Fiber Optics Illustrated Dictionary - Part 62 pot

In telephone systems, a loop comprises the wire transmission path that extends from the central office to the residential or business subscriber and back.. See local loop, Fiber Distribu

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 oftypes

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

network-ing standard by companies such as Echelon

Corpo-ration See LONWORKS, Neuron Chip

LONWORKSAninternationally 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

cou-pling the node controller to the communications

me-dium 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,

com-mercially available processor with LONTalk support

built in

In 1999, LONWORKS was approved as an open

in-dustry 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

devel-oper of LONWORKS-compatible products See

CEBus, ICELAN 2000, LONTalk, Neuron Chip,

X-10

Look AheadSee Query on Release

Loomis, Mahlon(1826-1886)AnAmerican 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 offine copper wire and

dem-onstrated 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

loop1 Acomplete transmissions circuit, or electrical

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 endstart-ing points meetstart-ing 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 oftwo adjacent lines, one which sends, the other which re-ceives Some loops send and receive on the same line (especially if it'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, programmingIn software, a programming loop is a series ofinstructions 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.Anendless 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 antennaA type of radio direction-finding an-tenna with one or more complete continuous loops

of wire, the ends of which connect to complete the circuit

Loop Data Maintenance CenterLDMC See Loop Facility Assignment and Control System

Loop Facility Assignment and Control System LFACS Adatabase inventory ofrecords and assign-ments associated with outside telecommunications loop facilities, including connection points, terminals, cables, etc

loop startIn telephony, it is necessary to take con-trol ofa line before it can be used There are two

com-mon 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 calledtipandring)

with direct current (DC) This is done so that the sub-scriber 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, loopback testAprocedure by which a cir-cuit is connected in a loop in order to test for faults

or differences in signal strength or data integrity af-ter passing through the loop This is commonly used

in installation of new circuits or troubleshooting ex-isting circuits For example, when installing a mo-dem, looping the circuit through the computer sys-tem before connecting it to the public phone syssys-tem

ware, etc are correctly installed before adding the

additional factors associated with the phone circuit

loop testing system LTS.Intelephony, a subscriber

line diagnostic system for physical level testing of

copper wire circuits

loop-through wiring Atelephone wiring

configura-tion 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 breakinthe circuit will interrupt power

to all subsequent phones in the circuit The

alterna-tive ishonle-run wiring (a fonn of star topology) in

which separate wires run from the phone company

junction point to each device on the circuit so that a

breakina circuit affects only the device on that

cir-cuit Loop-through wiring is certainly adequate for a

circuit with only one or two communications devices,

but ifthe premises have a variety offax, modem, and

telephone devices, home-run wiring is preferable

loose cable In the fiber optics network industry,

jar-gon 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 ofdifferent types with

varying fiber counts and degrees of shielding

loopback test See loop test

loran long range navigation A system of distance

navigation in which several radio transmitters

(usu-ally 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

sys-tem Usefid for air- and watercraft under some

cir-cumstances, but limited by the availability and

dis-tance 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 servicein1905

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 telephoneAnearly telephone design

pow-ered by a central battery system and dialed with a

se-ries oflevers representing units, not unlike an old

cal-culating machine or cash register Setting levers

con-figured a telephone number

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 ofpatents on tele-phone switching technology that he was not able to implement in Brantford, Ontario

In New York, the group succeededincreating an au-tomatic 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 ofhis 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 be-came involved in telephone switching systems re-search with his brother and George's employer, Ro-maine Callender Together the Lorimers founded the Canadian Machine Telephone company in 1897 James 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 sig-nificant technological innovation occurred in the part-nership, although the products continued to be mar-keted See Callender, Romain; Lorimer, George Wil-liam

LOS1 launch on schedule 2 line of sight 3 See loss of signal and Loss of Signal

loss 1 A decrease in power of a transmission signal

as it travels toward its destination, usually expressed

indecibels (dB) Many factors contribute to loss, such

as distance, type of signal, weather, signal modifica-tions through switches and routers, equipment char-acteristics, etc Loss through a circuit is cumulative See amplifier, interference, noise 2.Ina network, a quantitative measure of a reduction in system re-sources 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 perfor-mance 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 perfor-mance 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-emit-ting 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,

Fiber Optics Illustrated Dictionary

moisture, loss oflight,etc.)

Loss in Optical Fibers

C2_.

C3~~

There are many sources ofloss injiber optic cables.

Here are examples ofsome ofthe most common.

Imperfections, bubbles, impurities, and

crystalliza-tion duringfabricacrystalliza-tion can all lead to loss as the light

beams are reflected by the impediments against the

direction ofthe signal or out through the cladding (A I).

Coupling losses, in the form of misaligned joints

(BI) or particles trapped in the joints (B2) can cause

light to escape or reflect backwards.

Bend losses can be related to structures within the

fiber or to the overall geometry ofthefiber Microbends

in theform ofpits (el) or irregularities between the

core and cladding ratios(C2)may contribute to

sig-nal loss Macrobends from the cable being installed

with too great a bend can cause light to hit the

clad-ding at too high an angle to be reflected along the

lightguide through total internal reflection (TIR),

re-sulting in significant losses through the cladding(C3).

Loss of SignalLOS.InATM networking, a

perfor-mance measure indicating that the receiver is not

get-ting the expected signal, or that there is simply no

sig-nal because nothing is currently connected The LOF

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 compressionA type of data compression technique which does not lose information contained

in the image in the compression stage Some com-pression algorithms average, sample, or remove im-age information in order to achieve a high degree of compression, e.g., JPEG Others retain all the infor-mation, e.g., TIFF See compression Contrast with lossy compression

lossy compressionAtype ofdata compression tech-nique which selectively or randomly loses informa-tion contained in the image in the compression stage These algorithms average, sample, or remove image information in order to achieve a high degree ofcom-pression, 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 compres-sion, discrete cosine transform, fractal transform, wavelet Contrast with lossless compression LOTOSSee Language ofTemporal Ordering Speci-fication

loupeAcompact handheld magnifying tool designed

to comfortably enlarge small details Loupes are typi-cally used with one eye held close to the magnifying lens They are useful for visual inspection ofdefects, 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.

Neverthless, 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

Itis 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, Ada Augusta (1815-1851or1852) 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 ofusing computers to compose music or pro-duce graphics

A computer language (ADA) was developed by the u.S Department ofDefense and named in her honor See ADA; Babbage, Charles

low Earth orbitLEO.Anorbiting 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 re-ceive at lower altitudes; the main disadvantage is that

it requires a larger number ofsatellites to provide full global coverage Other factors include lower

radia-of low-orbit satellites tend to be around 5 to 8 years.

Most low-orbit satellites travel at about 500 to 2000

kInoutside Earth A region called the Van Allen

ra-diation belt at the outer regions oflow 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 of satellites than those for higher

or-bits 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

satel-lites The trade-offis that higher-placed satellite

trans-mitters 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 Frequency ArrayLOFAR.Anelectronic array

functioning as an electromagnetic imaging

interfer-ometer in the approximately 10- to 150-MHz

fre-quency range The goals of the LOFAR

astronomi-cal project include the study of solar and planetary

radio emissions and imaging of the high-redshift

emissions It is hoped the LOFAR research may

re-veal new classes of physical phenomena in the

pro-cess of investigating new regions of the

electromag-netic spectrum The work is being carried out by

members ofthe LOFAR 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 the future capbilities

of Hthinking machines "

drives and cartridge drives, formatting is the process

of arranging the magnetic media on the storage sur-face to conform to a recognized pattern so the oper-ating 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 of other 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 ofthe diskette, rather than the native operating system format This provides the user with a lot of flexibility 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 languageA computer control or program-ming 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 of processors

It is much more common now to use high-level pro-gramming languages to create source code, and then engage an intermediary program, called a compiler,

to translate the high-level language into machine in-structions A certain amount of bit-twiddling can be accomplished in some of the medium- or high-level languages, but is needed only in limited circum-stances Contrast with high-level language

low noise amplifierLNA A component which am-plifies 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 probeLNA probe Acomponent 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 para-bolic antennas

low noise block converterLNB Acomponent which converts amplified signals, usually to a lower fre-quency 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

Fiber Optics Illustrated Dictionary

have a broader range than LNCs, as they are able to

convert a range of frequencies (provided they have

the same polarization) rather than just a single

fre-quency, asin LNCs See low noise amplifier, low

noise converter, parabolic antenna, satellite antennas

low noise converter LNC Acomponent which

con-verts 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,

satel-lite antennas

low pass fIlter A filter that passes transmissions

be-Iowa specified cutofffrequency, with little or no loss

or distortion, but effectively filters out higher

frequen-cies See high pass filter

Low-power Atmospheric Compensation

Experi-ment LACE.Anexperiment begun in the mid-1980s

in which a spacebome target with a single 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 of a set ofsensors on a host satellite

By 1987, the sensor arrays carried a total of210

sen-sors 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

Fed-era1Communications Commission (FCC) and

vari-ous spectra and licenses are granted to broadcast

sta-tions dependent upon operator qualificasta-tions, content,

viewing audience, and the power and frequency of

the communications LPTV serves a large number of

educational and social niche markets and small

com-munities that may not be of interest to larger

broad-casting agencies See Communications Policy

Project, Community Broadcasters Association,

Fed-eral Communications Commission

lower sidebandInelectromagnetic signals, the lower

frequency half of a wave.Inmodulated signals,

es-pecially amplitude-modulated radio carrier waves, the

sidebands contain the infonnational content of the

signal See single sideband

lower sideband suppressed carrier LSSC

Amodu-lated 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

pres-sure

LPCSee linear predictive coding

LPRF1 low-power radio frequency 2 low pulse-repetition frequency

LPTVSee low-power television

LRCSee longitudinal redundancy check

LRFSee 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 sdescrib-ingle chip See large scale integration

LSMA Large-Scale Multicast Applications LSN 1 See Large Scale Networking group 2 local signal number

LSP1 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

LTCSee line trunk controller

LTE See Line Terminating Equipment

LTO See linear tape-open

LTS See loop testing system

LTSP See Linux Tenninal Server Project

LUCESee laser-using communications equipment Lucent Technologies A company created following the AT&T/Bell divestiture Lucent was established with the Bell Laboratories research staff and a num-ber ofthe electronics, network, and business commu-nications groups, including Systems for Network Op-erators, Business Communications Systems, Micro-electronics, and Consumer Products The organiza-tion has become prominent as a developer of many new optical telephone network technologies See AT&T; Barton, Enos

Lucent Technologies 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 ofAT&T Canada Inc

in 1984

LUF lowest usable frequency

lug 1 A projecting attachment point, especially for electrical circuits See terminal 2.Anattachment added to the end ofawire which provides an eye, or forked end, which allows the wire to be more easily attached to a bolt under a binding screw

LUMSee line utilization monitor

lumberg The older tenn for a Talbot, now superseded

by lumen seconds See lumen seconds

lumen (Latin -light)AstandardizedSIunit of light

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

de-scription offlux density) is one lumen per square foot

(lux is now more commonly used).Anindoor lamp

might output 2,000 lumens See candela, steradian

lumen seconds, Talbot A standardized unit

oflumi-nous energy over time, equal to the illumination from

a one lumen light source emitted for one second,

usu-ally expressed in millijoules for a specified

wave-length It is also known as a Talbot after W.H.F

Tal-bot, replacing the term lumberg See photon

lumen hour Ameasure ofluminous 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

par-ticular 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/m2),sometimes called anit.In fact,

lumi-nance 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

re-flected light from spotlights used for photography

They measure an aspect of luminance called

lumi-nance flux orlux. 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 Aratio of light flux to its corresponding

radiant flux at a specific wavelength, expressed in

lumens per watt

luminous flux The visible energy (light) produced

per unit oftime, expressed in lumens Luminous flux

may be measured with an integrating sphere

associ-ated with a photometer See lumens

luminous intensity A measure of the quantity of

lu-minous 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

in-tensity

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

an-tennas to increase gain for ultra-high frequency

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 ofone lumen is uniformly distributed See flux, luminance

luxmeter A type of light-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 telecom-munications 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 ofthe Board

of Directors since 1994

Lynx A text-based Web browser developed at the University ofKansas 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 ofWeb 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

LZ77See Lempel-Ziv

LZ78See Lempel-Ziv

LZARILempel-Ziv arithmetic A lossless compres-sion 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 dic-tionary 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 de-vices with limited memory resources

LZB80 Linienzugbeeinflussung 80 Asignaling sys-tem 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

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 Afast, lossless

com-pression scheme developed in 1989 by Fiala and

Green (U.S patent #4906991), based upon

Lempel-Ziv LZ77 and LZ78 concepts LZFG is a sliding

win-dow 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 Adictionary-based

loss-less compression scheme developed in 1985 by

Jakobsson It is based upon LZW containing

point-ers only, with the pointpoint-ers 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 com-pression) With additional work, LZHUF evolved into LHarc See LHarc, LZARI

LZMW A lossless compression scheme developed

in 1984 by Miller and Wegman While LZMW im-proved 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 Alossless 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 ofthe earlier LZ77 scheme Interestingly,

an LZR scheme has been suggested for the compres-sion of repetitive DNA sequences See Lempel-Ziv LZS See Lempel-Ziv-Stac

LZSS See Lempel-Ziv-Storer-Szymanski

LZW See Lempel-Ziv-Welsh

M 1 abbrev mega- See mega 2 symb mixed

po-larization (ITU)

M bit, Mark bit, More bitInX.25network data

transmissions, a signal bit used to indicate that

addi-tional packets in a sequence are to be expected Abit

set to 1 or "true" indicates further packets will be

coming, whereas 0or "false" signals that packets

were (intentionally) not sent This helps the

receiv-ing system to distreceiv-inguish between packets not sent

and lost packets In Realtime Transport Protocol

(RTP), theM 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, theMbit can signal frame boundaries

See D bit,Qbit

MHop

Hops between satellites can be repeated to pass

through an intermediate station or hub (e.g., a ground

station) en route to the final receiver There may be

a number ofreasons for sending to an intermediate

hub, including amplification, filtering o.f the

broad-cast channels, and redistribution to subscribers

through Earth stations at more than one location.

MhopAtype ofpattern that results when

communi-cations transmissions are bounced from an Earth

sta-tion to an airborne receiver, back to an Earth stasta-tion

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

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 ofa

rect-angle rather than the letter M, as shown in the Basic

hop/M hop diagram.

M portIn a Fiber Distributed Data Interface (FDDI) network, extra port on a concentrator for attaching other nodes in a branching tree topology

Mports can be on both single attachment and dual attachment concentrators The M port is an addition

to the basic FDDI network On a dual attachment sta-tion (DAS), a redundant link can be created by con-necting the A and B ports on different concentrators

on theMports On a single attachment concentrator, theMport may be connected to the Sport.Mports are never connected to one another The other end of theMport may be attached to a patch panel through

a data grade cable See Aport

M Ports in FDDI Ring-Based Network

A and B ports are the main points ofentry 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.

Fiber Optics Illustrated Dictionary

P~rformaJl.cemonitoring·Qn

il'ltemati9Ail·traIlsmissiQl1systemsand equipment

·Principlesconcemingline-up and maintenance limits

I.Jseof telecom.· terms for maintenance

Maintenaric~tenninologyand

definitions Guidingprinciples on general tnaintenanceorganiz fortelepbone-typeil1t~rp~tion~l ~rcuits

~echnicalservice

Controlstations Faultreport points Sub-control stations Service circuits Circuit testing Access points for maintenance pigitalloopback mechanisms

$tabilityoFtransmission Bringing newintemational transmissionsystem into service

supergroup,etc.links int()service Settingupf;lDdlining uP analog channels for international telecom services

~~ttingup~dliningupmixed analogi

digitalchantl~l&forinternational

telecom.services Transmission restoration and transmission route diversity:

tertllillology:a~d g~neralprinciples Functionalorganiz for automatic transmission restoration

M.70

M.SO

M.60

M.3604Applicationofmaintenance principles

toISDN primary rate access M.360S ~pplicatio~ofmaintenanceJJrinciples

tostaticm141tiplexed ISDN basic rate access

M.3610 Principles forapplyingTMN concept

to.the managementalB-ISDN

M:.36111estI11an~$etnf'Ilt ofl~.ISDNATM

layer usingth~TMN

M.3620 Principles for the use of ISDN test

M.3621.•• Itltegra.t~dp;:l~ageDlent()fISDN

customer·access M.3640 Managemelltofthe D-channel -data

link layer a.g.d network layer M.3641Mana.gement info 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 ofsupergroups within

mastergroup

Nl.1ffib~r1ll~ ofm~t~fgrouPs within

superrn~t~~gr(,')~l?

Nqmberjng in coaxialsystems

Numbering in systems on symmetric

pairc~ble

Numberinginradj~~relay Hnk:$or

open"\Vire line· systems

Numberingofdigitalblocks in

transmissionsys~ms.

ISDN

M.400

M.410

M.380

M.390

Scope, Philosophy, General Principles

M.3600 Princ~plesfor tnal'1agementofISDNs

M.3602 Application of maintenance principles

to ISDN subscriberinstallations

M.3603 Applic;atiollpfIAAintellanpepJ"iIwiples

toISDN basic rate··access

ITU-T M Series Recommendations

M;··l·O Scope••••lt.tid·•.•appliQ~~jpl1···.of

recori:unendationsfOrmaintenariceof

telecom.t1etworksand·services

M.lS Maintenance.considerationsfOfl1ew

systems

M:20 Maintenancepbilq$ophy fortelecom

networks

servi(:es • • ••• • ··0<·:

M.·32rtjnciples··for·using···.·~arm····info.·(or.·· ·•.·

.maintenance·of international

transnlission systems and equipment

M.S60 InteI'IJ.lltional telephollecircuit&v

prillciples,.defi~iti9nSt··at1dr~lative

transmission levels

M.1130 General· definitions andgeneral

principles of operation/maintenance

proq~q.to b~ us,~clip$~tellitemQ~ile

systems

M.1140 Maritime mobiletel~com.servicesvia

satellite

M.1301 General clescriptioJiandoperational

circuits

M.1535 Principles for maintenance info tobe

exchanged at customer contactpoint

(MICe)

M.tS3? Defiriitionof mllinttel1anceinfotobe

exchanged at customer contactpoint

(MICe)

M.3100 Generic networkinfo.model

M.~600 Principles·.form~g~tl1ent·QfISDNs

Numbering

M.320

M.330

M.340

M.3S0

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