Layer Entity-LES

Layer Entity

An active element within a layer. See also OSI Reference Model.

Layer Function

A part of the activity of the layer entities. See also OSI Reference Model.

Layer Management

An ATM term . As described in the ATM Protocol Reference Model, Layer Management is an element of the Management Plane. Layer Management acts on the management of the resources at each of the various specific layers of the model. For example, Operation, Administration and Maintenance (OA&M) information is exchanged between the layers . See ATM Protocol Reference Model for a graphic representation of the three-dimensional model.

Layer Service

A capability of a layer and the layers beneath it that is provided to the upper layer entities at the boundary between that layer and the next higher layer.

Layer Service Provider

Each layer of the OSI Reference Model is a Layer Service Provider. Examples of layers are Presentation, Session, Transport, Network, and Link. The Layer Service is made available through Service Access Points. See also OSI Reference Model.

Layer User Data

Data transferred between corresponding entities on behalf of the upper layer or layer management entities for which they are providing services.

Layered Arrays

A large array that combines arrays instead of individual hard drives . This can improve performance and reliability but requires additional hard disks.

Layered Network Architectures

Currently the basis of all telecommunication network architecture standards, with functions allocated to different layers and standardized interfaces between layers. The OSI Reference Model and SNA (Systems Network Architecture) are examples of layered network architectures. See also Layering, OSI Reference Model, and SNA.


Layering is a technique to write complex software faster and more easily. Layering is often used with public, open software. The idea is to have layers of software on top of other layers. Each performs a specific task, yet each is interrelated to layers above and below it. The idea is that if your software works at one layer (i.e., conforms to the rules of that layer), it should be compatible with the layers of software above and below it. The most famous layered software model is the seven-layer OSI (Open Systems Interconnection) Reference Model. It breaks each step of a transmission between two devices into a discrete set of functions. These functions are grouped within a layer according to what they are meant to accomplish. Layer 2, the Data Link Layer, for example, is concerned with the transmission of frames of data between devices and covers protocols that are aimed at packaging raw data characters into frames, detecting and correcting errors when frames get lost or mutilated, arranging for retransmission and adding flags and headers so that DTE (Data Terminal Equipment) can recognize the beginning and end of a frame. Other layers serve other purposes. Each layer communicates with its counterpart through header records. The flexibility offered through the layering approach allows products and services to evolve . Accommodating changes are made at the layer level rather than having to rework the entire OSI model. Another layered software architecture is Microsoft/Intel's Windows Telephony. It has three layers. At the lowest is SAPI, which is the Service providers' API. In the center is the actual Windows Telephony code. At the top is the TAPI ” Telephony applications API. See also OSI Reference Model and Windows Telephony.

Laying Pipe

Deploying transmission facilities, most especially optical fiber. Carriers are laying a lot of pipe these days ” big pipes. If you were thinking of another definition, you should pray for forgiveness .


The twists in twisted pair cable. Two single wires are twisted together to form a pair; by varying the length of the twists , or lays, the potential for signal interference between pairs is reduced.


Leaky Bucket. An ATM term. Leaky Bucket is the term used as an analogous description of the algorithm used for conformance checking of cell flows from a user or network. The "leaking hole in the bucket" applies to the sustained rate at which cells can be accommodated, while the "bucket depth" applies to the tolerance to cell bursting above the rate of the ATM "contract" negotiated between the user premises equipment and the network over a given time period. ATM cells which exceed that limit are discarded at the network edge. In other words, they "leak" out of the bucket and spill out on the switchroom floor. See GCRA, UPC and NPC.


An abbreviation for Logical Block Address. See Logical Block Address.


Electrical Line Build Out.


Low Bit Rate Voice. Digitized voice that requires a bandwidth of fewer than 32 Kbps. LBRV digitizing techniques include packetized voice, APV, DSI, and LPC.


Location Based Services. See Location Services.


Local Calling Area.


Link Capacity Adjustment Scheme. LCAS is a non-standard technology proposed by a number of equipment manufacturers to improve the efficiency with which SONET (Synchronous Optical Network) transmission systems handle data traffic such as Ethernet. SONET supports payloads from 1.544 Mbps (T-1) or 2.048 Mbps (E-1), but only in frames of 51.84 Mbps (OC-1), concatenated frames of 155 Mbps (OC-3), or larger. In other words, SONET is not highly granular, to say the least. An end user organization desiring to transmit Ethernet at a rate of 100 Mbps, for example, therefore must lease an OC-3, of which approximately 50 Mbps of bandwidth is wasted , even under full load. LCAS intends to resolve these issues of transmission rate mismatch by shaping data into SONET VT1.5 payloads (i.e., Virtual Tributary 1.544 Mbps, which is T-1 speed), which can be concatenated (i.e., linked together). Further, the VT1.5 payloads can be dynamically incremented or decremented as necessary in support of LAN traffic, which is inherently bursty in nature. Some manufacturers claim to be able to break LCAS payloads down into increments as small as 0.5 Mbps. See also Concatenation, Ethernet, SONET, T-1, and VT1.5.


  1. Liquid Crystal Display. An alphanumeric display using liquid crystal sealed between two pieces of glass. The display is divided into hundreds or thousands of individual dots, which are charged or not charged, reflecting or not reflecting external light to form characters, letters and numbers . LCD displays have certain advantages. They use little electricity and react reasonably quickly ” though not nearly as quickly as a glass cathode ray tube or a gas plasma screen. They are reasonably legible. They require external light to reflect their information to the user. The newer so-called "supertwist" LCDs are much more readable. You see LCDs on computer laptops and telephone screens. The reason computer laptop LCD screens are brighter than phone screens is that laptops use fluorescent or other light sources to illuminate the LCD (typically from the back or the side). Phones typically don't have the power. The only way for a phone to get the power is to plug the phone and its screen into an AC outlet. Most users, however, don't want to have to plug their phone into both AC and phone outlets. It's cumbersome. In newer LCDs, called active matrix displays, the circuit board contains individual transistors for each pixel, or dot on the screen. The enables the crystals to shift quickly, resulting in a higher quality image and the ability to display full-motion video. Active matrix displays in color are hard to manufacture. Low production yields are common, though improving.

  2. Loss of Cell Delineation. An ATM term. See Loss of Cell Delineation for a full explanation.


Line Conditioning Equipment.


The ANSI X3T9.5 standard which defines the requirements for the transmission of data over low cost fiber in an FDDI topology. Also refers to the ANSI working group responsible for the development and perpetuation of the standard.


  1. Line Control Module.

  2. Line Concentrating Module is a cabinetized peripheral which contains two duplicated Enhanced Line Concentrating Modules (LCME) to interface analog circuits.


Logical Channel Number. An ISDN term which applies when multiple users share a single B or D channel for X.25 data communications. Each user is assigned a LCN. For instance, as many as eight users can share a single access to a single B channel through an 8-port Terminal Adapter in a BRI application. Effectively eight logical virtual channels are derived from a single B channel.


See Link Control Protocol.


  1. Least Cost Routing. A software-based telephone system feature that automatically chooses the lowest cost phone line to the destination. What actually is the "lowest cost" is determined by algorithms, equations and decision trees programmed into the PBX. Least Cost Routing typically works with "look-up" tables in the PBX's memory. These tables are put into the PBX by the user. The PBX does not automatically know how to route each call. It must be told so by the user. That "telling" might be as simple as saying "all 312 area codes will go via the AT&T FX (foreign exchange) line." Or it might be as complex as actually listing which exchanges in the 312 area code go by which method. Least cost routing tells the calls to go over the lines which are perceived by the user to be the least cost way of getting the call from point A to point B. There are typically two types of "least cost routing" translation ” that which examines the first three digits of the phone number (i.e. just the area code) and the first six digits of the phone number (i.e. the area code and the three digits of the local central office). Six digit translation is preferred because it allows you more flexibility in routing ” particularly to big area codes, like 213 in LA, where there are long distance calls within the area code. These days, least cost routing can virtually be "no cost" routing. For example, a company might choose to ship its voice calls via VoIP over its own internal data network. If there's unused capacity on that network the voice calls are essentially going for free. Least cost routing can also be done in stages. For a New York to LA call, a company might choose to use the company's data network as a VoIP call and then to hop off the end as a local call. Least cost routing was a huge advance in telephony when coast to coast calls in the U.S. were 35 cents a minute. Now they're one cent a minute for big companies, least cost routing is less significant. See also Automatic Route Selection, Alternate Routing and Six Digit Translation.

  2. Line Concentration Ratio. A CO (Central Office) design and engineering term for the optimization of system capacity through the classic act of balancing cost and performance. LCR is used to determine central office switching equipment quantities and configurations based upon line usage. It is neither necessary nor economical to equip every outside line with a dedicated path through the switch. With the possible exceptions of Mother's Day or when George Strait concert tickets go on sale, not every line goes off hook at the same time. The higher ratios have been predominantly used in rural areas while the lower, more equipment intensive ratios have been the standard in urban and suburban areas. An LCR of xx:1 indicates that there exists one predetermined dial tone path for any given number (xx) of lines at a given time; in other words, an LCR of 6:1 means that six lines would have access to one dial tone path through the switch.

While the specific architecture of the CO switch manufacturer impacts the LCR calculations, in the AT&T 5ESS switch, the following calculations show the maximum allowable lines per line unit when assuming an average holding time. Exceeding the maximum allowed lines would require load balancing of line units, deloading line units, or extra line unit equipment. The following is based on the relatively short holding times characteristic of voice communications.

4:1 concentration ratio, 256 lines/unit, 5.74 ccs/line, 1470 ccs/unit

6:1 concentration ratio, 384 lines/unit, 4.30 ccs/line, 1650 ccs/unit

8:1 concentration ratio, 512 lines/unit, 3.32 ccs/line, 1700 ccs/unit

Note that there are 64 voice-grade channels of 64 Kbps per unit. Also note that "ccs" means "centum call seconds," which translates to "100 call seconds." A voice-grade channel supports up to 36 ccs, which is 3600 seconds (60 seconds x 60 minutes = 3600 seconds per hour ) of traffic capacity.

The Internet has forced the re-evaluation of the LCR and equipment capacities , as circuit-switched connections through the CO to your ISP tend to last a very long time compared to voice conversations. Holding time for internet usage commonly assumes an average of 10 ccs/attempt at 9pm busy hour, with 20% of Internet customers online during busy hour, at least according to GTE internet. This definition courtesy of Kevin Knox, ADSL DSA Project Manager for Pac Bell.


Live Call Screening. This is a wonderful phone/voice mail feature, at this stage confined to some Panasonic phone systems and a very few other makers '. Here's how it works. Someone calls you and ends up in your voice mail. You can hit a LCS button on your phone (or it will happen automatically) and you will hear the message being left in your voice mail. If you choose to speak to this person (based on what you're hearing) you press a button or simply pick up your handset. There are various options with this feature. You can listen through your speakerphone or through your handset. You can have it happen on every voice mail call or just the ones you choose. You'll know if someone is leaving you a voice mail because a special light lights on your phone.


  1. Long Distance.

  2. Loop Disconnect.


Low Delay-Code Excited Linear Prediction. Standardized by the ITU-T as G.728, LD-CELP is variation of CELP. LD-CELP compresses voice at the same rate of 16 Kbps as does CELP, but it offers the advantage of lower delay levels, which yields improved voice quality with a lesser demand on the computational processes accomplished by the codecs. LDCELP accomplishes this lower level of delay by gathering only 5 PCM samples in a buffer, rather than the 80 gathered by CELP. Therefore, each transmitted data block represents only 0.625 milliseconds of a voice stream. The concept behind the "Low Delay" is really very simple. If you stop to gather only 5 things, it takes a lot less time than if you stopped to gather 80 things. So LD-CELP gathers 5 voice samples, sends them through the network, gathers 5 more, and so on. See CELP for the full background on LD-CELP. See also ACELP.


Long Distance Alerting.


Lightweight Directory Access Protocol. LDAP grew out of the X.500 directory standards efforts of the past decade . As Tim Howes and a small group of other students at The University of Michigan were searching for a way to run the X.500 protocol on their PCs, they created a lighter method of access. The resulting directory protocol, which they named DIXIE, was the precursor for LDAP. LDAP defines a standard manner of organizing directory hierarchies and a standard interface for clients to access directory servers. LDAP does not require vendors to mess around with the internal workings of their proprietary directories ,and they can add an LDAP to existing directories without too much trouble. This is why virtually all directory vendors support LDAP. LDAP is being touted as an Internet-based solution to the intricacies of DAP, the predecessor protocol. See DAP and X.500.


Local Data Base Services.




See Limited Distance Modem.


Listed Directory Number. Your main phone number. The one you list in the telephone directory and Directory Assistance.


Local Digital Services. LDS is a term used by long distance companies to describe "last mile" services provided by local phone companies. LDS is generic word to describe any digital services, including T-1, T-3, OC-12, Frame Relay and dedicated Internet services.


Line appearance on a Digital Trunk.


Line Director Unit.


Low Definition TeleVision (e.g. VHS).


LAN Emulation. Refer to LANE.


An ATM term. LAN Emulation Address Resolution Protocol: A message issued by a LE client to solicit the ATM address of another function.

Lead Agent

The first agent in an ACD group. See also Automatic Call Distributor.

Lead Cable

Before plastic (polyethylene) was invented telephone cable was insulated with paper and covered in lead. Much of this cable is still used by the RBOCs. This cable is heavy and nonbuoyant in underwater applications. It is now being removed due to the effects of lead on the environment.

Lead In

  1. Wire or cable from antenna to TV set.

  2. The conductor from the antenna to the radio receiver.


The section at the beginning of a roll of magnetic tape which holds no data and often is not even magnetic tape. A leader is used to feed the magnetic tape through the tape mechanism and secure it onto the roll.

Leadership Priority

An ATM term. The priority with which a logical node wishes to be elected peer group leader of its peer group. Generally, of all nodes in a peer group, the one with the highest leadership priority will be elected as peer group leader.

Leading Current

The phrase difference in a capacitive alternating current where the current leads the E. M. F.


  1. Law Enforcement Access Field. See Clipper Chip and the NSA.

  2. Large Effective Area Fiber. A high capacity fiber that can carry much data over long distances without amplification. www. corning .com.

  3. See Leaf POP.

Leaf Internetwork

In a star topology, an internetwork whose sole access to other internetworks in the star is through a core router.

Leaf POP

The word leaf is used to describe POPs (Point of Presences) that are on the fringe of the network, like a leaf on a tree. Leaf POPs do not communicate with one another. They follow the chain up to get their information. They have a many-to-one relationship with their region-cores. The leaf POPs in turn have a many-to-one relationship with their users since they are the connection between the user and the Internet. Leaf POPs can also be called customer aggregation points. See POP.


  1. A cable TV term. Leakage occurs when certain radio frequencies ooze out of the CATV coaxial cable in such strength that they are evident outside the home. They might be sufficiently strong to interfere with aircraft navigation. Leakage is really a shielding problem. See Ingress.

  2. See Leaking Memory.

  3. A condition that occurs when a carrier cannot bill for a call. Leakage can occur due to system errors, bypass, or fraud. Leakage is especially a problem for the carriers when the call originates from a PBX system supporting hotel/motel, prison , dormitory, and campus environments. See also Leaky PBX.

Leaking Memory

Under Windows (3.xx or Windows 95), when you close a program, Windows sometimes fails to release all the memory that it's used. This is called "leakage." It is a cumulative problem. The more programs you open and close, the more memory you lose. This can create problems. The simplest solution is to get out of Windows regularly and reboot your computer.

Leaky Bridge

A type of LAN bridge that forwards packets from one LAN to another even though the packet should not be forwarded. Usually due to poor engineering.

Leaky Bucket

See LB and the next definition.

Leaky Bucket Algorithm

An algorithm designed to monitor the flow of cells to verify they conform to the stated traffic contract for the associated connection.

Leaky Coax

A device to assist wireless transmission. A leaky coax is a coaxial cable that has the tops of the corrugated shield milled of to make a series of holes on one side of the cable. Instead of preventing signal loss, the cable will now leak the signal the entire length. This provides a much easier method of evenly covering tunnels, underpasses, stairwells, elevator shafts and basements. Any building constructed with steel , or re-enforced concrete will have dead areas (called nulls) that are in the shadows of traditional transmitters. Instead of boosting the power output and overpowering nearby receivers, a length of leaky coax run high in the ceiling will cover the same areas evenly. The outer insulation is applied after the holes have been cut to provide a weather tight cable. You must orient the cable so the holes are pointed where you want the coverage. Many cellular carriers are working with subways to install leaky coax in subway stations and tunnels. The English Channel Tunnel has leaky coax installed in its tunnels so people can make cell phone calls while they're traveling on that overpriced high-speed train that runs between London and Paris.

Leaky PBX

One of those really silly terms for which the phone industry is famous. Picture this. You dial into your company's PBX, accessing it through a DISA (Direct Inward System Access) port. You get dial tone, enter an authorization code, get a second dial tone, and place an outgoing call on a trunk-to-trunk basis. The PBX is referred to as "leaky." If you are an authorized user, the advantage is that you can place a low-cost call through the corporate network rather than placing that same business call from your home or your hotel room. The disadvantage is that toll fraud artists can do the same thing if they can hack your PBX's authorization codes. All PBXs are, of course, "leaky," or at least capable of being made leaky. DISA ports are very dangerous. Do not install them. If they are installed, disable them permanently.

Another definition for "leaky PBX" builds on the first. Picture this. You are at work at your office in Seattle and you want to call your brother in Richardson, Texas, a suburb of Dallas. Or you are home in Bellevue, Washington, a suburb of Seattle, and you dial a local number to access the PBX in Seattle for the same reason. You dial your brother's telephone number. The LCR (Least Cost Routing) software in the PBX routes the call over the corporate leased-line network to the Dallas PBX, since that is a free call, and the capacity is available. At the Dallas PBX, the call is connected to the PSTN on a trunk-to-trunk basis, in what is known as Tail-End Hop Off (TEHO). At both ends, the call was local in nature, and no charges applied. The long-haul portion of the call traveled over the corporate network, and no charges applied since the IXC (IntereXchange Carrier) was bypassed. Technically speaking, your company just became an IXC. The PBX is "leaky," since the call is not billable by any authorized IXC. See also DISA and Leakage.

Leaky Reply

A message to an unintended recipient, often caused by hitting the Reply To All option on an email program. On some programs you actually can send your replies to people who have been blind copied . The whole experience can be embarrassing.

Leaky Roof Syndrome

You don't notice that your roof is leaky when the sun is shining. When it rains and the roof leaks, it's too late to fix it.


Long-term Equipment AnticiPation Securities. Introduced in 1990, LEAPS are simply longer-term options with expirations of up to three years . LEAPs can be very profitable or they can be very expensive.


LATA Equal Access System.

Leased Circuit

Same as Leased Line or Private Line.

Leased Line

Same as a leased or dedicated circuit, private line, leased channel. A leased line is a telephone line rented for exclusive use of the customer 24-hour a day, seven days a week from a telephone company ” a local phone company (like Bell Atlantic) or a long distance company like AT&T or MCI Worldcom.

Least Cost Routing

LCR. A telephone system feature which automatically chooses the "least cost" long distance line to send out a local, regional or long distance call. The user typically dials "9" and then his 10-digit long distance number which is routed over the least costly service. For a longer explanation, see also LCR.

Least Privilege Administration

A recommended security practice in which every user is provided with only the minimum privileges needed to accomplish the tasks they are authorized to perform, and no others.


The first U.S. Marines wore high leather collars to protect their necks from sabres. Hence the name "leathernecks."

Leave Word Calling

For AT&T System 75 and 85 users for internal messages. The caller's name, time of call and extension number are taken and can be retrieved on a Digital Display Monitor or BCT. The service is accompanied by an Integrated Directory ” a simple electronic listing of employee names and extension numbers, access by a terminal equipped with a DDM or via the attendant console.


  1. Local Exchange Carrier. The local phone companies, which can be either a Bell Operating Company (BOC) or an independent (e.g., GTE) which traditionally had the exclusive, franchised right and responsibility to provide local transmission and switching services. Prior to divestiture, the LECs were called telephone companies or telcos. With the advent of deregulation and competition, LECs now are known as ILECs (Incumbent LECs). This terminology delineates them from CLECs (Competitive LECs).

  2. LAN Emulation Client: An ATM term for a router capable of supporting LANE (LAN Emulation). It works like this: A LAN-attached device, typically in the form of a PC, addresses another LAN-attached device-of course, the originating device hasn't a clue where the other device is physically located. When the router receives the data packets, it exercises its LEC capability, establishing a connection to an edge ATM switch, mapping the native LAN MAC addresses to ATM addresses. Through the ATM network, a matching connection is established to a matching LEC. MPOA (MultiProtocol Over ATM) is much better, but less mature. See also LANE and MPOA.


An ATM term. LAN Emulation Client Identifier: This identifier, contained in the LAN Emulation header, indicates the ID of the ATM host or ATM-LAN bridge. It is unique for every ATM Client.


An ATM term. LAN Emulation Configuration Server: This implements the policy controlled assignment of individual LE clients to different emulated LANs by providing the LES ATM addresses.


Light Emitting Diode. A semiconductor diode which emits light when a current is passed through it, the intensity of the light varying with the amount of current. A diode only allows current to flow in one direction. You need two conductive materials sandwiched together to made a diode. When electricity is passed through the diode the atoms in one material (in the semiconductor chip) are excited to a higher energy level. The atoms in that first material have too much energy and need to release that energy. The energy is then released as the atoms shed electrons to the other material within the chip. During this energy release, light is created. The color of the light from an LED is a function of the ingredients (materials) and recipes (processes) that make up the chip. In lightwave transmission systems, light emitting diodes or lasers are used as sources of light. These devices are fabricated from multi layered structures of compound semiconductors epitaxially grown on a single-crystal substrate. LEDs are used as sources for optical data link applications in which the data rates are less than about 500 megabits per second and the transmission distances do not exceed a few kilometers. LEDs are also used in alphanumeric displays on calculators and computer devices. LEDs use less power than normal incandescent light bulbs , but more power than LCDs (Liquid Crystal Displays). Contrast with Laser Diodes.


People who pull items off bulletin boards and consume knowledge without ever making a contribution. An old term.


My definition: A segment of a multipoint circuit which lies between any two of the points. Bellcore's definition: An object within a connection view that represents a communication path toward some addressable entity.

Leg Iron

  1. Also called spurs and climbers. What personnel wear to climb wooden poles. Officially linesman's climbers. They consist of a steel shanks that strap to a person's leg. The inside has a spike used to stab the pole.

  2. Worn by prisoners to prevent them running away. Many customers want their telephone technicians to wear them until their system is up-and-running 100%.


  1. Noun. All the stuff you have on hand ” equipment, software, files and paperwork. In short, everything of a data processing/telecommunications nature in your business today. The use of the word "legacy" suggests that you've inherited all this stuff from previous generations of obsolete management. Most English dictionaries define the word legacy as "Anything handed down from the past. The idea is that you're forced to update it, without junking it altogether ” which is expensive and potentially problematical. All you have is the legacy of previous generations. Preserve it, because no one can afford to junk it. Or so the theory goes.

  2. Microsoft defines legacy in its Windows 95 Resource Kit as hardware and devices cards that don't conform to its Plug and Play standard.

  3. As an adjective, you'll find the word in legacy system, legacy media, legacy bank. In this case, it's often referred to as pre-Internet way of the doing things.

Legacy Technology

Outdated stuff that is basically obsolete but still too expensive to trash. Also called "heritage system."

Legacy Wiring

Preinstalled wiring that may or may not be suitable for use with a network.

Legal Holiday

A call center term. Any holiday for which special wages are paid to employees who work on that day.

Legion of Doom

See Master of Deception .


Lego is a Danish-created child's game of many standard plastic pieces which fit together to make wonderful objects. Lego was invented by Gottfried Christiansen in Denmark. In 1947 he bought the first plastic moulding-injection machine and in 1949 began making plastic " bricks ." I include this term in this dictionary because many people see open, standards-based telecommunications as "lego" telecommunications. They see open telecom as comprising standard building blocks ” hardware and software ” which fit together to make wonderful objects, just like Lego. See Legoware Telecom.

Legoware Telecom

The British term for what North Americans know as Lego Set or the British term Erector Set Telecom.


A lemon is a product (often a car or a computer) that is so unreliable it leaves a sour taste in your mouth. This definition courtesy Sara Hartman who once bought a lemon car.


LZW. The Lempel-Ziv-Welsh compression algorithm is way of reducing the number of bits to transfer. See LZW for a full explanation.


Line Equipment Number.


The number of bits or bytes in a computer word, a field, a record, etc.


Lenses were named during the 13th century for their vague resemblance in shape to lentils ” from the Italian word lenticchie for "lentils," which was later changed to the Italian lente for "lens." For more than 300 years, lenses were called "glass lentils."


Low Earth Orbit satellites. Also called LEOS, as in Low Earth Orbiting Satellites. LEO satellites orbit 400 to 1,600 miles (644 to 2,575 kilometers) above the earth's surface. 48 to 66 LEOs are needed to cover the entire earth. Low Earth Orbit satellites move around the earth in various orbits like electrons whizzing around the nucleus of an atom (remember your high school physics). A group of such satellites is known as a "constellation." To establish a connection, you gain access to one of these satellites much as you gain access to a cell site in close proximity in the case of cellular telephony. When that satellite moves out of range, you are handed off to another satellite which has come into view. During a lengthy conversation, this process may take place many times. LEOs are being promoted for functions as diverse as worldwide paging with acknowledgement , worldwide handheld telephone service and tracking cargo (with the truck sending up a continuous stream of info about its whereabouts). A primary advantage of LEOs is that the transmitting terminal ” the one on earth ” doesn't have to be very powerful, because the LEO satellite is so much closer than traditional geostationary satellites, which are satellites placed in an geosynchronous orbit ” 22,300 miles (or 42,164 kilometers) directly over the earth's equator. The close proximity of the satellites also minimizes propagation delay, thereby avoiding that aggravating CB-radio like problem of conversation delay and clipping. LEOs are divided into two groups, Little LEOs and Big LEOs, with each group having been assigned specific radio frequencies by international agreement. Little LEOs support data services, while Big LEOs support both voice and data communications. See Iridium and GLOBALSTAR. Contrast with GEO and MEO.


Low Earth Orbiting Satellites. Iridium and Globalstar are LEOS. See LEO and Iridium.


Large Electron Positron Collider.


Label Edge Router: Converts IP packets into MPLS packets, and MPLS packets into IP packets. On the ingress side, the LER examines the incoming packet to determine whether the packet should be labeled. A special database in the LER matches the destination address to the label. An MPLS shim header is attached and the packet is sent on its way. The LER adds and/or removes (pops or pushes) labels. See MPLS.


Local Exchange Routing Guide. A Bellcore document which lists all North American Class 5 offices (Central Offices, or end offices) and which describes their relationships to Class 4 offices (Tandem Offices). Carriers use the LERG in the network design process. See also Bellcore, Central Office and Tandem Office.


  1. An ATM term. LAN Emulation Server: This implements the control coordination function for the emulated LAN, in order to perform LAN Emulation (LANE) over an ATM network. Examples are enabling a LEC or IXC to extend a LAN, resolving issues of addressing between LAN MAC addresses and ATM addresses. The LES works in conjunction with a BUS (Broadcast and Unknown Server), which distributes the broadcast and multicast packets. See Emulation and LANE.

  2. Label Edge Switch. A switch at the edge of an MPLS (MultiProtocol Label Switching) network. See also MPLS.

  3. Loop Emulation Service. A developing specification from the ATM Forum, LES is a service designed to emulate a conventional voice local loop over a DSL loop equipped to support VoATM (Voice over ATM). LES employs AAL2 (ATM Adaptation Layer type 2) for support of rt-VBR (realtime Variable Bit Rate) compressed voice. The DSL loop supports VoATM using AAL2 between a premises-based ATM IAD (Integrated Access Device) and a network-based ATM switch or DSLAM (DSL Access Multiplexer). Simultaneously, LES supports high-speed packet data over the bandwidth not required for voice traffic, which always takes precedence in such a convergence scenario. For example, a DSL loop running at T-1 speed might support 16 voice channels using AAL2 running compressed voice in ADPCM (Adaptive Differential Pulse Code Modulation) and using silence suppression, and claiming bandwidth of only approximately 350 Kbps. This compares with the 1.024 Mbps required to carry 16 voice channels in traditional uncompressed PCM format. This LES approach leaves bandwidth of over 1 Mbps available for packet data traffic destined for the Internet. Where LES is employed in a circuit-switched PSTN scenario, the extended concept is known as BLES (Broadband LES). Where LES is employed in a scenario where the voice data terminates in a packet-switched network based on VoIP (Voice over Internet Protocol) or VoATM (Voice over ATM), the extended concept is known as VoMBN (Voice over Multiservice Broadband Network). See also AAL2, ADPCM, BLES, DSL, DSLAM, IAD, PCM, rt-VBR, VoATM, VoIP, and VoMBN.

Newton[ap]s Telecom Dictionary
Newton[ap]s Telecom Dictionary
ISBN: 979387345
Year: 2004
Pages: 133 © 2008-2017.
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