Fiber Optics Illustrated Dictionary - Part 20 doc

Fiber Optics Illustrated Dictionary circuit switching A type ofend-to-end transmission system common in phone connections. In the process of setting up the connection, a number ofresources are allocated to that specific call, most of which are tied up until the call is completed and the connection terminated. One advantage of this system is that it can guarantee a certain level of performance. A disadvan- tage is that the resources are tied up whether or not there is active communication. See message switching, packet switching. circular antennaA horizontally polarized, half-wave dipole antenna formed into the shape ofa circle except that the terminating ends do not touch to make a continuous loop. circular magnetic wave A magnetic wave in which the lines offorce describe acircular pattern. circular polarization An electromagnetic wave whose lines of flux are oriented in a plane, usually horizontal or vertical, or where the "edge" of the field describes a circular shape. Circular polarization is used in antennas, where electricity serves to uni- formly rotate the electromagnetic field through the antenna. It is possible to use one circularly polarized wave to communicate with another, or the circularly polarized wave can be manipulated to yield linearly polarized waves perpendicular to one another. circular scanning Scanning in which the sweep of the sensor and/or the display monitor describes a full 360 0 arc, which can be pictured as a cone shape spreading out toward the direction of the region being scanned (e.g., some types of radar). circulator I. A process or device that moves something from hand to hand, or device to device. 2. In microwave transmissions, a multiterminal coupling device in which the transmission is passed down through adjacent terminals. 3. In radar transmissions, a device that alternates the signal between the transmitter and the receiver. 4. In data communications, a mechanism for allocating or transferring information or control among ports. CISC See Complex Instruction Set Computing. CISCC Collocation Interconnection Service Cross Connection. Cisco lOS Cisco Internetwork Operating System. An OS incorporated as part of the CiscoFusion architecture to help the system administrator centralize, in- tegrate, install, and manage internetworks. Cisco Systems Inc. Asignificant vendor of routers, switchers, and related hardware and software for network systems. The author gained a greater under- standing of the function and implementation of network routing systems through Cisco seminars. CiscoFusion A Cisco Systems intemetworking architecture that integrates scalable, stable, secure technologies with ATM, local area networks (LAN), and virtual local area networks (VLANs). Cisco View A graphical device-management application that dynamically provides administrative, monitoring, and configuration information for Cisco internetwork devices. CISE See Computer and Information Science and Engineering. 182 CISPR See International Special Committee on Ra- dio Interference. CITA See Canadian Independent TelephoneAssociation. CITEL Inter-American Telecommunications Com- mission. citizens band radio, citizens radio service CB radio. Radio frequencies set aside for the use of rela- tively low power consumer radios and radio control- lers (for model cars and planes). These have a limited range (up to about 10 or 15 miles for mobile units), although sunspot activity and local weather can sometimes provide some surprisingly long connections when broadcasting conditions are optimal. In the United States, CB radios are commonly used by truckers, travellers, and radio hobbyists. Commu- nications over 150 miles are prohibited by the Fed- eral Communications Commission (FCC). The frequencies originally allocated by the FCC were around 27 Mhz, but have been changed to around 463 to 470 MHz. Before computer bulletin board systems and the Internet, CB radio was a popular means of com- munity interaction. Not all countries are free, and ci- vilian use ofradios is not permitted in some regions of the world. See OSCAR, AMSAT. CITR Canadian Institute for Telecommunications Research. CITRIS See Information Technology Research Center. CITU See Central IT Unit. City and Suburban Telegraph Company The first company in Cincinnati, OR to provide direct communication between homes and businesses, incorporated in 1873. In 1878, it contracted with the Bell Telephone Company of Boston, MA to provide Bell services in the Queen City area and, in 1882, contracted with American Bell to provide long-distance services. Its first payphone was installed in 1904 and mobile phones were introduced in 1946. In 1952, it became the first Bell company to provide 100% dial service. The company became Cincinnati Bell Tele- phone in 1971. CIV See cell interarrival variation. CIVDL See Collaboration for Interactive Visual Dis- tance Learning. CIX See Commercial Internet Exchange. CJC See Canadian Journal of Communication. CKAC The first Canadian television broadcasting station, which began experimenting with mechanical television transmitted over wires in 1926. ABaird disc camera and Jenkins scanning disc television receiver were early inventions that were tried around this time. Sound and images were transmitted sepa- rately so the sound could be played on a radio receiver. Shortwave bands were used for the images. Alphonse Ouimet, who later became the president of the CBC, was a technician for the first historic CKAC broadcast in 1931, a musical performance that was sent out to 20 viewers. See Canadian Broadcasting Corporation. CL symb. left-hand circular or indirect polarization. cladding I. A coating, something that overlays, a protective covering, sheath. 2. A substance, such as © 2003 by CRC Press LLC metal, bonded to another to cover it by various means, such as pressure rolling or extruding. A process sometimes used in producing transmission cables. 3. A layer in a laminate (which may be planar or spheri- cal) with a lower refractive index than its associative conductive materials, as in a fiber optic transmission cable, such that incident light is reflected away from the cladding rather than passing through. Glass and plastics are commonly used as fiber cladding materials but planar laminates may use other materials as well. Depending upon the materials and their refractive indexes, there are effective ratios between a cladding layer (as in a fiber bundle) and an inner conducting core as well as limits established by economics and whether the cable needs to be flexible. Different cladding arrangements have some interesting effects on light transmission in a fiber cable. For example, the materials in the cladding may be designed to reflect some wavelengths and absorb or transmit others. The cladding may also be designed so that it be- comes thin at certain bend radiuses to emit rather than reflect light (thus radiating modes exceed guided modes). This may seem impractical, but it allows the fabrication of illuminated "fabric" sheets by weaving the fibers over a warp layer that deliberately bends the fiber filament at periodic intervals. See index of refraction, spilling, stray light, total internal reflec- tance, V number. cladding alignment splicer CAS. A precision indus- trial tool for preparing a variety of types of cladded fibers (single-mode, multimode, dispersion-shifted, etc.) for assembly and installation. The device provides a tension and alignment mechanism (e.g., a groove) to facilitate precise splicing of cleaved fiber filaments. It may optionally have fiber end angle measurement, defect detection and pigtail continu- ity assessment capabilities. Passive alignment systems ( on two axes) provide cladding alignment rather than core-to-core alignment. A CAS typically uses heat (fusion splicing) to join fiber filaments into a continuous waveguide. Automatic units can create a splice in about 10 to 20 seconds (not including a technician's assessment of the visual display of the splice and its accompanying data parameters). A CAS typically includes a small built-in display or a connection to a computer display to provide an image of the assembly and alignment in the X and Y coordinates, usually magnified about 100 times. This enables a technician to visually inspect the assembly. Since there are many different splice modes, depending upon the type of fiber and components, the unit may be preprogrammed or programmable for quick setup. Depending upon the splicing capabilities, it may be possible to store and retrieve a log of splicing activities, including the selected splice modes, arc conditions, estimated efficiency (e.g., loss estimates), and optional comments. Stand-alone units may log from ca. 300 to 1000 splices. Units with computer connections could provide unlimited logging with re- movable mass storage, which may aid companies in monitoring quality control, production changes, staff training statistics, etc. See cleave, fusion splice. cladding diameter In a cable that includes a cladding layer, such as a metal wire with a bonded coating, or a two-glass cladded fiber cable, the diameter that includes the cladding layer. Ina perfectly round fiber, this can simply be measured; however, as the cable may be elliptical, the diameter may be calculated by taking the average of the smallest circular outer diameter and the largest circular inner diameter. Cladding & Core Ratios in Optical Cables A_~-=- B G~~_:·_·· _ In single-modefibers (A), the cladding thickness (1) is typically much larger than the diameter of the tiny filament thatforms the core (2). In multimodefibers, the relationship is typically reversed. The core has a higher diameter in relation to the cladding thickness, providing room for multiple wavelengths to travel along the waveguide. The ideal ratio depends upon manyfactors, including the cable materials, the wavelengths transmitted, and the degree of bend that might be expected of the cable during installation. cladding glass A type of glass or other transparent material used in fiber optic cables that has a lower refractive index than the glass used in the inner core. cladding mode In a transmission through a cladded conductor, a signal conducted through the outer cladding in addition to any signals that may be transmitted through the cladded core. See cladding beam. clamping 1. Holding within an established operating, baseline, or midline range in a circuit, in order to maintain various processes or electrical charges at stable or safe levels. 2. In a cathode-ray tube (CRT), a process that establishes a level for the picture display at the beginning of each scan line within a frame. clamping voltage An established level of voltage around, under, or over which an electrical device is pennitted to operate. For example, clamping voltages can be used to establish a range within which a device operates, by setting them so that any fluctuations above or below that voltage will cause a system shut- down or other protective reactions. Clark cell A type of historic low-volt energy cell using mercury and zinc amalgam in the cathodes and anodes. Clark, David (ca. 1943- ) David Clark has been a chairman and active participant in various Internet as- sociations, including the IRTF and lAB. He has par- ticipated in numerous research efforts in high speed, very large networks, and network video applications, and various development efforts including the Swift 183 .?:' ;, :::~.~.,.F .z~ -,tt © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary operating system, Multics and Token-Ring local area networks (LANs). Clark, James "Jim" H. (1944- ) Formerly ofSGI, in 1994 Clark co-founded Mosaic Communications Corporation with Mark Andreessen, which later become Netscape Communications, distributors of the most broadly used browser applications on the World Wide Web. See World Wide Web. Clarke, Arthur C. (1917- ) An English-born scien- tist and writer. With remarkable prescience, Clarke anticipated the age of satellites and long-distance communications. He was talking about it as early as 1942, while still in his twenties, and published an ar- ticle about it called "Extra-Terrestrial Relays" in Wireless World in 1945. Clarke further wrote detailed descriptions of geostationary satellite orbits and satellite transmitting and receiving stations in the 1950s, years before the first Sputnik was launched. In the 1960s, he collaborated with Stanley Kubrick in the making of the movie 2001: A Space Odyssey (1968), which has since become a classic. See satellite, Sputnik I. Clark, George Howard (1881-1956) A Canadian- born American telegraph operator and significant col- lector of historical radio artifacts, Clark worked for the Boston and Maine Railroad. A scrapbook enthu- siast as a child, Clark began collecting wireless radio materials in 1902. In 1903, he graduated from MIT in Electrical Engineering, specializing in radio work. He then worked for the Stone Telegraph and Telephone Company in Boston. In 1915, while in the Navy, Clark helped devise aclassification system for blueprints, photographs, documents, and general data. In 1918, he adopted the system for organizing his radio collection and coined the term "Radioana." In 1919, he joined the staff at the Marconi Telegraph Company of America and later the Radio Corporation of America (RCA). Clark devised the 'type number system' used by RCA for classifying equipment (e.g., vacuum tubes). From 1922 to 1934, he was in charge of exhibits of radio apparatus at shows and fairs on behalf of RCA. In 1928, he started a radio museum for RCA. The museum collection was turned over to the Rosenwald Museum in Chicago, IL and the Henry Ford Museum in Dearborn, MI. Clark's collection began to assume some importance when patent in- fringement cases came to court and the documents provided substantive evidence about the radio industry. At his death, the collection was given to MIT and, in 1959, turned over to the Smithsonian Institution. See Clark, George H. Radioana Collection. Clark, George H. Radioana Collection An archive ofhistorical radio memorabilia and documents col- lected primarily between 1900 and 1935 by radio engineer George H. Clark. It was transferred from the Massachusetts Institute of Technology to the Smithsonian's National Museum of American His- tory in 1959. It is one of the most extensive collec- tions ofwireless radio history in the U.S., compris- ing more than 276 linear feet of shelf space at the Amplifier Operations and Emissions Class Categories Amplifier Categories Description Class A amplifier A single-ended circuit in which output current flows during the input cycle, as related to the grid bias and grid voltage. Provides good fidelity at low receiving levels. Class AB amplifier A circuit in which output current flows for more than half, but less than the full, duration of the input cycle. Better efficiency than a Class A amplifier but also has higher power requirements. Class B amplifier A circuit in which output current flows for halfof the input cycle. More efficient than Class A or Class AB but has higher power requirements and can't be configured as a single-ended circuit. Class C amplifier A circuit in which output current flows for somewhat less than halfof the input cycle. This provides high efficiency but also has higher power requirements. Emissions Categories Description Class AO emission Incidental radiation emanating from an unmodulated carrier wave transmission. Class A1 emission A low-speed carrier wave (as those used for early telegraphy) unmodulated by an audio signal. Class A2 emission An amplitude-modulated carrier wave modulated by low audio signals t~ transmit simple tones or Morse code. Class A3 emission An amplitude-modulated carrier wave modulated by audio signals so intelligible conversation can be transmitted. 184 © 2003 by CRC Press LLC National Archives in Washington, D.C. The collection includes biographical information on the pio- neers developing radio and photographs and documents on the growth and operations of radio companies, particularly National Electric Signaling Com- pany and RCA. Interestingly, the collection is arranged according to a Navy filing system devised in part by Clark in 1915. See Clark, George Howard. CLASS Custom Local Area Signaling Services. Tele- phone subscriber calling options including, but not limited to, Automatic Callback, Call Trace, Caller ill, Selective Call Rejection. In the past, when demand for these services was lower, they were billed indi- vidually, depending upon which ones were selected. More recently, phone companies have been offering monthly flat rate bundles on a variety of these caller options. Class, facsimile For information on Class 1 and Class 2 facsimile standards and related concepts, see facsimile, formats. Class, IP See IF Class. class of service CoS. A general designation for an agreed or specified level of functioning or security, which varies from industry to industry. In telecommunications, network configuration and tuning and sometimes billing levels are established according to class of service parameters. See quality of service. Classical IP A set ofspecifications for an asynchro- nous transfer mode (ATM) implementation model described in the early 1990s by the Internet Engineer- ing Task Force (IETF) for local area internetworking. In Classical IP implementations, IP headers are processed at each router, creating latency and limiting throughput. Due to the increase in demand for multi- media capabilities, Classical IF is showing its age. One of the limitations of Classical IP is that direct ATM connectivity exists only between nodes with the same IP address prefix. See ATM models for a chart of some historic and new ATM models. See RFC 1577. ClassmarkAn electronic designation that identifies privileges and restrictions associated with a particular communications line or trunk. See class of service. CLC 1. Carrier Liaison Committee. 2. Competitive Local Carrier. cleaning arcAbriefelectrical spark generated by an electrode for the purpose of removing particulate matter from a surface. Cleaning arcs are used in fusion splicers for cleaning the ends of fiber optic filaments prior to joining since any undesired particles in the joint could interfere with light transmission. See fusion splicing. clear 1. In computer monitor displays, to blank a screen, applications window, or tenninal window. The clear command provides a clean slate, a visual working space without clutter, obsolete information, or dis- tractions. 2. In programming, to set a storage location (a buffer, address, etc.) to a zero state, blank state (as with space characters), previous state, or default state. 3. In communications, a clear signal is one without noise or interference and ofsufficient volume or intensity to be heard or seen distinctly. clear channell. In telephone communications a transmission line that is used entirely for communication, and no control or other signaling bits are being transmitted. In other words, all the resources are available for the infonnational communication. 2. In radio communications, a station that is permitted to dominate a frequency and broadcast at a certain power level or up to a certain distance (e.g., 750 miles) during a specified time of day. A type of ex- clusive frequency arrangement. clear to send CTS. A handshaking signal provided when the communication has been set up over a serial link, and the called modem is ready to receive information. See RS-232. clearance In electrical installation, the shortest distance between separated live conductors, or between live conductors separated from physical structures, or between live conductors separated from associated grounds. See gap. cleavage plane Aplanar direction in a material in which the molecular bonds that hold the substance together can be more readily cleaved. Many materials have a "grain," a general direction in which the fibers or lattice structure are aligned. Thus, most paper tears more readily in one direction than another and a number of materials used in electronic compoents will cleave more readily depending upon the orientation of the material with respect to the cleaver. For example, birefringent materials, those with a molecular structure that is the same in two planes and different in a third, will generally cleave more readily when nicked, broken, sawed, or sliced across the plane in which the bonds are weaker. Knowledge of the composition of materials and their cleavage plane is useful in materials science and materials and component fabrication. See cleave. cleave To cut or break a cable or component so the broken surface meets certain needs, as in junctions, solder joints, or optical connections. With basic electricity-conducting wires, the angle or cleanliness of the break in a line is not usually critical, as wire can be readily wrapped or soldered in place without significant loss to the signal. However, with layered wires or certain electronic components, where a smooth or straight surface might be important to the electrical contact, or in fiber optic cable, where rough edges can degrade the light-carrying properties of the fiber, a precise cleave is critical. Wire is usually cleaved with scissors, knives, or specialized cutters, depending upon the gauge of wire and the importance ofa clean cleave. Fiber optic filaments are usually cleaved with mechanical blades, but some systems use ultrasonics for the very precise cleaves desired for fusion splicing. See cleavage plane, cleave angle, cleaver, crimp, fiber optic; fusion splice. cleave angle The angle at which a surface is cut relative to a reference. Cleaving is often done prior to creating a glued or fused joint or adding a connector, but it may also be used to provide an unimpeded exit path for an optical signal (e.g., a fiber optic sign or lighting fixture). 185 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Cleave - Basic Types that produce a cleaner cleave and claim that polishing is not necessary. For complex bundled assemblies, polishing may still be necessary. 1 C C __ B A There are anumber of ways to cleave a wire or cable, depending upon the materials. Wires andplastics can often be cut all the way through with a knife (A) or snippers that cut from both sides, especially if rough edges aren 1a concern. Hard plastics and some metallic compounds often cleave better ifnickedfirstand bent until they break at the point of the nick (B) (the effectiveness of snapping depends partly upon the direction of the grain). Glass may break more cleanly and evenly if nicked or scored (C) and then snapped. Nicking and snapping often provides the best cleave forfiber opticfilaments. Fiber optic cleavers come in many shapes and sizes. Some resemble microscope components, with view- ing and testing capabilities, some have computer in- terfaces for magnifying or analyzing diffraction pat- terns in the filament that has been cleaved, some support polishing components, and some are compact units resembling staplers. Sizes range from handheld to table-top. Mid-sized cleavers for field work may have tripod mounts for securing in a mobile lab or an outdoor or in-plant location where there is no flat workspace for setting up the cleaver. Since fiber scraps can get in the way and present a safety hazard (the shards are small and sharp) a tray for collecting the fiber end scraps is sometimes included with cleaving devices. It is important to shield the eyes with safety goggles and to remove any filament shards not discarded into trays when working with cleavers. " It, The angle of a cleave will influence the amount of surface area that is availablefor connectingorfusing a fiber optic filament. The smaller the angle, the greater the surface area. This has advantages and dis- advantages. A largersurface area may provide added strength in certain directions andastrongerfuse, due to the larger surface area, but it also is more difficult to cut and match and creates a larger area in which contaminants or aberrations in a joint can interfere with light transmission. A straight (90") angle is used when the filament is being terminated, hand spliced, orspliced with a machine that is set to rotate the two ends independently prior to splicing. Angle cuts must be carefully matched if they are to be spliced, because even the smallest angle, if the ends are aligned perfectly, can cause a gap that interferes with light propagation. Cleave Angle Effects y x In wires and fiber optic filaments, the angle is measured relative to the lengthwise conductive core and is usually described and handled in two planes. Thus, if the core is horizontal (in the X plane), the cleave angle is described in terms of its angle as it rotates through the X-V plane. There's no reason why the angle in the Z plane couldn't also be described, but in most fabrication technologies for wire and cable splicing and attachment, the Z plane is kept at right angles to the X reference for simplicity (and because there's usually no added benefit in altering Z angles). Cleave angles vary depending upon the materials being cut, the cleaver, the purpose of the cleave, and any tension factors that may act upon a cable that is to be cleaved and spliced. A 90 0 cleave may be easier to cut and fuse and may provide abetter unimpeded path for signals due to the smaller fused cross-sec- tion, but an angled cleave (e.g., 45°) may provide a stronger connection due to the larger fusing area and may withstand better forces against the fused joint. F or end-emitting fiber filaments intended for signage, artworks, or lighting fixtures, an angled cleave can influence the shape and the amount of light that es- capes from the endpoint. See cleave. cleaver, fiber optic A device specifically designed to provide the precise, clean cleaves required for fusing fiber optic filaments together, or for attaching connectors to a fiber filament. Tolerances are usually within 0.5°. Traditionally, optical fibers to be coupled with other components were cleaved and then polished to provide the cleanest surface possible at the terminal ends. However, some manufacturers now promote products 186 © 2003 by CRC Press LLC The cleaving blades may be specialized for the diameter range and type of fiber to be cut (glass or plastic). There may be different blade heights and ro- tations to accommodate different sizes. See cladding alignment splicer, crimp, interferometer. Cleave Area and Strength t 't, 90° t f', In fiberfilaments, cleaves intendedfor splicing must be clean and precise to prevent inte171lption or back reflection of a light signal passing through the joint. The angle of the cleaves to bejoinedshouldmatch (in most cases) tofacilitatefusion. Narrower angles (e.g., 45 0 from perpendicular in the orientation shown above) create larger surface areasforfusion and may resist breakage from forces in certain directions, but may also influence the lightguiding properties of the joint if the angles don ~ match rotational characteris- tics of the fiber (e.g., in polarized cables). Angle cleaves are generally more difficult to cut and splice, especially with hand tools. CLEC See Competitive Local Exchange Carrier. Clerk-Maxwell,James See Maxwell, James Clerk click tones A signaling system common on phone systems, especially wireless phones, that alerts the user that the call is being processed. clickstreamslangA description of the flow of events and sites visited when a user navigates the Internet, particularly the Web, which is connected through clickable hyperlinks. Product vendors have an intense commercial interest in monitoring user behavior and maneuvering users to their sites. cleavage client A system or application that serves the user but that may seek or require information or operating parameters through a host with a higher priority or greater capabilities. In the past, host and client have had almost opposite meanings for some computer administrators, but for consistency in this dictionary, and because the trend is in this direction, client is defined as the adjunct or subservient system or application. See host. client application In a client/server computer software application, the client is typically the application used by the user to communicate to a source or destination through a related higher priority or more powerful (or just different) server program. The N et- scape Communications Web browser is an example of a common client application that communicates to Web sites through a Web server, handles the traffic, and provides some measure of security. client operating system On a network, the operating systems run on client machines, user tenninals, and subsidiary machines. These do not have to be the same as the server operating system. A good server can handle a variety ofclient OSs and network between them seamlessly, using standard network pro- tocols. For example, you may have a network that is configured with a Sun workstation and Sun operating system (SunOS, Solaris) as the main server, with a number of different client platfonns connected to it, running different client operating systems and operating environments, such as Linux, Apple Computer's as x, Be Inc. 's BeOS, or Microsoft Win- dows. client/server modelA computer processing method of improving efficiency, and sometimes security, by selectively distributing activities. In human enter- prises, there is often a manager with an overall knowledge of the work to be done, security clearance, and the authority to designate tasks and respond to requests. In conjunction with the manager are workers with knowledge of specific tasks and needs, lower security clearance, and instructions to report their findings and to direct their questions and requests for resources to the manager. Aclient/server model on a computer system is similar to this. An ISP's Web server has the logic and security clearance to accept requests from many Web browsers, and to fetch the infonnation and serve it back to the browsers which then fonnat and display the information for the user. Most networks work on client/server models, where the server handles administrative details, file management, and security, and the client machines, usually tenninals or desktop computers, handle input and output, local processing, and display. CLIP calling line identification presentation (e.g., as in ISDN Q.81 and Q.731 number identification services). clipboard In most operating systems, and in some software programs, an area of memory or a file on a hard drive designated to hold information (usually images or text, but may also be sound or video clips) that has been cut by the user for later retrieval. Most clipboards store only one clip at a time, with subse- quent clips over-writing previous ones, so that only the most recent can be retrieved. Some clipboards can handle multiple clips, and some store the information on disk for later retrieval. On the Macintosh, for example, auser can save clips by copying or cutting them and storing them in the Scrapbook. Clips can be retrieved later by paging through the clips, select- ing those desired, and copying and pasting them back into an application. ClipperchipA microprocessor chip that provides security encryption features that can be incorporated into electronic devices. The Clipper chip has become the focal point for broad and heated debates over the privacy of global communications. The U.S. federal 187 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary governing bodies had initiated plans to include the chip in consumer telecommunications products, to secure conversations from anyone but the government. The plans were initially announced in 1993 through the White House Escrowed Encryption Ini- tiative. The system was designed by the National Security Agency (NSA). Three versions of the pro- posal, Clipper I, II, and III were promoted between 1993 and 1996. Most people agree that there is a need for voluntary, widely available encryption options for government and private use, and vendors agree that standards provide a means for them to distribute products with intercompatibility. But on this issue, concern has been expressed about how the government is intending to implement and enforce encryption policies, and on their assertion that the system will work only if made mandatory. There has been a considerable outcry from vendors and the public, who questioned the ro- bustness of the technology, and who are gravely con- cerned about too much power being in the hands of too few people. In spite of the negative feedback, the Department of Commerce approved the Escrowed Encryption Stan- dard (EES) as a voluntary Federal Information Pro- cessing Standard (FIPS) in 1994. One of the requirements would be that every Clipper chip would have its unique key registered with the federal government and held in split form by two federal escrow agents (NIST and the Treasury Department), creating acces- sibility for the federal government to wiretap secure communications. The debate over the chip, privacy, and law enforcement led in the fall of 1994, to the Encryption Standards and Procedures Act, which described federal policy governing the development and use of encryption technology for unclassified information. Back references were made to The Computer Security Act of 1987. The public responded in many ways to the various proposals regarding the Clipper chip. Some sought to point out flaws in the process and design; others created free user-encryption programs that would de- feat the Clipper system. One of the more significant challenges to the system was the X9 Accredited Stan- dards Committee (ASe) announcement that it would develop a competing data security standard based upon triple-DES. The ASC sets data security standards for the U.S. financial industry. The Clipper chip uses a nonpublic encryption algo- rithm called SKIPJACK which cannot be read off the chip and is designed so that it cannot be reverse en- gineered. According to the EES, when two devices negotiate a communication, they must both have security devices with Clipper chips and must agree on a session key, which may be a public key such as RSA or Diffie-Hellman. The message is then encrypted and sent with a law enforcement access field (LEAF), a serial number, authentication string, and a family key. When received, the LEAF is decrypted, the authentication string verified, and the message decrypted with the key. See Capstone chip, LEAF, Pretty Good Privacy, SKIPJACK. 188 clipping I. In software applications, cutting out information, such as graphics, text, sound or video, usually for later retrieval or insertion elsewhere. See clipboard. 2. In graphics programs, the process ofre- moving parts of an image, or of the display outside some designated boundary, usually the outer margin ofapicture, or of an application's window. Informa- tion that is clipped mayor may not be retained in memory. Often a program will retain the information, even if the user can't see it, so the user can quickly restore the information or scroll quickly through the image without recreating it or having to wait for the computer to reread it from disk. 3. In audio, a brief loss of sound, especially at the beginning or end ofa transmission due to limitations of the technology (limited frequency range, direction flipping, ramp-up time). 4. In audio communications, especially phone calls over satellite links, the equipment may be operating part of the time in half duplex mode, transmitting in only one direction at a time, so gaps in the conversation may cause a switch in the other direction and clip part of the conversation. CLIR calling line identification restriction (e.g., as in ISDN Q. 81 or Q. 731 number identification services). CLLI See Common Location Language Identifier. clock 1. A time-keeping and reporting device that uses various gravity (sand, weights) or oscillating mecha- nisms (radioactive decay, emissions, crystal vibrations) to track time. Quartz crystals have extremely consistent vibrations that are sometimes used to make very accurate clocks. 2. A device that provides regu- lar signals for use as a timing reference. On a computer, instruction speeds are expressed in clock cycles. clock bias The discrepancy between the time indi- cated on a clock and True Universal Time. See Co- ordinated Universal Time. clock doubling A means ofgetting a little more performance out ofa computer instead of having to re- place the system. With constant demands for faster systems, balanced by the high cost of replacing a system that may be only a year old or less, some manufacturers have provided versions of the CPU chip or accelerator accessories that effectively double the speed of the CPU. This does NOT mean performance is doubled. The CPU is only one part ofa system, and the bus rates, coprocessing chips, sofrware design, operating system parameters, and other factors, will af- fect the actual performance increments to a great ex- tent. In other words, the speedup is usually more on the order of20% or so but, for graphics computations or resource-hungry sofrware, that might be an important 20%. Sometimes it's worth it; it depends upon the cost of the doubler. clock speed In computer systems, an expression of the speed ofa central processing unit (CPU) or other processing chip, usually expressed in megahertz. Mi- crocomputers in the 1970s ran at clock speeds rang- ing from about I to 4 MHz. In the 1990s , they ran at about 200 to 300 MHz. Current microcomputers in consumer price ranges run at over 700+ MHz. Clock speed is not equivalent to system speed. Doubling the clock speed doesn't mean doubling the © 2003 by CRC Press LLC computing speed; sometimes the efficiency is just slightly more, and sometimes it is three or four times more. Determining the overall speed ofa computing system is complex and requires evaluation of the general architecture of the system, the efficiency of the operating software, the amount of memory, the in- clusion of coprocessing chips, and the type of application being run. For example, the author's first 8-kilobyte RAM (yes, kilobyte, not megabyte), 1.8-MHz system ran telecommunications software and word processors very effectively at typing speeds of over 80 wmp. A fea- ture-rich, well-written graphical word processor can run very efficiently on an 8-MByte RAM, 10-MHz system. The same software running on a 16-MByte 233-MHz system often is not perceptually faster because text entry, at its basic level, is not a computing intensive application. In contrast with basic word processing, computing- intensive applications, however, can be dramatically affected by clock speed. A stock 1.8- MHz system is essentially incapable of doing 3D ray-tracing in a rea- sonable amount of time, whereas an older Amiga computer with a clock speed of only 7.16 MHz can render a complex 3D scene in 3 or 4 days, faster than many 25-MHz computers with different architectures. Amigas with 40- MHz accelerator cards can render the same scene in 3 or 4 hours, and dedicated graphics systems, running on parallel processing systems, or current Silicon Graphics Machines, for example, can accomplish the same feat in minutes or seconds. Since computing speed is important to computer elec- tronics designers, a number of measures have been established to provide information for comparing chips, systems, or architectures. These benchmark tests are not absolute measures of clock speed, but they provide some information that is helpful and they generate some pretty entertaining controversy. See benchmark, clock doubling, Dhrystone, Whetstone. clone n. 1. Duplicate, exact copy, genetically identi- cal individual. 2. A software program or device configured to masquerade as another device, either for diagnostic purposes, interim use, or fraud. clone fraud A method of gaining entry to a system, or using a device, by simulating a user, serial number, or access code. Cellular phones are particularly susceptible to clone fraud, as it is not difficult to program a legitimate serial number into another cellular unit. See tumbling. closed architectureA proprietary design that is supported and enhanced by peripherals that conform to its particular specifications, and that may not be manufactured by third party vendors, except perhaps by obtaining special permissions or paying royalties. Contrast with open architecture. closed captioning CC. A broadcast technique for transmitting text, usually to be superimposed over a corresponding television image. CC is provided mainly as an aid for the hearing impaired, although in some cases it may also be used to provide subtitle translations. It is typically sent on the vertical blank- ing interval of the transmission, and a decoder may be required to interpret the signals. closed circuitA broadcast circuit in which the send- ing and/or receiving components are limited to a certain frequency range or power level. Thus, a closed circuit radio system within a complex may be set to send and receive FM signals at 89 hertz. A radio station may have permission to broadcast at only 91.7 hertz on frequency modulated (FM) signals. In contrast, an open circuit is one that is not restricted to a narrow frequency range, as a CB radio, for example, which may be set to pick up signals broadcast over a variety of channels. closed circuit broadcast, closed circuit TV A radio or television transmission that is broadcast to a small or restricted audience, often within a specific build- ing complex or campus. Low power frequency modulated (FM) ranges are often used for this type of transmission because they are not as strictly regulated as higher power transmissions. closet A room, cabinet, or case used for terminating blocks or patch panels for wiring configurations. The . closet serves a variety of aesthetic, safety, organiza- tion, and security purposes. cloud network Frame Relay network connections are now offered as a lower cost alternative for small businesses and educational institutions, and a cloud relay is one connectionless option of this type in which resources are shared, usually among four or five small subscribing organizations. CLP cell loss priority. A one-bit ATM networking cell header toggle indicating the relative importance of the cell. CLP is important as there are various mecha- nisms in ATM for prioritizing cell traffic, or discard- ing cells in congested situations. See cell rate. CLR See cell loss ratio. CLTP See Connectionless Transport Protocol. CLTS Connectionless Transport Service. cluster 1. In cellular communications, a unit consisting ofa group of adjacent cells within which channels are not reused. See cell, cellular phone, mobile phone. 2. A set of workstations or terminals in the same general physical or virtual networked grouping. These may share more than physical connectivity; they may also have shared devices that manage processing input and output, or specialized requests of the cluster. See cluster controller. 3. A combined unit of disk storage allocation, usually consisting of four or more sectors. clustercontrollerA device controlling communications input/output for multiple connected devices. clutter Wave reflections from obstructions such as terrain and buildings, which may show up as echoes or unidentifiable blips on a radar screen, thus inter- fering with scanning. CMA See Communications Management Association. CMC See connection management controller. CMI See coded mark inversion. CMIP See Common Management Information Protocol. CMOL CMIP Over LLC (Logical Link Control). See Common Management Information Protocol. 189 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary CMOS Complementary Metal Oxide Semiconduc- tor. A semiconductor chip that combines p-channel and n-channel MOS in a single substrate with push- pull circuits. Slow, but noise resistant, and good for battery-operated devices. CMOS RAM needs a small stream of constant power to preserve information stored in its memory, which is typically supplied by a lithium battery (available in photography and elec- tronics stores). Default settings and sometimes video card and other peripheral parameters may be stored in CMOS RAM linked with a lithium battery on a computer's motherboard. See PRAM. CMOT CMIP Over TCP. See Common Management Information Protocol. CMR See cell misinsertion rate. CMRS/PMRS commercial mobile radio service/private mobile radio service. The Federal Communica- tions Commission (FCC) was directed, through the Omnibus Budget Reconciliation Act of 1993, to auc- tion radio spectrum for CMRS. Unfortunately, the initial spectrum allocations in the C and F blocks, intended for small businesses, did not work out well in practical use. After numerous discussions and bankruptcy lawsuits, the FCC announced the cancel- . lation ofcertain licenses and began to reauction por- tions of the C and FBlock radio spectrum, beginning in 2000. See ABlock for a chart offrequencies. See Omnibus Budget Reconciliation Act. CMTS Cellular Mobile Telephone System. CMYKA color model widely used in the paper printing industry. The initials signify cyan, magenta, yel- low, and black, which are the four colors combined as tiny dots in process color printing jobs to simulate all hues and black. Black is included because the combination of the first three does not give a dark, rich, black pigment. Metallic colors cannot be pro- duced within this color model, and extra runs through the press or spot application of metallics on a multi color printer are necessary to accommodate metallic effects. Computer publishing software often seeks to simulate these colors on the monitor in order to provide WYSIWYG in the [mal printed result. CN complementary network. CNA I. Centralized Network Administration. A means ofconsolidating network-related connections in a single location, usually a wiring closet or panel, rather than distributing them in various parts of the premises. 2. Cooperative Network Architecture. CND I. Calling Number Delivery. 2. Calling Num- ber Display. . CNET Centre National d'Etudes des Telecom- munication, now France Telecom R&D. CNG A calling tone emitted by facsimile machines that lasts about half a second and repeats as many times as the software dictates, to signal its presence and to try to establish a negotiation with a receiving fax machine. Most machines default to about 45 seconds of tone sequence before they disconnect, ifthere is no successful connection. This time may not be enough for some systems or for a long-distance connection and some fax machines and fax modems have an option for extending it. 190 Most fax machines now automatically dial and emit the CNG. However, some of the older fax machines, or bargain basement varieties, still require a human operator to dial the number. The operator must then wait to hear a fax response and start the fax machine CNG by pressing abutton. This method is a problem if the system that has been dialed has a sensing device to route incoming calls to a phone, modem, or fax machine depending upon the tone. If a human dials the line as a voice call, the switcher will route it to a phone, and then starting the calling fax's CNG does no good, as the phone has no way of routing the call back thJough the switcher to the fax machine. However, with increasing automation and decreas- ing cost ofbetter fax machines, this problem is be- coming less prevalent. CNIS Calling Number Identification Services. CNR I. See Complex Node Representation. 2. customer not ready. CNRI Corporation for National Research Initiatives. CO I. cash order. 2. See central office. 3. command- ing officer. co-channel interference CCl. Aquantitative expression ofinteference in acommunications circuit when multiple channels are arranged in such a way that they may interfere with transmission on a neighboring or associated channel. This concept is especially important in wireless communications in which increasing numbers of subscribers are being accommodated within limited frequency allocations. One way to reduce CCI is with guard bands, but the tradeoff is lost bandwidth. Another way ofreducing CCI is with adaptive beam forming. See antenna, smart. COAM See Customer Owned And Maintained. coaxial cableA transmission cable consisting essentially of an irmer conducting core surrounded by a conducting tube, each insulated and all wrapped together in an outer protective sheath. The inner core is a metallic conductor surrounded by a metal shield, that acts as a Faraday cage, with a dielectric material interposed between them. Typically, the signals are propagated in one direction along the conducting core. Coaxial cable was an important development for the transmission of telegraph, telephone, and television signals as it was found to conduct radio frequency (RF) signals well. By the late I 940s, much of the east- ern United States was interconnected with coaxial cable. Coaxial cables are typically described in terms oftheir impedance; values from 50 to 95 ohms are common. The video industry makes extensive use of75- ohm coaxial cables for interfacing cameras, frame synchronizers, and recording decks. In computer networking, 75-ohm cables are used for unbalanced EI connections. Higher impedance 100- to 120-ohm twisted-pair wire is used for balanced EI connections, and subrate cabling in trunk/circuit lines. coaxial omniguide Alightguiding cable based upon layered film mirror technology developed at MIT in the late 1990s in a project led by Francis W. Davis. © 2003 by CRC Press LLC By 2000, project participants had established Omniguide Communications to further develop and market a transmission cable based upon the technology that would reflect awider range of wavelengths in a smaller space without changing the polarity or creating pulse distortion characteristic of traditional cables. COBOL Common Business-Oriented Language. A verbose, high-level programming language once widely used for business applications and still taught in business schools, but which is slowly being re- placed by other languages. See OO-COBOL. CoBRAA commercial, portable, ISDN analyzer for installation, maintenance, and troubleshooting of ISDN Basic or Primary Rate networks, from Consultronics. Consultronics now markets the CoBRA-CQ as a portable local loop test set for ISDN, ADSL, G.lite and other formats. COBRA A frequent misspelling of CORBA, Com- mon Object Request Broker Architecture. See CORBA, Object Request Broker. COBRAS Cosmic Background Radiation Anisotropy Satellite. COCOT customer-owned coin-operated telephone. See payphone, private. COD connection-oriented data. code 1. A system of symbols, cyphers, characters, images, movements, sounds, or other meaningful marks or actions that serve to represent ideas and language in a way that is not commonly understood or recognized. Not all symbolic forms of communication are considered to be codes. For example, Ameri- can Sign Language is not understood by many, but it is not considered a code in the sense that information on learning it is readily available in schools and libraries. Social changes can alter the perception ofwhether something is a code. Before the development of the printing press and public education, text and reading were mainly restricted to the elite political leaders, and common people probably considered it as a sort of code. The use ofcoded information is common in wartime, or with politically or economically sensi- tive infonnation. Some codes are exceedingly sophis- ticated and difficult to break. Until recently, most analog communications have not been coded to pro- tect privacy, due to the difficulty of doing so. With recent digital technology, it has become much easier to code communications, and many software devel- opers and equipment makers are adding encoding to their products. Many satellite communications, cell phone messages, and computer data communications are now encoded. 2. An abbreviated means ofrepre- senting information in order to save time in its tran- scription or transmission, or to send it over limited transmissions devices, and sometimes also to shield it somewhat from prying eyes. Shorthand is a type of code intended to save time in taking oral dictation. Drumbeats or smoke signals are two types of codes designed to abbreviate information so that it is practical to transmit through these basic means. Basic telecommunications codes have been in development since the 1600s. Schilling developed a needle telegraph code in 1832. Morse (Vail) code is a widely used alphabet coding system developed in the early 1830s. It is still often used in telegraph and radio communications, particularly in countries with limited access to computer equipment. See semaphore, Baudot code, Hollerith, Morse code. 3. Computer programming code is a system of linguistic and symbolic characters and syntax that serves to represent computer instructions so they can be run directly by the machine or compiled into machine-readable form. Code designations in packet networking See Link Control Protocol codes. Code Division Multiple Access CDMA. A digital, wireless communications service based upon spread- spectrum technology, which claims to provide about 10 times the capacity of analog. Access to the local exchange is wireless. This technology was originally used in military satellites for its security features and resistance to jam- ming. Now more widely used in commercial applications, it provides access to many users at a time without the multiple user interference associated with other modulation techniques. The same frequencies in adjacent beams can be reused by assigning vary- ing spreading codes to users. The method offers authentication of the source transmitter and is very secure against eavesdropping. Frequency reuse logistics in AMPS and DAMPS systems are eliminated in CDMA by assigning codes to users so they can share carrier frequencies. The system capacity is not fixed but is influenced by the ac- cumulated noise and interference associated with power levels and simultaneous users. CDMA, supported by companies like Sprint and PrimeCO, is somewhat similar to TDMA, with somewhat less built-in support for private branch applications. B-CDMA is also in development as a proprietary technology by a group of vendors supporting InterDigital Communications. See B-CDMA, spread spectrum. Technique Description DS-CDMA Spread spectrum technology in which codes are used to modulate information bits such that each code is assigned to prevent the overlap of signals from user to user. The receiver regenerates the code and uses the information to demodulate the transmission. FH-CDMA A group of changing frequencies are modulated by the information bits in a two step process. First, the carrier frequency is modulated, and these modulated frequencies further modulate frequencies while still keeping them independent. 191 © 2003 by CRC Press LLC . :::~.~.,.F .z~ -, tt © 200 3 by CRC Press LLC Fiber Optics Illustrated Dictionary operating system, Multics and Token-Ring local area networks (LANs). Clark, James "Jim" H. (194 4- ) Formerly ofSGI, in 1994 Clark co-founded Mosaic Communications Corporation with Mark Andreessen, which later become Netscape Communications, distributors. angle The angle at which a surface is cut relative to a reference. Cleaving is often done prior to creating a glued or fused joint or adding a connector, but it may also be used to provide an unimpeded exit path for an optical signal (e.g., a fiber optic sign or lighting fixture). 185 © 200 3 by CRC Press LLC Fiber Optics Illustrated Dictionary Cleave - Basic Types that produce a cleaner cleave and claim that polishing is not necessary. For complex bundled assemblies, polishing may still be necessary. 1 C C __ B A There are anumber of ways to cleave. Information Protocol. CMOL CMIP Over LLC (Logical Link Control). See Common Management Information Protocol. 189 © 200 3 by CRC Press LLC Fiber Optics Illustrated Dictionary CMOS Complementary Metal Oxide Semiconduc- tor. A semiconductor chip that combines p-channel and n-channel MOS in a

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