L Band -Layer 7 Switching

L Band

  1. A band of frequencies in the 0.5 to 2 GHz range that are used primarily for voice communications.

  2. Long Wavelength Band. The optical band, or window, specified by the ITU-T at a wavelength range between 1565nm and 1625nm (nanometers) for fiber optic transmission systems. See also C-Band, E-Band, O-Band, S-Band, and U-Band.

L Card

Analog Line Card.

L Carrier

A long haul frequency division multiplexed coax-cabled long haul carrier system. It was first introduced just before the second World War. Eventually it grew to a capacity of 13,300 voice channels over a pair of coaxial tubes. L Carrier systems are still used today. They are the most widely-used analog long distance transmission system.

L Multiplex

A system of analog multiplexers built up through groups, supergroups, master groups and jumbo groups of circuits. See L Carrier.


See L Band.

L-to-T Connector

A device that mates two FDM (Frequency Division Multiplexed) groups with one TDM (Time Division Multiplexed) digigroup to allow 24 voice conversations in analog form to talk to (tie into) a DS-1 line ” a T-1 line.

L2 Cache

Level 2 Cache A type of cache, normally external in nature. But some manufacturers are building internal caches to speed up computer processing. L2 cache speeds up processing an average of 25% over an external L2 cache


Layer 2 Forwarding: VPN protocol used to establish connectivity between Host / Service provider in an Overlay or Peer-to-Peer VPN model. Similar to L2TP. (Layer 2 Tunnel Protocol.)


Layer 2 Tunneling Protocol. An IETF (Internet Engineering Task Force) standard tunneling protocol for VPNs (Virtual Private Networks). L2TP evolved from a combination of PPTP (Point-to-Point Tunneling Protocol) and the proprietary Layer 2 Forwarding (L2F) protocol from Cisco. L2TP is implemented by ISPs (Internet Service Providers) to provide secure, node-to-node communications in support of multiple, simultaneous tunnels in the core of the Internet or other IP-based network. End user access to the ISP is on an insecure basis. The ISP assumes responsibility for encryption at the network edge. See also IETF, L2F, PPTP, Tunneling, and VPN.


An acronym for layer 3 switching. See Layer 3 and Layer 3 Switching.


Later. Shorthand added to an email.


Listed Address.


A set of symbols used to identify or describe an item, record, message or file. It can also be the same as the address in storage.

Label Forwarding Information Base


Label Swapping

Routing algorithm used by APPN in which each router that a message passes through on its way to its destination independently determines the best path to the next router.

Label Switch Router

LSR. A device located in the core of the network that switches labeled packets according to precomputed switching rules. This device can be switch or a router. Also see Multiprotocol Label Switching (MPLS).

Labeling Algorithm

Algorithm for shortest path routing or similar problems which labels individual nodes, updating labels as appropriate to reach a solution.


LATA Architecture Database.


  1. Local Area Data Transport. One of a number of similar names for LEC service offerings of in-city data transport using baseband (short haul) modems rented from the LEC, with names such as LADS (Local Area Data Service) being typical. See also WAN.

  2. AT&T's product name for providing simultaneous voice and data (see SAD) by Frequency Division Multiplexing 4800 bps data above speech signals on a two-wire voice telephone exchange line; when used in combination with Centrex and a data PBX in the LEC's exchange building, the resultant data operation is called Datakit.


Location Area Identity. A wireless term . A LAI is part of GSM (Global System for Mobile Communications), used in the radio interface. An LAI is part of the GSM Temporary Mobile Subscriber Identity (TMSI). The TMSI is allocated by the GSM network on a location basis. More simply put, it identifies the cell that a mobile telephone user is in.

Lake Wobegon Effect

The tendency to treat all or most members of a group as above average, especially with respect to test scores or executive salaries; in a survey, you can see the Lake Wobegon Effect in the tendency for most people to describe themselves or their abilities as above average.


Local Automatic Message Accounting. A process using equipment in the central office which records the information necessary to bill your local phone calls by your local phone company.

Lamarr, Hedy

Silver Screen actress Hedy Lamarr (born 1914) enjoyed one of the more memorable careers in Hollywood. Her name still ranks among the brightest lights in the history of movies. But what many people may not know is that she helped the United States win World War II. On June 10, 1941, Lamarr and composer George Antheil received Patent No. 2,292,387 for their invention of a classified communication system that was especially useful for submarines. The system was a stroke of genius. It was based on radio frequencies changed at irregular periods that were synchronized between the transmitter and receiver. While a message was being sent, both the transmitter and the receiver would simultaneously change radio frequencies according to a special code. At each end of the transmission, identical slotted paper rolls, similar to those used on player pianos, dictated the code according to their pattern of slots. Just as a player piano holds and changes notes at different intervals to make a melody, their invention held and changed radio frequencies to make an unbreakable code. Signals could be transmitted without being detected , deciphered or jammed . See Frequency Hopping.


The 11th letter of the Greek alphabet. Lambda is used as the symbol for a wavelength in lightwave systems. A single strand of fiber typically carries many different colored wavelengths of light. The process is called WDM (Wavelength Division Multiplexing) or DWDM (Dense WDM), with each range of wavelengths appearing in a "window," roughly corresponding to a color in the visible light spectrum. Light wavelengths are measured in nanometers, with a nanometer being one billionth of a meter. Each wavelength is now called a lambda. When you hear a telecom carrier selling lambdas, it means he's selling the capacity of one or more wavelengths of information-carrying capacity. See also DWDM and Lambda Switch.

Lambda Miles

The measurement, in miles, of individual wavelengths transmitted within a single fiber (i.e., fiber miles multiplied by Wavelength Division Multiplexing channels).

Lambda Switch

A type of switch which is capable of switching light signals. Such a switch is capable of identifying different wavelengths (frequencies) of light, which roughly correspond to visible colors in the light spectrum. In a fiber optic transmission systems employing DWDM (Dense Wavelength Division Multiplexing), the lambda switch would identify those separate wavelengths of light in an incoming fiber and perhaps switch each over a separate fiber on the outgoing side. Or perhaps a lambda switch would identify various data streams in multiple wavelength light streams, select those intended to travel in a particular direction, pluck them out and redirect them to a particular fiber going in the right direction, multiplex them, and shift them to a different wavelength. If this definition seems a bit fuzzy, it's because there is no such thing as a lambda switch at the time of this writing...at least not one that's commercially available. But, that is expected to change by 2005 or so. See also Lambda, DWDM, SONET, and WDM.


A word created by George Gilder to celebrate the idea of pumping multiple wavelengths of light down one thin strand of fiber. George writes , "On the Forum, in the Gilder Technology Reviews, in my books, and on the road, for the last decade I have been celebrating the lightwave or "lambda" network ” a circuit switched system as simple and robust and enduring for multimedia communications as the public switched telephone network has been for voice. Essential to fulfill the dreams and business plans of Internet entrepreneurs, such a broadband bonanza can spur the economy out of its current doldrums. Enabled by Wavelength Division Multiplexing (WDM) many colors of infrared light on each fiber thread, this new lambdasphere can both fuel and fund a multi-trillion dollar agenda for thousands of vendors of optical equipment over the next decade."


The correct spelling is Lambda. See Lambda.


A user who behaves in a stupid or uneducated manner.

Lame Bug

A fancy way of saying that a piece of software contains a bug, but the bug is so bleeding obvious and so minor it should have fixed eons ago by the programmers. I first heard this term from Sean Purcell, a smart fellow working on the excellent product called Outlook from Microsoft.

Lame Delegation

On the Internet, there are Domain Name Servers, also known as resolvers , which are a system of computers which convert domain names (like www.HarryNewton.com) into IP addresses, which consist of a string of four numbers up to three digits each. Each applicant for a domain name must provide both a primary and a secondary DNS server. A domain name which fails to provide both primary and secondary DNS servers and thuse whose Name Server Record points to an incorrect server is known as a "lame delegation." This can be caused when a zone is delegated to a server that has not been properly configured to be authoritative (i.e. to work) for the zone. A server that is authoritative for the zone has an NS record that points to another that is not authoritative for the zone. This will cause resolvers to direct queries to servers that will not respond authoritatively, if at all. This causes unnecessary network traffic and extra work for servers. ONe quarter of all zones allegedly have lame delegations. See also DNS.


The whole structure in the mold, consisting of several piles. A layer in a composite is called a "ply."


Thin sheets of steel used as the magnetic core in electrical apparatus, (e.g., the core of an audio frequency transformer is normally composed of laminations).


The technically correct term for light bulb, which nontechnical folks put into their lamps.

Lamp Battery

A steady (unpulsing) 10 volt AC source of power to operate the lamps in key telephone sets; usually one of the outputs of the local Key System Power Supply.

Lamp Flash

A pulsed 10 VAC source of lamp power sent to a key telephone set to indicate a CO or PBX line is ringing in. Pulse repetition rate is normally 60 Hertz with a duty cycle of .5 sec on and .5 sec off. This signal is usually provided by the local Interrupter KTU.

Lamp Leads

Lamp and Lamp Ground (L&LG) wires connected to all lamps in the key telephone set over which steady and pulsed 10 VAC signals from the Line Card KTU are sent.

Lamp Steady

A steady (unpulsed) 10 VAC source of lamp power sent to a key telephone set to indicate that the line is in use. See also Lamp Battery.

Lamp Wink

A pulsed 10 VAC source of lamp power sent to a key telephone set to indicate that the line is on Hold status; pulse repetition rate is normally 120 Hertz with a duty cycle of .4 sec on and .1 sec off. This signal is usually provided by the local Interrupter KTU.


Line Adapter Modules.


Local Area Network. A fancy name for a communications network connecting personal computers, workstations, printers, file servers and other devices inside a building or a campus. Devices on a LAN can transmit between each other. They can see each other email. One PC can send another a file. One PC can print to any number of printers connected to the LAN ” high-speed ones, expensive color printers, etc. Devices on one LAN can often transmit to the outside world if the LAN is connected to a telecommunications link to somewhere. That "somewhere" might be a link to the Internet. It may be a link into the corporate network, which would let this LAN connect to a LAN across the country. That connection is called a "WAN," which stands for wide area network. LANs come in many flavors. But by far the most popular is Ethernet. LANs have come a long way. LAN software used to be difficult to install and expensive to buy. Now all Windows software and Apple computers have built-in LAN software. To install a LAN in your office or home, you'll need LAN network adapter cards for each PC (some already come with them), sufficient wiring and devices known as "hubs," which do what hubs for the railroads ” move trains from one track to another. For a more detailed explanation, see Hub, Ethernet and Local Area Network. See also AppleTalk, Ethernet, LocalTalk and token ring.

LAN Adapter

Also called a NIC card. A LAN adapter is a a PC-compatible circuit card that provides the PC-to-LAN hardware connection. In addition, LAN software drivers and LAN operating systems need to be run on the PC for it to function as a LAN station. See LAN.

LAN Aware

Applications that have file and record locking for use on a network.

LAN Emulation

Also known as LAN-E, it is a set of specifications developed by the ATM Forum for the operation of LAN-to-LAN bridged connectivity over an ATM network, allowing ATM to be deployed on a legacy LAN or with legacy LAN applications.

LAN Ignorant

Applications written for single users only. These are not recommended for use on LANs (local area networks).

LAN Intrinsic

Applications written for client-server networks.

LAN Manager

  1. A person who manages a LAN. Duties can includes adding new users, installing new hardware and software, diagnosing network problems, helping users, performing backup and setting up a security system. Unlike MIS managers, LAN managers are rarely formally trained in LAN management. Sometimes they're called LAN Network Managers.

  2. The multi-user network operating system co-developed by Microsoft and 3Com. LAN Manager offers a wide range of network-management and control capabilities. It has been superseded by Windows NT Advanced Server.

LAN Network Manager

An IBM-developed network management tool. It is a software program that runs under OS/2 and which provides management and diagnostics tools needed to manage a Token Ring LAN. A PS/2 running LAN Network Manager collects vital statistics and special management data packets on the ring to which it is connected. When multiple rings are involved, the LAN Network Manager relies on the token ring bridges and routers to help in managing those token ring LANs that are not directly connected to the LAN Network Manager station. IBM has installed software in its bridges called the LAN Network Manager Agent. The agent software acts as the eyes and ears for the LAN Network Manager station so that the station can manage the remote rings as if it were connected directly to them. If there were no such agents , managers of networks would be blind to what's going on these LANs. Remote management with LAN Network Manager includes the ability to perform ring testing, analyze traffic and error statistics, and force adapters off the network.

LAN Server

IBM's implementation of LAN manager, now largely superseded by OS/2 2.1.

Land Attack

A land attack occurs when a malicious person sends instructions over a network to a server attempting to crash the server. Officially known as land.c code, Land Attack works by tricking the targeted server into trying to set up a TCP session with itself. If the machine falls for this form of IP spoofing, it goes into a TCP closed loop and has to be physically rebooted. A number of security experts, including Chris Klaus, chief technology officer at Internet Security Systems, Inc., agree there is no reason a machine would want to talk to itself like this. Systems should be designed to prevent such attacks.

Land Line

See Landline , the preferred spelling.


Local Area Network Dealers Association. It runs a number of excellent trade shows each year. Its members are LAN resellers , distributors , manufacturers, and consultants . In 1993 it merged with NOMDA, the National Office Machine Dealers Association. And shortly, thereafter, NOMDA/LANDA changed its name to the Business Technology Association, headquartered in Kansas City. www.btanet.org. See BTA.


Also referred to as Land Line. A terrestrial circuit, whether wired (i.e., twisted pair, coax, or fiber) or wireless (i.e., microwave or some other form or radio, or free space optics), or some combination. A landline is different to a satellite link, which is not terrestrial in nature.


Most computer screens are horizontal, i.e. they are wider than they are high. In the new language of computer screens, such screens are called "landscape." When a computer screen is higher than it is wide, it's called "portrait." Some computer screens can actually work both ways. Some even have a small mercury switch in them that determines which way the screen is standing (portrait or landscape) and will adjust their image accordingly .


An ATM term. LAN Emulation: The set of services, functional groups and protocols which provide for the emulation of Ethernet and Token Ring LANs over an ATM backbone. Operating at the Link Layer (Layer 2 of the OSI Reference Model), LAN Emulation takes over the MAC (Medium Access Control) layer function found on Ethernet and Token Ring NICs (Network Interface Cards). LANE supports connectionless service in either a broadcast or multicast mode. The network addresses of the LECs (LAN Emulation Clients are resolved through a LES (LAN Emulation Server), by virtue of a LUNI (LAN emulation User-to-Network Interface), as defined by the ATM Forum. The LES maintains a table of MAC-to-ATM addresses in order that the native MAC addresses of the LAN-attached devices (e.g., workstations) can be mapped into ATM addresses, with the process being reversed on the destination end of the transmission. Another server, known as a BUS (Broadcast and Unknown Server) handles data addressed to the MAC broadcast address, all multicast and unicast traffic sent by a LEC prior to the establishment of an ATM address for the destination LEC. As a Layer 2 ATM service, LANE functions only within a single ELAN (Emulated LAN) environment, but offers significant advantage in the establishment of a VLAN (Virtual LAN) consisting of multiple physical LAN segments interconnected over the WAN via an ATM VC (Virtual Channel). LANE is not simple and is prone to bottlenecks, but is a cool way to internetwork LANs over ATM. MPOA (MultiProtocol Over ATM) is even more cool, as it operates at the Network Layer (Layer 3 of the OSI Reference Model). Thereby, MPOA overcomes the limitations of LANE by supporting multiple network protocols such as IP, IPX, and AppleTalk. See also MPOA.


A single interactive multimedia network.


Computer software that allows you to write programs.

Language Interpreter

Any processor, assembler or software that accepts statements in one software language and then produces equivalent statements in another language.


Local Automatic Number Identification.


Link Access Procedure.


LAPB. Link Access Procedure Balanced, the most common data-link control protocol used to interface X.25 DTEs with X.25 also specifies a LAP or link access procedure (not balanced). Both LAP and LAP-B are full-duplex , point-to-point bit-synchronous protocols. The unit of data transmission is called a frame. Frames may contain one or more X.25 packets. LAP-B is the data link level of X.25 in a packet switched network. Same as a subset of the asynchronous balanced mode of HDLC. It is the link initialization procedure that establishes and maintains communications between the data terminal equipment (DTE) and data communications equipment (DCE). All public packet data networks (PDNs) support LAPB.


Or LAPD. Link Access Procedure-D. Also called Link Access Protocol for the D channel. Link-level protocol devised for ISDN connections, differing from LAPB (LAP-Balanced) in its framing sequence. Likely to be used as basis for LAPM, the proposed ITU-T modem error-control standard.


The increasingly common practice, especially in airports, of stealing laptop computers. Definition courtesy Wireless Magazine.


Laplink is originally the name of a DOS program that transferred files between laptop and desktop computers. It came with a special cable that attached from one computer's serial port to the other. You plugged the cable in, loaded the LapLink software and transferred files back and forth. You could do the transferring from either machine. It was a nifty program, the brainchild of Mark Eppley and he formed a company to sell it, called Traveling Software in Bothell, WA. Eventually the program became so successful that the word "to laplink" became a common verb to connote the transferring of files between computers, as in "I'll go laplink these files over to Mary's machine." Eppley's program is now in Windows format. You can transfer across a parallel port cable (which is faster than the serial port). You can also transfer files across phone lines and network links. You don't even have to be in the same city to transfer files. And Eppley has a new feature called SpeedSync that cuts transfer time down by sending only the changed parts of the file. We used to use LapLink every day. But when it became too complex, we switched to Powerdesk and email for file transfer and FileSync for backing up files. We still use Laplink III occasionally.


Link Access Procedure for Modems. A type of error control used in V.42 and V.42bis modems. LAPM uses the Automatic Repeat Request (ARR) method, whereby a request for retransmission of an errored data frame is automatically requested by the receiving device. As I was writing this entry, a reader asked "if I can transmit HDLC format data thru the GSM network. The data sheet for one of the GSM engines states it can handle V42 bis data transfer." According to Ray Horak, LAPM and both V.42 and V.42bis are specifically linked. If GSM supports v.42, then it supports LAPM, by definition. Such modems also use HDLC frames, which and are synchronous modems, by definition. Therefore, he should be able to accomplish all of this via GSM, as best I can determine.

Laptop Computer

A portable computer you can use on your lap. Also called a notebook. Usually a laptop weighs fewer than than ten pounds. Mine weighs eight pounds . Laptops weighing fewer than four pounds are called subnotebooks. To get a laptop to weigh that little, you typically have to sacrifice something ” the floppy disk drive and the CD-ROM drive, for example. Laptops are probably the most useful gadget to come along in years . I wrote much of this dictionary on a laptop in planes, trains, airports, etc. My laptop has a data modem and an Ethernet network card. I don't own a desktop. I do all my work on my laptop.

Large Squaring Capability

A feature on some key systems which permits all lines to appear on all telephone sets.


An acronym for Light Amplification by Stimulated Emission of Radiation. It is a device which produces light. Tunable lasers can produce light of a single frequency, or visible color, in human terms. By turning the laser light signal on and off quickly, you can transmit the ones and zeros of a digital communications channel. Lasers carried through glass fiber are ideal for telecommunications transmission for two major reasons.

  1. Glass fiber of such purity has now been developed that only a very minute portion of the laser light traveling through it is lost. In telecom terms, this means very little of the laser signal is attenuated, or loses power. The signal maintains its strength and thus reduces the need for frequent and expensive repeaters (the digital word for " amplifiers "). Laser transmission systems can now carry many thousands of voice conversations for hundreds of miles without repeaters on two fibers no thicker than a human hair. (You need two fibers ” one for transmission in each direction)

  2. The glass fibers in laser fiber optic telecom systems are totally immune to electromagnetic interference of any kind. There's no humming from electrical motors. You can't pick up the local TV station in the background. You can't pick up any interference from adjacent cables. In recent years, laser fiber optic transmission has been getting cheaper, more reliable and more powerful at roughly the same rate as computers, and like computers, nobody believes there is an end in sight. As we were writing the first edition of this dictionary, Russell Dewitt of Contel (since acquired by GTE, since acquired by Bell Atlantic, now renamed Verizon) delivered a paper entitled Evolution of fiber optics in rural telephone networks. In it, he talked about "Fiber Optics Progress" and said: "In 1860, the Pony Express could deliver a letter from St. Louis to San Francisco in ten days. For three typed pages the data transmission rate was about three bits per minute. In comparison, today in Contel we are transmitting at the rate of 565 Mbps (million bits per second) over single mode fiber. This is a capacity of 8,064 voice channels. Gigabit per second systems will be available for use this year (a gigabit is a thousand million bits) and a 20 Gbps system has been demonstrated in the laboratory. For the future, the ultimate potential of a single mode fiber has been estimated. It is about 25,000 Gbps (25,000,000,000,000 bits per second). At that rate you could transmit all the knowledge recorded since the beginning of time in 20 seconds."

That sounded pretty incredible a few years ago, and it was. SONET (Synchronous Optical NETwork) optical fiber systems currently run at speeds up to 40 Gbps on a single lambda (i.e., wavelength of light). DWDM (Dense Wavelength Division Multiplexing) hundreds of lambdas can be multiplexed to yield aggregate speeds in the range of Tbps, at least in the labs. Free-space optics systems are used in WLL (Wireless Local Loop) applications, routinely running at speeds up to 622 Mbps, with some running at up to 1 Tbps. Free-space systems run over distances of up to several miles through the air, with no associated requirement for trenching or planting poles, splicing fibers, etc. See also DWDM, Laser Diode, Laser Fax, LCD, LED, Fiber Optics, Free-Space Optics, Single Mode Fiber, and SONET.

Laser Diode

Conceptually similar to LEDs, Laser Diodes are the light sources in high- speed fiber optic systems. While LEDs are limited to transmission rates of 500 Mbps or so, Laser Diodes operate at speeds of many Gbps.

Laser Fax

A conventional laser printer that is also capable of being used as a FAX machine when combined with an optional plug-in cartridge and used with a personal computer.

Laser Optical

System of recording on grooveless discs using a laser-optical-tracking pickup. Originally, the technology was WORM ” Write Once (i.e. not erasable) Read Many. It's now erasable.

Laser Printer

A high speed non impact dot matrix printer which uses a laser beam to electrostatically form characters on paper. The printer then heats the paper which melts a metallic dust attracted to the electrostatic areas which form the inked images on the paper. Laser printers are fast and the quality of their printing beautiful, rivaling that produced by conventional photo typeset (the way this book was produced).


Attachment of a cable to a support strand by wrapping steel wire or dielectric filament around the cable.

click to expand

LASIK Surgery

Laser in Situ Keratomileusis. Eye surgery using a laser which corrects vision problems by sculpting the cornea.


See Local Area Signaling Services.


Local Area Systems Technology. A Digital (DEC) protocol.

Last Digit Dialed Signal

Allows the use of the # sign on Touchtone telephones to indicate that the last digit has been dialed on outgoing calls. This signal enables the PBX to process calls more rapidly , since some PBXs count the time after a digit was dialed. If nothing else is dialed within a certain time, it assumes that the dialing is complete and then pulses out the call.

Last Extension Called

Same as Last Number Redial.

Last In First Out

LIFO. The last phone call (or data) arriving is the first call (or data) to leave ” to be processed , to be saved, whatever. The term LIFO comes from accounting. It's one of several ways to value an inventory. See also FIFO.

Last Known Good Configuration

In Microsoft Windows NT, the last configuration that was used to boot the computer successfully. Windows NT saves this configuration and offers it as a startup option during the boot process.

Last Mile

"Last mile" is an imprecise term that typically means the link between an end-user and the telephone company central office ” local, long distance or Internet. Of course, it doesn't mean a "mile," since that "mile" could be less than a mile or several miles. The term has entered the language referring to the problems of your telecommunications making it that last mile at a price you can afford and using a modern technology. Let's take price first. Competition in telecom has been heavily concentrated on long distance and international hauls. Carriers in long distance and international have relied on local phone to deliver their customers' communications. Since there was little competition, the price has often been very high. Second, there's the issue of the technology and quality of that last mile. Often that last mile runs over old, limited bandwidth copper wire that has been in the ground for eons and is supplied by a sleepy phone company who doesn't have any competition and not much incentive to perform and hasn't improved the quality of the cable in the loop. This changing slowly. In early 2003, Motorola introduced radio equipment to solve the last mile problem (i.e. you could use their equipment to bypass the local phone company). They changed the name of the "last mile" and called it the "first mile." I thought this was an innovative use of the language.

Last Number Redial

Most modern electronic phones have a button on them called "Last Number Redial." When you touch this button, your phone will automatically dial the last number you dialed. If you also have speed dial numbers on your phone, any number you dialed with a Speed Dial button will not appear in Last Number Redial. Most Last Number Redial buttons on electronic phones attached to a PBX will only recognize completely-dialed numbers. Last Number Redial buttons are useful. Also useful ” but less common ” is a stored number dial button. Dial a number, punch in "save," then that number will be saved to that button, ready to be dialed later, even though you might dial some other numbers in the meantime.

Last Piece of Unfinished Business

What Joel Novak's mother used to call him before he finally succumbed and got married.


  1. Local Area Transport. A proprietary communications protocol developed by DEC for terminal-to-host communications. LAT allows terminal emulators to access VAX and VMS systems over Ethernet. See LAT Protocol.

  2. A proprietary protocol used in Digital Equipment Corp. terminal servers, providing communication for terminals across an Ethernet LAN. See LAT Protocol.

LAT Protocol

The LAT protocol, announced by Digital Equipment Corporation in the mid-80s, is today one of the industry's most widely used protocols for supporting character terminals over Ethernet networks. LAT is currently licensed by more than 40 third party hardware and software developers, and is compatible with the products of more than 30 major system vendors, from Apollo, and Apple to IBM, Tandem and Wang. The basic function of the LAT protocol is to permit a terminal server to connect multiple asynchronous devices ” video display terminals, printers or plotters ” to a host timeshare computer. To do this, LAT (or any other terminal server protocol) puts data into packets that can be understood by both the asynchronous device and the host. Essentially, a terminal server protocol is responsible for establishing lower level communications connections, and for routing appropriate transmissions to their destinations.


Local Access and Transport Area, also called Service Areas by some telephone companies. One of 196 local geographical areas in the US within which a local telephone company may offer telecommunications services ” local or long distance. At one stage, AT&T was expressly prohibited from offering intraLATA calls by the terms of the Divestiture. But it is now allowed to offer intraLATA phone calls. Other competitors , such as MCI and Sprint, though rules vary by state, have always been allowed to offer intraLATA phone calls and do so in many states. LATAs serve basically two purposes. First, they provide a method for delineating the area within which the Bell Operating Companies may offer service. Second, they provided a basis for determining how the assets of the former Bell System were to be divided between the Bell Operating Companies and AT&T. While writing this edition of the dictionary, Ray Horak and I got into an argument about LATAs. I thought there were fewer than 196 LATAs. But Ray researched the subject to death and affirms 196 is the correct number. In the midst of his research, he sent me the following memo:

Dear Harry, I've got the story on LATAs...and it is very strange , indeed! There originally were 161 LATAs established by the MFJ. Those LATAs were identified by three-digit codes, as follows : 1xx designated NYNEX (now Verizon) LATAs; 2xx, Bell Atlantic (now Verizon);, 3xx, Ameritech; 4xx, BellSouth; 5xx Southwestern Bell; 6xx, US West now Qwest); and 7xx, Pacific Telesis (now SBC). 8xx was assigned by Bellcore (now Telcordia Technologies) to areas such as the Commonwealth of North Mariana Islands, Midway/Wake, Guam, and other Caribbean islands. 9xx was assigned by Bellcore to areas covered by Southern New England Telephone (SNET), Cincinnati Bell, and the Navajo Nation (one LATA in Arizona and one in Utah). Since the initial designation of LATAs, a number of subLATAs have been identified, for a variety of reasons.

There are 17 subLATAs in Florida, mandated in 1984 by the Florida Public Utilities Commission for equal access purposes. There are 23 "900" LATAs set aside for places like SNET (CT), Cincinnati Bell (OH), and the Navajo nation (1 in AZ and 1 in UT). Add to that the "800" LATAs for Puerto Rico, the Virgin Islands, the Bahamas, Jamaica, AK, HI, and the various other Caribbean, Atlantic and Pacific Islands and it gets very strange. Most of these are pseudo-LATAs set up by Bellcore for toll routing purposes, especially since many of the island nations were only recently added to the NANP. Equally interesting, if not more so, is the story on the 8xx area codes. There are 8 NPAs in the 8xx range ”with 1,298 NXXs ” set aside for "non-dialable toll points." These are remote areas served by a cord- board. The subscribers are reached from the cordboard via ring-down circuits.

Late Collision

A networking term. Late Collision is an Ethernet collision that takes place on the local segment after 64 bytes of a frame have been placed on the network by the originating device. Late collisions are usually detected only on coax networks, because the 10Base-T monitor station would have to be transmitting at the same time in order to detect a late collision. Late collisions may also be inferred by detecting the presence of a "jam" signal at the end of a frame that is larger than 64 bytes. Note that traditional Ethernet (versus Gigabit Ethernet) specifies a frame size minimum of 64 octets (bytes) and a maximum of 1,514 octets. Also note that a single logical Ethernet may comprise multiple physical segments, with the segments being connected by bridges, hubs, switches or routers. If all of this seems a trite confusing, it's because it is. At some level, however, it's really pretty simple. First, it takes a certain amount of time for a data bit, and certainly a frame of data bits, to propagate (move) across a wire and through all of the intermediate devices that might be involved. The original Ethernet standard specifies big, thick coaxial cable that will support LAN (Local Area Network) communications over a maximum reach of 2.5 kilometers, from one extreme end of the cable to the other. As many as 1,024 devices may be attached, each with a minimum spatial separation of one meter (due to issues of echo, or signal reflection) and with a maximum spatial separation of 500 meters (due to issues of signal attenuation, or power loss). In the most extreme case, therefore, as many as 1,022 devices might be positioned between transmitting device and receiving device. Each device must read the incoming frame of data, determine if it is intended for it, and, if not, pass it on. This process takes some time, and it takes some time for the frame of data to work its way across the wire to the next device, where the process is repeated. Second, Medium Access Control (MAC), or collision control, technique used in Ethernet is CSMA/CD (Carrier Sense Multiple Access with Collision Detection). CSMA/CD allows multiple devices to sense the status of the carrier frequency to determine whether it is "clear" to send a frame of data. Assuming that they sense that it is "clear," they can access the wire at their own option, and at their own risk. If multiple devices access the wire at about the same time, a collision is likely. All attached devices constantly monitor the wire. If a collision is detected, they broadcast a "jam" signal, or collision detection, over a separate subcarrier frequency. All attached devices also monitor the subcarrier frequency, and adjust as necessary, backing off and re-accessing the wire when it becomes available again. Third, a transmitting device is assumed to be transmitting a series of frames of data. The series of frames is assumed to be associated with the transmission of a set of information, which is organized into frames of certain minimum and maximum sizes, 46 bytes and 1,500 bytes, respectively. Small sets of information, such as a query, are very small. Some sets of information, such as file transfers, are potentially very large, and are fragmented into data frames of as much as 1,500 bytes, plus overhead. The maximum size of 1,500 is set so that no single transmitting device can lay claim to all of the capacity of the network, thereby giving other devices a chance. The minimum size is mandated so that a device can be advised of a collision, and have a chance to adjust in that event, and before it assumes that the first frame was received without collision. When you extend the traditional Ethernet with intermediate hubs and switches, you mess with the original concept, and with the underlying physics of signal propagation, which is tuned to network length and link length and number of attached devices and the processes, all of which is tuned to minimum and maximum frame sizes, in consideration of assumptions about the supported applications. It's all very confusing at some level, but relatively simple at another. Read this lucid explanation by Ray Horak several times. You'll get it. See also Ethernet and CSMA/CD.

LATA Access

Any activity or function performed by a local phone company in connection with the origination or termination of interLATA telecommunications for an IC. This includes, but is not limited to, the provision of network control signaling, answer supervision, automatic calling number identification, carrier access codes, directory services, testing and maintenance of facilities, and the provision of information necessary to bill customers. See LATA.

LATA Tandem

LT. An LEC switching system that provides an intraLATA traffic concentration/distribution point for end office switching systems or other tandems within a LATA.

Late Target Channel Keyup

A cellular term. A condition when the target cell does not receive the execute target order in time for the arriving mobile, caused by link delays between MTSO and target cell site. After the mobile retunes to the target cell, noise will be heard on the downlink audio from the target cell, as the assigned voice channel is not on the air (yet). This results in noise during the handoff .


A fancy term for waiting time or time delay. The time it takes to get information through a network. Real-time, interactive applications such as voice and desktop conferencing are sensitive to accumulated delay, which is referred to as latency. For example, telephone networks are engineered to provide less than 400 milliseconds (ms) round-trip latency. You can get latency in several ways:

  1. From propagation delay ” the length of time it takes information to travel the distance of the line. This period is mostly determined by the speed of light; therefore, the propagation delay factor is not affected by the networking technology in use.

  2. From transmission delay ” the length of time it takes to send the packet across the given media. Transmission delay is determined by the speed of the media and the size of the packet.

  3. From processing delay - the time required by a networking device for route lookup, changing the header, and other switching tasks . In some cases, the packet also must be manipulated; for instance, changing the encapsulation type, changing the hop count, and so on. Each of these steps can contribute to the processing delay.

  4. Rotation delay. The delay in accessing data which comes from waiting for a disk to rotate to the currant location.

In a bridge or a router, latency is the amount of time elapsed between receiving and retransmitting the LAN packet. The length of time the packet is stuck in a bridge or router. See Interrupt Latency.

Latent Cooling Capacity

An air conditioner's capability to remove moisture from the air.


A fancy word for a trench. In the parlance of digging up roads and the countryside and laying cable, trenching (i.e. building a trench in which to lay cable) is often called "building laterals." As one wag put it, it's where the rubber meets the road as far as enterprise customers go.


The distance, expressed in degrees, from the Earth's equator to points North and South. The equator is assigned the value of 0 degrees; North and South poles are 90 degrees.

Lattice Tower

A Lattice tower is a self supported tower without guyed wires. There are generally three types of telecommunications towers : Monopole - Straight solid pole, Guyed Tower ” Tower with angled guyed wires attached to support it and Lattice ” which has an upside down V look to it.


Local Area Transport Tariff Information System.


A new term for starting a program from within another. Typically what might happen is you're working in a messaging program, which has individual lines showing you've just received several faxes, voice mails , electronic mail documents. You click on one of the lines. Your program recognizes that it's an electronic mail message and says "quickly open the electronic messaging software and get it to read the message." So it "launches" the messaging software.

Launch Fiber

An optical fiber used to couple and condition light form an optical source into an optical fiber. Often the launch fiber is used to create an equilibrium mode distribution in multimode fiber. Also called launching fiber.

Laurus Unit

A rack for T-1 interface units.


Local Area VAX Cluster.

Law of Unintended Consequences

this "Law" states that for every action, there is an excellent chance of producing an opposite and totally disproportionate reaction.

Lawn Sale

See Yard Sale.


Limited Airport Weather Station.


Action at law, attorney's apparel. In 1970, an Arizona lawyer named Russell H. Tansie filed a $100,000 damage suit against God. The action was filed on behalf of his secretary, Betty Penrose, who accused God of negligence in His power over the weather when He allowed a lightning bolt to strike her home. Ms. Penrose won the case when the Defendant failed to appear in court . It is not recorded whether or not she collected.


They're like nuclear warheads. They have theirs. I have mine. Once you use them, everything gets messed up. No one gains. ” Danny DeVito in Other People's Money.


A term used in cable manufacturing to denote the distance of advance of one member of a group of spirally twisted members, in one turn , measured axially. The term originally referred to the process of placing and twisting or braiding fibers to make ropes or hawsers.

Lay Length

Twist Length. The distance between twists in a twisted pair cable. For example, a cable with a lay length of 3 inches has 4 twists per foot (TPF). See also Twisted Pair and Twists Per Foot.


See Layering.

Layer 1

The OSI (Open Systems Interconnection) Reference Model, organizes the communications process into seven separate and distinct, interrelated categories in a layered sequence. Layer 1 is the Physical Layer (PHY). It deals with the physical means of sending data over lines (i.e., the electrical, mechanical and functional control of data circuits). T-carrier and SONET are examples of Layer 1 protocols. See also OSI Reference Model.

Layer 2

The OSI (Open Systems Interconnection) Reference Model, organizes the communications process into seven separate and distinct, interrelated categories in a layered sequence. Layer 2 is the Data Link Layer (DLL). It is concerned with procedures and protocols for operating the communications lines, including the detection and correction of message errors. X.25 and Frame Relay are examples of Layer 2 protocols. See also OSI Reference Model.

Layer 2 Switching

Switches run at Layers 1 & 2 of the OSI Reference Model, so Layer 2 Switching is just plain old switching. Layer 3, 4, and 7 Switching always involve routers, which are highly intelligent switches capable of running at higher layers. Layer 2 switches are simple, compared to routers. Since they run only at the Physical Layer (Layer 1) and the Data Link Layer (Layer 2), they don't make complex decisions. Rather, they simply receive incoming traffic, set up a path from incoming port to outgoing port through a switching matrix, and send it on its way. Layer 2 switches operate independently, although usually under the control of a centralized signaling and control system that coordinates their actions. Examples of pure Layer 2 switches include circuit switching and ATM. See also ATM, Circuit Switching, Layer 3 Switching, Layer 4 Switching, Layer 7 Switching, and OSI Reference Model.

Layer 2 Tunneling Protocol

L2TP. A networking protocol standard that can be used to route non-IP traffic over an IP network and to authenticate sends and receivers; L2TP can be combined with IPSec to provide greater security (e.g. data privacy) if needed. See L2TP.

Layer 3

In the widely-adopted OSI (Open Standards Interconnection) model, there are seven levels defined of interconnection. Layer 3 is the Network layer. It determines how data is transferred between computers. It also addresses routing within and between individual networks. See next definitions.

Layer 3 Switching

Layer 3 switching is a combination of Layer 2 switching and Layer 3 routing for use in large and complex internetworks, such as the Internet. Cisco generally is credited with inventing the concept through its development of the proprietary TAG Switching product line. TAG Switching, and competing product specifications, formed the basis for the IETF's specifications for MPLS (MultiProtocol Label Switching). Layer 3 switching typically makes use of both pure switches, which operate at Layers 1 and 2 of the OSI Reference Model, and routers, which are highly intelligent switches operating at least at Layers 1-3, and often capable of operating at all seven layers. Most commonly the routers are positioned at the edges of the networks, where they perform the processes of header analysis and packet priority assignment. As such processes can be quite complex, they can be fairly time-consuming , which translates into latency-inducing. The edge routers attach an abbreviated tag address to the front of the packet, and each packet associated with a given packet stream. In the core of the network, Layer 2 switches read the abbreviated tag address, and set up an appropriate link to the next switch, which repeats the process, and so on until the destination edge router is reached. The advantage of Layer 3 switching is that the complex (read slow and expensive) processes are performed only at the edges of the network by routers, thereby enabling simple (read fast and inexpensive) switches to perform their tasks with much greater speed. Overall, Layer 3 Switching integrates routing and switching to provide high-speed performance without the drawbacks of a of a flat Layer 2 network, including broadcast storms, address limitations and spanning-tree loops . Additionally, Layer 3 Switching can include traffic prioritization, security, and bandwidth allocation mechanisms. Layer 3 Switching can control larger network segments than Layer 2 Switching, thereby eliminating the need to create and isolate subnets. See also Layer 2 Switching, Layer 4 Switching, Layer 7 Switching, MPLS, and OSI Reference Model.

Layer 4

The OSI (Open Systems Interconnection) Reference Model, organizes the communications process into seven separate and distinct, interrelated categories in a layered sequence. Layer 4 is the Transport Layer, which defines the rules for information exchange and manages end-to-end delivery of information within and between networks, including error recovery and flow control. TCP (Transmission Control Protocol) is an example of a Layer 4 Protocol. See also OSI Reference Model.

Layer 4 Switching

Layer 4 switching refers to hardware-based routing that considers the application being processed prior to processing. In transmission control protocol (TCP) or user datagram protocol (UDP) flows, the application is encoded as a port number in the packet header. The switch then uses this information to make decisions on the flow of data. For example, the following applications are associated with the following port numbers:

Application: FTP

Port # 20





TCP provides transport functions that ensure the total amount of bytes sent is received correctly at the other end. UDP is an alternate transport that does not guarantee delivery. It is widely used for real-time voice and video transmissions where erroneous packets are not retransmitted.

Layer 5

The OSI (Open Systems Interconnection) Reference Model, organizes the communications process into seven separate and distinct, interrelated categories in a layered sequence. Layer 5, the Session Layer, is concerned with dialog management. Layer 5 controls the use of the basic communications facility provided by Layer 4, the Transport Layer. Specifically, Layer 5 deals with the establishment, maintenance, and termination of a session between computing nodes. See also OSI Reference Model.

Layer 6

The OSI (Open Systems Interconnection) Reference Model, organizes the communications process into seven separate and distinct, interrelated categories in a layered sequence. Layer 6, the Presentation Layer, deals with data formatting, code conversion (e.g., conversion between character coding schemes such as ASCII and EBCDIC), and compression and decompression . See also OSI Reference Model.

Layer 7

The OSI (Open Systems Interconnection) Reference Model, organizes the communications process into seven separate and distinct, interrelated categories in a layered sequence. Layer 7 is the Applications layer. It addresses functions associated with particular applications services, such as file transfer, remote file access and virtual terminals. File Transfer Protocol (FTP), Telecommunications Network (TELNET), and User Datagram Protocol (UDP) are all Layer 7 extensions of the TCP/IP protocol suite, which runs at Layers 3 and 4. See also OSI Reference Model.

Layer 7 Switching

A packet switching approach that differentiates between packet datastreams based on Layer 7 (Application Layer) information. In other words, information identifying the general nature of the application is used by the routers to set up a path that most closely matches the expectations of the application. Such information, which generally is buried deep in the packet header, includes H.323 or SIP (Session Initiation Protocol) information. Layer Switching also is known as Content Switching. See also H.323, Layer 2 Switching, Layer 4 Switching, Layer 7 Switching, MPLS, and OSI Reference Model, and SIP.

Newton[ap]s Telecom Dictionary
Newton[ap]s Telecom Dictionary
ISBN: 979387345
Year: 2004
Pages: 133

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