Fiber Optics Illustrated Dictionary - Part 62 pot

Fiber Optics Illustrated Dictionary LONTalk is powerful. Each node supports Network Management Services (NMS) such that they can re- spond to LONTalk commands from any node sup- porting NMS functions. Hierarchical addressing through domain, subnet, and node addresses can be used to interact with the network at any level. LONTalk can be implemented over a variety of types of media, including twisted pair, power line (similar to X-lO), radio links, and coaxial or fiber optics cables. The LONTalk protocol can be implemented into mi- croprocessors under the EIA-709.l control networking standard by companies such as Echelon Corpo- ration. See LONWORKS, Neuron Chip. LONWORKS An internationally installed, open network automation and control system for industrial and residential markets developed and trademarked by Echelon Corporation. LON stands for local operating network. The LONWORKS system uses intelligent control nodes intercommunicating with a common protocol called LONTalk. Each node includes embedded protocol and control functions and a physical interface for coupling the node controller to the communications medium. Nodes may be a variety of drives, relays, and sensing devices and may be used for automation, pro- duction lines, security, and more. Local control nodes are the basic network devices for operational control and actuation. Supervisory nodes collect and log data from the local control nodes or coordinate their be- havior. Routers provide connectivity and flow between LONWORKS network channels. The LONWORKS protocol can be embedded into processors, from 8-bit microcontrollers to 32-bit mi- croprocessors. The Neuron Chip is a low-cost, commercially available processor with LONTalk support built in. In 1999, LONWORKS was approved as an open industry standard by the American National Standards Institute (ANSI/EIA 709.1-A-1999 Control Network Protocol Specification). The protocol is also approved by IEEE and other professional societies. Intelligent Technologies (IEC) is a significant third-party developer of LONWORKS-compatible products. See CEBus, ICELAN 2000, LONTalk, Neuron Chip, X- 10. LookAhead See Query on Release. Loomis, Mahlon (1826-1886) An American dentist and researcher who was intrigued by the fact that early telegraphs could be run with only one wire, with earth providing the conductor for the return circuit. He reasoned that if earth could act as one conductor, then perhaps air could act as another, especially since Benjamin Franklin's experiments had alerted scien- tists to the electricity in the air. In 1865 or 1866 Loomis devised an experiment in which he raised kites with equal lengths of fine copper wire and demonstrated that a signal could be transmitted from one to the other without direct physical contact. He re- ceived a U.S. patent for his improved wireless tele- graphic system in 1872. loop 1. A complete transmissions circuit, or electrical 602 circuit. 2. In telephone systems, a loop comprises the wire transmission path that extends from the central office to the residential or business subscriber and back. loop, communications hardwareA circuit, conduit, or line which comprises a continuous path with start- ing and ending points meeting at the same geographi- cal point. The start and end points mayor may not be joined. A loop mayor may not include nodes. Com- munications through the loop may be unidirectional or bidirectional. A loop need not be roughly circular, although it sometimes is; often a loop consists of two adjacent lines, one which sends, the other which re- ceives. Some loops send and receive on the same line (especially ifit's a wider bandwidth medium such as fiber), so the loop aspect is based more on the nature of the transmission than the configuration of the cable. See local loop, Fiber Distributed Data Inter- face, Token-Ring. loop, programming In software, a programming loop is a series of instructions which will repeat until some event or condition occurs to cause the software to drop out of the loop, or to branch to a specified destination. An endless loop is one which, theoreti- cally, goes on forever. In actual practice, an endless loop often indicates a fault condition and is usually externally terminated. See nesting, recursion. loop antenna A type of radio direction-finding antenna with one or more complete continuous loops of wire, the ends of which connect to complete the circuit. Loop DataMaintenanceCenter LDMC. See Loop Facility Assignment and Control System. Loop Facility Assignment and Control System LFACS. A database inventory of records and assign- ments associated with outside telecommunications loop facilities, including connection points, terminals, cables, etc. loop start In telephony, it is necessary to take control ofa line before it can be used. There are two common ways to do this, with a ground start or a loop start. The loop start commonly used in residential and other single line phone lines. When a caller picks up, the plunger is released (off-hook) and the circuit sends a supervisory signal by bridging the two wires in the phone connection (traditionally called tip and ring) with direct current (DC). This is done so that the subscriber will get a dial tone and a circuit through which to connect the call. The central telephone switching office sends a signal to the phone the caller is trying to reach and rings the number until it goes off-hook when it is picked up by the callee. When the loop is detected, the ringing signal is no longer set. See ground start. loop test, loopbacktest A procedure by which a circuit is connected in a loop in order to test for faults or differences in signal strength or data integrity after passing through the loop. This is commonly used in installation of new circuits or troubleshooting ex- isting circuits. For example, when installing a modem, looping the circuit through the computer system before connecting it to the public phone system © 2003 by CRC Press LLC can help predetennine whether the basic circuits, software, etc. are correctly installed before adding the additional factors associated with the phone circuit. loop testing system LTS. In telephony, a subscriber line diagnostic system for physical level testing of copper wire circuits. loop-through wiring A telephone wiring configuration commonly found in residences and other circuits where economy tends to be a higher priority than high reliability or redundancy. The wire runs from the junction point where the telephone company's wire reaches the house, then travels from room to room in electrical parallel while being physically wired in series. Like lights in older, serially wired Christmas light strings, a break in the circuit will interrupt power to all subsequent phones in the circuit. The alterna- tive is honle-run wiring (a fonn ofstar topology) in which separate wires run from the phone company junction point to each device on the circuit so that a break in a circuit affects only the device on that circuit. Loop-through wiring is certainly adequate for a circuit with only one or two communications devices, but if the premises have a variety of fax, modem, and telephone devices, home-run wiring is preferable. loose cable In the fiber optics network industry, jargon for general purpose outdoor cables (as compared to indoor interconnect cables, for example). Loose cables are used for aerial, underground, and outdoor conduit installations and sometimes for indoor use. Loose cables come in a variety of different types with varying fiber counts and degrees of shielding. loop back test See loop test. loran long range navigation. A system of distance navigation in which several radio transmitters (usually land-based) are used to send out pulsed signals from different directions in order to detennine the geographic location of the craft using the loran system. U sefid for air- and watercraft under some circumstances, but limited by the availability and distance of loran stations. See Global Positioning Sys- tem. LORG 1. Marketing jargon for large organization. 2. localized orbitaillocal origin. Methods that can be applied, for example, to shielding/chemical shift cal- culations. Lorimer switch One of the first commercially pro- moted automatic telephone switches, patented by the Lorimer brothers in 1900 and put into service in 1905. While it had many improvements on its predecessor, the Callender switch, it probably owes some of the impetus for its development to this earlier invention. It was installed in a number of switching systems in Europe, but was never fully reliable. However, the technology was modular and could be extended, an important influence on future telephone switching systems. See panel switch, rotary switch, Strowger switch. Lorimer telephone An early telephone design pow- ered by a central battery system and dialed with a series of levers representing units, not unlike an old cal- culating machine or cash register. Setting levers con- figured a telephone number. Lorimer, George William A Canadian employee of inventor Romaine Callender, George William worked as a telephone operator at the Callender Telephone Exchange Company. He and his brother, James Hoyt Lorimer, later accompanied Callender to New York where Callender was seeking financing to establish a new company after filing a series of patents on telephone switching technology that he was not able to implement in Brantford, Ontario. In New York, the group succeeded in creating an automatic switching system, after which they returned to Brantford. Callender traveled to England to found the Callender Rapid Telephone Company, and the Lorimer brothers founded the Canadian machine Telephone in Peterborough in 1897. After the death of his brother, James, Egbert Lorimer joined George in marketing their technology. See Lorimer switch; Callender, Romain; Lorimer, James Hoyt. Lorimer, James Hoyt The brother of George Will- iam Lorimer, James originally studied law, but became involved in telephone switching systems research with his brother and George's employer, Ro- maine Callender. Together the Lorimers founded the Canadian Machine Telephone company in 1897. J ames had a strong mechanical aptitude, and the brothers continued to improve on the Callender switching technology until it was patentable in 1900. James Hoyt met an untimely death after which no significant technological innovation occurred in the part- nership, although the products continued to be mar- keted. See Callender, Romain; Lorimer, George Wil- liam. LOS 1. launch on schedule. 2. line of sight. 3. See loss of signal and Loss of Signal. loss 1. A decrease in power ofa transmission signal as it travels toward its destination, usually expressed in decibels (dB). Many factors contribute to loss, such as distance, type of signal, weather, signal modifica- tions through switches and routers, equipment characteristics, etc. Loss through a circuit is cumulative. See amplifier, interference, noise. 2. In a network, a quantitative measure of a reduction in system resources or services arising from undesired factors such as faulty equipment or configuration, vandal- ism, or incorrect usage. Loss of Cell LOC. In ATM networking, a performance monitoring function of the PRY (physical) layer in which a maintenance signal is transmitted in the overhead indicating that the receiving end has lost cell delineation. Loss of Frame LOF. In ATM networking, a performance measure indicating whether frame delineation has been lost. The LOF is transmitted through the physical (PRY) overhead. On some systems, a LOF condition will be signaled on a port with a light-emitting diode (LED), or as a ''yellow alarm." loss of signal LOS. In a general sense, the sudden, undesired, or unexpected loss of a transmission or other signal such as a beep, alarm, light signal, code, speech, or data signal. LOS results from many causes: interference, a break in the circuit, a change in the surrounding environment (pressure, sun spots, 603 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary moisture, loss oflight, etc.). Loss in Optical Fibers C1 .'.~'!I!~'~t~I~'il!!li,:!!i C2_. C3~~ There are manysources of loss injiberoptic cables. Here are examples ofsome of the most common. Imperfections, bubbles, impurities, and crystalliza- tion duringfabrication can all lead to loss as the light beams are reflected by the impediments against the direction of the signalorout through the cladding (A I). Coupling losses, in the form of misaligned joints (BI) orparticles trapped in thejoints (B2) can cause light to escape or reflect backwards. Bend losses can be related to structures within the fiber or to the overallgeometry of the fiber. Microbends in theform of pits (el) or irregularities between the core and cladding ratios (C2) may contribute to signal loss. Macrobends from the cable being installed with too great a bend can cause light to hit the cladding at too high an angle to be reflected along the lightguide through total internal reflection (TIR), resulting in significantlosses through the cladding (C3). Loss ofSignal LOS. In ATM networking, a performance measure indicating that the receiver is not get- ting the expected signal, or that there is simply no signal because nothing is currently connected. The LOF 604 is transmitted through the physical (PHY) overhead. On some systems, a LOS condition will be signaled on a port with a light-emitting diode (LED). lossless compression A type of data compression technique which does not lose information contained in the image in the compression stage. Some compression algorithms average, sample, or remove image information in order to achieve a high degree of compression, e.g., JPEG. Others retain all the information, e.g., TIFF. See compression. Contrast with lossy compression. lossy compression A type of data compression technique which selectively or randomly loses information contained in the image in the compression stage. These algorithms average, sample, or remove image information in order to achieve a high degree of compression, e.g., JPEG. New wavelet mathematics is providing some very interesting compression options which provide a high degree of compression with a surprising degree of fidelity to the original image when decompressed and displayed. Other techniques retain all the information, e.g., TIFF. See compression, discrete cosine transform, fractal transform, wavelet. Contrast with lossless compression. LOTOS See Language of Temporal Ordering Speci- fication. loupeA compact handheld magnifying tool designed to comfortably enlarge small details. Loupes are typically used with one eye held close to the magnifying lens. They are useful for visual inspection of defects, cleaves, circuits, surfaces to be bonded or cleaned, and other structures that are just a little too small for normal viewing. Because they are small, loupes are not high magnifi- cation devices; they typically magnify about lOx. N everthless, they are useful as fiber optic filament endface inspection tools in the field. Some loupes include mounts for attaching them to stabilizing equipment or combination lens devices. It is important to remember that loupes will magnify a light beam and thus should never be held over a light source (e.g., laser light) that could harm the eye. Lovelace,AdaAugusta (1815-1851 or 1852) Count- ess Ada Lovelace (nee Byron) was the daughter of the famed English poet Lord Byron. Ada Lovelace worked with the computer pioneer Charles Babbage, and is regarded as the first computer programmer for her description of how an analytical machine might compute Bernoulli numbers. She proposed the pos- sibility of using computers to compose music or pro- duce graphics. A computer language (ADA) was developed by the u.S. Department of Defense and named in her honor. See ADA; Babbage, Charles. low Earth orbit LEO. An orbiting region around the Earth into which certain types of communications satellites are launched. There are advantages and dis- advantages to a low orbit. The main advantage is that it generally requires less power to transmii and receive at lower altitudes; the main disadvantage is that it requires a larger number of satellites to provide full global coverage. Other factors include lower radia- © 2003 by CRC Press LLC tion levels and lower launching costs. The lifespans of low-orbit satellites tend to be around 5 to 8 years. Most low-orbit satellites travel at about 500 to 2000 kIn outside Earth. A region called the Van Allen radiation belt at the outer regions of low Earth orbit is generally avoided between the LEO and medium Earth orbits (MEOs). LEO satellites are primarily used for cell phone and data communications. Communications designed for lower orbits require a larger number ofsatellites than those for higher orbits. This necessitates greater coordination to handle the larger number of systems and to deal with the shorter periods during which each satellite is within range. In contrast, high Earth orbit (HEO) systems can blanket the Earth with only three or four satellites. The trade-off is that higher-placed satellite transmitters require more power to beam the greater dis- tances. See Ellipso, Global Positioning Service, Globalstar, high Earth orbit, Iridium, medium Earth orbit, Orbcomm, Teledesic. Low FrequencyArray LOFAR. An electronic array functioning as an electromagnetic imaging interfer- ometer in the approximately 10- to 150-MHz frequency range. The goals of the LOFAR astronomi- cal project include the study ofsolar and planetary radio emissions and imaging of the high-redshift emissions. It is hoped the LOFAR research may re- veal new classes ofphysical phenomena in the process ofinvestigating new regions of the electromagnetic spectrum. The work is being carried out by members of the LOF AR Consortium, which includes the U.S. Naval Research Laboratory, MIT, and the Netherlands Foundation for Research in Astronomy. Ada Lovelace - Pioneer Software Designer Ada Lovelace had an active interest in the sciences and the arts and speculated on thefuture capbilities of Hthinking machines. " low level formatting In storage devices such as hard drives and cartridge drives, formatting is the process ofarranging the magnetic media on the storage surface to conform to a recognized pattern so the operating system can further organize data on the drive (the next step is usually to high-level format [initial- ize] and partition the drive). Each operating system has its own file formats, the protocols that allow it to create directories, organize files and file pointers, and read and write infonnation from and to the drive. Some operating systems are designed to recognize the file formats ofother systems as well. For example, on Macintosh and NeXT systems, ifa DOS/Windows disk is inserted in the drive, the Mac or NeXT OS will recognize the foreign drive and read and write data files to the drive (and perform minor conversions as necessary) in the format of the diskette, rather than the native operating system format. This provides the user with a lot offlexibility in terms of data transfer and conversion. This does not mean that executable files from other systems can be run on any platform, but rather that files can be moved about as needed. Most drives now come low-level formatted from the ;~~~~:n~~ta~ Ifa~thr~:~~~~~~~:rtan~~~ t~nr:f=:t. the drive to make it usable again. low level language Acomputer control or programming language at the machine or assembly level at which individual registers, accumulators, and other aspects of the physical architecture can be directly or nearly directly controlled Low level languages are rarely used these days except for writing simulators for various types ofprocessors. It is much more common now to use high-level programming languages to create source code, and then engage an intermediary program, called a compiler, to translate the high-level language into machine instructions. A certain amount of bit-twiddling can be accomplished in some of the medium- or high-level languages, but is needed only in limited circumstances. Contrast with high-level language. low noise amplifier LNA. Acomponent which amplifies and sometimes converts telecommunications signals, typically from satellite transmissions. In a satellite receiving station, the LNA takes signals from the feed hom, amplifies them, and then converts them or sends them to a separate low noise converter (LNC); from there they are transmitted to the receiver, usually inside a building. See feed hom, low noise converter, parabolic antenna, satellite antennas. low noise amplifier probe LNA probe. A component that works in conjunction with a low noise amplifier to control the signal polarity, which can be set to ei- ther horizontal or vertical, in order to accommodate more channels on a single system. The LNA probe is typically built into the feed hom mechanism on parabolic antennas. low noise block converter LNB. A component which converts amplified signals, usually to a lower frequency to send to a receiver. In telecommunications, it is commonly used with satellites and may be in- corporated into the low noise amplifier (LNA). LNBs 605 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary have a broader range than LNCs, as they are able to convert a range offrequencies (provided they have the same polarization) rather than just a single frequency, as in LNCs. See low noise amplifier, low noise converter, parabolic antenna, satellite antennas. low noise converter LNC. Acomponent which converts amplified signals, usually to a lower frequency to send to a receiver. In telecommunications, it is commonly used with satellites and may be incorpo- rated into the low noise amplifier (LNA). LNCs work with specific frequencies. See low noise amplifier, low noise block converter, parabolic antenna, satellite antennas. low pass fIlter Afilter that passes transmissions be- Iowa specified cutoff frequency, with little or no loss or distortion, but effectively filters out higher frequencies. See high pass filter. Low-power Atmospheric Compensation Experi- ment LACE. An experiment begun in the mid-1980s in which a spacebome target with asingle sensor was used to assess compensation schemes associated with laser beams traveling through the atmosphere from the ground. This infonnation was needed to support laser defense system research and development. LACE was built by the U.S. Naval Research Labo- ratory (NRL). LACE was originally a fairly simple sensor system carried on a shuttle. In 1986, LACE became a full satellite instead ofa set of sensors on a host satellite. By 1987, the sensor arrays carried a total of210 sensors capable of characterizing ground-based laser beams. In 1990, the LACE satellite was launched and successfully demonstrated that techniques for com- pensating for atmospheric distortion of laser beams originating from the ground were tenable. low-power television LPTV. Television broadcast technology with limited power commonly used to serve a local region such as a rural community. Broad- cast technologies are closely regulated by the F ed- era 1 Communications Commission (FCC) and various spectra and licenses are granted to broadcast stations dependent upon operator qualifications, content, viewing audience, and the power and frequency of the communications. LPTV serves a large number of educational and social niche markets and small communi ties that may not be ofinterest to larger broad- casting agencies. See Communications Policy Proj ect, Community Broadcasters Association, F ed- eral Communications Commission. lower sideband In electromagnetic signals, the lower frequency half ofa wave. In modulated signals, especially amplitude-modulated radio carrier waves, the sidebands contain the infonnational content of the signal. See single sideband. lower sideband suppressed carrier LSSC. A modulated carrier wave that has had part of the signal stripped away in order to save bandwidth. This lower sideband is rebuilt mathematically at the receiving end to recover the original signal infonnation. See sideband. LP 1. linear programming. 2. low power. 3. low pressure. 606 LPC See linear predictive coding. LPRF 1. low-power radio frequency. 2. low pulse- repetition frequency. LPTV See low-power television. LRC See longitudinal redundancy check. LRF See laser range finder. LRN See Location Routing Number. LRS line repeater station. LSA See link state advertisement. LSD 1. See least significant bit. 2. lower sideband. See sideband. LSDU Link layer Service Data Unit. LSI A tenn in the semiconductor industry describ- ing capabilities aggregated onto a single chip. See large scale integration. LSMA Large-Scale Multicast Applications. LSN 1. See Large Scale Networking group. 2. local signal number. LSP 1. See label-switched path. 2. See Local Services Provider. LSR See local service request. LSS loop switching system. See switching. LSSC See lower sideband suppressed carrier. LSSGR LATA Switching System General Require- ments. LSTP 1. See local signal transfer point. 2. linear search & track processor. LSU 1. See line switching unit. 2. See Logical Stor- age Unit. LTD Last Trunk Busy. LTC See line trunk controller. LTE See Line Terminating Equipment. LTO See linear tape-open. LTS See loop testing system. LTSP See Linux Tenninal Server Project. LUCE See laser-using communications equipment. Lucent Technologies Acompany created following the AT&T/Bell divestiture. Lucent was established with the Bell Laboratories research staff and a number of the electronics, network, and business communications groups, including Systems for Network Op- erators, Business Communications Systems, Micro- electronics, and Consumer Products. The organization has become prominent as a developer of many new optical telephone network technologies. See AT&T; Barton, Enos. LucentTechnologies Canada Inc.Awholly owned subsidiary ofLucent Technologies, based in Ontario, Lucent Technologies Canada Inc. formed as a result of the restructuring of AT&T after the divestiture. Lucent began in Canada as part of AT&T Canada Inc. in 1984. LUF lowest usable frequency. lug 1. A projecting attachment point, especially for electrical circuits. See terminal. 2. An attachment added to the end of awire which provides an eye, or forked end, which allows the wire to be more easily attached to a bolt under a binding screw. LUM See line utilization monitor. lumberg The older tenn for a Talbot, now superseded by lumen seconds. See lumen seconds. lumen (Latin -light) A standardized SI unit oflight © 2003 by CRC Press LLC (luminous) flux equal to the light produced by one candela intensity on a unit area of a flat surface of uniform distance from the light source. A lumen indicates photonic energy flow. A footcandle (a description offlux density) is one lumen per square foot (lux is now more commonly used). An indoor lamp might output 2,000 lumens. See candela, steradian. lumen seconds, TalbotA standardized unit oflumi- nous energy over time, equal to the illumination from a one lumen light source emitted for one second, usually expressed in millijoules for a specified wavelength. It is also known as a Talbot after W.H.F. Tal- bot, replacing the term lumberg. See photon. lumen hourA measure of luminous energy over time, equal to the illumination from a one lumen light source emitted continuously over the course of an hour. luminance (symb. - L) The luminous (light-emitting) flux reflected or transmitted, as measured from a particular direction, from a source such as a TV screen, light-emitting diode, or laser light source per unit area as measured in a specified direction. A luminance unit is expressed as a candela per square meter (cd/m 2 ), sometimes called a nit. In fact, luminance measuring devices have been dubbed "nitmeters." Nitmeters may also have electronics for measuring lux. Luminance meters or "light meters" are frequently used for assessing ambient light or reflected light from spotlights used for photography. They measure an aspect of luminance called luminance flux or lux. Spectroradiometers can quickly measure low light levels. Luminance colorimeters can measure luminance and other light-related properties such as chromaticity and color temperature. These tenns luminance and nit have superseded older expressions of luminance such as footcandle, Lam- bert, or footLambert. In casual tenns, luminance is often called brightness. See photometer. luminosity A ratio oflight flux to its corresponding radiant flux at a specific wavelength, expressed in lumens per watt. luminous flux The visible energy (light) produced per unit of time, expressed in lumens. Luminous flux may be measured with an integrating sphere associated with a photometer. See lumens. luminous intensity A measure of the quantity of luminous flux in a given direction at a frequency of 540 x 1012 Hz at a particular solid angle (1/683 W per steradian), expressed in candelas. Specialized photometers can be calibrated to detect luminous intensity. At the U.K National Physical Laboratory the candela has been measured with a reported uncertainty of 0.02%, using a cryogenic radiometer which equates the thermal effect of optical radiation with that of electrical power. Luminous intensity standards have been developed for many technologies including public lighting, signage, and street lights. See candela, steradian. LUN See logical unit number. Luneberg lens A type of focusing lens used in antennas to increase gain for ultra-high frequency (UHF) transmissions. lux A combining word from luminance and flux also referred to as illuminance. A basic metric unit for expressing illumination (a footcandle equals 10.76 lux). The illumination on a one-square-meter area on which the flux of one lumen is uniformly distributed. See flux, luminance. luxmeter A type oflight-measuring instrument that records intensities. Light meters are commonly in- corporated into cameras to help to detennine aper- ture and speed settings. LTS lightwave transmission system. Transmis~ion through a light-guiding medium such as fiber optics. LVD low voltage disconnect. See load distribution unit. LWER See LightWeight Encoding Rules. Lynch, Daniel C. (ca. 1940- ) Lynch organized the first TCP/IP Implementor's Workshop in 1986, which later developed into Interop in 1988, a large gather- ing of Internet, network, and other telecommunications professionals. Lynch is also Jrnown for his role in the ARPANET transition from NCP to Internet Protocol (IP). He is a cofounder of CyberCash, Inc. and has been a member of the Board of Directors since 1994. Lynx A text-based Web browser developed at the University of Kansas in the early 1990s by M. Grobe, C. Rezac, L. Montulli, and many others. Lynx en- ables limited-resource devices such as portable or desktop text-based terminals to navigate the Web. It is also useful for fast searches of Web content for situ- ations where viewing graphics is not desired. Lynx is descended from a client/server-based distributed computing hypertext browser. See Microsoft Ex- plorer; Netscape. LZ77 See Lempel-Ziv. LZ78 See Lempel-Ziv. LZARI Lempel-Ziv arithmetic. A loss less compression and archiving utility developed by Okumura in 1988, based originally on LZSS, but which incorpo- rated adaptive and static algebraic compression to encode characters and position fields, respectively. Thus, it is a statistical compressor, rather than a dictionary compressor as was its predecessor. LZARI was not the fastest archiver for its time, but it had good compression performance. LZARI was later adapted into LHarc by Yoshizaki. See Lempel-Ziv, LHarc. LZB Lempel-Ziv Bell. A lossless variable-length- code compression scheme developed in 1987 by Bell, based upon LZ77 concepts. In terms of compression performance for text files, LZB is a little better than LZH and its predecessors, but not as efficient as the popular GZIP. LZB has fairly small memory require- ments for decompression making it suitable for devices with limited memory resources. LZB 80 Linienzugbeeinflussung 80. A signaling system developed by the Gennan Federal Railways. LZB systems are sold internationally for high-speed train systems control and safety. LZC A dictionary-based lossless compression scheme developed in 1985 by Thomas et a1. based upon LZW, which is patented. LZC incorporates a 607 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary variable-size pointer scheme. It dynamically monitors progress and can flush and rebuild the dictionary to suit the circumstances. As examples, Unix compress and MacCompress use the LZC algorithm. LZC is also used in some schemes to increase disk space availability by dynamically compressing stored files. (Don't confuse this with the wavelet-related LZC developed by Thaubman and Zakhor.) See Lempel- Ziv-Welch. LZC layered zero coding. A rate-scalable encoding scheme described by D. Thaubman and A. Zakhor in 1994. LZC takes advantage of a strong correlation among subband coefficients, resulting in good image compression performance. LZC and its descendants have been used in a number of applications related to scalable image compression and have been incor- porated into embedded wavelet-based video coders. (Don't confuse this with the dictionary-based LZC developed by Thomas et a1.) See wavelet. LZFG Lempel-Ziv-Fiala-Green. A fast, lossless compression scheme developed in 1989 by Fiala and Green (U.S. patent #4906991), based upon Lempel- Ziv LZ77 and LZ78 concepts. LZFG is a sliding window scheme with data stored in a modified trie (Pa- tricia tree) data structure. The position of the text in the trie is output. LZFG has some speed benefits over Lempel-Ziv-Jakobsson (LZJ). LZHSeeLHA. LZJ Lempel-Ziv-Jakobsson. A dictionary-based lossless compression scheme developed in 1985 by Jakobsson. It is based upon LZW containing point- 608 ers only, with the pointers able to point to anywhere in the previous character data to indicate a substring. See LZFG. LZHUF Lempel-Ziv Huffman. The algorithm incor- porated into the LHarc data archiving utility by Yoshizaki that replaces LZARI's adaptive arithmetic coding with adaptive Huffman coding to improve the speed ofLZARI (LZAR! already had good data compression). With additional work, LZHUF evolved into LHarc. See LHarc, LZARI. LZMW A lossless compression scheme developed in 1984 by Miller and Wegman. While LZMW improved upon its predecessor LZ77 (Lempel and Ziv), there was so much interest in adapting LZ77 that LZMW was short-lived, superseded by LZH, LZB, and the efficient and popular GZIP. LZP Lempel-Ziv prediction. A loss less dictionary and hash-based compression scheme developed in 1995 by Charles Bloom. Bloom designed the scheme to be fast, scalable, and retargetable. It is descended from LZ77 and shares some characteristics with LZNW and PPMCB. It is distributed for noncommercial use under a Public License. See Lempel-Ziv. LZR A lossless compression utility developed in 1981 by Roden et a1. that does not have the window limitations of the earlier LZ77 scheme. Interestingly, an LZR scheme has been suggested for the compression ofrepetitive DNA sequences. See Lempel-Ziv. LZS See Lempel-Ziv-Stac. LZSS See Lempel-Ziv-Storer-Szymanski. LZW See Lempel-Ziv-Welsh. © 2003 by CRC Press LLC m 1. abbrev. meter. See meter. 2. abbrev. milli See milli M 1. abbrev. mega See mega. 2. symb. mixed polarization (ITU). M bit, Mark bit, More bit In X.25 network data transmissions, a signal bit used to indicate that additional packets in a sequence are to be expected. A bit set to 1 or "true" indicates further packets will be coming, whereas 0 or "false" signals that packets were (intentionally) not sent. This helps the receiving system to distinguish between packets not sent and lost packets. In Realtime Transport Protocol (RTP), the M bit can signal the transport of at least one complete media frame or the remaining fragment in a frame. For frames fragmented across multiple RTP packets, the M bit can signal frame boundaries. See D bit, Q bit. MHop Hops between satellites can be repeated to pass through an intermediatestation orhub (e.g., a ground station) en route to thefinal receiver. There may be a number of reasons for sending to an intermediate hub, including amplification, filtering o.fthe broadcast channels, and redistribution to subscribers through Earth stations at more than one location. M hop A type of pattern that results when communications transmissions are bounced from an Earth station to an airborne receiver, back to an Earth station or intermediary hub, up to an airborne receiver and back down to the final receiving station, thus resem- bling the letter "M." This is a common configuration in hub topology satellite communications. Newer satellites are being designed for intersatellite commu- nication, so the signal goes from an Earth station to a satellite, to another satellite and then down to Earth again, thus forming a shape like three sides ofarect- angle rather than the letter M, as shown in the Basic hop/M hop diagram. M port In aFiber Distributed Data Interface (FDDI) network, extra port on a concentrator for attaching other nodes in a branching tree topology. M ports can be on both single attachment and dual attachment concentrators. The Mport is an addition to the basic FDDI network. On a dual attachment station (DAS), a redundant link can be created by connecting the A and B ports on different concentrators on the M ports. On asingle attachment concentrator, the M port may be connected to the Sport. M ports are never connected to one another. The other end of the M port may be attached to apatch panel through a data grade cable. See Aport. M Ports in FDDI Ring-Based Network A and B ports are the mainpoints of entry between FDDI cabling "rings" and dual attachment stations (DASs). However, it is also possible to configure M ports onto the ring for adding more stations. 609 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary P~rformaJl.cemonitoring·Qn il'ltemati9Ail·traIlsmissiQl1systemsand equipment ·Principlesconcemingline-up and maintenance limits I.J seof telecom.·terms .for maintenance Maintenaric~tenninologyand definitions Guiding principles on general tnaintenanceorganiz. fortelepbone- type il1t~rp~tion~l ~rcuits ~echnicalservice Control stations Fault report points Sub-control stations Service circuits Circuit testing Access points for maintenance pigitalloopbackmechanisms $tabilityoFtransmission Bringing newintemational transmissionsystem into service Bringing.in~mational group, supergroup, etc. links int()service Settingupf;lDd lining uP analog channels for international telecom. services ~~ttingup~dlining up mixed analogi digitalchantl~l&forinternational telecom.services Transmission restoration and transmission route diversity: tertllillology: a~d g~neral principles Functionalorganiz. for automatic transmission restoration M.70 M.SO M.60 M.3604Applicationofmaintenance principles to ISDN primary rate access M.360S ~pplicatio~ofmaintenanceJJrinciples tostaticm141tiplexed ISDN basic rate access M.3610 Principles forapplyingTMN concept to. the management alB-ISDN M:.36111estI11an~$etnf'Ilt ofl~. ISDNATM layer using th~TMN M.3620 Principles for the use of ISDN test ~alls, system.s,and responders M.3621 .•• Itltegra.t~dp;:l~ageDlent()fISDN customer· access M.3640 Managemellt of the D-channel - data link layer a.g.d network layer M.3641Mana.gementinfo model.for management of datalil1kand network ,layer of ISQN D-channel M.3650Networkperfonnance measurements of ISDN calls M.~66(}ISPN interf~emana.g~m~nt services Monitoring,· Maintenance ,Performance, Service, Testing, Misc., etc M.34 M.3S M.75 M.80 M.SS M.90 M.IOa M.lIO M.120 M.125 M.160 M.4S0 M.460 M.470 M.496 Numbering of chcmIlels in group NumberingofgrQ1J.p~within supergroup Numbering of super groups within mastergroup Nl.1ffib~r1ll~ ofm~t~fgrouPs within superrn~t~~gr(,')~l? . Nqmberjng in coaxial systems Numbering in systems on symmetric pairc~ble Numbering inradj~~relay Hnk:$or open"\Vire line· systems Numbering of digitalblocks in transmission sys~ms. ISDN M.400 M.410 M.380 M.390 Scope, Philosophy, General Principles M.3600 Princ~ples fortnal'1agementofISDNs M.3602 Application of maintenance principles to ISDN subscriber installations M.3603 Applic;atiollpfIAAintellanpepJ"iIwiples to ISDN. basic rate ··access ITU-TM Series Recommendations M;··l·O Scope •••• lt.tid· •.• appliQ~~jpl1···.of recori:unendationsfOrmaintenariceof telecom. t1etworks and· services M.lS Maintenance.considerations fOfl1ew systems M:20 Maintenancepbilq$ophyfortelecom. networks M.21 Maintenancephilo~()phy for.telecom. servi(:es • • ••• • ··0<·: M.·32rtjnciples··for·using···.·~arm····info.·(or.·· ·•.·. .maintenance·ofinternational transnlission systems and equipment M.S60 InteI'IJ.lltional telephollecircuit&v prillciples,.defi~iti9nSt··at1dr~lative transmission levels M.1130 General· definitions and general principles of operation/maintenance proq~q.to. b~ us,~clip$~tellitemQ~ile systems M.1140 Maritime. mobile tel~com. services via satellite M.1301 General clescriptioJiand operational proccq~for inte11}sijonal.SPHleased circuits M.1535 Principles for maintenance info to be exchanged at customer contactpoint (MICe) M.tS3? Defiriitionofmllinttel1anceinfotobe exchanged at customer contactpoint (MICe) M.3100. Generic network info. model M.~600 Principles·.form~g~tl1ent·QfISDNs Numbering M.320 M.330 M.340 M.3S0 610 © 2003 by CRC Press LLC M.510 M.520 M.51S M.530 M.535 M.540 M.556 M.S80 M.600 M.605 M.610 M.620 M 8S0: M.630 M.650 M.660 M.665 M.6'70 M.675 M.710 M.720 611 © 2003 by CRC Press LLC . developed in 1981 by Roden et a1. that does not have the window limitations of the earlier LZ77 scheme. Interestingly, an LZR scheme has been suggested for the compression ofrepetitive DNA sequences. See Lempel-Ziv. LZS See Lempel-Ziv-Stac. LZSS See Lempel-Ziv-Storer-Szymanski. LZW See Lempel-Ziv-Welsh. © 2003 by CRC Press LLC m 1. abbrev. meter. See meter. 2. abbrev. milli. a strong correlation among subband coefficients, resulting in good image compression performance. LZC and its descendants have been used in a number of applications related to scalable image compression and have been incor- porated into embedded wavelet-based video coders. (Don't confuse this with the dictionary- based LZC developed by Thomas et a1.) See wavelet. LZFG Lempel-Ziv-Fiala-Green. A fast, lossless compression scheme developed in 1989 by Fiala and Green (U.S. patent #4906991), based upon Lempel- Ziv LZ77 and LZ78 concepts. LZFG is a sliding window scheme with data stored in a modified trie (Pa- tricia tree) data structure. The position of the text in the trie is output. LZFG has some speed benefits over Lempel-Ziv-Jakobsson (LZJ). LZHSeeLHA. LZJ Lempel-Ziv-Jakobsson. A dictionary- based lossless. a strong correlation among subband coefficients, resulting in good image compression performance. LZC and its descendants have been used in a number of applications related to scalable image compression and have been incor- porated into embedded wavelet-based video coders. (Don't confuse this with the dictionary- based LZC developed by Thomas et a1.) See wavelet. LZFG Lempel-Ziv-Fiala-Green. A fast, lossless compression scheme developed in 1989 by Fiala and Green (U.S. patent #4906991), based upon Lempel- Ziv LZ77 and LZ78 concepts. LZFG is a sliding window scheme with data stored in a modified trie (Pa- tricia tree) data structure. The position of the text in the trie is output. LZFG has some speed benefits over Lempel-Ziv-Jakobsson (LZJ). LZHSeeLHA. LZJ Lempel-Ziv-Jakobsson. A dictionary- based lossless