Fiber Optics Illustrated Dictionary - Part 35 pdf

Fiber Optics Illustrated Dictionary and input/output peripherals are event-driven or event initiators. eventual Byzantine agreement EBA. In EBA, a number of coordinated processors (with some specified upper value for faulty processors) agree on a state or value among those considered to be reliable. Thus, a state of mutual agreement is negotiated among nonfaulty processors in a fault-tolerant system, but the processing does not have to be simultaneous. See Byzantine agreement and Byzantine Generals prob- lem for a history and fuller explanation. EWOS See European Workshop in Open Systems, Open Systems Interconnection. EWP electronic white pages. An electronic database ofpersonal, and sometimes business, phone and address listings. There are many EWP lookup services on the Web. ex a- E. A prefix for an SI unit quantity of 10 18 , or 1,000,000,000,000,000,000. It's a gargantuan quantity. See zeta-, atto- ExCa Exchangeable Card Architecture. An open socket architecture extension to PCMCIA 2.0 for use on Intel x86-based computers, introduced by Intel in the early 1990s. The software specification provides standardized socket, card, and client services. ExCA allows interfacing ofPCMCIA devices with computers, particularly mobile computers, which are more likely to have PCMCIA slots. See Personal Computer Memory Card International Association. exception I. error or unusual occurrence, such as an abnormal signal, data falling outside a certain specified range or a deviation from normal program execution. Common exception conditions in programming include stack overflow and divide-by-zero er- rors. In software development, exception handlers can be included in the code to detect and manage error conditions and resume program execution. 2. In ATM, a connectivity advertisement in a PNNI complex node representation that represents something other than the default setting of the node representation. excess burst size See burst size, excess. excess noise, current noise Undesirable noise that results from current passing through semiconductor components. exchange Acentral location for making connections, directing traffic, and redirecting traffic. Apublic telephone switching office or regional system is often called a telephone exchange. exchange access Defined in the Telecommunications Act of 1996, and published by the Federal Commu- nications Commission (FCC), as " the offering ofaccess to telephone exchange services or facilities for the purpose of the origi- nation or termination oftelephone toll services." See Federal Communications Commission, Telecom- munications Act of 1996. Exchange Access SMDS XA-SMDS, Exchange Access Switched Multimegabit Data Service. A con- nectionless, cell-switched, security-enabled data transport service for extending network features through standard interconnections with interexchange carriers (IXC). XA-SMDS is similar in structure to 332 ATM and is designed so that migration to ATM may be possible as ATM becomes more widely implemented. Multiple node local area networks (LANs) and wide area networks (WANs) can be interconnected without installing a dedicated path, at speeds ranging from 1.17 to 34 Mbps. XA-SMDS is a public level service, with auniversal addressing plan, so various XA-SMDS networks can intercommunicate as desired. exchange carrier EC. A telecommunications pro- vider operating under specified territorial and operating parameters designated within the industry. Exchange CarriersAssociation ECA. An organiza- tion established to support the interests and account- ing administrative concerns of long-distance telephone companies. Exchange Carriers Standards Association ECSA. More familiarly known as the Alliance for Telecom- munications Industry Solutions (ATIS) since 1993, the Washington, D.C based ECSA was established in 1983 to develop and promote standards related to the needs of various telecommunications carriers. The ECSA works in conjunction with a number of com- mittees, including the Carrier Liaison Committee (CLC), Information Industry Liaison Committee (IILC), and Telecommunications Industry Forum (TCIF). See Alliance for Telecommunications Indus- try Solutions for more information. exchange line The connection between a telephone subscriber and the local telephone switching exchange. See local loop. Exchange Message Record EMR. An industry standard for the exchange ofsample, study, and billable data messages among local exchange carriers (LECs). Exchange Service ES. Basic subscriber phone service with a unique local telephone number and access to the public switched telecommunications network. Includes residence and business services and private branch trunk line services. Private lines and Special Access services are not considered to be Ex- change Services. excitation The application of an external stimulus to a system resulting in a reaction or response. The application of a charge, potential, or electromagnetic influence. excitation voltage The minimum or sufficient voltage required for a circuit to be functional. exciton An excited state in a crystal substance with the characteristic ofmoving and recombining holes and electrons. See p-njunction, quantum. execution In a software process, the carrying out of preprogrammed, realtime, or heuristic steps in order for the program to run through its instructions or logical structure. It mayor may not be an interactive process. execution time Ameasure of the time in steps, minutes, or machine cycles that aprocess, or a particular computer instruction, takes to be carried out. Executive CellularProcessor ECP. In wireless Mo- bile Switching Centers (MSCs), the capabilities for intelligent call handling, mobility management, and system control and configuration. In Lucent © 2003 by CRC Press LLC Technologies systems, the ECP, with the Operations and Management Platforms (OMPs), comprise the Access Manager. EXFO Electro-Optical Engineering,Inc. Expertise in Fiber Optics. A publicly traded leading designer and manufacturer of global fiber optic test, measure- ment, and automation solutions for telecommunications. The products are aimed at handheld and modu- lar instruments telecommunications markets and high-performance optical instrument component lab users and systems vendors. In August 2001, EXFO announced an agreement to acquire Avantas Net- works Corporation, a pre-revenue company develop- ing data communications and telephony testing systems. exosphereA region beyond the Earth's surface at the edge of the atmospheric "envelope" surrounding the planet. See ionosphere. ExpandedInterconnection Service EIS. A colloca- tion arrangement, in which the switch services for a private branch are located within the premises of the local telephone carrier. expansion slots Peripheral slots in an expansion bay or a computer intended for the placement of control- lers, cards, and other device interfaces, usually comprised of printed circuit boards, which are used to ex- tend a system. VESA, EISA, ISA, MCA, and PCI are various common standards for the electrical and transmissions protocols used with slot peripherals for personal computers. expert system An expert system is a type of information-handling approach which grew out ofartifi- cial intelligence research. Various types of expert systems exist for information creation, storage, and manipulation. An expert system is one that involves the manipulation and creation of information in a way that is rule based and evaluative, rather than search and query. The traditional means ofproviding information to computer users is through a database, which usually involves storing and retrieving the data on a keyword basis, but an expert system can take in a richer mix of inputs, or nontraditional inputs, including natural language queries, visual queries, or other contextual input. An expert system also incorporates the combined knowledge of many experts in that it is not just a collection of facts but may further include data relationships, means of analyzing and evaluat- ing the data, and other pertinent evaluative characteristics. Expert systems grew out of efforts to mimic the ease and naturalness of human communications through machine interfaces, in order to enhance the usefulness of computers. Because expert systems often handle different types of data, different types of input, and process the information in different ways from other types of information repositories, they sometimes require different programming languages than those commonly used for commercial applications. Cobol, Fortran, C, and BASIC are used for many programs used in business and educational settings. However, because expert systems often require a di fferent programming approach, good text parsing languages like Perl, and good information parsing and rule-based languages like LISP and Prolog may be used. Of the various types of products that have evolved from artificial intelligence research, expert systems are some of the most commercially successful results. explicit congestion notification ECN. An IETF IP standard proposed in the late 1990s for detecting and managing end-to-end network transmissions and congestion. A congestion experienced (eE) bit in the header serves as a data congestion indicator in con- :~~~~:ra~:~~~ ff~g~l~ 6ea~~:: t:~~pa::,~~~o~: ••• livery ofdelay-sensitive applications, such as broadcasts on the Web, or for improving security and in- trusion detection. One might expect a trade-off in transmission efficiency from having to encode and detect the ECN; however, in testing it has been found that bulk and transactional data transmissions may be more efficient when packets are marked rather than dropped. See random early detection, ~C 2481, RFC 2884. explicit forward congestion indicator EFCI. In ATM networking, a traffic flow control congestion, or impending congestion, indicator contained in the ATM cell header. The congestion signal is sent to the end destination to adjust accordingly. See cell rate, leaky bucket. Explicit Rate ER. A network congestion feedback mode provided in available bit rate (ABR) service. Network rates that can be received are indicated within Resource Management cells. See cell rate. Explorer See Microsoft Explorer. ExplorerI The first successful U.S. satellite launched on January 31, 1958. Its mission was scientific, and it included instruments to measure radiation in space. At first, it was thought that the instruments might be defective, as the readings were much higher than expected' but the measurements were later verified. Explorer8 The first NASA satellite launched by the United States. The Explorer 8 was launched on No- vember 3, 1960, to study the ionosphere. export To save information in a format that is not the native format of the application doing the saving. For example, a word processed document may be saved in ASCII to facilitate transfer over a 7 -bit network. This procedure is often done to create a version ofa file which is compatible with other applications or transport mechanisms. Exporting is usually done through a conversion filter, and there may also be fil- ters for importing. exposure Contact with radiant energy, bacterial or viral toxins, or chemicals. Sun exposure can cause fading, burning, melting, or other chemical reactions. Exposure to radiation from X -rays or laser light can can cause burns, deep cellular damage, chemical changes, or death to biological organisms at high doses. Exposure is a concern in industrial environments for both equipment and humans. It is also a consideration in medical environments, where exposure to viruses, bacteria, X-radiation, chemicals, and other contaminants or hazards may cause harm. See CDRH classification. 333 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary express circuit An interurban phone carrier circuit connected without multiplexing equipment. eXpress Transfer Protocol XTP. A lightweight network protocol originally developed by Protocol En- gines, Inc., in the late 1980s. In its early development it was sometimes also called Xpress Transfer Proto- col. It is a reliable, realtime, transfer layer (combined network and protocol layer) protocol. It was designed to be implemented as a VLSI chip set. XTP is designed for parallel processing and the various func- tions such as address translation and flow/rate/error control can be executed in parallel. XTP utilizes control packet and information packet frame formats. In multicast mode, one-to-many transmissions can be supported. Protocol Engines, as a company, was no longer able to continue development after the early 1990s, but interest in XTP as a protocol continued from outside the company. The protocol is used in the European RACE and DeTeBekom projects. The XTP collaborators are the University of Dresden, The University of Salzburg, and the University of Ottawa. A number of extensions were added to the XTP 3.6 standard to support Qual- ity of Service (QoS). This version is known as XTPX (XTP eXtended). It might be best to abbreviate it as eXTP rather than XTP to distinguish it from the commercial multicasting protocol known as Xpress Transport Protocol. The author was unable to find clarification as to whether the Xpress Transport Pro- tocols had its origins in the eXpress Transfer Proto- color whether the protocols were developed indepen- dently. extended ASCII A colloquial designation for a vari- ety of noncompatible 8-bit character code designa- tions in which the first 128 characters conform to the ASCII standard, but the subsequent 128 characters (which mostly include symbols and accented letters) are variously assigned by different developers. Extended-defmition Television See Enhanced-definition TV. Extended Digital Subscriber Line EDSL. A version of Digital Subscriber Line (DSL) services that supports 23 B channels and one 64-Kbps D channel transmitted over a single line. See Digital Subscriber Line, Primary Rate Interface. extended graphics adapter EGA. A color graphics standard introduced by International Business Ma- chines (ffiM) in 1984, considered the successor to color graphics adapter (CGA). EGA was widely implemented by third party developers on Intel-based personal computers. EGA could display up to 640 x 350 in 16 colors. Actually, to say "16 colors" is stretching it a bit because, in fact, there were eight colors, plus eight half-intensity versions of those same colors, rather than 16 colors selected for their usefulness to a limited palette. Not long after, ffiM introduced PGA, which had slightly better vertical resolution than EGA (640 x 400) but was otherwise not a significant evolution. See color graphics adapter. extended graphics array XGA. A 1024 x 768-color graphics format used in liquid crystal display (LCD) data projectors. 334 Extended Industry Standard Architecture EISA. A 188-pin bus interface specification to succeed Industry Standard Architecture (ISA), which in tum succeeded the IBM PC/AT bus specifications. EISA supports 32-bit memory addressing, and 16- or 32- bit data transfers. EISA was designed to support 32- bit Intel 80386 and 80486 processors. The specification works with various system resources, including input/output ports, memory, and DMA channels. On EISA boards, configuration is done with EISA Configuration Utility (ECU) software, rather than through hardware, using a CFG file supplied with the board. EISA boards, while faster, are somewhat physically compatible with legacy boards, preserv- ing the old AT pin specifications on the upper 98 pins. The rest are used for the EISA bus signals. The slot into which an EISA card is inserted is assigned a unique address so that the system can recognize and initialize the interface. EISA is widely supported by many manufacturers but is being gradually superseded by newer formats. extended play A designation for a technology that plays beyond that generally expected to be the maximum limit. Historic phonograph cylinders played for two or three minutes, but some companies found a way to make them play for four minutes on standard equipment, thus creating extended play albums. Extended SuperFrame ESF. A frame format for 1.544 Mbps communications (2.048 in Europe with 30 channels) evolved from DS-I in 1962 and Super- Frame in 1969, widely used in T1 systems. ESF provides improved error correction and can be serviced without taking down the entire system. Twenty-four frames are combined to create one Extended Super- Frame. Six frames are used for frame synchroniza- tion, six for error tracking, and twelve for Facility Data Link (FDL). Signaling is accomplished through robbed bits in frames 6, 12, 18, and 24, except in transparent mode, in which the 24th channel is used in order to provide Clear Channel Signaling (CCS). Facility Link Data (FDL) is used to transmit to telephone monitoring stations. extended time division multiple access E- TDMA. A type of digital transmission scheme favored by cellular providers over older analog-based systems. See time division multiple access. Extensible Markup Language XML. XML is a markup meta language that allows more flexibility and complexity of presentation than HyperText Markup Language (HTML) and is not limited to Web publishing. Like HTML, it is based upon the Stan- dard Generalized Markup Language (SGML - ISO 8879). Some have promoted it as the successor to HTML, but the industry has not yet formed a con- sensus on this possibility. XML has been recommended for use with the International Development Markup Language and is integral to the WebDAV Distributed Authoring Protocol. XML MIME entities are of four types: document entities, external DTD subsets, external parsed entities, and external parameter entities. In Jan. 2001, Murata et a1. submitted a Standards © 2003 by CRC Press LLC Track RFC to standardize five new XML media types to facilitate the exchange of XML network entities. XML MIME entities contain information to be parsed and processed by the receiving XML system and may include system-level commands. The proposed new media types were intended to overcome problems inherent in trying to adapt SGML text/sgml and application/sgml media types for use with XML. The new media types follow the conventions of the IETF media types tree, for consistency, and include Media Type Notes text/xml Preferred over application/xml for unprocessed, readable documents (as with plaintext). Use of the parameter is op- tional but recommended. application/xml Use of the parameter is op- tional, but recommended, to distinguish between the recommended utf-8 or utf-16 character sets; otherwise the default is us-ascii. text/xml-external-parsed-entity application/xm I-extern a I-pars ed-en tity application-xml-dtd See IDML Initiative. HTML, SGML, World Wide Web Consortium. See RFC 1874 for SGML media types. See RFC 3023. extension, file name A suffix, often preceded by a period, as a subsection delimiter on systems that require it, and as a visual locator on systems that don't. It helps to indicate the file format, such as . txt, . bmp, . tiff, .ilbm, frame, . wrd, etc. File extensions need not be restricted to three characters except on some systems with older types of file structures. In the mid- 1980s most types of computer platforms (Atari, Macintosh, Amiga, Sun, Apollo, NeXT, SGI, etc.) did away with the mandatory period and three-character limitation, as did Intel-based machines running OS/ 2 and Microsoft Windows NT. Surprisingly, many consumer Intel-based desktop computers running Microsoft Windows retained the limitation until 1996 and even later on some of the machines running legacy software. extension, phone An extra phone line that uses the same phone number as the originally installed phone with which it is associated. Exterior Gateway Protocol An Internet protocol developed in the early 1980s for the exchange of routing information between autonomous systems. See RFC 827. External Data Representation XDR. A standard representation for platform-independent data structures for remote procedure call systems, developed by Sun Microsystems. See RFC 1014. ExternalEnvironment In the X/Open Architectural Framework Technical Reference Mode, the External Environment is one of five basic elements. The EE comprises all the external entities with which the Application Platform (AP) exchanges data. The EE links to the AP through the External Environment Interface (EEl). Printers, scanners, other computers in a network, public switched telephone networks (PSTNs), human operators, etc. are all common elements of the EE. See External Environment Interface. external environment interface EEL Generically, a transmissions linking device between a local device (e.g., personal computer) and outside devices (keyboards, mice, printers, scanners, public phone services, surveillance cameras, packet radio transmissions, etc.) Serial, parallel, SCSI, IDE, USB, Apple- Talk Data Bus (ADB), Ethernet, and Firewire peripheral cards are examples of some common external environment interfaces on commercial computing systems. External Environment Interface EEL In the XI Open Architectural Framework Technical Reference Model, the External Environment Interface is one of five basic elements and one of two basic interface types. It provides the data link between the application platform and the external environment (EE). The EE is comprised of the various entities and systems with which the application platform exchanges data. Thus, the EEl may link to various devices such as printers, modems, scanners, keyboards, mice, moni- tors, etc. Open systems EEl standards facilitate interoperability among platforms interconnected through the EEl. See Application Program Interface. external memory Any memory outside the direct access memory peripherals or chips in a system. Thus, information stored on punch cards or paper tape would be considered external memory, as would re- movable cartridges or tapes. Chip memory and internal hard drives would be considered internal memory. extinction potential The lowest voltage level at which plat current in a plat will flow in a gas-filled electron tube. EXTN Extension. An industry abbreviation designat- ing the last four digits ofa phone number. A 10-digit number is expressed with symbolic characters as: NPA-NXX-EXTN. extraneous emission Any emission in addition to, or external to, the desired emission. Thus, emissions outside the case ofa computer system or outside the sheath of an insulated wire are considered extraneous. Since these emissions can interfere with radio transmissions (radio broadcasts, intercoms, cordless phones, etc.), they are strictly regulated by the F ed- eral Communications Commission (FCC), and electronic components must conform to stated emission requirements. extranet A larger network, based upon Internet- working technology, for connecting local area networks (intranets) and other authorized users within a virtual 'closed loop' system. The extranet is seen as having the potential to significantly support and change electronic commerce and to take some of the traffic load off the Internet. Those promoting the concept suggest that it will enable customers to connect 335 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary more directly to vendors than is typical in the current Web-based system and that security will be more easily supported on the system. Extranets will potentially be used for monitoring transactions, accessing databases, requesting product information, etc. For example, bookstores might be connected directly to book distributors, to expedite orders, shipments, and account handling. Marshall Industries, Federal Express, and Dell Com- puter are some of the early adopters of the extranet concept. Extranets are also seen as a way to give pri- 0rity services to elite customers. For example, Charles Schwab & Company has developed SchwabLink Web, a redesigned online trading and research service available only to the company's top 5,000 invest- ment manager customers. The system is Java-based, conforming to CORBA and InterORB Protocol standards. The original use of the term has been attributed to Bob Metcalfe in 1996, though a number of electronic commerce work groups may have begun using the term around the same time. Steven Telleen was describing intranets in 1994, with a definition that is now more commonly expressed with the term extranet. Telleen described intranets as an "infrastruc- ture based on Internet standards and technologies that supports sharin~ of content within a limited and well- defined group.' The concept of an extranet is not new, even if current implementations represent a significant evolution. In the earliest days of telegraph and telephone technology, it was not unusual for related businesses to have direct connections to one another without going through the local switchboard exchange, and later incarnations of this system used leased lines and sometimes hot lines for direct connections between building complexes or cooperating businesses. extremely high frequency EHF. The frequency spectrum designated as 30 to 300 GHz, typically used for satellite communications. These very short wavelengths can be apprehended with small antenna assemblies. See band allocations for a chart. extremely low frequency ELF. The frequency spectrum designated as 30 to 300 Hz. Waves in this range are extremely long and not of much practical use for communications with our present technologies (the 336 same was formerly said of microwave frequencies, and they are now widely used). See band allocations for a chart. extrinsic semiconductor A type of semiconductor that includes impurities that contribute to its electromagnetic properties, usually to enhance them. See doping. extrusion 1. Forming by forcing through an opening, which may contribute to the shape of the extruded material. Extrusion is often accompanied by a heat- ing or cooling process in order for the extruded material to retain the desired shape. 2. A means to pro- duce or apply insulating materials to wire or cable by forcing plastic or other materials through an opening. eye phone 1. A proj ect by a N olWegian group, Me- dia Lunde and Tollefsen, Ltd (MediaLT), that designs products for the visually impaired. MediaLT plan to use video telephony as a communication channel to a sighted eye. 2. A body-worn helmet or laser-to- retina transmission system associated with electronics for communications. The user views images on the inside surface of the eyepiece, on a tiny screen next to the eye, or through a direct projection on the retina. A number of companies have produced work- able systems ofdifferent types. This technology is of special interest to the virtual reality (VR) community, and research is fueled in part by demand from the games-playing community, with spinoffs for business markets and handicapped individuals. Potentially an eye phone can be integrated with a mobile communications link to the Internet (stock market day trad- ers would probably love this kind of system). 3. A visual interface on a computer system equipped with an Internet phone that enables calls to be clicked and controlled through a computer mouse/pen-type interface. This is a less common use of the phrase and will probably fade away as Internet phone technology becomes more familiar and common, but it may continue to be applicable to phone interfaces that can be controlled by eye movements (e.g., by someone with quadriplegia) . eyeletA small, washer-like flat cylinder or short tube for threading or supporting various wires, cables, or other narrow parts. EYP See electronic yellow pages. © 2003 by CRC Press LLC f 1. abbrev. farad. See farad. 2. symb. femto See femto 3. symb. focal length (usually italicized). See focal length. 4. symb. frequency. See frequency. F 1. abbrev. Fahrenheit. See Fahrenheit. 2. abbrev. fiber. 3. symb. filament. 4. symb. off with N as the corresponding symbol for on. 4. symb. 15 in the hexadecimal number system. The symbols used are 0 12 34 56 7 89 ABC D E F. Thus, "A" in hexadecimal represents"1 0" in the familiar decimal system, and "F3" represents "18" in decimal. Hexadecimal nu- merals are sometimes preceded with "X" or "OX" to indicate that the subsequent digits are represented in the hexadecimal system. For example, "15" in decimal may be represented as "OXOF.'~ See the ASCII chart in the Appendix for a list of decimal, hexadecimal, and octal equivalents up to 127 decimal. F Block Federal Communications Commission (FCC) designation for a Personal Communications Services (peS) license granted to a telephone company serving a Major Trading Area (MTA). The license grants pennission to operate at certain FCC- specified frequencies. See ABlock for a chart of frequencies. See C Block for a history and a more de- tailed explanation. F connector A small coupling connector used at the end of coaxial cable that is common in video editing, broadcast components, and local area network (LAN) cables. The F connector is recognizable by its center pin or plug opening for the center pin that is commonly seen on consumer television sets and on the cables run to the house by local television cable providers. 75-ohm F connector cables are commonly used for TV, VCR, satellite, and radio frequency (RF) device connections. See connector for a diagram. F -ES The designation for a fixed, Le., nonmobile, end system in a digital cellular network. The F-ES can both send and receive data and typically receives data from a mobile end system (M-ES). F region A region of the Earth's ionosphere in which F1 and F2 regions tend to fonn. The F1 region is ac- tive in daytime. The F2 region is commonly used for the propagation of radio waves, due to its high ion- ization levels. See ionospheric subregions for a chart. F link In Signaling System 7 (SS7), a fully associated transmission link directly connecting two signaling endpoints. The F link connects the host directly to a Service Switching Point (SSP) or a Service Con- trol Point (SCP) without passing through intermedi- ate Signal Transfer Points (STPs). For security rea- sons, F links are generally used for local applications rather than for links between networks. F port, fabric port. On a Fibre Channel network, a fabric-attached loop or node that connects point-to- point to an N port. In commercial products, the Fport may be self-discovering. See FL port. F Series Recommendations Aseries of ITU -T recommendations that provides guidelines for nontelephone telecommunications services. These guidelines are available as publications from the ITU- T for purchase. Since ITU- T specifications and recommendations are widely followed by vendors in the telecommunications industry, those wanting to maxi- mize interoperability with other systems need to be aware of the information disseminated by the ITU- T. A full list ofgeneral categories is listed in Appendix C, and specific series topics are listed under indi- vidual entries in this dictionary, e.g., A Series Rec- ommendations. See ITU-T F Series Recommenda- tions chart. Ionospheric Regions Topside. beyond F region F region. ca. 150+ km E roglon. ca. 95·150 Ian o region. ca. 75·95 km Earth An illustration of the general ionospheric regions enveloping Earth. These regions vary with tempera- ture and distance. The F2 region is particularly important for reflectingradiowavesoverlongdistances. 337 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary F-number Anumeric expression of the luminance associated with an aperture. Smaller F numbers are typically associated with higher luminance. Larger apertures are generally associated with higher F numbers up to the maximum luminance available. For lenses, the F number is the ratio of the focal length to the diameter of the aperture. On camera lenses, the F number associated with the maximum aperture is often inscribed on the lens casing. See candela, }stop, luminance. .fstop An expression of the open region of an aperture that admits light in a fixed or adjustable lens assembly as in a camera or other imaging device. The scale is commonly used with optical lenses to indicate the amount of light entering a sensing or imaging device (based upon the diameter of the aperture). Lower numbered fstops indicate larger openings, hence a wider diameter and more room for light to enter. Typical 35mm camera fstop settings range from 4 to 22. There is a relationship between fstop openings and the depth of field of the image in most lens assemblies (e.g., cameras). Awider aperture (lower .fstop) images over abroader area of the lens and thus is sub- ject to greater curvature. Asmaller aperture typically focuses through the central part of the lens, thus having less curvature over the extents of the image. The fstop is often balanced with the shutter speed to further control the imaging factors. Some imaging devices (e.g., consumer cameras) can balance fstops and shutter speeds automatically. See F-number, focal length. MESSAGE HANDLINGSERVlCES DIRECTORY SERVICES TELEGRAPH SERVICE F.l-F.19 F.2Q-P.29 FJ6-F.39 F.40 F.58 F. 59-F. 89 F.96-P.99 F.IO().lF.I04 F.I05~F.I09 MOBILE SERVICE F.I1o-P.159 TELEMATIC·SERVICES F.16o-F.199 F.20o-F.299 F.30G-F.349 F.3SG-R.39,9 Description Operating methods for.the international public telegram service The gentex network Message switching The international telelllessage service Theintemational telex service Statistics··and.publicationsonintemational telegraph services Scheduled and leased communication services Phototelegraph service Mobile services and multidestination satellite services Public facsimile service Teletex service Videotex service General. provision~JQrtelematic services DOCUMENTCOMMU'NICATION F. SSo-F. 579 Document communication F.58o-F.S99 Programming communication interfaces DATA TRANSMISSION SERVICES AUDIOVISUAL SERVICES ISDN SERVICES UNIVERSAL PERSONAL TELECOMMUNICATlON HUMAN FACTORS 338 F.60o-F.699 F.70o F 799 F.80o-F.849 F 85G-F.899 F. 9 OO'-F. 999 © 2003 by CRC Press LLC fab, fab plant A fabrication facility, a phrase often applied to a plant that produces computer chips or optical components. fabric A generic term for describing the interlinked! interwoven architecture or nature of a network's physical and logical interdependencies. A Fibre Chan- nel fabric is a system with interconnecting Nx -ports capable of routing frames using only D-ID data in Fe- 2 signaling protocol fame headers. The term is especially applicable to systems in which the speed of transmission across a network link, such as Fibre Channel, is near to, or exceeds, the speed of the processor in the machines that are being linked. Thus, the network as a whole begins to take on some of the characteristics ofa machine organism, as opposed to discrete machines simply sharing information over much slower links. With intelligent routing algorithms, it becomes impossible in a larger network to fully know or predict the routes that data will take when being transmitted across the communications links. Taken as a whole, fabric-related networking is an interesting evolutionary development in digital technology and will change not just the speed of computing, but its very nature. fabric/fibre loop port See FL port. fabric port See F port. Fabry-PerotinterferometerA detection instrument with an optical cavity composed of highly reflective surfaces that can be variably separated. When illu- minated with highly coherent light from a laser, the reflectors will bounce the light back and forth. If the reflecting waves resonate in phase, amplification of the wave, or resonance, occurs and the wave assumes enough power to "escape" through the reflective mir- rors and stimulate a phototube that converts the light energy to electricity in order to measure and display its characteristics. The resonant process is sometimes called constructive interference due to the amplify- ing effect of the interaction between the waves. To work effectively, the distance between the reflective surfaces is set in a mathematical relationship to the wavelength of the laser input (hence the variable separation of the reflective surfaces). An integral number ofhalf wavelengths is related to the distance between the reflective surfaces. See Fabry-Perot laser. Fabry-PerotlaserF -P laser. A reasonable-cost semiconductor laser component with a constant index of refraction that lases simultaneously at different wavelengths; in other words, it emits a wider frequency spectrum than a distributed-feedback laser. Fabry- Perot laser diode amplifiers can be used to electro- optically modulate a signal and can be monolithically integrated with quantum well transistors. See distributed- feedback laser, F abry- Perot interferometer. face A geometric surface oriented toward the viewer, another component, the host system in general, or a radiant energy source. Thus, the endface of a fiber optic filament is the end where light enters and!or exits the fiber. The face of an imaging surface is the surface that is oriented toward the image and, generally, the source of illiumination (which may be reflected). See endface, faceplate. face model A graphically modeled image of facial features, particularly eyes, lips, nose, and the general contours of the face. These images can be used in conjunction with computer applications for videophone, graphical answering services, simula- tions, police identification, artistic works, educational applications, and computer animations. Just as we now have synthesized speech for responding to user inquiries, we may someday have computer generated facial images responding to videophones and other interactive electronic devices, in effect, electronic ~~~:~~~~~s~~. :~~ ~~~i~d :~=~~~~:~~~~:~~: ;a ply of and demand for anthropomorphic imaging technologies. face time Time spent in a face-to-face encounter, as in social or business interchanges. A few years ago, one would never have thought to include this in a dictionary, but with so many human exchanges now being carried out remotely, by email, videoconferenc- ing, etc., the distinction is becoming more significant. In fact, in the future, you might not know what a per- son looks like, even if you communicate with him or her audio/visually through a fast link, since people might design virtual environments and avatars to take their place in such encounters, projecting a personal image rather than an image of what they look like in real life and avoiding face time altogether. faceplate At its most basic level, a protective plate, usually of plastic or metal, that fits over the front surface of a console or other device, which may have openings to accommodate various knobs or dials or sensors. The faceplate may be engraved, painted, or otherwise labelled to indicate settings. The term is also used to describe protective plates that have built- in connectors and sometimes some basic, compact electronics associated with those connections. Face- plates for supporting connections to wire or fiber- based data, voice, and video couplers may need to meet NEMA standards for electrical boxes. In cable networks, specialized faceplates can be used to upgrade passive taps to addressable taps to facilitate connection and disconnection of subscriber links. Single- or multiple-gang faceplates canbe used in conjunction with fiber optic adapters (e.g., ST adapters). In fiber fabrications testing, specialized microscopes may be equipped with a faceplate for inserting and steadying common fiber optic connectorsto facilitate inspection of the ends. See bezel; faceplate, fiber optic. faceplate, fiber opticAplanar surface comprised of an array of aligned fiber optic filaments that serves as an electromagnetic energy-guiding surface. Unlike traditional electrical faceplates that are mainly used as a protective surface, a fiber optic faceplate is a so- phisticated component assembly that may replace or complement lens components for transmiting a signal from an input to an output surface. It may inten- sify the signal for imaging applications and may be customized for various thermal expansion or radiation- 339 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary resistant tolerances. It can guide various electromagnetic phenomena, including X -ray emissions and vis- ible light for use in X-ray crystallography cameras, dental X -ray technologies, and biometric sensing systems, when coupled with CCD and CMOS components. In a molecular microscope, a fiber optic faceplate can be used on an interfaced camera to com- pensate for interference from the monochromatic laser light source. For some applications, a fiber optic faceplate may be used with or in place ofatraditional energy-emitting component, such as a scintillator, providing higher resolution and lower scattering. It is capable of imaging areas (up to about a square foot) without the curvature distortion characteristic oflenses. The imaging area on a CCD array coupled with a fiber optic faceplate may be divided into quadrants to facilitate independent processing (e.g., timing) ofsections of the imaging area. When combined with electrical components, a fiber optic faceplate may be vulnerable to heat from nearby electrical discharges (e.g., sparks). An accumulation of tiny indentations in the surface would gradually compromise the utility of the plate. Some assemblies include components for monitoring electrical spikes or conditioning the power source to avoid this prob- lem. See faceplate, fiber optic taper, phototube, scintillator. Fiber Optic Faceplate Bonded to Components A basic jiber optic faceplate consists of tightly packed, coherentlyalignedopticalfibers (left) bonded to electronic sensing technology (e.g., CCD imaging components). Attaching the faceplate to the image sensing components must bedone with extremepreci- sion to prevent signal loss or distortion - chemical gluing and oil coupling are two common bonding methods. facet In transmission technologies, aplanar geometric surface that reflects or refracts radiant energy. The term usually connotes more than one facet as in a multifaceted grating, lens, or resonating cavity. Thus, the facets ofa gem may prismatically refract light, 340 the facets ofa blazed grating may selectively reflect certain wavelengths, and the facets of a parabolic antenna may reflect radio waves toward a centtral feedhorn. facilities An installation designed for a particular purpose. The term typically encompasses related buildings, equipment, and operations, though some people use it loosely to include the personnel as well. Facilities ofsignificance in telecommunications include broadcast sending and receiving stations, computer terminal rooms, Internet link facilities (which may include tens of thousands of modems or terminal devices), and other wiring and access installations. facilities-based carrier FBe. Phone carriers that use their own facilities and switching equipment to provide phone service, often long-distance service. Con- trast this with those who lease or resell services from established carriers, although even facilities-based carriers enlist other can-iers as needed. facility-associated signaling FAS. In ISDN networks, a type ofsignaling in which the D channel is at the same primary rate interface (PRI) as an associated set ofB channels. In contrast, in nonfacility-associated signaling (NFAS) the B channels are sepa- rate from the D channel PRI. Delivery of FAS is through a link access protocol. FAS over Internet Pro- tocol is essentially the same as FAS over ISDN, but uses Internet Protocol (IP) as the transport mecha- nism. See channel-associated signaling. facom A distance radio navigation system or mea- suring system. Facom is a means ofanalyzing local signals and received signals using the low frequency band for distances up to several thousand miles to determine distances. See band allocations. FACOM fully automatic computer. A series of commercial large-scale computing systems first introduced in the mid-1970s by Fujitsu Limited, at about the same time the first microcomputers were being developed for commercial distribution. The FACOM M-190 is significant for being based upon large-scale integration (LSI) semiconductor circuitry that was new at the time. In 1981, Fujitsu released a large-scale general purpose system, FACOM M-380/382, the same year its first fiber optic communication systems were delivered. facsimile device, fax device A device for sending an image transmission through wireless or wireline phone transmissions. The word 'facsimile' implies an exact copy, though on some of the cheaper fax machines, that's wishful thinking. The two most common ways to transmit and receive facsimiles (faxes) are through dedicated fax machines and through fax modems. Often a fax generated on one type of system will be received on the other type. The most common form of fax machine is a dedicated system resembling a small printer that connects to a phone line. It sends faxes by scanning apiece of paper fed through the machine. Received faxes are printed in much the same way as they would be on a computer printer. Some faxes use continuous feed thermal paper, though more commonly now fax machines can work with sheet-fed plain paper. Many © 2003 by CRC Press LLC faxes optionally function as photocopiers and printers. See facsimile modem. facsimile formats In order for facsimile (fax) machines to exchange data, a number of international standards have been defined for image encoding and transmission. In addition to this, dialup modem transmission protocols with compression and error correction for fax/modems, called the V Series Recommen- dations, are used for data transfer in conjunction with fax formats. Tag Image File Format (TIFF) is an important raster image encoding format widely used in facsimile transmissions, with TIFF-FX as an offshoot of TIFF developed specifically to facilitate faxing over computer networks. Since a high proportion offacsimile transmissions are still basic black-and-white text documents, guidelines have been established for the encoding of minimal black-and-white images and text. These formats also have the advantages of small file sizes and fast transmission speeds. The Profile S and Profile F subsets of the TIFF specification support the transmission of basic black-and-white documents. Basic Facsimile Formats Class 1 EIAITIA (EIA-578) standard for basic computer fax/modem interface. Class 2 EIA/TIA standard for extended computer fax/modem interface which includes AT commands. Group 1 Single page transmission in six minutes. Common in the 1970s. Group 2 Single page transmission in three minutes. Common in the late 1970s. Group 3 (There is also a Group 3 bis, or Group 3 enhanced format.) 14,400 bps facsimile protocol. Two resolution modes include 103 x 98 dpi (standard), and 203 x 196 dpi (fine). Compression is supported. This is the most common protocol used with fax machines and fax modems, either Class 1 or Class 2. See V Series Recommendations V.27. Single page transmission in under 30 seconds. Group 4 ISDN B facsimile protocol adopted in 1987 but not widespread in subsequent years. For metric equivalents and higher resolutions (e.g., 400 x 400), added in the early 1990s, reference the ITU- T T.30 recommendations. Over the years, Group 3 has become the de facto standard for facsimile transmissions over standard phone lines, supporting two basic resolutions commonly called standard andfine. Three compression schemes are commonly used in Group 3 transmissions: Modi- fied Huffman (MH), Modified READ (MR), and Modified Modified READ (MMR) (Group 3 and Group 4), with MH the most common. Due to the limitations of data transmissions over phone lines with traditional modems, black-and- white imaging and bit- and stream-oriented transmissions predominate. However, as the Internet increases in importance and accessibility, byte- and file-ori- E~~:~;:~:1~~ii:::r::~:i~:!~~!i. channel network fax transmissions to appropriate servers and devices (e.g., a fax device can be assigned an email address) and other means of document transmissions have evolved alongside traditional facsimiles. Faxing over computer networks is of great interest to individuals and businesses, as it frequently saves long-distance phone charges. There are proposed and standardized formats for including fax information in existing email as opposed to distinct fax- over- Internet formats. Another approach is to send original "facsimiles" such as word-processed files as email attachments. When viewed or printed, the files contain all the colors, text, images, symbols, and formatting found in the original files up to the capability of the display or printer upon which it is viewed, which is almost invariably higher quality than atraditionallow-resolution, black-and-white fax transmission. Even if the file is printed on a fax machine that doubles as a printer, it will not be skewed or smudged (or blank) as are many scanned and manually transmitted fax documents. Adobe Portable Document Format (PDF) has become an important vehicle for disseminating high-quality PostScript documents over the Internet, in essence, providing a high-quality "facsimile" that is the same as the original as opposed to being a lower-quality copy. With the wide availability of free PDF readers, PDF may supersede facsimile formats for many types of documents and forms (many state governments now use PDF for informational brochures and license application forms). For people who don't like to look at documents on computer screens or who require a physical printout on a fax machine, PDF files sent over the Internet (or over phone lines) could be fed to a dedicated reader on a PostScript-capable facsimile machine, resulting in perfect copies of the original (no smudging or blurring) at whatever resolution is available on the printer (most consumer laser printers now image between 400 and 1000 dpi). Thus, the very concept ofa fax transmission is chang- ing, as more and more documents are created in electronic formats that can be transmitted directly, without first being scanned and encoded! decoded. In other words, legacy faxes, based on the current lossy scan-encode-transmit-decode scheme, may largely be superseded by future faxes based on lossless 341 © 2003 by CRC Press LLC . recommended, to distinguish between the recommended utf-8 or utf-16 character sets; otherwise the default is us-ascii. text/xml-external-parsed-entity application/xm I-extern a I-pars ed-en tity application-xml-dtd See IDML Initiative. HTML, SGML, World Wide Web Consortium. See RFC 1874 for SGML media types. See RFC 3023. extension, file name. loop' system. The extranet is seen as having the potential to significantly support and change electronic commerce and to take some of the traffic load off the Internet. Those promoting the concept suggest that it will enable customers to connect 335 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary more directly to vendors than is typical in the current Web-based system and that security will be more easily supported on the system. Extranets will potentially be used for monitoring transactions, accessing databases, requesting product information, etc. For example, bookstores might be connected directly to book distributors, to expedite orders, shipments, and account handling. Marshall Industries, Federal Express, and Dell Com- puter are some of the early adopters of the extranet concept. Extranets are also seen as a way to give pri- 0rity services to elite customers. For example, Charles Schwab & Company has developed. with tempera- ture and distance. The F2 region is particularly important for reflectingradiowavesoverlongdistances. 337 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary F-number Anumeric

Định dạng
Số trang	10
Dung lượng	837,01 KB