Fiber Optics Illustrated Dictionary - Part 15 ppt

Fiber Optics Illustrated Dictionary Brewster's Angle Applied to Light different degrees, depending upon the angle, with Brewster's angle being the relationship where polar- ization is at its maximum. If the incident light is al- ready polarized in a direction parallel to the dielec- tric surface, it will not be reflected. There is a particular angle at which unpolarized light, when encounteringa dielectric surface, reflects as maximally polarized, called Brewster's angle, ex- pressed as 8 p • The angle of reflection, relative to the dielectric surface normal, is complementary to the angle of the refracted light, relative to normal. Con- versely, if light that is already polarized (in a direc- tion parallel to the surface plane) is incident to the surface, thepolarizingeffect of the dielectric cancels outthepolarizedincident light and nopolarizedlight is reflected. Brewster sangle is consistent for incident light and dielectric materials with the samecharacteristics, but varies with the wavelength and index of refraction of the dielectric with which the incident light interacts. polarized reflected light Ci E o c unpolarized incident light Brewster's law With respect to electromagnetic en- ergy encountering a dielectric material, the relation- ship between the angle of propagation of the reflected energy relative to the perpendicular of the. surface (nonnal), and the refractive index of the dielectric ma- terial, can be described in an equation derived by Brewster, known as Brewster slaw sO,6 p r· 4 ••• · •• ::· ••• ·.~} ••• ~· •• il~fl8p ·PQ~f.ip. In this equation,ep(ih~:~lli'gieai~hich the polariza- tion effect for the reflected energy is at its maximum for a given material and wavelength) is Brewster s angle. The index of refraction of the dielectric mate- rial is expressed as n. Thus, the refractive index is equal to the tangent of the angle of the reflected en- ergy (relative to surface normal). This information is useful for designing components that are intended to maximally polarize unpolarized radiant energy or to not reflect already-polarized energy (polarized par- allel to the surface plane). The accompanying dia- grams help clarify these relationships. Examples of applications that exploit Brewster's law which excessive voltage is detected and the circuit tripped or broken in order to prevent overload, elec- trical fires or damage to appliances or the main panel. 2. In radio communications, anyone who drops in on a channel to communicate when others are already engaged in conversation. 3. In public online forums, a person who breaks into an ongoing conversation or thread with irrelevant or unkind and unwanted com- ments. breaking strength 1. An industrial measure of the force needed to break a specific structure or material (or a combination of the two). Used in structural and safety design and selection and installation of appro- priate wires and cables. breakout An exit point for electrical conductors (wires, cables, etc.) along the length of the circuit, between the endpoints of the circuit. Breakouts can be used for additional installations or testing and di- agnosis of the circuit. Breakouts are usually covered or capped in some way to prevent interference with the circuit and shock or fire hazards. breakout box A diagnostic instrument used to tap into an existing circuit to evaluate its functioning, to see whether individual lines within a group are cor- rectly connected, and, in some cases, to detect which signals are being transmitted. Breakout boxes often have indicators such as tones or light-emitting diodes (LEOs) to help assess the line and may include jump- ers to temporarily switch connections. One useful application of a breakout box is to test a serial cir- cuit, since computer equipment manufacturers don't consistently follow the RS-232 or RS-423 specifica- tions. In the case ofa temporary need for a null mo- dem cable (e.g., for transferring information from one computer to another through telecommunications software), a breakout box can be used to cross the transmit and receive lines. See breakout. Brewster's angle In the context of an electromag- netic wave encountering a dielectric material, there is a particular angle, called Brewster's angle, at which the polarization effect of the interaction is at a maxi- mum, whether this is the polarization and reflection of unpolarized radiant energy (e.g., white light from the Sun) or the "cancellation" of energy through ab- sorption, ifit is already polarized parallel to the di- electric surface before contact. Different materials refract light to different extents. Much of David Brewster's research centered on studying the different optical properties of crystals, including their reflective and refractive properties. The specific angle at which Brewsterian effects oc- cur was found to be related to the refractive index of the dielectric material encountered by the propagat- ing incident wave and the polarization and other char- acteristics of the incident radiant wave. Brewster's angle will be between 0° - 90° since no polarization occurs if the radiant energy hits the dielectric at an angle perpendicular to the material (0° - straight on) or travels parallel to the dielectric's contact surface (90 0 - thus not being reflected). If the incident light is unpolarized when it encounters the dielectric, the reflected light will be polarized to 132 © 2003 by CRC Press LLC and Brewster's angle include photographic filters, sunglasses, radio signal conditioners, fiber optic cou- plers, photographic films, and a wide variety of com- ponents for scientific instruments such as micro- scopes. Brewster's law has broad and consistent applications in optics that are very useful but may sometimes be a hindrance. Novel ways to overcome some of its ef- fects have been recently developed. In the 1990s, it was found that highly birefringent, layered, polymer film could be assembled in alternating layers to con- trollight so that the net effect was to avoid polariza- tion of the reflected light that is characterized by Brewster's angle. This led to the development of lay- ered film components capable of reflecting light uni- formly, which has many potential applications in communications, astronomy, and medical imaging. See acceptance angle, blaze angle, Brewster's angle, dichroic, incidence angle, Malus's law, Snell's law. Brewster, David (1781-1868) Scottish-born British author, qleric, educator, and scientist who built tele- scopes as a child and entered university as a young adolescent. Brewster fulfilled his early promise and demonstrated talent in many fields of endeavor. He was admitted to the Royal Societies of Edinburgh and London and received many medals and honors dur- ing his lifetime. He served as editor of the Edinburgh Encyclopedia for two decades and as president of the University of Edinburgh for almost a decade near the end of his life. Much of Brewster 's important experimental research was in the field of optics, with a focus on the struc- tural components of the eye, as well as the interac- tion of light with the optical properties of crystals which, in turn, led to the formulation of Brewster s law to describe properties related to polarization. Around 1811-1813, he noted that there was a particu- lar angle, Brewster s angle, at which the interaction of light with a mineral substance has a maximal ef- fect related to polarization. Over the next two de- cades, he extended his studies into the spectral char- acteristic of glasses and gases and studied fluores- cence in chlorophyll. Brewster balanced his experimental observations with his talent for building things. He invented a com- pact kaleidoscope that was granted a patent in 1817, and also established the foundation for a new optical lens system that could transmit bright light suitable for lighthouses, in1835. See Brewster's angle. BRI See Basic Rate Interface. bridge 1. A link that provides a connection across a physical or conceptual gap. This link mayor may not be intended to affect the quality or format of the ob- jects or information crossing the gap. 2. In networks, a device commonly used to handle communications between separate local area networks (LAN s) which mayor may not use the same protocols. Thus, To- ken-Ring networks and Ethernet networks may be connected via a bridge. In Frame Relays, a bridge encapsulates LAN frames and feeds them to a Frame Angles ofIncidence, Reflection, and Refraction polarized reflected light "ii E o c ~~ refracted '" light '" B incident light Incident light A This diagram shows the basic relationships between incident electromagnetic energy interacting with dielectric materials with different properties. Imagine that thepropagating wave is white lightfrom the Sun traveling through air (which is itself a dielectric) to encounter a solid dielectric material. Materials with different refractive indexes (A and B) are shownfor comparison. The collision of the incidentlight with the surface of the dielectric (a material that does not readily conduct energy) causes the direction of travel and polarity of the light to change. Depending upon the properties of the dielectric solids, some of the light will be reflected, some will be absorbed, and some will continue on down through the dielectric but at a different angle, called the angle of refraction. In both (A) and (B), the angle of the incident light (the light hitting the suiface) and the reflected lightare the same relative to the suiface normal (perpendicular to the suiface) and there is a direct relationship between the index of refraction and the direction of travel of the scatteredlight. As the refractive index and the angle of the incident light increases, so does the angle of the reflected light, up to thepoint at which it is parallelto the surface (in which case it doesn ~ reflect). Depending upon theproperties of the reflective material, not allthe light willbe reflected. Some may be absorbed and some may be refracted through the material. The angle of refraction (light that passes through the material ratherthan reflecting off of it) is relatedto the angle of the incidentlight andits interaction with therefractive material. 133 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Basic Categories of Network Bridges bridge number BN. Aring network designator used in source routing. Together a segment number (SN) and bridge number (BN) comprise a route designa- tor. When a destination is located on the ring itself, the bridge number is 0 (zero). Bridge Protocol Data Unit BPDU.InATM network- ing, a message type used by bridges to exchange man- agement and control information. BPDU is a Media Access Control (MAC) management control proto- col used to implement Spanning Tree Protocol (STP). It provides a mechanism for routing data traffic Relay switch for subsequent transmission. It also re- ceives frames from the network, strips the Frame Relay frame, and passes the LAN frame on to the end device. Bridges in computer networks are associated with the Media Access Control (MAC) layer (or in OSI, the MAC sublayer). Bridges fall somewhere between repeaters and routers, although with increasing tech- nological sophistication the distinction between bridges and routers is less clear. Bridges can be clas- sified into general categories. See brouter, eXtranet, Media Access Control address, repeater, router, spanning tree algorithm. bridge, acoustic In acoustic instruments, the bridge elevates and spaces the strings and transfers vibra- tions to the body (soundbox) of the instrument. In electronic instruments, the bridge elevates and spaces the strings and transfers vibrations to the body of the instrument where they are, in tum, converted into electrical signals, usually by an energy-conversion device called a pickup. Type of Bridge transparent source routing source routing transparent Description A general purpose bridge widely used on Ethernet networks that supports multiple bridges in a spanning tree configuration. Atransparent bridge builds its own MAC address table based on source information from incoming traffic. Reference IEEE 802.1. Specific to Token-Ring networks. Routing is determined at the source, rather than at the bridge and, hence, incoming frames contain routing information and an indicator as to whether it should be used. Reference IEEE 802.5. A less common hybrid configuration used in a small percentage of implementations. through a single conduit when more than one physical conduit exists (e.g., a backup loop for use if the root loop fails). The BPDU consists of flags, Hello time, and root, port, bridge, protocol, delay, and aging in- formation. bridger switching A technique for improving low return transmissions, as in cable networks, by sequen- tially turning on and off each leg of the distribution circuit. It is sometimes used in conjunction with high pass filters. While improvements in reliability can be attained in this way, it is at the cost of greater com- plexity and, hence, greater expense. bridging clip Asmall piece of conducting apparatus used to connect nearby terminals, contacts, or other circuit elements that are close together, either for the purpose of changing a circuit (usually temporarily) or for testing it. Bright, Charles Tilson (1832-1888) An English in- ventor and chiefengineer for the Magnetic Telegraph Company. Bright was the first to undertake under- ground cable installation with gutta-percha as an in- sulating material. When Edison was installing the historic Washington-Baltimore line in the 1830s, problems with insulation and ground-breaking caused the line construction to be changed from underground to overhead, so Bright's success with an underground line was important. Later, Bright installed the first cables to be laid in deep water, first with a shallower line across the English Channel in 1851, and two years later adeepwater line between England and Ire- land. Further lines around the world followed. brightness The level of luminosity or amount of il- lumination emanating from a surface or display me- dium. Luminance is used to describe the lightness or brightness component of a television broadcast sig- nal. Brightness across the visible spectrum is not equally perceived for different colors. See contrast. Brillouin, Leon (1889-1969) AFrench-born Ameri- can quantum physicist who studied band structures in crystalline solids. Brillouin is best known for de- scribing Brillouin scattering, a quantum effect in acoustic modes in refractive materials. In the I920s, Brillouin made important discoveries in quantum dynamics, developing a means of ap- proximating solutions to the Schrodinger equation. He accepted a position at the Sorbonne in the late 1920s. In the 1930s, he was associated with the Born Institute in Goettingen. In the 1940s, he took posi- tions at American universities and authored Wave Propagation in Periodic Structures. In 1948, he be- came director of Electronic Education at IBM. Brillouin then joined Columbia University at a time when exciting evolutionary advancements in lasers were being made by scientists such as C. Townes. See Brillouin scattering. The Laboratoire Leon Brillouin is named in his honor. Brillouin scatteringAfrequency change/phase shift effect that occurs in scattered light from compres- sions/decompressions in an elastic, refractive mate- rial. Thus, photons are interacting with vibrational structures at the quantum level within the light-re- fracting medium as opposed to simply encountering 134 © 2003 by CRC Press LLC incongruities within the structure (Rayleigh scattering). Brillouin scattering occurs when the light-refracting structure exhibits transverse and pseudo-transverse elastic compressibility (called acoustic modes due to the compression/decompression character of sound waves traveling through a medium). Brillouin effects are complex and subtle interactions that can be chal- lenging to measure and that depend upon many fac- tors, including density, refractive index, elasticity, temperature, humidity, vibrational intensity, the di- rection of the incident light, etc. Neverthless, scien- tists are endeavoring to characterize and harness Brillouin effects for use in fiber optic and other tech- nologies. This effect was first studied by Leon Brillouin, ca. 1920. The mathematics of the scattering effect was not well understood until the study and development of lasers and fiber optics in the early 1970s gave it a wider context in which to be researched. This, in turn, furthered development ofnonlinear fiber optics and the understanding of other optical phenomena and modulation technologies. Brillouin scattering may impose limitations. For ex- ample, in optical fibers, increasing the power of the light in a cable causes it to reach athreshold at which point Brillouin effects impose physical limitations on light propagation. Acoustic noise arising from Brownian molecular motion can stimulate spontane- ous Brillouin scattering causing back reflection. Brillouin scattering is a useful tool for researching molecular excitation and Brillouin effects may be deliberately stimulated for use by testing and correc- tion components. The effect can also be exploited in the development of fiber-based sensors. S. Burgett et al. have described the use ofBrillouin optical time domain reflectometry to carry out strain measurments in precision-wound optical fibers and L. Thevenaz et al. have described strain and temperature sensing us- ing embedded optical fibers. See acoustical Doppler effect, Bragg's law, Raman scattering, Rayleigh scat- tering, Stoke's shift. British Academy of Film and Television Arts BAFTA. Established by Alexander Korda in 1946 as a club for the British film elite, the club evolved into the British Film Academy, founded in April 1947. It later merged with the Guild of Television Producers and Directors to form the Society of Film and Tele- vision Arts. BAFTAsupports the Film Awards as well as Television and Children's Awards programs. http://www.bafta.org/ BritishApprovals Boardfor Telecommunications BABT. A U.K based telecommunications regulatory organization, the BABT provides third-party accred- ited regulatory and certification services. BABT Cer- tification marks are commonly recognized in Europe. In AprU 2001, the BABT announced its affiliation with TUV SiiddeutschlandAG. The merger resulted, in part, in the creation of BABT Product Service USA, which focuses on telecommunications confor- mity assessment. BABT Product Service also has centers in several Asian countries. http://www. babt.co. uk! BritishBroadcasting Corporation BBC. A television broadcast provider since the late 1920s, when it be- gan its fITst experimental television transmissions, the BBC began widespread public broadcasting from London in 1936. British Computer Society See computer societies, national. British Film Institute BFI An independent Royal Charter body, founded in 1933, that promotes under- standing of the moving image arts, including televi- sion and film. It fulfils the cultural and educational roles of the Film Council. http://www.bfi.org.uk! BritishIndian SubmarineTelegraph CompanyAn underwater telegraph cable-laying company founded by John Pender, aBritish merchant, in 1869, not long after the laying of the first oceanic telegraph cable traversing the Atlantic Ocean. Through his involve- ment with the transatlantic cable project, Pender was inspired to propose a cable connection between Brit- ain and India, where the British had established large centers of trade and colonization. In 1872, he also es- tablished the Eastern Telegraph Company. Within a decade, the company supported a majority of tele- graph traffic to India and had expanded to include Australia, China, and Japan through overland and underwater cables. Eventually Pender achieved his ambitious dream when London, England and Bombay, India were linked in 1879. BritishNationalCorpus BNC. A very large linguis- tic collection of written and spoken British English compiled from 1991 to 1994 under the management of an academic/industrial consortium led by Oxford University Press. In terms of technology, the collec- tion is ofinterest in the fields of speech recognition and synthesis (telephony, computer text dictation and generation, etc.) and artificial intelligence (especially natural language synthesis and processing). BNC Online is hosted by the British Library Initiatives for Access Programme. The BNC is licensed material, but its associated SARA Client is freely available, as is limited demo access to the database. British StandardsInstitution BSi, BSI. A U.K. stan- dards body which provides input to various interna- tional standards associations, including ISO and ITU- T. It originated as a Committee within the Council of the Institute of Civil Engineers in 1901, appointed to consider standardization in the steel industry. The Committee of engineers and naval architects was joined by the Institute of Electrical Engineers in 1902. In 1918, it became the British Engineering Standards Association, granted a Royal Charter in 1929. The current name was adopted in 1931. BSI currently sup- ports about 19,000 live standards. It owns the Kitemark quality mark. http://www.bsi-global.com/ British Telecom BT, British Telecommunications pIc. Originally affiliated with the British Ministry of Defence and British Post Office, the telephone net- work and telephony research arms separated from the Post Office to become British Telecom. BT publishes the quarterly BT Technology Journal (technical pa- pers) and sphere (BT technology) with copies avail- able on the Web. 135 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary BritishTelecom Research Laboratories BTRL. The research lab ofBritain's largest telecommunications provider, based in Marlesham Heath, Suffolk, En- gland. British Telecom is involved in many interna- tional collaborative projects including research with the Massachusetts Institute of Technology in artifi- cial intelligence natural language processing. British thermal unit Btu. The unit ofthennal energy required to raise the temperature of 1 pound of liq- uid water by 1 degree Fahrenheit at sea level. 1 Btu = 251.996 calories = 1054.8 Joules. Optical sensors have been developed to measure Btu's. While gener- ally used to express the energy-producing or trans- ferring capability ofheating/cooling systems, it is also used to express the heat generated by large-scale com- puting systems to facilitate the design of building cir- culation systems associated with their installation. brittleA quality ofa physical substance lacking elas- ticity, one that is vulnerable to breakage. Substances may be brittle in one set of circumstances and not another, e.g., electrical components or connectors may be vulnerable below or above certain operating temperatures. broadband A band of frequencies wide enough to be split into narrower bands, each capable of indi- vidual use for a variety of transmissions or for trans- missions by a variety of users. Broadband transmis- sion requires suitable hardware and cabling, capable of quickly transmitting and receiving a large amount of infonnation. Fiber optics are often used. The en- tire breadth of the band is not necessarily used for transmissions, depending upon supply and demand. Also, there may be gaps between bands to prevent interference. Cable TV is a ubiquitous example of broadband transmissions where the band is split into all the different channels to which the recipients have subscribed. As in many broadcast media, broadcast technologies tend to be one-way, or mostly one-way, but with the increased demand for interactivity, more two-way communications over broadband are being developed. See baseband, telecomputer, wideband. Broadband Connection-Oriented Bearer See BCOB. broadbanddigital cross-connectsystem B-DCS. A digital cross-connect system that accepts a variety of optical signals and is used to tenninate SONET and DS-3 signals. B-DCS accesses STS-l signals and switches at this level and is appropriately used as a SONET hub for routing and other functions. B-DCS is commonly implemented with node tennination via add/drop multiplexers (ADMs) and B-DC switches. Some newer optical systems that provide SONET-like capability can transmit without the B- DC switches. See wideband digital cross-connect system. Broadband High Layer Information BHLI. An ATM infonnation element that uniquely identifies an application (or session layer protocol of an applica- tion). BHLI is implemented in various ways, depend- ing upon whether the codepoint is user-specific, ven- dor-specific, or ISO. broadband integrated gateway BIG. A component ofHFC (Hybrid Fiber Coax) networks that converts 136 an ATM transmission into a signal that can be trans- mitted over the HFC. Working in conjunction with a connection management controller (CMC), the BIG strips infonnation from ATM cells and orders and addresses them for further transmission. See connec- tion management controller, HFC. Broadband ISDN See B-ISDN. Broadband Lightwave Sources and System See BLISS. broadband line termination B-LT. Optical or elec- tricalline tennination (LT) on a broadband network that provides a physical and link between an access network and a local digital exchange. The tennina- tion unit will convert signals as needed and, in some cases, provide multiplexing functions for multiple attached devices. Broadband Passive Optical Network BPON, Broadband paN. An optical communications net- work capable ofproviding high bandwidth services. Commercial implementations of consumer program- ming via BPON provide a range of up to about 20 kilometers on a single fiber serving a couple of dozen or more customers. Broadband Telecommunications Architecture BTA. An architecture introduced by General Instru- ment for multimedia networking. broadband terminal adapter BTA. A data commu- nications device that interfaces a broadband ISDN (B- ISON) connection to other terminal equipment that is not directly compatible with B-ISDN. broadbandtransport manager BTM. In telephony, atransport mechanism for long-distance portions of a connection. In the late 1990s, Tellabs, Inc., planned field trials ofa BTM for ATM networks. BROADBANDLOOP BBL. An ACTS project for defming and testing a concept for a cost-effective broadband access network allowing fiber to be inte- grated into local loops as telecommunications band- width demand increases. The target user base for the project is residential subscribers and small- and me- dium-sized businesses. Field trials were set up for Denmark, Poland, and Portugal with some trials con- sisting of overlays to existing telephony and CATV networks. See BLISS, UPGRADE, WOTAN. broadcast v. To transmit sound, images, or data over distance, in the context of more-or-Iess simultaneous receipt by alarger audience. Transmission can occur through a variety of media, over airwaves, satellite links, wire or fiber, or a combination of these. Re- ception can often be enhanced with antenna, cable, or satellite hookups. Radio, television, and Internet chat channels are common broadcast channels. Commercial and high power broadcasting is regu- lated. In the United States, the Federal Communica- tions Commission (FCC) is the primary regulatory body and has jurisdiction over the allocation of broad- cast frequencies. In Canada, the Canadian Radio Tele- vision and Telecommunications Commission (CRTC) handles many of the same functions. In most of North America, very low power broadcast- ing is permitted without a license; otherwise it wouldn't be possible for people to use cordless © 2003 by CRC Press LLC phones, baby monitors, and wireless intercoms with- out being licensed. Generally these low power broad- casts are limited to a signal strength of 250 micro- volts per meter, as measured three meters from the transmitter for FM transmissions, and 0.1 watts on a maximum three meter antenna for AM transmissions. This effectively limits the broadcast distance to 100 feet or so for FM and a couple of blocks for AM. Tra- ditional broadcasts are typically in the range of 535 to 1605 kHz. Commercial entertainment broadcasts are often fi- nanced by revenues from sponsors which are aired in the fonn of commercials. Since this revenue model has been successful for quite some time in the televi- sion and radio industries, it is not surprising that many broadcasters are turning to the same ideas in design- ing infonnation to be viewed over the Web. In con- trast to commercial stations, however, the Web is far less regulated and has many more participants, and it will be interesting to see how Webcasting evolves over the next several years. See television, radio, multicast, narrowcast, unicast. Broadcastand Unknown Server BUS. InATM net- works, this server handles data sent by an LE client to the broadcast Media Access Control (MAC) ad- dress, all multicast traffic, and initial unicast frames which are sent by a LAN Emulation (LANE) client.!t encompasses the functions that support establishment ofa virtual circuit (VC) connection. See Media Ac- cess Control address. broadcastdatatrigger Additional services are some- times delivered with audio/video broadcast program- ming. Closed captioning or subtitles are examples of traditional broadcast services and others are becom- ing available as digital broadcasting over computer networks increases. Depending on the medium, cer- tain standardized broadcast triggers have been de- fined and categorized, including transport type A and B triggers. Broadcast triggers are realtime data events associated with enhanced TV broadcasting delivered in a textual syntax based on the EIA - 746A standard presented through the ISO-8859-1 character set (U.S. ASCII or Latin-I). By adding triggers to the data stream, the viewing box or software program receives a signal to interpret and present the additional infor- mation or services. In recent years, attributes have been added to the triggers to accommodate Internet broadcasts; these generally require two-way commu- nications. The presence of two-way communications makes it possible to incorporate triggers as part of an on-demand interactive TV system. The ATVEF has defined two modes of data transport that incorporate triggers. Transport A delivers trig- gers by the forward path and pulls data by the return path. Transport B delivers triggers and data by the forward path, but the return path is optional. See ATVEF Enhanced Content Specification. broadcast list 1. On computer networks, a list of us- ers to whom broadcast messages are sent, usually by a system operator (sysop) or other privi leged admin- istrator. See broadcast message. 2. On fax machines, alistof recipients to whom the same fax will be sent. broadcast medium In general, the physical substrate or underlying electromagnetic phenomenon that pro- vides a conduit for electrical or other signals trans- missions. Electromagnetic phenomena are the most common broadcast media, though a disturbance in a medium (metal, water, wood, etc.) that produces sound waves can also constitute abroadcast medium (albeit slower and less effective than electromagnetic media). In some networks, a physical layer capable of supporting broadcast messages. broadcast message 1. Amessage sent to a selected group ofusers (or all users) on a computer or radio network. A common computer network broadcast message infonns users that the system will shut down in 5 or 10 minutes. This message allows users to save work, close files, and finish up before being logged out. On networks, broadcast functions are usually available only to those with system privileges, as it is a capability that is easily abused. Schools are be- ginning to use broadcast phone or email messages to infonn parents of registration, reporting, or meeting events with respect to their school-aged children. See allcall, anycall, broadcast list. 2. A message broad- cast over apublic broadcast medium, such as a news flash or Emergency Alert System (EAS) message. 3. A message broadcast over a paging or public ad- dress (PA) system. broadcast over network In ATM networking, data transmissions to all addresses or functions on the sys- tem. Broadcast Pioneers Library An education and re- search resource located in the Hornbake Library at the University of Maryland, College Park, founded in 1972. The collection includes correspondence, books, film, video, periodicals, historic photographs, scripts, and transcripts. More infonnation is available online through the Pioneers' Web site. http://www.lib.umd.edu/UMCPILAB/ broadcast standards Established in the late 1930s in the U.S., professional standards still exist as im- portant guidelines for ethical business practices, safety standards, and standardized broadcast formats in the broadcast industry. See Canadian Broadcast Standards Council, Federal Communications Com- mission. broadcast storm A broadcasting clamor that is ex- cessively busy, frequent, or powerful that it overrides other communications. In radio broadcasts, a broad- cast storms occur in times of emergency, when nu- merous operators simultaneously try to call for help or send messages to friends and relatives. In end-to- end systems, such as analog wireline telephone sys- tems, broadcast storms as such don't occur (except, perhaps, in adifferent sense, on aparty line), because excessive calling will result in a fast busy being sent to the caller, indicating that no trunks are available, rather than in many people talking at once. In data networks, however, abroadcast stonn can occur as a fault condition in which some process goes wild and starts broadcasting to all workstations and disrupting user interactions and work. Astonn may occasionally be caused on unsecured networks by a virus 137 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary distributed by a vandal. See allcall, broadcast mes- sage. Broadcast Wave Format See EBU Broadcast Wave Format. broadcasting satellite service BSS. One of two di- visions into which Ku-band satellite broadcast ser- vices have been split. BSS operates in the 12.2- to 12.7-GHz range. The other is fixed satellite service (FSS). See ANIK, Ku-band. broadside array antenna Aphased array (with har- nesses) of antennas with the maximum radiation di- rected perpendicularly to the plane that holds the driven elements. This antenna arrangement can be configured as abillboard antenna by adding a reflect- ing sheet behind the array. See billboard antenna. Broadway The internal development code name for The X Window System 11 Release 6.3 (XIIR6.3) from The Open Group. See X Window System 11 Release 6.3. Brocade Fabric Aware program BFA. A testing and configuration initiative for fostering end-to-end inter- operability for storage area networks (SANs) in multi- vendor, heterogenous environments. Participating firms agree to specify, test, and support pretested SAN configurations with a mix of servers, switches, and storage subsystems. Brocade Fabric Aware qualifi- cations may be presented after the completion of rig- orous testing for interoperability within specified multivendor configurations. Brocade Communica- tions Systems, Inc., has set up an interoperability laboratory testing environment to support the Fabric Aware program. bronze An alloy consisting primarily ofcopper with tin and occasionally other elements added. Brooks' law Adding manpower to a late software project makes it later. From Frederick P. Brooks, au- thor of The Mythical Man-Month, a much-quoted provocative book about the engineering development culture. brouter, b-router bridge router. Combination de- vices that function as links between different net- works. The combination ofa bridge and arouter pro- vides the physical and logical connections between networks, which mayor may not have different pro- tocols, and routing tables to facilitate the efficient transmission of information to the desired destination. A brouter typically performs its functions based on information in the data link layer (bridging) and the network layer (routing). See bridge, router. Brown & Sharpe Wire Gauge See American Wire Gauge. Brownian movement, Brownian motion Botanist R. Brown observed in early 1827 that pollen grains suspended in water were in a continual state of agi- tated motion. This motion has been widely observed for small particles suspended in fluids. It is said that the molecules of the suspension medium continually buffet the particles, resulting in the characteristic movement. Einstein later provided a mathematical explanation of Brownian motion. Theoretical mod- els for queueing and aggregated connectionless net- work traffic, based on fractional Brownian motion, 138 have been proposed. brownout 1. When power is partially, but not com- pletely lost. Some companies use an industry-specific definition for a brownout, usually based on arelative or specific drop in voltage. Complete loss of power is called ablackout. 2. In cellular systems, asecurity precaution used by some companies to prevent fraudulent use. When brownout is in effect, there may be roaming areas in which asubscriber's system will not function. browser 1. An object-oriented software development tool for inspecting a class hierarchy. 2. A software utility for displaying and traversing files and direc- tories. 3. A software client for accessing the resources of the World Wide Web. See browser, Web. browser, Web A historic milestone in software ap- plications, designed to make it easy to access World Wide Web client/server resources stored on avariety of computers on the Internet. Prior to the develop- ment of Web browsers, there were many publicly available and valuable data repositories on the Inter- net, but access was through inscrutable line com- mands or uninspiring textual menus. The repositories themselves sometimes included images, but the im- ages were seldom directly viewable over a remote link. They had to be copied and then loaded into a compatible application supporting the various for- mats in order to be useful on the local machine. Web browsers simplified this process by providing a 'front end' that transparently automated, integrated, and standardized access to the more sought-after types of information stored for distribution on the Internet. The Web browser client/server model was originally developed for NeXTStep by Time Berners-Lee, in 1989. As the concept spread through various systems and became associated with the Internet, another im- portant change was taking place, the commercializa- tion of the Internet from a research system to a sys- tem that could be used for commerce; this develop- ment got the attention of the general public, even those with no previous interest in computers. Avariety of Web browsers were quickly developed to meet the growing demand for Web access from different types of computers, resulting in phenomenal growth and interest over the next decade and beyond. Within a few years NCSA Mosaic, OmniWeb, Lynx (text browser), AWeb (Amiga Web), Netscape Navi- gator, and Internet Explorer had become popular browsers for 'surfing' the Web. The Web gained in commercial prominence in the early 1990s, and browsers developed into practical tools for accessing, traversing, and displaying files on the Internet. A browser interprets standardized HTML tags that are used to describe the Web page, and displays the results on the user's system. Sun Microsystems Java applets are used by many devel- opers to further enhance the capabilities ofabrowser with programming algorithms that aren't directly sup- ported by HTML tag interpretation. Browsers typically download HTML pages onto the local drive, so they can be more quickly redisplayed when the user moves back through previously viewed © 2003 by CRC Press LLC pages, and further facilitate the transfer of files through File Transfer Protocol (FTP) and other ex- ternal utilities. Some browsers incorporate email functionality as well or will launch the email utility of choice when an email anchor is selected on a Web page. Most browsers supportplugins, browser-com- pliant applications for processing multimedia file for- mats from a variety of vendors. Plugins are popular for enabling the user to play music, movies, stream- ing video news broadcasts, and other television-like fonns ofinfonnation and entertainment. A Web browser's simple, accessible means ofmak- ing available infonnation on the Internet has resulted in an explosion ofinterest and participation, increas- ing from a handful of users in 1989, to more than 30 million in 1998. The number of data respositories available on the Internet has grown in conjunction with the increase in users. One of the issues that becomes more important, as Internet commerce grows and data repositories in- clude more and more personal information, is secu- rity. Security enhancements have been gradually added to Web browsers since the mid-1990s, but these are not impervious to skilled hackers. Web browsers were originally designed to be open and easy to use, and no one fully anticipated how quickly and aggres- sively banks, stores, and other institutions of com- merce would set up their entire service line and cus- tomer access databases to be Web-accessible. As Web browsers become more powerful, they become more and more like operating systems that can be poten- tially accessed and controlled from remote sources in sophisticated ways. Already, by 1999, there were companies using their Web browsers to 'look' at in- fonnation on the desktop of the individuals who in- stalled the browsers on their computers. The compa- nies didn't necessarily inform the user of this intru- sion, or did so in small print or vague ways not un- derstood by those not technically acquainted with computers. If computers are to be secure in the future, it is im- portant for the community at large to understand the potential for abuse and hold companies to high ethi- cal standards in the matter of computer and individual privacy associated with Web browsers. Unfortunately, many people don't understand the technical or po- litical issues and others don't consider the long-tenn consequences. While they may not be willing to give out name and address information on a moment-to- moment basis, they can often be persuaded to do so when offered the possibility of winning million dol- lar sweepstakes. Once their personal information gets into an unethical Web respository, it can be redistrib- uted to millions ofother computers within seconds; there's currently no way to undo this type of infor- mation theft, which may include social security num- ber, credit card numbers, and more. Think twice be- fore volunteering information to unfamiliar Web sites through your Web browser. Another security-related browser issue is the use of cookies, identifiers within a browser that enable a Web site to recognize automatically areturning user without querying that person about his or her iden- tity a second time. Users should take time to under- stand what cookies are, how they work, and whether they should be explicitly turned off in the browser to help safeguard privacy. Always read the privacy policy statements associated with each site before providing personal information and boycott sites that require more information than you feel they need to carry out a transaction. Web browsers have opened up aworld of communi- cation, education, and opportunity for millions of people and will likely be an essential aspect of the Internet for a long time to come. Many Web brows- ers are freely available for download and Netscape Navigator is open source software that can be down- loaded and modified by developers. See FTP, Java, HTML, HTTP, Internet, NCSA Mosaic, PDA mac- robrowser, PDA microbrowser, SGML, World Wide Web. browsing Searchingor scanning through data for in- formation or to get a general feel for the format or contents of a body of information. The information may take a variety of forms: text, files, directories, images, sounds, etc. See browser. brush A conducting structure that provides an elec- trical connection between a motor and its power source. brute force 1. A problem-solving method that in- volves trying every possible combination and permu- tation. This method is only practical for small prob- lems of limited scope and is usually unwieldy for larger or more complex problems. Sometimes it is used in conjunction with other problem-solving meth- ods such as heuristics. 2. A programming approach that involves reliance on a system's basic capabili- ties and processing power, rather than on efficient algorithms and elegance of design and concept. A brute force application generally does not run quickly on legacy systems. brute force attack An attack on a security system using every possible combination, password, login name, or other entry data rather than using atargeted strategy. Brute force attack data are often generated automatically with computer software. This type of attack is usually easily detected and is often not very effective. BS 1. See backscatter. 2. band signaling. 3. See base station. 4. See beam splitter. BSAM See basic sequential access method. BSCC BellSouth Cellular Corporation. A corporation serving about 10% of the U.s. wireless market, formed in 1991. BSD See Berkeley Software Distribution. BSE 1. back-scattered electrons. 2. Basic Service Element. 3. Basic Switching Element. In packet switched networking, a basic unit which may be com- bined with other BSEs to emulate alarger switching topology. BSF bit scan forward. An assembly language bit manipulation in which a bit string is searched for a set or cleared bit, from low-order to high-order. See BSR. 139 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary BSFT See Byte Stream File Transfer. BSI See British Standards Institution. BSL See British Sign Language. BSMS 1. billing and subscriber maintenance service. 2. Broadcast Short Message Service. BSMTP See Batch Simple Mail Transfer Protocol. BSP 1. Bell System Practice. Bell internal policies and procedures for creating instructional manuals for the servicing, support, and operation of phone equip- ment. 2. See byte-stream protocol. BSR 1. bit scan rate. 2. bit scan reverse. An assem- bly language bit manipulation in which a bit string is searched for a set or cleared bit, from high-order to low-order. See BSF. BSS 1. Base Station System. 2. See broadcasting sat- ellite service. 2. Business Support System. BSVC 1. Broadcast Switched Virtual Connections. 2. The name for an object-oriented, generic micro- processor simulation framework for building a vir- tual computer that evolved from a Motorola 68000 simulator supporting the 6850 UART. BT 1. See British Telecom. 2. Burst Tolerance. In asynchronous transmissions mode (ATM) connec- tions supporting variable bit rate (VBR) services, BT is the limit parameter of the GCRA. See cell rate. BTcutcrystalA type of crystal with vibratory quali- ties that makes it suitable for crystal radios. BTPhonebaseA service of British Telecom since the early 1990s that enables subscribers to make direc- tory enquiries through a computer modem. The da- tabase is updated continuously and is more up-to-date than a yearly paper-based telephone directory. The call is billed at long-distance phone rates but is gen- erally still less expensive than Directory Enquiry (U .K. Directory Assistance service). The typical con- nect speed is 2400 baud, though higher rates became available in some areas as of 1999. See TeleDirectory. BTA 1. See Basic Trading Area. 2. See Broadband Telecommunications Architecture. 3. See broadband terminal adaptor. BTag Beginning Tag. In ATM, a one-octet field of the CPCS_PDU used in conjunction with the Etag octet to fonn an association between the beginning ofa message and end ofa message. BTBT band-to-band tunneling. Direct transfer of electrons from filled valence band (VB) states to empty states or recombination of electrons with holes in the valence band. BTE 1. Boltzmann Transport Equation. 2. broadband terminal equipment. BTl 1. British Telecom International. 2. Broadband Trial Integration. An ACTS project to demonstrate the role of Quality of Service (QoS) on Internet Proto- col (IP) over ATM in order to develop optimization data for networks and to improve user perception of network services. The project involves development of an integrated IPv6 and switched ATM multicast- ing network with QoS support of user-controlled bandwidth and delay. The project is designed in three phases, the establishment of the technical platform, implementation of signaling and management of rout- ers and switches, and the development of integrated 140 protocols. International connections will be through PVC-based ATM networks using UNI 4.0 SVCs for bandwidth management. See BID, BLISS, BONA- PARTE, BOURBON, UPGRADE, WOTAN. BTL Bell Telephone Laboratories. See Bell Labora- tories. BTM See broadband transport manager. BTN See Billing Telephone Number. BTRL 1. B Theory Research Labs. 2. Breward Teach- ing & Research Laboratories. 3. See British Telecom Research Laboratories. BTS 1. Base Transceiver Station. In mobile communi- cations, an end transmission point. 2. bit test and set. Btu See British thennal unit. BTU basic transmission unit. BTUInternationalA major supplier of thermal pro- cessing systems to the electronics industry, primarily semiconductor packaging and printed circuit boards. bubble memory A type of nonvolatile memory; it doesn't have to be constantly electrically refreshed to retain the data. Bubble memory, as used in com- puters, consists ofa thin layer of material that has magnetic properties. A magnetic field is used to ma- nipulate a circular area such that the diameter be- comes smaller, forming a bubble. bucket truck See cherry picker. buffer 1. A circuit or device designed to separate elec- trical circuits one from another. 2. A physical or elec- tronic storage device designed to compensate for a difference in the rate of use or flow of objects or in- formation. Generally a buffer is intended to increase speed of access and efficiency. In a computer, a buffer is often used as a storage area for frequently accessed information, so the software doesn't have to con- stantly access slower storage devices such as a hard drive, if sufficient fast access chip memory (e.g., RAM) is available. Cut and paste functions make use ofa buffer. Data in a buffer tends to be temporary and volatile. See cache, frame buffer, RAM disk. buffer, cable A layer of material to protect inner or outer components from abrasion, moisture, pressure, flexing, or tampering. In fiber optic cable assemblies, the buffer layer encircles the coating, cladding, and inner light-conducting core to provide protection from the elements. See swelling tape. buffer box See Logical Storage Unit. buffer condenser A condenser installed in an elec- tronic circuit to provide protection to other compo- nents by reducing excessive voltages, especially surges. buffermemory, bufferstorage Electronic memory, usually RAM, used for information storage and re- trieval, particularly for applications programs which make use of chunks of information that are frequently recalled. See buffer, cache. bugA small, concealed listening device used in sur- veillance and espionage. Placing a covert bug in a room or on a phone line is almost always illegal. The term is also used in conjunction with small, hobbyist transceiver projects for electronics education, wire- less intercoms, child monitors, and other legitimate uses. See bug, software/hardware; wire tapping. © 2003 by CRC Press LLC bug, software/hardware A software or hardware error that adversely affects operations or user inter- action. Grace Hopper is credited with relating the first story about a computer bug that was found by a tech- nician, and for preserving the bug itself in a log book. This story has long been a part of hacker lore as the origin of the term "bug" in computer technology. The bug in the story apparently was moved to the Smith- sonian Institution in the early 1990s (after an earlier unsuccessful attempt to have it accepted) but was not immediately exhibited. However, there are earlier an- ecdotes about bugs in industrial settings that indicate the term may go back decades, if not longer. Removing bugs from software (debugging) is an art form, and not all programmers who are good at writ- ing code are good at finding and correcting bugs. Unfortunately for developers, removing one bug of- ten introduces one (or more) elsewhere. Unfortu- nately for consumers, some commercial software vendors release products knowing they are full of bugs, and there are no specific regulations prohibit- ing it. Because computer technology is technical, the user may not know whether a problem is from bugs or from incorrect use of the software. Another unfortunate aspect to bugs is that companies often combine software enhancements with bug fixes and sell the new product as an upgrade with no guar- antee that it is more robust than the previous version (sometimes it is less so). This situation is like buy- ing a $15,000 car with a faulty engine, and having the manufacturer refuse to fix it and, instead, advise you to pay $5,000 to upgrade to next year's model. When you do, you find that the engine's been fixed, but the axles are defective, and the car has racing stripes that you didn't want in the first place. This situ- ation in the software industry won't change until con- sumers stop buying substandard software and en- hanced upgrades, and support instead the more re- sponsible vendors who provide patches for bugs sepa- rately from releases of enhanced versions. bug, telegraph A telegraph lever which, depending upon its position, can be used to send dots or dashes to partly automate transmission. build 1. An increase in diameter ofa line or object attributable to insulating materials. 2. In software de- velopment, the process of combining, compiling, or linking code so as to build an application. bulb The sealed glass enclosure for an incandescent or fluorescent lamp. Bulbs provide protection for the gaseous environments and the delicate filaments that they enclose. See Edison, Thomas Alva; lamp. bulkencryption Simultaneous encryption ofa group or set of communications, such as multiple data mes- sages or multiple channels on a broadcast medium. bulkeraser, bulkdegausser An electromagnetic de- vice designed to save time by clearing the data from a large number of floppy disks at one time. By rear- ranging the particles on the physical disk, the elec- tronic infonnation is destroyed. It is handy for recy- cling the diskettes or for providing a measure of se- curity with data that needs to be destroyed. It is wise to keep magnetic storage media away from computer monitors, which have magnets, or you may inadvert- ently erase or damage the data on them. A large-scale pirate software vendor, who was apprehended in Van- couver, B.C., is rumored to have had a bulk eraser in a storage cabinet wired to a button under the service counter to destroy evidence in the case of a police raid. See diskette. bulkstorage Media on which large amounts of elec- tronic data can be stored. The amount of storage that constitutes large keeps increasing. In the mid-1970s, a tape holding 100 kilobytes was considered bulk storage! In the mid-1980s, a writable optical disk holding 600 MBytes was bulk storage. Now hard disks and tapes holding 4 GBytes or more are being bundled with consumer machines. bulletin board system BBS. The forerunner to the Internet, BBS systems are typically individual com- puters set up for public or private modem access, by a number of users, on which there are shared files, mail, and chat services. The administrator is usually called the SysOp (System Operator). In the late 1970s and early 1980s, it was extremely rare for a BBS to be password-protected; there was open access to all. Unfortunately, persistent abuse has made this type of BBS almost extinct. In the mid-80s, there were still many BBSs running on TRS-80s, Color Computers (CoCo), Commodore 64s, Apple lIe's, and Amigas, with only 5 or 10 MBytes of hard drive storage for the entire system. BBSs have since become more so- phisticated, offering credit card payment options, and increasingly are being linked to the Internet through telnet. See FidoNet. bump contacts Small conductive lumps on electronic circuits that protrude to enhance electrical contact, such as those that allow chips to touch terminal pads. bunch strandingA technique used to combine wires so they fit tightly together, with individual strands retaining the same directional relationship to one an- other to form a stranded wire. Stranded wire is use- ful in situations where flexibility is desired or when the electrical properties of the wires are influenced by proximity to others. bunching An alternating convection-current effect in an electron stream caused by velocity modulation. Bunching is quantified as a parameter based on the relationship of the depth ofvelocity modulation to the absence of modulation. Used in electron tubes to generate ultrahigh and microwave frequencies. See klystron. Bundesamt fur Zulassungen in der Tele- kommunikation BZT. A German telecommunica- tions approval authority established in the early 1980s. bundled 1. Combined products or services, some- times from a variety of manufacturers, offered at a combined price. Phone and cable companies often have bundled or packaged deals, such as regular tele- phone service and Caller ID-related services offered at a flat rate, or movie and educational channels com- bined. Software products are often bundled with com- puter systems. Operating systems are almost always bundled with computers, often along with various 141 © 2003 by CRC Press LLC . High Layer Information BHLI. An ATM infonnation element that uniquely identifies an application (or session layer protocol of an applica- tion). BHLI is implemented in various ways, depend- ing upon whether the codepoint is user-specific, ven- dor-specific, or ISO. broadband integrated gateway BIG. A component ofHFC (Hybrid Fiber Coax) networks that converts 136 an ATM transmission into a signal that can be trans- mitted over the HFC. Working in conjunction with a connection management controller (CMC), the BIG strips infonnation from ATM cells and orders and addresses them for further transmission. See connec- tion management controller, HFC. Broadband. service BSS. One of two di- visions into which Ku-band satellite broadcast ser- vices have been split. BSS operates in the 12. 2- to 12.7-GHz range. The other is fixed satellite service (FSS). See ANIK, Ku-band. broadside. string is searched for a set or cleared bit, from low-order to high-order. See BSR. 139 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary BSFT See Byte Stream File Transfer. BSI See British Standards Institution. BSL See British Sign Language. BSMS 1. billing and subscriber maintenance service. 2. Broadcast Short Message Service. BSMTP See Batch Simple Mail Transfer Protocol. BSP 1. Bell System Practice. Bell internal policies and procedures for creating instructional manuals for the servicing, support, and operation of phone equip- ment. 2. See byte-stream protocol. BSR 1. bit scan rate. 2. bit scan reverse. An assem- bly language bit manipulation in which a bit string is searched for a set or cleared bit, from high-order to low-order. See BSF. BSS 1. Base Station System. 2. See broadcasting sat- ellite service. 2. Business Support System. BSVC 1. Broadcast Switched Virtual Connections. 2. The name for an object-oriented, generic micro- processor simulation framework for building a vir- tual computer that evolved from a Motorola 68000 simulator supporting the 6850 UART. BT 1. See British Telecom. 2. Burst Tolerance. In asynchronous transmissions mode (ATM) connec- tions supporting variable bit rate (VBR) services, BT is the limit parameter of the GCRA. See cell rate. BTcutcrystalA type of crystal with vibratory quali- ties that makes it suitable for crystal radios. BTPhonebaseA service of British Telecom since the early 1990s that enables subscribers to make direc- tory enquiries through a computer modem. The da- tabase is updated continuously and is more up-to-date than a yearly paper-based telephone directory. The call is billed at long-distance phone rates but is gen- erally