ~1'~caJ$,Ym~~~~angrule§{~tJ1e ~tion. Qf«Q~\DIlel1taticil1m' . telecpmmunicatiQDS B.ll 1988 Le.~Ititne-~~fthe term·UTe B·l~ , 1988Y~:;~fW~~~~~li~tl1~lJCJl:~in ;~t~I~Imr-nUIli$.~:·· B.l~ c 1988 ·'fEi anddefi l1if.jpDS. B.14· 1988· .:t'et11'lS and ~1.s for infbrn1J1tion q~~~~ .••. ~ •.• ~I~~llnj~~. B.lS ;.J99§NQIil~cl.~~~t'::~~#eq't~~~::1ltl4 wa'V~leJ1gth'llJl4~;U$ed ~. '. tele(:Oll1tnunicltiQJ1S B.16 1988 q~9fcertain~linked.witb g~~~i~lJgll~I~~r ·· •.••.•• •.•••.•• •.••••.•• ·i: .• B.l1 1988. AAAptionofme.~fPIrTSp~*~cation an4descriptiQ1.lJapguage (SDL) B.18 19~1 Traftjcintensity~t B.19 1996 J\.ll~~~~lltioIl~~~:initblls· us~m jel~~mm~~@ti.9gs . . BSeries StandardsA series ofTIA/EIA documents related to cabling standards, many of which are directly relevant to fiber optic cable design and instal- lation, as illustrated in the accompanying chart. The text of these documents is available for purchase from the TIA online. See TIA/EIA B Series chart. Bsignal See Grade B signal. B-911 A telephone emergency response system with a subset of the capabilities ofa fu1l911 system. Most notably, it doesn't include Automatic Location Infor- mation (ALI). B-CDMA Broadband Code Division Multiple Ac- cess. InterDigital Communication Corporation's commercial wireless local loop TrueLink product 92 Category conversation interactive Example activities telephone, conferencing, audio graphics, videotelephone, videoconferencing distance education, services-on- demand, Web browsing, retrieval services such as news, stocks, etc. © 2003 by CRC Press LLC lTU-T in 1990. These developed into broader standards and specific recommendations for implementation, including network architecture, operations, and maintenance. Recommendations to use ATM as the switching infrastructure for B-ISDN contributed to the formation of the international ATM Forum which promotes commercial implementation of ATM and related tech- nologies. Physical layer transmission for B- ISDN is accom- plished through the Synchronous Optical Network (SONET) system. See I Series Recommendations. B-LT See broadband line termination. B-MAC, BMAC Broadcast Master Antenna Control. A device to control a communications antenna (e.g., microwave radio antenna). Traditionally it has been a self-contained unit, but computer software applications that emulate a controller unit are gaining popularity (with the traditional switches and dials being graphically displayed on the screen). B-NT broadband network termination. See broadband line termination. B-picture bidirectionally predictive-coded picture. In MPEG animations, a picture intended to become a frame that is encoded according to infonnation derived from both past or later frames in the sequence, using predicted motion compensation algorithms. Once encoded, it is considered to be a B- frame. See MPEG encoder. B-scope, E-Scope A radar screen displaying information on range (V-axis) and bearing in rectangular coordinates. See A-scope, C-scope. B- TE Broadband Terminal Equipment. An equipment category for broadband ISDN (B-ISDN) connecting devices, B- TE encompasses terminal adapt- ers and terminals. See ISDN. B8ZS binarylbipolar eight-zero substitution. A line- code substitution technique to guarantee density in network transmissions independent of the data stream. It is used on T1 and E1 network lines. The zeros can be replaced at the receiving end to restore the original signal. Babbage, Charles (1791-1871) An E.nglish re- searcher who contributed a great deal to the theory and practice of computing and conceived his now- famous analytical engine by 1834. While Babbage's Document Date TIAIEIA B Series Standards Committee/Description TIA/EIA-568-B.3 1 Apr 02 TR-42 Optical Fiber Cabling Components Standard (ANSI/TIA/EIA-568-B.3-2000) Specifies the component and transmission requirements for an optical fiber cabling system (e.g., cable, connectors). TIAlEIA-568-B.2-2 1 Dec 01 TR-42 Commercial Building Telecommunications Cabling Standard - Part 2.· Balanced Twisted-Pair Cabling Components - Addendum 2 (ANSI/TIA/EIA-568-B.2-2-2001) Provides corrections to the 568-B.2 Standard. TIA/EIA-568-B.l-l 1 Aug 01 TR-42 Commercial Building Telecommunications Cabling Standard - Part 1: General Requirements - Addendum 1 - Minimum 4-Pair UTP and 4-Pair ScTP Patch Cable Bend Radius Applies to minimum 4-pair unshielded twisted-pair (UTP) and 4-pair screened twisted-pair (ScTP) patch cable bend radius. TIAlEIA-568-B.1 1 Apr 01 TR-42 Commercial Building Telecommunications Cabling Standard - Part 1: General Requirements This standard specifies a generic telecommunications cabling system for commercial buildings that will support a multi-product, multi-vendor environment. TIA/EIA-568-B.2 1 Apr 01 TR-42 Commercial Building Telecommunications Cabling Standard - Part 2: Balanced TWisted Pair Cabling Components This standard specifies cabling components, transmission, system models, and the measurement procedures needed for verification of balanced twisted pair cabling. TIA/EIA-568-B.2-3 1 Mar 02 TR-42.7 Commercial Building Telecommunications CablingStandard - Part 2: Balanced TWisted-Pair Cabling - Addendum 3 - Additional Considerations for Insertion Loss and Return Loss Pass/Fail Determination (ANSI/TIA/EIA-568-B.2-3-2002). This addendum adds clause 1.2.5 to TIA/EIA-568-B.2. 93 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary ideas for computers could not be easily built with technology available in the 1800s, the basic ideas were sound and have stood the test of time. Ada Love- lace collaborated with him in his work. There is a cra- ter on the moon named after Charles Babbage. See Charles Babbage Institute. babble Crosstalk from other communications circuits and the noise resulting from such crosstalk. This is typical of electrical circuits and is not a significant problem in fiber optic circuits except where electrical switches or loop sections are part of the system. The term generally implies a number of noise sources combined. babble signal A deliberate transmission consisting of composite or otheJ.Wise confusing signals to obscure the intended transmission from unwanted listeners. A babble signal may be used as a jamming mechanism to deliberately interfere with other transmissions. See frequency hopping, j am signal. BABT See British Approvals Board for Telecommu- nications. BAC See binary asymmetric channel. back bias 1. A technique for restoring the environment in a vacuum tube which may have been altered by external forces, by applying a voltage to the control grid. 2. A means of feeding a circuit back on it- selfbefore its point of origin or contact. One important application of this technique has been the cre- ation of regenerative circuits in electron tubes, an important milestone in radio signal amplification. Re- generation was developed independently by E. Arm- strong and L. de Forest and hotly contested in a patent suit. 3. In semiconductors, back bias is sometimes more commonly called reverse bias. It refers to an external voltage used to reduce the flow of current across a p-njunction, thus increasing the breadth of the depletion region. back doorA security hole that is accessible without going through the normal login/password procedure. A back door may be deliberately left by the develop- ers or maintainers ofa software application or operating system in order to gain entry later, sometimes much later. Back doors have legitimate uses for maintenance and configuration but are sometimes abused by disgruntled ex-employees or employees engaged in embezzlement or other illegal or unauthorized activities. See back porch. back electromotive force, back EMF An electromotive force opposing the main flow of force in a circuit. back end 1. A program that sends output to a particular device or front end. See client/server. 2. The final step in a transparent (to the user) task or process. 3. In networking, the manner in which a lower layer provides a service to the one above it. 4. In elec- tronics, the final production stages of assembly and testing. back end processor In computing, a chip or set of chips or separate computing unit that handles 'back end' tasks such as data storage and retrieval in order to free up the main CPU for processing tasks. back haul See backhaul. 94 back lobe In a directional antenna, there is a main lobe and there may be additional lobes, one of which extends backward from the direction of the channeled signal, called a back lobe. back porch 1. On a computer system, a file access point to the system or an application with limited privileges which may not be publicly announced or which may have a group password. In other words, there may be some files available to certain employees that may not be generally accessible by all employees. It's like a meeting place on a friendly neigh- borhood porch in a back yard where invited people are welcome to visit as long as they don't go inside the house and disturb the privacy of the home own- ers. This environment is somewhat like an unadver- tised anonymous FTP environment in that users of the 'porch' do not have full privileges or access to all parts of the system. A back porch differs from a back door in that it is a circumscribed, known area, with limited privileges. A back door, on the other hand, may provide full privileges and is often not known to anyone but the person who programmed the software. A front porch would be apublicly visible, limited access area open to anyone. 2. In video broadcasts, the portion ofa composite picture signal before the video signal which is between the edge of the horizontal synchronization pulse and the edge of the associated blanking pulse. back projectionA means of presenting information on a visual display system by illuminating, or otherwise activating, the display elements from behind. In its broadest sense, most TV and computer screens are back projection systems. However, a further distinc- tion can be made that a projection system implies a larger display system, as would be used in a seminar, theater, or lecture hall, environments traditionally equipped with front projection systems (film projectors, slide projectors, etc.) that are separate devices from the actual display screen. In these environments, back projection screens are less common. One of the main advantages ofa back projection system is that the audience and various speakers can stand or sit directly in front of the display without obscuring the image projection with shadows. Back projection also tends to show up better in rooms where there is sufficient ambient light for people to take notes. The main disadvantage of such a system is that it usually requires specialized equipment for both the projection and the display screen, whereas films and slides can be shown on many types of surfaces, including a plain wall. backreflection Ina fiber lightguide, light that reflects back in the originating direction. Thus, it may inter- act with the original propagating signal. In most cases back reflection is undesirable and occurs where there are excessive bends, foreign particles, poorly fused joints, bad doping characteristics, or bad terminators. Fiber optic filament endfaces are commonly polished to fine tolerances and particular angles to control or eliminate back reflection. Sometimes a slightly concave endface can reduce back reflection better than a flat endface by reducing the fiber-to-air interface © 2003 by CRC Press LLC that exists at the coupling joint. Super polishing a concave endface can provide up to an additional-IS dB of back reflection for high-speed, high-bandwidth, systems such as broadband digital communications systems. An angled interface (e.g., 8°) is more difficult to "machine" and connect due to rotational align- ment requirements, but provides even better contact and back reflection tolerances of up to -15 dB better than super polished endfaces (up to about -70 dB). Once a fiber filament is polished, it is still important to ensure that the end is thoroughly cleaned without introducing scratches, otherwise back reflection can result from particle interference. Since a single- mode fiber core is only about 9 microns in diameter, even small particles can potentially obscure the core. Hand cleaning with an air blower and isopropyl alcohol or machine cleaning should be done just before coupling, especially if the fibers have been shipped or stored for any length of time. The endface should be checked with a magnifier (e.g., a micro- scope) before coupling, otherwise any stray particles could mar the surface when subjected to pressure in the joint. See attenuation, fusion splice. See accep- tance angle, Littrow configuration. backscatter See backscatter. backboardA sturdy surface on which to mount electrical panel boxes, punchdown blocks, or other threading or wiring equipment that needs a firm back- ing and wouldn't be secure if mounted on plaster, wallboard, or some other brittle surface. Sometimes equipment is preinstalled and tested on a backboard, so it can be assembled lying down in a convenient position, e.g., off-premises, and then quickly mounted where desired. backboneA primary ridge, connection link, or foun- dation, generally represented as longitudinal with branches. A telecommunications backbone is a ma- jor supporting transmission link from which smaller links, nodes, and drops are connected. Since the late 1990s, the number and scope of optical fiber-based communications backbones has been steadily increasing. In 1999, RCN Corporation, a large regional Internet service provider (ISP), announced that it had selected a dense wavelength division multiplexing (DWDM) optical transport system for its east coast fiber backbone. The system was intended to support up to 40 wavelength paths transmitted over a single strand of fiber. In spring 2000, Metromedia Fiber Network, Inc. (MFN) announced an acceleration strategy for de- ploying and extending their optical Internet infrastructure internationally throughout North America and Europe. The company's intention is to be the largest global provider of fiber-based infrastructure by 2004. In late 2000, China Telecom began building China's largest capacity broadband network, projected to ex- tend about 40,000 cable kilometers in a rapidly grow- ing region that did not previously employ optical fiber. The system is being built upon Coming LEAF® fiber, an advanced non-zero dispersion-shifted fiber. In August 2001, Cogent Communications, Inc. announced completion of the majority of an 80-Gbps bandwidth expansion to its I2,400-mile long-haul OC-192-based backbone that serves Internet Proto- col communications to reach 45 of the 50 largest metropolitan service areas (MSAs). Not all optical service providers are expanding, however. In late January 2002, it became known that Glo- bal Crossing was filing for the fourth largest corpo- rate bankruptcy ever recorded in the U.S. Global Crossing had laid approx. 100,000 miles offiber optic cables around the world, including submarine cables in the Atlantic and Pacific Oceans. Sale of the company as a whole or some of its assets were both put forward as Chapter 11 strategies for continuance of the company. See 6bone, Mbone. backbone data circuitA main data communications circuit, usually of national distribution, from which there are secondary branches. The term was originally used to describe key USENET/email sites but is now used more generally. A backbone is sometimes defined in terms of the speed of communications and primary nature of the data, and it is sometimes considered the part of the circuit that customarily carries the heaviest traffic. Abackbone can connect a main- frame with local area networks (LAN s) or individual terminals or individual systems with peripherals such as modems, printers, video cameras, etc. Bridges, routers, and switches perform a variety of traffic control and direction functions within the system. More regional, medium-sized installations, as at universi- ties and large corporations, may be called campus backbones. Backbones can generally be categorized into three types: distributed backbones, utilizing multiple routers; collapsed backbones, with a configuration switching hub generally contained within a single building complex; and hybrid backbones which include collapsed backbones in individual building complexes interlinked with FOOl distributed backbones, for example. See campus backbone. backbone radio circuit In packet radio communications, a packet-radio bulletin board system (PBBS) that provides automatic routing services for a number of users. background communication Data communication that occurs while other user actions are taking place; it carries on in the background without intruding on other activities. For example, a user may be using a word processor while a file is uploading or downloading in the background. Single-tasking systems don't do this. Background communications are character- istic ofmultitasking systems and some task-switching systems, which will time-splice the processor between the two activities. background noise Ambient noise, environmental noise, noise without significant meaning. If background noise levels are too high, they can interfere with communications. There are now digital systems, such as cellular phones, that can selectively screen out background noise and increase the clarity of a transmission from a noisy environment. This 95 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary capability has both industrial and social communication advantages. The same types of algorithms are often used in videoconferencing and audio editing systems to enable users to condition the sound to filter out unwanted frequencies or noise. background process, background taskA computer program operating or waiting in the background, not in immediate sight or use of the user, often at a lower priority level, becoming active quickly when needed or brought to the foreground, or when other processes are idle. On data and phone systems, tasks such as system operations, archiving, cleanup of temporary files, print spooling, diagnostics, etc., are frequently run as background tasks and may function primarily on off-peak hours or when more CPU time is available. backhaul In telephone and computer network communications, to send a signal beyond a destination and then back to the destination. For example, a phone call from Seattle to north San Francisco may be routed through Palo Alto and back to San Francisco. Backhauling happens for a number of reasons, including cost, availability, and traffic levels. Backhauling may also occur in companies with a number of branch offices. A call to one branch may, for various busi- ness reasons, be backhauled to another, in order to serve the caller's needs. Backhauling on the Internet is quite common. For example, in some cases it may be cheaper or easier to Telnet to an ISP in a distant city with better rates and services, and then access ftp sites, chat channels, or other services by backhauling, perhaps even to the originating city, than to call out from a more limited local service. backhaul broadcasting In cable broadcasting, to bring back a signal (haul) from a remote site (such as a big sports event or hot news tornado zone) to the local TV station or network head station for processing before being distributed to viewers. backoffA retransmission delay which may occur when a transmission cannot get through to its destination, due to an interruption, collision, a medium already in use, etc. Ifa transmission fails, rather than trying again immediately, the sending or interim system may wait momentarily before retransmitting. The retransmission interval may be random or may be set within a certain range by backoff algorithms incor- porated into the protocols being used. Backoff (one word) is the noun fonn; back off (two words) is the verb form. backplane, backplane bus 1. In desktop computers, the physical connection between a data bus and power bus (both of which are usually on the motherboard) and an interface link or card (which are usually in- serted into slots). See bus. 2. In phone exchanges, the high-speed line and power sources that connect individual components, often through circuit board slots. The speed and quantity of transmissions through the exchange are in large part determined by the capacity of the backplane. See bus. backpressure, backpressure propagationIn a network, the information that is being transferred is 96 almost always accompanied by metadata describing the infonnation content and, on large networks, about its progress from source to destination. In hop-by-hop routing, there is network communication about the location and subsequent routing as well. This overhead can sometimes add up if there is congestion on the network, and it may propagate upstream to form backpressure. backscatter Backscatter is a phenomenon in which radiant energy is propagated in areverse direction to the incident radiation, sometimes in a diffuse pattern. Backscatterusually happens when the radiant energy comes in contact with an object, particles, or various projections in an uneven terrain, or when it encoun- ters outer boundaries or particles in a transmissions medium, as in fiber optic cables. Sometimes backscattering is useful, and sometimes it is undesirable. In radar, the signals returned when radar waves hit a target and are reflected back to the sensing device are used to track the location and movement of the target. In directional antenna assem- blies, backscattering of signals to the rear of the antenna may cause interference. See zone of silence. backscatter, ionospheric In the E and F ionospheric regions (where many radio waves are bounced from the sender to the receiver) at the general angle at which the wave hits the ionized particles, some of the waves are propagated back in the direction from which they came. Backscatter may cause interference to the original signal or may result in the transmission being heard by receivers near the transmitting station (although the signal is generally weak). See E layer, F layer, ionosphere. backup An alternate resource in case of failure or malfunction of the primary resource. The alternate may be identical (or as close as possible) to the original, as in data archives, or may be a substitute which is just sufficient for short-term functioning, as in a backup light source or power supply. backup link A secondary link which may not typi- cally carry traffic or may carry only overload traffic unless there is a failure in the primary link, in which case it becomes available for transmission until the fault is corrected. See alternate routing. backup ring On Token-Ring networks, a second ring is often set up to provide a backup in case of failure of the first ring. Depending upon the setup, the system may switch automatically or may need to be switched manually. See Fiber Distributed Data Interface. backup serverA server system expressly designated to automate the handling of data protection tasks. The server can be configured to back up certain machines, directories, or files at predetermined times, or when processing overhead from other tasks is low. A backup server is usually configured with drivers for a number of backup devices, such as tape drives and mag- neto-optical disks, and may be secured against fire or public access to protect the backed up data. backwardchannelA channel in which transmissions are flowing in the direction opposite to the flow of the majority of the data, usually the infonnational © 2003 by CRC Press LLC data. Some interactive systems are designed so that control signals and queries flow through the back channel, while the majority of the data flows through the fOlWard channels, as in video-on-demand. Thus, the system can be optimized to accommodate faster data flow rates in the forward direction. Some sim- plified Internet access systems are designed this way, with a modem or other connect line set for faster data rates for downloading, and slower data rates for que- rying as, for example, for Web browsing. backward compatibility The capability ofa system to run legacy (older model) programs or to support older equipment. For example, 1.4 megabyte floppy drives are usually backwardly compatible with 770 kilobyte floppy diskettes; they can read, write, and format the older, lower capacity floppy diskettes. Similarly, a new version of a word processing program may be able to read and write data files created by an older version of the software. Backward Explicit Congestion Notification BEeN. In Frame Relay networking, a flow control technique that employs abit set to notify an interface device that transmissions flowing in the other direction are congested and that congestion avoidance procedures should be initiated by the sending device for traffic moving in the direction opposite to that of the received frame. backward indicator bit BIB. 1. In data networking, a signal bit or sequence of bits that is used to request retransmission when an error condition is detected. 2. A flow control status bit used in Signaling System 7 (SS7). In MTP Layer 2, a Message Signal Unit (MSU) indicator carried in bit 8 of the first octet in conjunction with the backward sequence number (BSN). backward learning An information routing system based upon the assumption that network conditions in one direction will be symmetric with those in the opposite direction. Thus, a transmission moving ef- ficiently through a path in one direction would as- sume this to be an available, efficient route in the other direction as well. backwave In radiotelegraphy, an undesirable interference heard between code signals. Bacon, Roger (ca. 1220-1292) An English philoso- pher, scientist, and a member of the Franciscan Or- der. In 1265, he completed an encyclopedic document of the knowledge of the time entitled Opus majus. BACP See Bandwidth Allocation Control Protocol. BADC binary asymmetric dependent channel. See binary asymmetric channel. bad blockInmagnetic storage that is segmented into blocks, a section with write or read failures. Some operating systems will map out bad block sectors on a diskette or hard drive during formatting so they will not be addressed or used and will continue to format the remaining good parts of a disk. This is one of the reasons why the amount displayed for the usable portion of a disk can differ from the total storage capacity of the disk. Bad Frame Indicator BFI. A means of signaling an error condition in a frame-based communications medium such as apacket networking error condition alert or a cellular radio speech decoder frame error alert. In its simplest form, BFI uses binary logic to indicate an error-free frame (usually "1") or a bad ~a;!~:~;~;2}::S~~:~~:~~~~~e~:::. aged him to get a good education to improve his op- portunities in life. He had an agile mind and emigrated to the United States to pursue his interests and pro- fessional connections. He is responsible for the in- vention of Bakelite, the frrst synthetic polymer, and Velox, a new type of photographic paper. See Bake- lite, Bakelyzer. barne, heat A corrugated, latticed, or slitted structure that aids in controlling heat. In fiber optics a fiber routing tray for handling the positioning of multiple fiber cables can also serve as a heat baffle for channeling heated ambient air away from components or joints that might be adversely affected by heat. See heat sink. baffle, lightAdevice to selectively control the emis- sion oflight. When the device can be readily opened or closed or is frequently done so, it is more often called a shutter. When it is generally fixed, or is only infrequently opened or closed, it is usually called a baffle. Baffles are common in scientific instruments that il- luminate specimens or work stages. Such devices may have a baffle to prevent light from directly illuminating a sample and may optionally have a baffle to prevent stray light from disturbing nearby work areas. A baffle may be one of the components of an integrating sphere, which is acomponent installed in the entrance port of a monochromator. By rotating the sphere, the viewing angle can be controlled. A baffle may also be used to selectively cast a shadow against which a fiber optic light source can be directed for calibration purposes. Since optical components can be impaired by dust and moisture, it is sometimes advisable to close or cover a baffle during storage or times of low use. Since a baffle has many small surfaces, it may be difficult to clean. Removing it and cleaning it in alcohol or water or vacuuming it, if it is difficult to remove, can help prevent contamination of nearby components. See stray light. baffle, sound A device to direct sound and to prevent sound waves from interfering with one another. Abaffle consists of a series of carefully spaced cor- rugations that provide a longer path within a limited amount of space. It can be constructed of wood, metal, or synthetics and works by lengthening the air path along the diaphragm through which the sound waves travel and by reducing interaction among them. Baffles are commonly used in speaker systems to improve the clarity of the sound. BAFTA See British Academy ofFilm and Television Arts. bag phone slang See transportable phone. Bain, Alexander (1811-1877 [dates approximate; reports vary]) A Scottish chemist and clockmaker 97 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary who developed an electrochemical paper tape record- ing system in the mid-1800s, suitable for telegraphic signals, at about the same time Samuel Morse was developing a somewhat similar system. The Bain system worked reasonably well except in situations with high noise on the line, which would create spu- rious marks on the tape. Bain received a patent for his version of the telegraph in the 1840s which was contested by Morse but was sufficiently different to hold up in court. Morse sub- sequently bought out the Bain systems and converted them to his own. See Bain Chemical Telegraph. Bain ChemicalTelegraph A historic automatic print- ing telegraph based on chemical methods, patented in 1848 and 1849 (U.S. #5,957 & 6,328). If you have seen the output from a facsimile machine on thermal paper, you have the general idea of how it worked. Bain's system used paper that was coated with a chemical that was sensitive to electrical impulses on the receiving end of the transmission. When a message was received, the electrical impulses would ini- tiate a chemical reaction that would change the color of the paper in the active areas, creating an image to match the one that had been transmitted, essentially a historic facsimile machine. Later enhancements of the general principles of the Bain machine led to very fast telegraphic systems. Seen Bain, Alexander; telegraph, history. Baird,John Logie (1888-1946) Although historical research makes it clear that a number of people independently developed different aspects of television reception and display, in the late 1800s John Baird, a Scottish inventor, was one of the earliest successful experimenters. He was able to transmit a two-tone image ofa face onto a small television screen in 1926 and by 1932 had developed a practical system for broadcasting images. Baird used some of the principles of the Nipkow disc to develop his system. Alight-sensitive camera was placed behind a perforated rotating disc, just as Nipkow had placed light-sensitive selenium behind a perforated rotating disc. The Baird system could only display a crude 30-line image at a frame rate a little less than halfof that used now, but the 'proofof concept' technology launched an industry that is still going strong. In the 1920s, in collaboration with Clarence W. Hansell, Baird patented the concept of using conduct- ing rods or pipes to transmit images, a forerunner to fiber optic transmissions. However, it was Heinrich Lamm who successfully used optical fibers for image transmission. See Lamm, Heinrich; Nipkow, Paul. Bakelite The development ofBakelite in 1907 revo- lutionized industrial production and heralded the "age ofplastic." Inventor Leo Baekeland created this first synthetic polymer with a trademarked mixture of phe- nol, formaldehyde, and coloring agents. He was awarded a patent for Bakelite in December 1909 (U.S. #942,809). This new material was hard and acid-, heat-, and water-resistant. It was quickly put to use in thousands of industrial products as a noncorrosive coating and chemical binder for composite materials. Bakelite Frequency Range Designations ITU Designation Abbrev. Frequency Wavelength Typical or Example Uses 2 extremely low ELF 30-300 Hz 10 Mm-l Mm 3 ultra low ULF 300-3000 Hz IMm-30 km 4 very low VLF 10-30 kHz 30 km-l0 km 5 low LF 30-300 kHz 10 km-l km Facom distance measurement and navigation 6 medium MF 300 kHz-3 MHz 1 km-l00 m AM radio 7 high HF 3-30 MHz 100 m-l0 m CB radio 8 very high VHF 30-300 MHz 10 m-l m TV channels, FM radio, land mobile radio (cellular), ISM, LAWN, amateur radio 9 ultra high UHF 300 MHz-3 GHz 1 m-l00 mm TV channels, CB radio, land mobile radio (cellular), PCS, radar 10 super high SHF 3-30 GHz 100 mm-l0 mm Satellite, amateur satellite, U-NIl bands, radar 11 extremely high EHF 30-300 GHz 10mm-l mm Satellite 12 tremendously high THF 300-3000 GHz Note: In the above frequency ranges, the lower limit is exclusive, the upper limit inclusive. 98 © 2003 by CRC Press LLC also provided new ways to create colorful, water-resistant, moldable household products, dials, small ap- pliance casings, and even jewelry. Many early tele- phones and radios used Bakelite in their construction. See Baekeland, Leo. Bakelynr It looks like a B-movie adaptation of a Jules Vern diving bell on wheels, but it actually is a floor-standing iron pressure cooker devised by Leo Baekeland to mix simple organic chemicals into his versatile Bakelite synthetic resin. See Bakelite. Bakken Library and Museum A museum located in Minneapolis, Minnesota, that houses a collection of about 11,000 books, journals, and manuscripts documenting the history ofelectricity and magnetism and their applications in life sciences and medicine. The collection focuses on 18th through 20th century works, including those of Franklin, Galvani, Volta, and other well-known pioneers. In 1969, the collection of historical electrical machines was added to the activities of the museum, including several Oudin and D' Arsonval coils and many electrostatic generators. http://bakkenmuseum.org/ balance To equalize, to counterbalance, to bring into harmony or equipoise, to offset in equal proportion, to arrange such that opposing elements cancel one another out or are of comparable weight, size, construction, value, strength, or importance. Balancing is commonly done in electrical circuits to equalize loads or to diagnose the location ofbreaks or inter- ruptions in a line. Stereo volume is usually balanced to equalize the volume or perceptual evenness of the left and right channels. balanced bridgeAbridge circuit in which the measured output voltage is equal to zero. Bridge circuits are sometimes used diagnostically to seek out and measure unbalanced circuits in order to detect abreak or anomaly in the wiring. See Wheatstone bridge. balanced circuit A circuit in which the electrical properties are symmetric and equal with respect to ground. See balanced bridge. balanced configurationApoint-to-point High Level Data Link Control (HDLC) network configuration with two combined stations. balanced line An electrical circuit consisting of two conductors with matched voltages at any correspond- ing point along the circuit, and which have opposite polarities with respect to ground. It is not uncommon to use more than one line to carry related transmissions or a split transmission, especially in newer mul- timedia applications. By matching voltages and set- ting opposite polarities, it is possible to reduce the incidence ofcrosstalk and interference, resulting in cleaner signals. balanced modulation Modulation is a means of adding information to acarrier signal by varying its properties such as amplitude or frequency. In the early days of radio wave broadcasting, experimenters sought ways to manipulate or reduce the amount of bandwidth that was needed to carry the desired information. It was found in amplitude modulation (AM), using electron tubes, that the control grids of two tubes could be connected in parallel, and the screen grids connected for push-pull operation such that the sidebands were singled out for transmission without the carrier. Double sideband modulation is another name for balanced modulation. Inelectronic music, balanced modulation refers to a way of com- f~::; ~~~~~:l :~~~: ~~c~~~~~~e a':J~:: :~:~~:. phase is valid for positive and negative signals. As in radio communications, only the sidebands from the original signal remain. See amplitude modulation, modulation, single sideband. balcony A small ledge or platform for aerial jobs used by film crews, antenna technicians, or utility pole workers. bale, bonfire Asignal fire, one of the oldest optical networks, and one which could be used at night. In the 1400s in Scotland, a simple signal code, using one to four bales, was established by an act of Parliament. ballast 1. A physical object that improves stability through its mass or can be jettisoned to reduce mass. Ballast is commonly used in boats and hot air bal- loons. 2. In an electrical circuit, a device that stabi- lizes a current or provides sufficient voltage to start up amechanism (such as afluorescent bulb) or transmission. Apparently about 50% of fluorescent light- ing ballasts produced until the late 1970s contain haz- ardous PCBs of 50 ppm or higher in the potting material that surrounds the capacitor and should not be disposed of in landfills. They can be sent to autho- rized disposal centers. balun balanced/unbalanced. A small, passive trans- forming device used to match impedance on unbalanced lines that are connected together, such as twisted-pair cable and coaxial cable, so the signal can pass through the differing types of lines. As with many interface devices, there may be some signal loss through the balun. See bazooka. BAN 1. base area network. 2. basement area network. 3. Bay Area network. 3. See Billing Account Num- ber. 4. See body area network. band 1. The range offrequencies between two defined limits, usually expressed in hertz (Hz). See bandwidth. 2. A group of electronic tracks or channels. 3. Agroup of channels assigned to a particular broadcast spectrum, e.g., UHF (300 to 3,000 MHz). See chart ofregulated band designations. 4. The range or scope of operations of an instrument. 5. An AT &T- designated WATS Service Area. band allocations Frequency ranges for radio wave communications have to be shared, and devices com- municating on similar frequencies can have devas- tating effects on one another. For this reason, the frequency spectrum is allocated and regulated in order to maximize use of the available spectrum, and also to designate waves suitable for different types of activities. In the U.S., this information is contained in the Federal Communications Commission (FCC) Table ofFrequencyAllocations and the U.S. Govern- ment Table of FrequencyAllocations, which together comprise the National Table of Frequency Alloca- tions. Other organizations such as the ITU have tables as well. The values in the tables change, and what is 99 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary represented in the Frequency Allocations and Com- mon Uses chart is avery generalized overview to provide a basic understanding. When new frequencies are available, they may be allocated to amateur or specialized uses or auctioned for commercial use. When a user stops using an allocated frequency, it is reassigned. The available spectrum ranges have been established for various types ofcommunications and some regions are unlicensed. Some of the more interesting unlicensed uses have been listed in the Frequency BandAllocations chart. band center The computed arithmetic mean between the upper and lower frequency limits of a frequency band. This measure can be used to adjust modulation, to constrain it, or to provide the maximum possible amplitude range for an amplitude modulated (AM) signal. band splitterAmultiplexer that subdivides an available frequency into anumber of smaller independent channels, using time division multiplexing (TOM) or frequency division multiplexing (FDM). See bandpass filter. Frequency Band Allocations (Radio Waves) and Common Uses Name Approx. Range Examples ofApplications AM band 535-1605 kHz Amplitude modulation, used commonly for radio broadcasts. Videoconf. around 24 MHz Certain local videoconferencing systems. Mobile various Frequencies around 48 MHz are used for consumer outdoor mobile intercom units. Radar 10-200 MHz Imaging radar applications. Amateur 50-54 MHz Amateur radio use. Frequencies allocated for amateur use are 144-146 MHz frequently changed as the FCC often puts a higher priority on commercial users. This is despite the fact that amateurs have contributed a great deal to radio communications technology. FMband 88-108 MHz Frequency modulation, used commonly for radio broadcasts and some low power FM transmitters (intercoms, bugs). SAR 141 MHz Synthetic Aperture Radar for environmental sensing and image processing. Radar 300 MHz + Approx. lower end ofradar for remote sensing applications. USDC 824-894 MHz U.S. Digital Cellular FDMA and TDMA cellular phone services. A-F block 1850-1910 MHz Personal Communications Services (peS) A to F block licenses 1930-1975 MHz granted to phone companies serving MTAs. UPCS 1890-1930 MHz Unlicensed Personal Communications Services (PCS). S-band 2310-2360 MHz Frequencies sensitive to terrain, making them unsuitable for some types of transmissions. U-NII 5150-5350 MHz Unlicensed National Information Infrastructure wireless communications, including PCS. P-band .22 39 GHz Experimental radar. SAR. C-band 4-8 GHz Microwave frequencies, more specifically 3.40 to 6.425 GHz. Satellite - larger antennas. VSATS. Incumbent telephony operations (2.0 GHz). Experimental radar. SAR. L-band 1-2 GHz Experimental radar. SAR. X-band 8-12.5 GHz Dedicated for use by the U.S. military for satellite communications. SLAR. Ku-band 10.95-14.5 GHz Now subdivided into fixed satellite service (FSS) at 11.7 to 12.2 GHz, and broadcasting satellite service (BSS) at 12.2 to 12.7 GHz. VSATs. K-band 18.5-26.5 GHz Satellite applications with smaller antennas, radar. Ka-band 26-40 GHz Satellite applications with smaller antennas, radar. Q-band 36-46 GHz Satellite, radar. V-band 40-75 GHz Radar band. W-band 75-110 GHz Radar band. 100 © 2003 by CRC Press LLC band, citizens See citizens band radio. band-elimination filter BEF. Aresonant circuit filter with a single, continuous attenuation band, in which the lower and higher cutoff frequencies are neither zero nor infinite. band-stop filter, band-rejection filter A resonant circuit filter for locking out a specified range, or ranges, of transmissions according to their frequency ranges. banded cable Two or more cables physically held in proximity to one another (aggregated) with metal or plastic straps or bands. bandpass The range of frequencies that will pass through a system without excessive weakening (attenuation), expressed in hertz. See bandpass filter. bandpass filter Adevice with aresonant circuit, often used in conjunction with frequency division techniques, that recognizes and selectively allows control offrequencies, letting through those that are desired. A band-reject filter is complementary in the sense that it recognizes and selectively screens out a range offrequencies in order to fonn a 'blackout' area within the full spectrum of available frequencies. See band splitter. bandspread tuning A means of spreading aband of frequencies over a wider area in order to adjust the tuning more precisely. This is most commonly found in shortwave radios and more than one set of dials may be used, with differently spaced tickmarks on the tuning gauges to aid in adjusting the settings. bandwidth 1. The extent ofa range offrequencies between the minimum and maximum endpoints, typi- cally measured in hertz (cycles per second). Techni- cally, the term bandwidth is associated with analog systems. In recent years, it has been more loosely applied to mean data rates in digital systems and, hence, is sometimes expressed in bits per second (bps). 2. The range of the frequency required for the successful transmission ofa signal. It may range from a few kHz for a slow-scan or sideband signal to 100 kHz for a frequency modulated (FM) signal. That is not to say that the bandwidth of a signal necessarily takes up the entire range ofthe band that may be designated for its use. See band spectrum table. 3. In a cathode-ray tube (CRT) device, the speed at which the electron gun can turn on and off. 4. The capacity to move information through asocial, data, or physical system. 5. Anumerical expression of the through- put of a system or network. bandwidth allocation, bandwidth reservation In a network, the process of assessing and allocating re- sources according to flow, priorities, type, etc. It en- ables priority administration of the network traffic when congestion occurs. BandwidthAllocation Control Protocol BACP. In ISDN, aprotocol providing mechanisms for controlling the addition and removal of channels from a mul- tichannellink. bandwidth augmentation 1. Adding additional frequencies or channels to an existing bandwidth range. 2. Replacing existing physical transmissions media with broader bandwidth media in asystem where the data transmission is capable of broader bandwidth, but the physical media caused abottleneck due to its inherent limitations (e.g., replacing copper wiring with fiber optic). bandwidth compression Techniques for increasing the amount of data that can be transmitted within a given frequency range. The increased demand for broadband applications such as video has motivated technologists to find more efficient ways to use existing transmissions media, resulting in better compression schemes and better management of the direction of transmission in bidirectional systems. Compression can be very medium-specific. For example, in sending voice, blanks between words may be removed; in sending images, white pages may be compressed or eliminated; in sending complex mul- ticolored images, lossy formats such as fractal compression or other lossy compressions such as JPEG may be used. bang colloq. !Exclamation point. 1. A common sym- bol used in many programming languages. For example, in C it represents a logical not. 2. Although its use is diminishing, it was at one time used in email addresses to designate a break between portions of an address, where an at sign (@) may now be used. Here is an example ofa bang path: {uunet,ucbvax} !galileo.berkeley.edu!usemame bankA row or matrix, usually of similarly sized or configured components or data cells. Individual units in a bank are often interrelated, by shape, function, or electrical contact. In its simplest sense, aphysical bank does not necessarily have connections between individual cells but may appear similar and be mounted in rows and columns. Banks may also be electrically related, either by induction, physical connections between the cells themselves, or by temporary electrical connections that occur when a bar drops down over a bank of cells, or a brush passes over the bank. Many large-scale telecommunications devices and junctions are set up in banks. Punchdown blocks at switching centers are set up in banks, often on racks or panels. Memory banks can be physical rows of memory chips in a circuit board. Large Internet Ac- cess Providers (lAPs) may have banks ofhundreds or thousands of modems, connected to phone wires. See bank switching. bank switching A method of extending access to banks of components, such as memory chips, beyond the extent of any of the individual components, especially in situations where the operating system or microprocessor can address only alimited amount of memory at one time. By paging or swapping between banks, the virtual memory capacity is extended beyond the default physical memory or operating system (OS) or central processing unit (CPU) capacity. Bank switching is a tradeoff that may slow down memory access. banner A clearly visible, often graphic representa- tion heralding an advertisement or a new section in a printout or other text or image communication. Its purpose is to command attention and often (1) to 101 © 2003 by CRC Press LLC . (ANSI/TIA/EIA-568-B. 3-2 000) Specifies the component and transmission requirements for an optical fiber cabling system (e.g., cable, connectors). TIAlEIA-568-B. 2-2 1 Dec 01 TR-42 Commercial Building Telecommunications Cabling Standard - Part 2.· Balanced Twisted-Pair Cabling Components - Addendum 2 (ANSI/TIA/EIA-568-B. 2-2 -2 001) Provides corrections to the 568-B.2 Standard. TIA/EIA-568-B.l-l. (ANSI/TIA/EIA-568-B. 2-2 -2 001) Provides corrections to the 568-B.2 Standard. TIA/EIA-568-B.l-l 1 Aug 01 TR-42 Commercial Building Telecommunications Cabling Standard - Part 1: General Requirements - Addendum 1 - Minimum 4-Pair UTP and 4-Pair ScTP. Pass/Fail Determination (ANSI/TIA/EIA-568-B. 2-3 -2 002). This addendum adds clause 1.2.5 to TIA/EIA-568-B.2. 93 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary ideas for computers could not be easily