Fiber Optics Illustrated Dictionary - Part 36 ppsx

Fiber Optics Illustrated Dictionary compress-send-decompress schemes, with the com- pression needed only to speed transmissions, and thus not degrading the quality of the original. See facsimile mode, Huffman encoding, TIFF-FX, RFC 2301, RFC 2304, RFC 2305. facsimile mode Facsimile machines have a number of operating modes, including various regular and fine resolutions, and can be manipulated to send in monochrome or grayscale, depending on the capa- bilities of the sender and receiver, and the software or hardware. Most fax machines and fax/modems send in Group 3 standard and fine modes, that is 203;dX;d98 pixels and 203;dX;d 196 pixels. Other modes have been defined (Group 3 203;dX;d39 I - su- perfine; Group 4 400;dX;d400 - standard), but they are not widely supported in consumer-priced prod- ucts. A fax can be only as good as the weakest link in the transmission. If the sending fax sends in the low- est resolution, a higher resolution receiving fax doesn't improve the image. Conversely, if the send- ing fax uses fine resolution, but the receiving fax can only support standard resolution, the details will still be lost. Since the orientation of most faxes is portrait, and the orientation of most computer monitors is landscape, fax/modem software usually has zoom, pan, and rotate features to aid in viewing documents. facsimile modem, fax modem A fax modem system consists of a fax-enabled data modem (one which works in two modes) hooked to a computer, some- times combined with a scanner. Instead ofcreating a document, printing it, feeding it through the fax ma- chine, receiving aprinted page at another destination fax machine, and then perhaps even typing or rescanning (and OCR-ing) the printout back into a computer at the other end, the fax modem system sends a digital fax directly from the software appli- cation that created the document, to the receiving end. Or, ifa scanner is used, the system sends the scanned file as the fax. If the receiving device is a fax modem system, rather than a fax machine, then the fax goes directly to the computer hard drive, and no paper is used in the transaction. Optionally, a fax machine may connect to a local net- work so that users can be notified if a fax has been received or even select an option to view the fax on a computer monitor (thus providing hybrid fax ma- chine/fax modem capabilities). In business environments some people erroneously use fax machines when they should be doing direct data transfers. This is a common scenario: the main office ofa corporation creates a new 80-page policy manual and wants to distribute it to all ten branch offices. The branch offices would like an electronic copy in order to customize it for their needs, or to easily make corrections as directed by the main of- fice, etc. The typist types a copy, faxes 80 pages to each of the ten branch offices; 880 pages are gener- ated in all, the original, and the 10 branch copies. Now the typists at each branch office retype the document into their word processors, thus duplicating the work already done. Rather than always using a fax machine, there are 342 better ways to distribute some types of documents. The first is a slight improvement. By using a fax! modem software program to send the document di- rectly to each branch to another fax/modem program, no paper is printed until the documents are complete to each branch's satisfaction, and the completed cus- tomized documents can be OCR-scanned back into a word processing text file at the destination. A better solution is to send the original file, in docu- ment format, through a modem or through the Inter- net, to each branch office, where the secretaries can load the received file directly into the word proces- sor. This can be accomplished by putting the file on an FTP site, and notifying the branches that they can access the site and download the latest version of the file. If different word processors are being used, the original can be saved in Microsoft Interchange For- mat (also known as RTF or Rich Text Format), a widely supported format that can be read and saved by all major word processing programs. The best solution to document exchange may be to have a secure centralized online document repository which can be accessed and modified dynamically by all branches through an Internet or private network connection. Fax machines are a great resource for sending short documents, but they are not the best solution for all document transfers, and the Internet provides distant branches with a way to dynamically produce and maintain documents without incurring long-distance charges. Integrated data, video, and voice services are increasingly offered by telecom- munications carriers; facsimile communications are being superseded to some degree by email attach- ments, especially PDF files. See facsimile device, fac- simile fonnat, facsimile history, facsimile modes, Portable Document Format. facsimile switch An external switching device that allows a single phone line to be used for more than one phone-related piece of equipment. Fax switches often can also handle telephone answering machines and computer modems. The fax switch is attached between the phone line plug and the various phone devices. When a call comes through, the device evalu- ates the tones and decides whether it's a voice call, a modem call, or a fax call, and routes the call to the appropriate device. Unfortunately, most fax switches can't detect when a manual fax machine is going to send a fax if the call originated as a voice call. If the person dials the phone manually and then wants to switch over to a fax call after the connection is es- tablished, many fax switches can't revert to data mode (newer ones may be switchable on receiving a par- ticular code). In spite of that limitation, it's a great tool for homes, home offices, and small businesses that can't afford extra phone lines. fade To diminish in strength, loudness, or visibility. In video or audio editing, fading is deliberately used to provide transitions that are perceptually pleasing. In data or broadcast transmissions, fade is usually an undesirable effect due to various factors such as dis- tance, loss of signal, obstructions, interference, etc. Undesired fade can sometimes be reduced or © 2003 by CRC Press LLC eliminated by amplifiers, repeaters, robust wiring mediums, and good insulation. fade margin Signal losses in satellite systems can occur from scattering, absorption, and various subtle types of interference. Consequently various fade margins are incorporated into the design of the sys- tems, and they will vary depending on the degree of fade expected from various sources and on the length of the broadcast waves, with shorter waves generally being more subject to fade. FahrenheitscaleA temperature scale that designates 32 degrees for the freezing point of water at normal pressure and212 degrees for the boilingpointofwa- ter at normal pressure, and other points relative to these. See centigrade scale, Celsius scale. Fahrenheit,Daniel Gabriel (1686-1736) A Polish- born German scientist who established the widely used Fahrenheit scale. Zero degrees was designated as the temperature of a mix of ice, water, and salt, and 90 degrees was considered to be the temperature of the human body (in fact, it's closer to 98.6 degrees). See Riimer, Ole Christensen. failsafe A designation that indicates that failure ofa system is unlikely or impossible, or that backups are available if needed. In networking, few, if any, sys- tems are completely failsafe, but there are steps that can be taken to prevent problems, such as the use of surge suppressors, backup power systems, redundant data storage or broadcast signals, etc. See fault toler- ant, redundant array of inexpensive disks. fake code See pseudocode. fallback A contingency mode, plan, or operation. In communications, a designation for another speed or mode of operations if the current mode is not func- tioning as well as might be desired. Many modems may fall back (two words) to a slower speed if the connect negotiation doesn't work at higher speeds. Many communications programs may fall back to smaller packet sizes if there is a lot of noise, or other impingements on a data file transfer. In software, a fallback (one word) may be one in which the appli- cation or operating system goes to another mode or another program if some error condition or slowdown is detected. A network may go to a fallback route if the usual one is not available or not responding as expected. falsing Spurious signals that accidentally are inter- preted by a system as commands, or that are deliber- ately introduced to fool a system, usually for unau- thorized purposes. In telephone systems, certain situ- ations can be simulated by playing particular tone se- quences, so the system is fooled into switching, trans- ferring, or connecting long-distance or other types of calls. In transmissions control for satellites and other radio-controlled devices, environmental noise, falsely interpreted signals, etc. can have major consequences if the system thinks it's a command and acts upon it. fan 1. Fan of science fiction. Since there are a large number of software developers who are science fic- tion fans, they have co-opted this term into many computer-related situations, video games, simula- tions, and virtual reality environments. 2. An active cooling device (as opposed to passive devices such as heat sinks) often used to cool computers so that chips and other components are kept at optimum op- erating temperatures. FAN See flexible access network. fanfold See z-fold. fanout A device that facilitates the separation of in- dividual fibers in a fiber optic cable bundle, enabling them to be more easily handled, attached, configured, or repaired. After being fanned, individual strands may be channeled through afurcation unit for rout- ing to its destination. See furcation unit. See fantail. FANP See Flow Attribute Notification Protocol. Fantail Fiber Optic Wiring Bundle A fantail wiring bundle secured at the point where it connects to the electronic components, with con- nectingpoints for individualfibers fanned out for cou- pling with the appropriate connectors. Individual fi- berpigtails typically haveprotective caps, in prepa- ration for adding a connector, or will have a connec- tor already attached to protect the precision-cut and polishedterminalpoint. They may be color coded to facilitate the correct connections. [NASAILangle photo, 1999.J fantail A descriptive term for a wiring bundle that is secured somewhat near the point at which the wire connectors spread apart for attachment to a wiring rack, thus creating a shape that fans out from the bundled point. The strap that secures the bundle aids in holding the wires together if one or more of the wire connectors are disconnected, as they will hang a few inches below the rack for easy location and re- attachment, if desired. The fantail configuration also makes it easier to disconnect and reconnect the en- tire bundle of wires. See fanout. FAQ See frequently asked questions. far end crosstalk FEXT. When wires are packed to- gether tightly, and signals are travelling through most or all the wires, the potential for interference from crosstalk increases. Far end crosstalk is a type of in- terference originating from multiple signals travel- ling in the same direction, typically through wire pairs, as in common copper twisted-pair installations. FEXT directly effects bit error rates (BERs), as it 343 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary cannot be cancelled as easily or as effectively as near end crosstalk (NEXT). See near end crosstalk. farad A unit ofcapacitance equal to one coulomb (of electricity) divided by (a potential of) one volt. Named after Michael Faraday. faradaic Relating to an asymmetric alternating cur- rent (AC) produced by an induction coil. faraday A measure ofelectrical charge transferred in the process ofelectrolysis per weight of an ion, or element, that is equal to about 96,500 international coulombs (or 96,490 absolute coulombs). Named af- ter Michael Faraday. Faraday cage Astructure, usually mesh- and cage- like, to isolate a person, device, or electronic system from damage or interference from outside electrical sources. These may sometimes be seen in science museums where electrical devices, especially large Van de Graaff generators, are demonstrated. Named after Michael Faraday. Faraday DarkSpace In a cathode discharge tube, a region between the positive column and the negative glow that appears dark. Regions in the tube become easier to distinguish if the pressure is lowered in a tube that has some air in it (normally air is removed to extend tube life and effectiveness). Then it becomes possible to distinguish the Faraday Dark Space as a region just outside a pale negative discharge glow, which in turn terminates in Crookes Dark Space, which borders the outside glow of the cathode. Named after Michael Faraday. See Crookes Dark Space. Faraday dynamo A historic electrical generator de- veloped in 1832 by Michael Faraday. Faraday effect A basic magneto-optical effect in which a plane ofpolarization of light in a magnetic field, traveling parallel to the lines of magnetic force, can be rotated to another plane by a transparent iso- tropic medium. Named after Michael Faraday, who described it in 1846, this effect was studied further three decades later by John Kerr. The distinction be- tween the Faraday effect and the Kerr magneto-opti- cal effect is that Faraday focused his attention on a beam that was transmitted through the magnetic ma- terial, while Kerr focused on a beam that was reflected off the magnetic material. The Faraday effect can be seen in a number of telecommunications technolo- gies.In satellite communications, the plane ofpolar- ization of radio waves traveling through the iono- sphere rotates about the direction of propagation, par- ticularly at lower frequencies. See Kerr magneto-op- tical effect. Faraday effect, acoustic The Faraday effect was described by Michael Faraday more than 150 years ago. It is a basic, fundamental effect that is exhibited in many different phenomena and is of continuing interest to scientists, both as to its properties and its practical applications. The acoustic Faraday effect is the acoustic analog ofFaraday's magneto-optical ef- fect. Typically, liquids do not propagate transverse waves, but L.D. Landau, in 1957, predicted that a quantum liquid phase of 3He might exhibit transverse sound waves under specific conditions. Lee et al. have 344 observed rotation of the polarization of transverse sound waves in superfluid 3He-B in amagnetic field, lending support to Landau's prediction. See Faraday effect. Historic Faraday Electromagnet This Faraday electromagnet, cobbled out of avail- able materials. was wound partly from Faraday s wife spel/icoat. [Classic Concepls ilIusrralion.} Faraday-Stark effect A novel effect resulting from the combination of the Faraday magneto-optical ro- tation and quantum-defined Stark effect. This phe- nomenon enables an electrical field to be used to in- fluence a Faraday or magneto-optic Kerr rotation. It is a photonic effect that was discovered in the mid- 1990s which, along with linear polarizers, may have applications for future high-frequency modulation devices. The Faraday-Stark effect was described by Lee et al. in Applied Physics in 1996, and Faraday- Stark magneto-optoelectronic (MOE) devices were patented by Lee and Heiman (U.S. #5,640,021, 1997). See Faraday effect, Stark effect. Faraday, Michael (1791-1867) An English physi- cist and chemist who was apprenticed to a bookbinder at the age of 13. He took time to read the books and to listen to local lectures by Humphry Davy, becom- ing his laboratory assistant in 1813. Faraday went on to conduct extensive experiments in electricity and magnetism. He passed electrical currents through so- lutions and observed their effects, adding new knowl- edge to the discoveries of A. Volta. Faraday demon- strated that the amount of an element deposited at an electrode is proportional to the current flowing through the solution. In 1831, he demonstrated that an electrical current can induce a current in a differ- ent circuit and made a historic entry in his journal linking electricity and magnetism. The following year he constructed a basic generator, calling it adynamo. Faraday also studied the properties of metals and glass and developed new types of optics. He coined © 2003 by CRC Press LLC the tenns electrolyte, electrode, and ion. Further im- portant investigations of inductance in electrical cir- cuits by other scientists grew out ofFaraday's work. Many electrical effects have been named after him. See Davy, Humphry. Faraday's laws Michael Faraday investigated the phenomena related to decomposition by galvanic current and made some important discoveries that have been investigated and variously stated by suc- ceeding scientists. Generally, Faraday's laws are de- scribed as follows: I. in electrolytic decomposition, the number of ions charged or discharged at an electrode is pro- portional to the current passed; 2. the amounts of different substances deposited or dissolved by the same quantity ofelectricity are proportional to their equivalent weights; 3. when passing a constant quantity ofelectricity through different electrolytes, the masses of the ions set free at the electrodes are directly pro- portional to the atomic weights of the ions di- vided by their valence. Faraday called his discovery the "law of definite elec- trolytic action." It was opposed by Berzelius and those who adhered to Volta's theory of galvanism. Through subsequent experiments, Faraday's concepts have been refined and confirmed, and his discover- ies are now known as Faraday's laws. Farber, David J. Originally a computer consultant to the Rand Corporation in the late 1970s, Farber later became a cofounder of CSnet (Computer Science Network), NSFNet, and others. In 1995, he was awarded the SIGCOMM Award for lifelong contri- butions to his field. Farber has served on the boards of AT&T and several other industry telecom compa- nies, as well as the Electronic Frontier Foundation and the Internet Society. In January 2000, the Fed- eral Communications Commission (FCC) announced his appointment as Chief Technologist for the FCC. He is known for his online discussion list "interest- ing People." FARNet See Federation of American Research Net- works. Farnsworth, Philo Taylor (1906-1971) A preco- cious American musician and inventor who built an electric motor at about 12 years of age and described a television system to friends. He is reported to have shown a drawing of the idea to J. Tolman, a teacher, in 1922. Fortunately,Tolman later remembered the incident and produced the drawing, or the young Farnsworth might not have received credit for being one of the earliest inventors of television technology. Farnsworth kept working on the idea, submitted a patent application in January 1927, and successfully transmitted his first TV image in September 1927. The television patent was awarded in August 1930 (U.S. #1,773,980). The versatile inventor also developed several types of amplifying systems, a system of pulse transmis- sion, a projection system, a microscope, and a type of cold cathode-ray tube (CRT), securing hundreds of technology patents during his lifetime. It should be noted that biographers and Farnsworth himself credit his wife Elma "Pem" Gardener-Farnsworth as contributing significantly to the construction of his devices. In September 1983, the U.S. Postal Service com- memorated the achievements of Philo T. Farnsworth with a 20-cent stamp and first day cover and later is- sued a 33-cent portrait stamp from the Great Ameri- can Inventors series. See television history. http://philotfarnsworth.com Farnsworth Historic Imaging Tube .~. Farnsworth steenage drawing of his concept of a historic television system emergedduringpatentdis- putes in the 1930s. {Philo T. Farnsworth, 1922.J FAS 1. See facility-associated signaling. 2. See frame alignment signal. fast busy A telephone busy signal that is distinctive in that it repeats at twice the rate ofaregular busy. A regular busy signal indicates the caller's phone is unavailable (it's off-hook or in use), whereas a fast busy indicates that all trunk lines are busy, and the call cannot currently be routed to the destination. FastEthernetA version ofEthernet enhanced to in- crease its 10 Mbps capacity up to 100 Mbps over cop- per or fiber, which brings it into the high speed net- working range along with asynchronous transfer mode (ATM) and FDDI. This enhanced capability requires the upgrade ofother devices such as hubs and network cards, partly because Ethernet hubs can be cascaded, whereas Fast Ethernet hubs are stacked. Fast Ethernet is an international open IEEE standard (802.3u, 1995) used in medium-scale networks such as campus backbones. See Fast Ethernet Alliance, Gigabit Ethernet. Fast Ethernet Alliance An open trade association established to develop and promote Fast Ethernet technologies for existing voice-grade traditional cop- per twisted pair, founded in July 1993. A major goal of the Alliance was to standardize 100 Mbps Ether- net technology. By 1994, it had submitted 100Base- TX and 1 OOBase- T4 wiring specifications for con- sideration to the IEEE for inclusion in the IEEE Fast Ethernet 1 OOBase- T standard. The Alliance member- ship totaled more than four dozen telecommunications 345 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary vendors including well-known companies such as NCR Microelectronics, National Semiconductor, Sun Microsystems. Fast Ethernet was adopted officially in June 1995 by the IEEE 802.3 group. See Fast Ether- net. fast Fouriertransform FFT. See Fourier transform, fast. Fast SCSI A means of configuring SCSI to provide faster transmission speeds, up to 10 Mbps. There have been a number of variations on the SCSI standards. One of the more commonly implemented versions is SCSI-2. See Small Computer System Interface for a detailed description of SCSI technology. FastIP, FastInternet ProtocolA 3Com commercial product in which just the first datagrams of the IF traf- fic are passed through the router and, ifa direct path is found, subsequent ones may bypass the router us- ing Next Hop Resolution Protocol (NHRP). It is em- bedded in local area network (LAN) adaptors and implemented in LAN switches rather than in Inter- net Protocol (IP) routers. See IP switching. FAT 1. File Allocation Table. See FAT format. 2. final acceptance testing. FAD See fixed access unit. fault A defect, incorrectly functioning system, mis- take, or accident. In fiber optic cables, faults may in- clude crystallization during fabrication, bubbles, un- desired particles (apart from deliberate fiber doping), misalignments, incorrect coupling or bonding, exces- sive bends, and dispersion problems. fault isolation In electronic circuitry or software de- bugging, a troubleshooting strategy for isolating the location ofa problem. In circuitry, it may involve shutting down parts of the system, wiring in shunts or bridges, or selectively stimulating particular areas. In software, it may involve setting breakpoints, print- ing debug messages, or tracing particular variables. See bridge, shunt, trace. fault threshold The level at which a system's struc- ture or function is considered to be compromised. This may be a certain number of lost packets, a speci- fied electrical level, a certain number of physical flaws, or any other measures particular to a system that affect its integrity and functioning for aparticu- lar purpose. fault tolerant A fault tolerant system is one that is designed so ifa problem occurs, the entire system or important parts of the system will continue to func- tion until the problem is corrected. Thus, system re- dundancy, backups, secondary routines or hardware paths, etc. can be incorporated to increase fault toler- ance. Good computer operating systems are designed so that individual applications don't crash the system. The application itself may crash, or need to be "killed" (by killing the individual processes associated with the program), but the system can handle the crash without affecting other programs or the general op- erations and will clean up stray files, memory, etc. See Byzantine Generals problem, failsafe. fax colloq. facsimile. See facsimile machine. fax mode See facsimile mode. FB See framing bit. 346 FBT See fused biconic taper. FBus Frame Transport Bus. FC 1. See feedback control. 2. frame control. FC- connector Arelatively common coupling part for fiber optic connections that physically resembles ST- connectors, but with a friction rather than a bayo- net mount. FC- connectors are used to couple single- mode fiber connections. They are also available in hotmelt styles. FC-x In the Fibre Channel hierarchical model, a se- ries of services and protocols. For more detailed information, see Fibre Channel, including the Fibre Channel Layers chart. FC-x Function Notes FC-O physical media, transport speeds, re- ceivers, and transmitters are defined at this level FC-l encodings transmission encodings and decodings FC-2 signaling a protocol for specifying mechanisms and rules for transfering data blocks, con- trolling data flow, and error detection mechanisms FC-3 services common services for N Ports on a node FC-4 protocols upper level protocols in terms of channels and net- works (e.g., SCSI and ATM) that map into the system FCA See Fibre Channel Association. FCIA See Fibre Channel Industry Association. FCC See Federal Communications Commission. FCC Glossary ofTelecommunications Terms See Glossary of Telecommunications Terms, FCC. FCLC See Fibre Channel Loop Community. FCS 1. See Federation of Communications Services. 2. See Fibre Channel specifications. 3. See Frame Check Sequence. 4. Fraud Control System FCSI See Fibre Channel Systems Initiative. FCW See Federal Computer Week Magazine. FDD See floppy disk drive. FDDI See Fiber Distributed Data Interface. FDM See frequency division multiplexing. FDMA See frequency division multiple access. FDMS See Fiber Dispersion Measurement System. feature code A number or character sequence used to activate a feature on a phone system, such as speed dialing, last number redial, etc. These are more com- mon on multiline business phones than on residen- tial phones. feature connectorA connector for coupling a periph- eral card or device to another peripheral card, such as a video graphics adapter, so the second card can perform direct memory access (DMA) through the card's bus, without having to load the system bus. The feature connector is commonly used on VESA -com- patible systems. © 2003 by CRC Press LLC Feature Group Switching Arrangements feature phone A phrase for phones that have extra features. Sometimes the features improve function- ality (redial, speakerphone, channel, etc.), but some- Feature Groups Designated groups representing various types oflong-distance carrier switching ar- rangements that are part of the Bell Operating Com- panies (BOC) system. Group A Group B Group.C GroupD A subscriber line connection rather than a trunk connection to a local exchange carrier's network. A trunk connection that uses an authorization code for billing. Used in areas where it is not practical to offer Feature Group D (Equal Access services), such as some older switching systems, and independent services. The older long-distance services offered by local exchange carriers to AT&T before divestiture. Mutually exclusive with Feature Group D. Equal Access services, facilities and signaling specifications, established since divestiture and implemented in the mid-1980s. Mutually exclusive with Feature Group C. times they are just a marketing enticement and may not be very useful. FEe 1. See Forwarding Equivalence Class. 2. See forward error correction. FECN See Forward Explicit Congestion Notifica- tion. Federal Communications Commission FCC. A sig- nificant U.S. federal regulatory organization origi- nally created through the Communications Act of 1934, evolving from the formation of the Federal Ra- dio Commission (FRC) in the Radio Act of 1927. The original mandate of the FCC was to regulate the E~~==:~~:t~l.::~]~:F~::~:~~~ iB time slots, and callsigns. Since then, its jurisdiction has been broadened, reflecting the growth in telecom- munications in general. The Commission is directly responsible to the U.S. Congress. The FCC has a powerful role to play in the fair and equitable enactment and distribution oftelecommu- nications resources in accordance with the Telecom- munications Act of 1996. It is the responsibility of the FCC to see that the Act meets its goals of open- ing the telecommunications business to anyone, and of promoting fair competition in the industry. The FCC now also oversees product emissions, en- suring that computing devices do not emit harmful radiation or unharmful radiation at levels that may nevertheless interfere with other radiant technologies such as radio waves. The FCC overall organization consists ofa number of commissioners, about nine offices (public affairs, plans and policy, general counsel, etc.) and six bu- reaus. See Primary Divisions chart. See Communi- cations Act of 1934. http://www.fcc.gov/ Primary Divisions of the Federal Communications Commission FCC Bureau Responsibilities Common Carrier (CCB) Enforcement, pricing, accounting, program planning, network services, and wire line services. Wireless Telecommunications (WTB) Domestic wireless communications, including paging, cell phone, PCS, and radio, excepting satellite communications. This bureau is further subdivided into Commercial Radio, Enforcement, Policy, Private Radio, Licensing, Customer Services, and Auctions divisions. Mass Media (MMB) Audio service, enforcement, policy and rules, video services, administration, and inspections. Compliance & Information (CIB) A national call center, and infonnation resources, management, compliance, technology, and regional offices. International International planning and negotiations, satellite and radio communications, and general administration. Cable Services (CSB) Consumer protection and competition, engineering and technical services, policy and rules, public outreach, management. 347 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Federal Communications Commission classes, FCC classes A series of designations or ratings ap- plied by the FCC to electronics devices. These are primarily intended to help prevent interference from devices like computers that may affect electromag- netic broadcast waves such as radio and television signals. If you have tried to use a cordless phone near a computer and experienced interference, you are fa- miliar with the type of problem excess emissions can create. Many commercial video devices, for example, are labeled 'For Commercial Use Only' to comply with FCC regulations. Federal Computer Week Magazine FCW. A news- paper providing up-to-date news and product infor- mation to U.S. government computer technology us- ers on sources and types of federal information tech- nology (IT). It especially focuses on desktop, client- server, and enterprise computing and issues of vol- ume procurement. FCW publishes online and print editions and maintains an online archive of past in- formation. FederalInformation Processing Standard FIPS. A set of standards for document processing, search, and retrieval. Examples include FIPS PUB 180-1 (secure hash standard) and FIPS PUB 144 (digital commu- nication performance parameters). A number ofFIPS publications are based upon ANSI and CCIT stan- dards. Federal Networking Council FNC. The FNC re- ports to the Federal Coordinating Committee on Sci- ence Engineering and Technology and was chartered by the National Science and Technology Council's Committee on Computing, Information and Commu- nications (CeIC). It provides a focal point and forum for networking collaboration among U.S. federal agencies with regard to education, research, intercom- munications, and network operations. Since 1997, the various activities of the FNC have been carried out through the Large Scale Networking (LSN) group. http://www.filc.gov/ Federal Standard Glossary of Telecommunica- tions Terms See Glossary of Telecommunications Terms, Federal Standard. Federal Technology Service FTS. A service of the U.S. General Services Administration (GSA) that provides infonnation technology and network ser- vices to U.S. government agencies, including its mo- bile workforces. http://www.fts.gsa.gov/ FederalTelecommunications StandardsCommit- tee FTSC. A U.S. government agency that promotes the standardization of communications interfaces, including computer networks. The FTSC is chaired Category Class A Class B Notes Computing devices rated for office use and that may not be used in the home. Computing devices rated for home use. by the Chiefof the Technology and Programs Divi- sion. Through the work of its technical subcommit- tees, it is the primary telecommunications standards mechanism supporting the National Communications System (NCS). The FTSC liaises with and evaluates the development of national and international stan- dards and develops federal standards recommenda- tions or the standards themselves in situations where existing standards are unavailable or unsuitable for U.S. government needs. The technical subcommit- tees have specialized expertise in various fields, in- cluding mobile, wireless, and multimedia telecom- munications. FederalTelecommunications System FTS. The in- tercommunications network used primarily by U.S. government civilian agencies. It includes intercon- nections to other agencies and to the public switched telephone network (PSTN). Federation of American Research Networks FARNet. An organization comprised of commercial providers, some telephone providers, and mid-level NSFNet networks that meet to discuss issues related to these businesses and the Internet. Federation of Communications Services FCS. A trade association representing the mobile communi- cations industry in the British Isles. FCS promotes and encourages a healthy market environment for the communications industry in the U.K. and represents its members to the government and various tele- communications agencies. http://www.fcs.org.uk/ feed horn, feedhorn A basic signal-capturing com- ponent in satellite receiving antennas that is mounted at the focal point. It must either be rotated to corre- spond to the polarity of the incoming signal (horizon- tal or vertical) or be attached to a dual coupler. The focal length of the feed hom is dependent on the depth and diameter of the parabolic dish in which it is mounted. The feed hom is attached to a signal am- plifier. See antenna, low noise amplifier, microwave antenna, parabolic antenna. feedback n. 1. Information or phenomena that are re- flected or translated and returned to the originating or transmitting source. 2. An opinion offered in re- sponse to some preceding event or infonnation. 3. Re- turned information about data that has been received or passed through. In networks, there are many feed- back mechanisms providing information data rates, congestion, traffic in the opposite direction, and the progress or success of a transmission. feedback control FC. A means of controlling a sys- tem by sensing impulses or signals that are compared to a reference or desired value and responding accord- ingly. For example, when humans get cold and their body temperatures drop, the nervous system senses the difference and causes the body to shiver to help it generate sufficient heat to maintain life. In a tele- phone system, ifa phone remains off-hook for more than a prescribed length of time, the system 'senses' the anomaly and responds with a beeping sound or message suggesting the subscriber hang up the phone. In Internet services using dynamic IP allocation, ifa 348 © 2003 by CRC Press LLC connected subscriber is inactive for a certain period of time, the service may disconnect the subscriber in order to make the IP number available to another sub- scriber. In robotics, feedback control is an important means to enable arobot to sense and navigate around its environment. Thus, feedback control systems are used throughout the telecommunications industry in a multitude ofways to start, stop, and maintain sys- tems in order to facilitate efficient operations. See hysteresis device. feedback signal 1. A signal that loops back around to its source. An undesirable audio or visual artifact can occur when the same signal that is being trans- mitted travels back through the original transmissions media. In sound systems, it commonly manifests as a piercing, shrieking sound, as when a microphone is located too near a speaker carrying signals from that microphone. If carefully controlled, audio feed- back can sometimes be used to boost a weak signal. In visual systems, feedback often manifests as ghost images or wiggly distortions. 2. An intentional diag- nostic looped back signal. In diagnostic systems, when a signal is transmitted and then compared with a reference when it returns (the returning signal is the feedback signal), it is possible to evaluate the similarities and differences between the two signals, or the information carried on those signals. feeder cable 1. A primary cable, extending from a service provider or central switching location, to a distribution panel or end-user. In large installations, there may be a main feeder cable and branch feeder cables. 2. The cable that connects a primary distri- bution frame with intermediate distribution frames. 3. A main network backbone cable, which may have branch feeder cables leading to the main host com- puters. 4. A heavy duty, primary, or high bandwidth wire or cable intended to carry the main part of traf- fic from the transmission source to its primary dropoff points or hosts. Thus, fiber optic cables and 25-pair cables are common feeder cables. FEFO first ended, first out. A priority queuing ar- rangement in which the first item processed, or the first process completed, is the first to be passed on, or further processed. Thus, processes that are finished are taken out of the queue in order to leave space or processing time for others. See FIFO, FILO, LIFO, LILO. femto- (symb. - f) An SI unit prefix for 10- 15 , a very, very small amount. In decimal, femto- is expressed as 0.000 000000000001. See atto FEP See Front End Processor. FER Frame Error Rate. Fermat, Pierrede(1601-1665)A French lawyer, lin- guist, and mathematician who made many contribu- tions to our understanding of mathematics and op- tics, in spite of his recreational approach to mathemat- ics, which meant that many of his discoveries initially went unpublished. Fermat's principle is named after him. Fermat's principle When electromagnetic radiation travels by reflection offa surface from one point to another, it will take the path that can be traversed in the least amount of time. Fermi level Avalue designated for electron energy at half the Fermi distribution function. Fermi,Enrico (1901-1954) An Italian physicist who investigated atomic physics by systematically irradi- ating the elements, work derived in part from the in- vestigations of James Chadwick. ferric oxide A metallic compound commonly used to coat thin tapes or platters used in magnetic stor- age media. The ferric oxide molecules can be selec- tively rearranged by magnetic impulses in order to encode the desired information on the medium. There are other types of coatings available for applications such as sound or video recording; the differences in various coatings can affect the quality of the recording. ferroelectric liquid crystal FLC. Crystals that are incorporated into spatial light modulators (SLMs) in optical computing technologies. They have the ca- pacity for very fast bipolar switching. Surface-stabi- lized FLCs, created by suppressing the natural heli- cal structure of FLCs, are used in a number ofhigh- resolution color display technologies, including low power microdisplays. They are also suitable for use in optical shutters. The Ferroelectric Liquid Crystal Materials Research Center is located at the Univer- sity of Colorado. ferromagnetic Having the property of being very easily magnetized with high hysteresis, Le., magne- tism that changes readily with changes in the mag- netizing force. See electromagnet. ferrule A snug ring or cap encircling a tool, pipe, or wire; a short length oftubing or bushing (insulating liner) that helps to strengthen or secure ajoint or cou- pling component. It is sometimes called a sleeve, though the term is usually applied to "hard" sleeves (as opposed to soft, flexible sleeves) made ofsturdy materials. It may include a flange. Ferrule Examples Ferrules are the most important single component in fiber optic connectors. They come in a variety of shapes, materials, andformats. They may be unflanged (bonom left) orflanged with plastic (left) or stainless steel (right), and they are commonlyfabricated from zirconia (a type of corrosion and heat-resistant ce- ramic - right), though plastic ferrules (left) are now available. Ferrules similar to those shown above are commonly incorporatedinto standardized ST- and FC- connectors. ferrule, fiber optic In fiber optics cable assemblies, a ferrule is the most important structural member. It 349 '··.:·a '.·:.:·':··~·'·'·f! .;s~~- :~~~ © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary surrounds, secures, and aligns the fiber filament and supports the surrounding housing. To meet the de- mands of optical alignment of fiber lightguides, fer- rules must be exact and should not stress or overly bend the joint, othetwise interference from imperfect coupling could adversely affect the angle of the light beams or allow them to leak at the joints. Ferrules are commonly made of zirconia (a ceramic made from a crystalline powder) or alumina. Zirco- nia is favored for its bending strength, resistance to corrosion, hardness, and heat resistance. It holds up well in the polishing process and over time once in- stalled. More recently, plastic and opaque glass-ce- ramic ferrules have been improved to the point where they exhibit acceptable strength and durability for cost-effective alternatives to zirconia for certain ap- plications in addition to which they may not require polishing. Commercial ferrules for fiber filaments may come with pre-domed or pre-angled endfaces to facilitate termination. They may be semifinished blanks or whole fmished standardized ferrules such as SC- and LC- styles. They are available with or without flanges. 3M has produced a line of connectors that use a V- groove rather than a ferrule for coupling optical fi- bers. Interferometers can be used to assess the char- acteristics of the ferrule-supportedjoint. See interfer- ometer. FES Fixed End System. Fessenden, Reginald Aubrey (1866-1932) A pro- lific, Canadian-born, American inventor and radio pioneer who was one of the fIrst to try to devise ways to carry information on top ofa carrier wave. In the process of trying to achieve this, he developed a high- frequency generator in 1901 that could create radio wave, and a hot-wire barretter, which was developed into an electrolytic detector, for detecting radio waves. On Christmas Eve 1906, to the astonishment of those who heard the broadcast, Fessenden suc- ceeded in transmitting voice and music, using an Alexanderson alternator, over public radio waves to the U.S. east coast. See barretter, carrier wave, elec- trolytic detector, radio history. FEXT See far end crosstalk. Feynman, Richard Phillips (1918-1988) A charis- matic, individualistic American physicist who con- tributed greatly to our understanding of physics, es- pecially in quantum electrodynamics (QED quod erat demonstrandum - that which has to be demon- strated), who developed Feynman diagrams and pro- vided insights into the theory of computing. FFT See Fourier transform, fast. FGDC See Federal Geographic Data Committee. fiber 1. A strand, filament, or other structure with long, slender threadlike qualities. 2. Colloquial for fiber optic (or optical fiber). See fiber optic. fiber bundle Two or more fiber optic filaments held in close proximity, either with a supporting structure or sheathing. Combining fibers in a bundle enables more light signals to be delivered to the destination. It is not uncommon for hundreds of fiber filaments to be contained within a single bundle as the indi- vidual filaments are very small. Why use many fi- bers instead ofa fatter fiber (jiber rod)? There are a Basic Components ofa Fiber Optic Cable Bundle filler (no fibers) tension member single cable assembly fiber optic filament Single Cable Assembly Bundled Cable Assembly The basic parts of a single multifiber cable (left) and a bundle of multifiber cables (right) containing four single multifiber cables, with reflectiveiprotective sheaths (cladding) and outer sheaths (e.g., armoring), as needed. 350 © 2003 by CRC Press LLC number of practical advantages to bundling fibers, including flexibility and the capability of splitting off fibers along the path as needed as for communica- tions "drops" (local service), signs, or ambient light fixtures. The arrangement of fibers within a bundle is related to the purpose, length, size, weight, and philosophy of the fabricator. Often large numbers of fibers are randomly bundled with small gaps between fibers. The gaps may be useful in providing added flexibil- ity to the cable, or may be filled with filler materials to provide structural cohesion to the bundle. Some bundles are loose along the running portion of the bundle but tightly aligned at the endfaces through a fusion joint process. This facilitates coupling and re- duces the space needed for the coupler. Bundles are sometimes carefully aligned for certain purposes, as in a single lightline or an arrayed face- plate of certain dimensions. Sometimes bundles are deliberately randomized in order to provide a ran- domly even light source at the point where the light exits the endfaces of the fibers in the bundle. Sometimes fibers are bundled for ease of handling and installation. It is practical to bundle many fibers together and provide extra external insulation and armoring against the elements in bundles that are to be laid hundreds of feet undetwater in deep oceans. Bundles are also practical in situations where the de- livery ofdifferent wavelengths over the same cable is desired. See faceplate, lightline. Fiber Channel See Fibre Channel Standard. fiber creelA device for spooling fiber optic filaments to facilitate handling. 1. W. Hicks was one of the first to spool optical fiber. See creel. Fiber Dispersion Measurement System FDMS. A fiber Bragg grating measurement system that utilizes interference phenomena to evaluate grating transmis- sion properties, developed by NASA. The system is quickly able to fully characterize fiber device phase, amplitude, transmission, and reflection from either direction. FiberDistributedDataInterface FDDI. An Ameri- can National Standards Institute (ANSI X3T12, for- merly X3T9.5) standard high-bandwidth 100 Mbps packet-switched protocol developed by the X3T9.5 committee. FDDI Architecture Standard Documents Abbreviation Item Notes MAC Media Access Control A network control mechanism for defining fonnats and methods. Like the PHY layer, the MAC layer is directly implemented in FDDI chips. The higher LLC sublayer provides data to the MAC. PHY Physical layer An electronic signal encoding/decoding layer which mediates between the higher MAC layer and the lower PMD layer. PMD Physical Medium Dependent The lowest sub layer, which specifies various physical media such as interface connectors, cables, power sources, photodetectors, etc. SMT Station Management A node manager and bandwidth allocator. The SMT is further subdivided into connection management (CMT) which controls access, ring management (RMT) which provides diagnostic capabilities, and frame services. FDDI Basic Port Types Port Type Characteristics Mport Master port Connects two concentrators and can communicate with DASs and SASs. Sport Slave port Connects single-attachment devices for interconnecting stations, or for connecting a station to a concentrator. Aport Dual-attachment Connected to the incoming primary ring, and outgoing secondary ring. See A port dictionary entry. B port Dual-attachment Connected to the incoming secondary ring and the outgoing primary ring. 351 © 2003 by CRC Press LLC . Fiber Optics Illustrated Dictionary compress-send-decompress schemes, with the com- pression needed only to speed transmissions, and thus not degrading the quality of the original. See facsimile mode,. A defect, incorrectly functioning system, mis- take, or accident. In fiber optic cables, faults may in- clude crystallization during fabrication, bubbles, un- desired particles (apart from deliberate fiber doping), misalignments, incorrect coupling or bonding, exces- sive bends, and dispersion problems. fault. Press LLC Fiber Optics Illustrated Dictionary surrounds, secures, and aligns the fiber filament and supports the surrounding housing. To meet the de- mands of optical alignment of fiber lightguides, fer- rules must be exact and should not stress or overly bend the joint, othetwise interference from imperfect coupling could adversely affect the angle of the light beams or allow them to leak at the joints. Ferrules are commonly made of zirconia (a ceramic made from a crystalline powder) or alumina. Zirco- nia is favored for its bending strength, resistance to corrosion, hardness, and heat resistance. It holds up well in the polishing process and over time once in- stalled. More recently, plastic and opaque glass-ce- ramic ferrules have been improved to the point where they exhibit acceptable strength and durability for cost-effective alternatives to zirconia for certain ap- plications in addition to which they may not require polishing. Commercial ferrules for fiber filaments may come with pre-domed or pre-angled endfaces to facilitate termination. They may be semifinished