Glossary- L
Data Communication Historical Series
By Bob Pollard

HOME                   INDEX

L BAND:

The microwave transmission frequencies in the range of 1 gHz.

LAA:

Longest Available Agent: The agent that has been continuously in the Available state for the longest time. The ICM can examine services or skill groups from different peripherals and route a call to the service or group with the longest available agent.

LABEL:

A short fixed-length label that tells switching nodes how the data (packets or cells) should be forwarded (routed): Each part of a full DNS (Domain Name System) name that represents a node in the domain namespace tree. Domain names are made up of a sequence of labels, such as, microsoft.com. Each label used in a DNS name must be 63 bytes or less in character length.

LABEL CONTROLLED SWITCH:

The label switch controller and the controlled ATM switch that it controls, viewed together as a unit.

LABEL IMPOSITION:

The act of inserting the first label on a packet

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:

A node that forwards units of data (packets or cells) on the basis of labels

LAC:

L2TP Access Concentrator: A node that acts as one side of an L2TP tunnel endpoint and is a peer to the L2TP network server (LNS). The LAC sits between an LNS and a remote system and forwards packets to and from each. Packets sent from the LAC to the LNS require tunneling with the L2TP protocol. The connection from the LAC to the remote system is either local or a PPP link.

LAD:

Local Area Data (Channel)

LADDR:

Local Address: Address of a host on a protected interface

LADT:

Local Area Data Transport: Provides simultaneous voice and data by Frequency Division Multiplexing, 4800 bps data above speech signals on a two-wire voice telephone exchange line.

LAMBDA:

The 11th letter of the Greek alphabet: Lambda is used as the symbol for wavelength in light-wave systems.

LAN:

Local Area Network: The data communications facilities used to provide communications within a limited geographical area, using medium to high speed data rates 9600 bps to 100 mbps. LAN(s) may have bridges or gateways to other networks but are usually confined to a building or cluster of buildings.

  High-speed, low-error data network covering a relatively small geographic area, up to a few thousand meters: LANs connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited area. LAN standards specify cabling and signaling at the physical and data link layers of the OSI model. Ethernet, FDDI, and Token Ring are widely used LAN technologies.

LAN EMULATION (LANE):

Local Area Network Emulation: A set of protocols that allow existing Ethernet and Token Ring LAN services to overlie an ATM network. LANE allows connectivity between LAN and ATM attached stations.

LAN EMULATION CLIENT (LEC):

The client on an ELAN that performs data forwarding, address resolution, and other control functions: The LEC resides on end stations in an ELAN.

LAN EMULATION CONFIGURATION SERVER:

The service that assigns individual Local Area Network Emulation (LANE) clients to particular Emulated Local Area Networks (ELAN) by directing them to the LAN Emulation Server (LES).

LAN MANAGER:

Distributed NOS, developed by Microsoft: Supports a variety of protocols and platforms.

LAN SERVER:

Server-based NOS developed by IBM and derived from LNM

LAN SWITCH:

High-speed switch that forwards packets between data-link segments: Most LAN switches forward traffic based on MAC addresses. LAN switches often are categorized according to the method they use to forward traffic; cut-through packet switching or store-and-forward packet switching. Multilayer switches are an intelligent subset of LAN switches.

LANDLINE:

A communications line (data/telephone) passing over land as opposed to underwater, radio or satellite.

LANDSAT:

Land Satellite

LANE:

LAN Emulation: Technology that allows an ATM network to function as a LAN backbone. The ATM network must provide multicast and broadcast support, address mapping (MAC-to-ATM), SVC management, and a usable packet format. LANE also defines Ethernet and Token Ring ELAN(s).

LANE UNI:

LANE User-Network Interface

LAP:

Line Access Procedure: A term used in packet switching networks to define the data link layer level protocol specified in the CCITT X.25 interface standard, which has been superseded by Line Access Procedure, Balanced (LAPB).

LAPB:

  Line Access Procedure, Balanced: A term used in packet switching networks to define a link initialization procedure designed to establish and maintain communications between the Data Terminal Equipment (DTE) and the Data Communication Equipment (DCE). All Packet Data Networks currently support LAPB, which involves the T1 timer and N2 count parameters.

   Link Access Procedure, Balanced: Data link layer protocol in the X.25 protocol stack. LAPB is a bit-oriented protocol derived from HDLC.

LAP-D and LAPD):

Link Access Procedure on the D channel: ISDN data link layer protocol for the D channel. LAPD was derived from the LAPB protocol and is designed primarily to satisfy the signaling requirements of ISDN basic access. Defined by ITU-T Recommendations Q.920 and Q.921.

See Link Access Procedure –D Channel

LAPM:

Link Access Procedure for MODEM(s): ARQ used by MODEM(S) using the V.42 protocol for error correction. See Link Access Procedure for MODEM(s)

LASER:

Light Amplification by Stimulated Emission of Radiation: Converters of electrical energy into light of great purity and controllability adequate for telecommunications through glass wave-guides. Used for high- capacity, long haul fiber-optic links of common carriers. Fiber links of end users most commonly employ less expensive devices and are used for shorter distances and lower capacities.

LAT:

Local-Area Transport: A network virtual terminal protocol developed by Digital Equipment Corporation.

LATA:

Local Access and Transport Area: Refers to the, approximately, 184 local telephone companies with different serving areas in the United States. The LATA areas are designated primarily by demographics, and are separate from long-distance service companies.

LATENCY:

1) The waiting time, or delay between a stations request to a transmission channel, and completion (answer) of the request.

 2) Rotation time for the Disk head to position over the addressed location is referred to as latency time

3) Delay time between when a device requests access to a network and the time it is granted permission to transmit.

4) Delay between the time a device receives a frame and the time that frame is forwarded out the destination port.

LAYER:

A term used to define one level (layer) of a functional hierarchy, as specified by the Open System Interconnections (OSI) reference model. OSI standards consist of seven layers used to perform different functions in data communications. Each layer performs a specific data communications function. Each of these layer’s, builds on the one below it. Although each step must be performed in order, each layer provides several options. The first three layers are physical, data link, and network, all of which are concerned with data transmission and routing. The fourth layer, transmission, provides an interface between the first three layers and last three layers. The last three layers are session, presentation, and application. These layers focus on user applications.

LAYER 1:

The first layer of the OSI model: Known as the physical layer. Layer 1 represents the actual electrical or mechanical hardware interface that connects a device to a transmission medium.

LAYER 2:

The data link layer of the OSI model: Layer 2 organizes data into frames and sequences for transfer across the physical layer. Layer 2 primarily detects and corrects message errors transmitted across any physical link, and allows the nodes on either end of a connection to signal one another when initiating a communications session.

LAYER 2 TUNNEL PROTOCOL (L2TP):

An Internet Engineering Task Force (IETF) standards track protocol defined in RFC 2661 that provides tunneling of PPP. Based upon the best features of L2F and PPTP; L2TP provides an industry-wide interoperable method of implementing VPDN.

LAYER 3 / LAYER 3 SWITCHING:

1) The network layer of the OSI model: Layer 3 routes data from one element to another until it reaches its final destination:

2) Layer 3 Switching: A Layer 3 switching technology that integrates routing with switching to yield very high routing throughput rates in the millions-of-packets- per-second range. The movement to Layer 3 switching is designed to address the downsides of the current generation of Layer 2 switches, which functionally are equivalent to bridges.

LAYER 4:

The transport layer of the OSI model: Layer 4 recovers data that may have been lost due to a node failure on the lower network layers, and maps transport and network addresses. Layer 4 also establishes and manages reliable network connections between end nodes, and controls packet flow, size, and sequence restrictions that prevent excessive amounts of data from entering the network.

LAYER 5:

The session layer of the OSI model: Layer 5 is a dialogue between two users or devices during which data is exchanged in a conversational manner.

LAYER 6:

The presentation layer of the OSI model: Layer 6 defines the way in which information is presented so that the communicating devices interpret it properly. This layer controls the format of screens and files, and defines syntax, control codes, special graphics, and character sets.

LAYER 7:

The application layer of the OSI model: Layer 7 applies to the actual meaning rather than the format or syntax of applications, and permits communication between users.

LB:

Originally a Line Block of 80 characters of data in punched paper card format (IBM format). Can be any length based on system requirements and restrictions.

LBR:

Label Bit Rate: Service category for label VC traffic. Link and per-VC bandwidth sharing can be controlled by relative bandwidth configuration at the edge and each switch along a label VC. No ATM traffic-related parameters are specified.

LC-ATM INTERFACE:

Label-Controlled ATM Interface: An MPLS interface in which labels are carried in the VPI or VCI fields of the ATM cells and in which VC connections are established under the control of MPLS software.

LCC:

Local Control Center

LCD:

Liquid Crystal Diode / Liquid Crystal Display: Alphanumeric display on computers, fax devices, etc., using liquid crystal diodes sealed between two pieces of glass. See Liquid Crystal Display

LCI:

Logical Channel Identifier

LCN:

Logical Channel number

LCP:

Link Control Protocol: Protocol that establishes, configures, and tests data-link connections for use by PPP.

LCR:

Least Cost Routing: The function of automatically or manually selecting the least expensive means (route) for connection of a circuit (line) or telephone call. Also used: Most Economical Route Selection (MERS), Automatic Route Selection (ARS) or Flexible Route Selection.

LCU:

Line Control Unit: A data communications term used for hardware that controls polling and access by remote terminals. Commonly found in minicomputer networks. LCU capability ranges from simple hardware to processor-based devices with a history dating to telegraph networks.

LCV:

Line Code Violation: Occurrence of a BPV or EXZ error event

LDAP:

Lightweight Directory Access Protocol: Protocol that provides access for management and browser applications for read/write interactive access to the X.500 Directory.

LDCELP:

Low-Delay CELP: CELP voice compression algorithm providing 16 kbps, or 4:1 compression; standardized in ITU-T Recommendation G.728.

LDIF:

LDAP Data Interchange Format: An LDAP server interchange format in which each records field value is on a separate line and records are separated by an empty line.

LDP:

Label Distribution Protocol: A standard protocol between MPLS-enabled routers to negotiate the labels (addresses) used to forward packets. The Cisco proprietary version of this protocol is the Tag Distribution Protocol (TDP).

LDX:

Long Distance Xerography: A past term used by the Xerox Corporation to identify its high-speed facsimile system.

LEAP:

Internet standard

LEARP:

LAN Emulation Address Resolution Protocol: Protocol that provides the ATM address that corresponds to a MAC address.

LEAF INTERNETWORK:

In a star topology, an inter-network whose sole access to other inter-networks in the star is through a core router.

LEAKY BUCKET:

In ATM, a metaphor for the GCRA: Used for conformance checking of cell flows from a user or a network. The hole in the bucket represents the sustained rate at which cells can be accommodated, and the bucket depth represents the tolerance for cell bursts over a period of time.

LEARNING BRIDGE:

A Bridge that performs MAC addresses learning function. Learning bridges manage a database of MAC addresses and the interfaces associated with each address; helps reduce traffic on the network.

LEASAT:

Leased Satellite

LEASED ASC:

The government, from the responsible contractors, leased the stateside (CONUS) ASC(s). Western Union was the original contractor, who installed and maintained the original Stateside sites (including Hawaii).

LEASED LINE:

A dedicated private line: Used primarily to link two remote locations together. This could be Local Area Networks (LANs), computers or terminals. This line can transmit data at speeds dictated by the purchased (leased) bandwidth. Customers pay a flat monthly rate for this service.

LEC:

1) Local Exchange Carrier: U. S. telephone access and service provider.

2) LAN Emulation Client. Entity in an end system that performs data forwarding, address resolution, and other control functions for a single ES within a single ELAN. An LEC also provides a standard LAN service interface to any higher-layer entity that interfaces to the LEC. Each LEC is identified by a unique ATM address, and is associated with one or more MAC addresses reachable through that ATM address.

LECS:

LAN Emulation Configuration Server: Entity that assigns individual LANE clients to particular ELAN(s) by directing them to the LES that corresponds to the ELAN. There is logically one LECS per administrative domain, and this serves all ELAN(s) within that domain.

LED:

Light Emitting Diode: An electrical component, offering greater reliability and less heat than an ordinary bulb, used to indicate status information; semiconductor device that emits light produced by converting electrical energy. Status lights on computers and hardware devices are typically LED(s).

LEGACY MESSAGING NETWORK:

A military term used to designate an AUTODIN Site; A system in existence prior to the target technical architecture or new system to be implemented.

LEGACY SYSTEMS:

Systems which existed prior to the target technical architecture or system

LEN NODE:

Low-Entry Networking Node: In SNA, a PU 2.1 that supports LU protocols, but whose CP cannot communicate with other nodes. Because there is no CP-to-CP session between a LEN node and its NN, the LEN node must have a statically defined image of the APPN network.

LES:

LAN Emulation Server: Entity that implements the control functions for a particular ELAN. There is only one logical LES per ELAN, and it is identified by a unique ATM address.

LETTERS SHIFT (LTRS):

A control character: Used in the Baudot Code to enable the printing of alphabetic characters. A letters and figures shift is used to electrically/mechanically shift the printer for alpha or numeric characters.

LEVEL 1 ROUTER:

Device that routes traffic within a single DEC-net or OSI area

LEVEL 2 ROUTERS:

Device that routes traffic between DEC-net or OSI areas: All Level 2 routers must form a contiguous network.

LF:

1) Line Feed: A Teletype or CRT (Cathode Ray Tube) format control character which causes the printing mechanism or cursor to move to the next printing line.

2) See Low Frequency

LFI:

Low-speed Link Features

LFIB:

Label Forwarding Information Base: A data structure and forwarding management in which destinations and incoming labels are associated with outgoing interfaces and labels.

LFSR:

Linear Feedback Shift Register: Mechanism for generating a sequence of binary bits. The register consists of a series of cells that are set by an initialization vector that is, most often, the secret key. The behavior of the register is regulated by a clock. At each clocking instant (cycle) the contents of the cells register is shifted right by one position, and the exclusive-or of a subset of the cell contents is placed in the leftmost cell. One bit of output usually is derived during this update procedure.

LGN:

Logical Group Node: The node that represents its peer group in the peer groups parent peer group.

LIBRARY:

A data-storage system: Usually managed by Removable Storage. A library consists of removable media (such as tapes or discs) and a hardware device that can read from or write to the media. There are two major types of libraries: robotic libraries, automated multiple-media, multi-drive devices, and stand-alone drive libraries, manually operated, single-drive devices. A robotic library is also called a jukebox or changer.

LIBRARY FILE:

Library files contain groups of often-used computer code that different programs can share. Programmers who use library code make their programs smaller since they do not need to include the code in their program. A virus that infects a library file automatically may appear to infect any program using the library file.

In Windows systems, the most common library file is the Dynamic Link Library; its extension is DLL.

LICENSE:

Purchased right to transmit RF waves over a given BTA for periods of 10 years. The license tightly governs the design parameters of an RF system and its use. RF licenses are usually purchased from the FCC on an auction basis.

The FCC provides licenses to ensure maximum competition in a free market and spectral efficiency, which is another way of insuring efficient use of the RF spectrum.

LIGHT EMITTING DIODE:

See LED

LIGHTPEN:

An input device in the form of a pen attached to the display station (CRT) as an extra feature. The light-pen may be pointed at an item on the screen and then activated, thereby selecting the item for subsequent processing.

LIGHT WAVE:

Fiber optic transmission using very high frequency light beams.

LIMITED RESOURCE LINK:

Resource defined by a device operator to remain active only when being used

LIMITED ROUTE EXPLORER PACKET:

Follows a statically configured spanning tree when looking for paths in an SRB network; also known as a limited-route explorer packet or a single-route explorer packet

LINE:

1) Communications channel, circuit or facility: An electrical- mechanical connection between two points for the purpose of transmitting data

1) In SNA, a connection to the network.

LINE ACCESS PROCEDURE:

See LAP

LINE ACCESS PROCEDURE, BALANCED:

See LAPB

LINE ADAPTER:

Refers to a communications interface unit between the bit-parallel I/O format of a computer and the bit-serial format of a channel (line).

LINE BLOCKING:

An asynchronous terminal blocking function performed by a switching center: Since the asynchronous terminal does not transmit data (messages) in line-blocks the switching center packs the message data into blocks internally within the system. This allows the computer-processing program to treat these messages as though they were received from a synchronous terminal (blocked). See Block Framing.

LINE CARD:

1) A circuit card: Sends signals from the Central Office to the equipment used on the customer's premises. These signals provide the intelligence (protocol) needed to make terminal equipment work.

2) Any Input / Output (I/O) card that can be inserted in a computer / device chassis.

LINE CODE TYPE:

One of a number of coding schemes used on serial lines to maintain data integrity and reliability: The line code type used is determined by the carrier service provider.

LINE CONDITIONING:

Common Carrier service: Reduces envelope delay, noise, and amplitude distortion on a channel (line). This allows the user to transmit at a higher data rate than would be possible over an unconditioned line.

LINE DISCIPLINE:

A term used in the past for line protocol procedures.

LINE DRIVER (LOCAL DATA SET):

A Data Communications Equipment (DCE) device: Functions as a signal converter. Line drivers are also used to ensure reliable transmission beyond the 50-foot RS-232 limit.

Inexpensive amplifier and signal converter that conditions digital signals to ensure reliable transmissions over extended distances.

LINE DROPOUT:

A lengthy or large change in the transmission characteristics of a circuit (line); may be a space condition (open line).

LINE FEED:

See LF

LINE HIT:

Short random disturbances in transmission facilities (lines) that cause data errors

LINE IMPEDANCE:

The impedance (resistance) of a transmission: measured across the terminals at each end of the transmission line. 

LINE LOADING:

1) The total of external resistance, inductance, and capacitance of a transmission line

2) A line conditioning function: Refers to the use of resistors, capacitors and inductors to compensate for frequency and delay distortion that occurs on communications lines. See Conditioned Circuit, Conditioning or Conditioning Equipment.

LINE OF SIGHT:

Characteristic of certain transmission systems in which no obstructions in a direct path between transmitter and receiver can exist, example: microwave, and infrared systems

LINE PRINTER:

A Computer printer that prints an entire line of characters at a time (each print cycle): A high-speed, high volume printer. See HSP.

LINE PRINTER DAEMON (LPD):

A service in the print server: Receives documents (print jobs) from Line Printer Remote (LPR) utilities running on client systems.

LINE PRINTER REMOTE (LPR):

A connectivity utility that runs on client systems and is used to print files

LINE PROTOCOL:

A communications program designed to perform data transmission functions over a network; the protocol requirements for a designated line(s).

LINE SIDE:

Reference to a line (circuit) from the sending end of a transmission path: Also: Equipment Side, Drop Side, and Terminal Side.

LINE SIGNALS:

Any of a wide variety of communications signals transiting a physical transmission medium (line, facility, circuit or channel).

LINE SPEED:

Refers to the rate of data transmission expressed in bits per second (bps). The maximum speed is dependent upon the capability of the line, MODEM and transmitting and receiving devices.

LINE SWITCHING:

Normally refers to an electrical/mechanical switch connection between two communication lines. This is accomplished either manually or automatically, such as in the Circuit Switching Unit.

LINE TURNAROUND:

1) A reference to the reversal of direction in a half-duplex (HDX) communications circuit

2) MODEM turn around time, such as the change from sending to receiving or receiving to sending.

3) Total time required to change data transmission direction on a communications or telephone line.

LINE UP:

A technician’s term for testing and adjusting the data transmission performance on a circuit to specified levels

LINK:

1) Could refer to a channel, circuit, line or Hyper-Link; a point-to-point circuit functioning as one component of a network.

2) Network communications channel consisting of a circuit or transmission path and all related equipment between a sender and a receiver; quite often used to refer to a WAN connection.

3) In the context of a transmission network, a link is a point-to-point connection between adjacent nodes, such as two Cisco ONS 15900s. There can be more than one link between adjacent nodes.

LINK ACCESS PROCEDURE FOR MODEMS (LAPM):

A type of error control used by some types of MODEM

LINK ACCESS PROCEDURE-D CHANNEL (LAP-D and LAPD):

A signaling protocol on ISDN-D channels: LAP-D is a part of the high-level data link control (HDLC) protocol.

LINK-BY-LINK ENCRYPTION:

Stepwise protection of data that flows between two points in a network, provided by encrypting data separately on each network link, that is, by encrypting data when it leaves a host or sub-network relay and decrypting when it arrives at the next host or relay. Each link can use a different key or even a different algorithm.

LINK LAYER:

A reference to Data Link Layer: The second layer in the Open Systems Interconnection (OSI) model that establishes / maintains and releases data link connections between the network layer and physical layer. While the data link layer is not responsible for error correction, it does perform error detection, transmission and reception of data-grams, packet reception and local addressing

LINK LOADING:

The amount of communication traffic carried by a Link or by the most heavily loaded link in the system. Contention increases as link loading increases

LINK ROT:

A Term used to describe the frequent problem caused by the constant changing in URLs (Uniform Resource Locator). A Web page or search tool offers a link and when you click on it, you get an error message (‘not available’) or a page saying the site has moved to a new URL. Search engine spiders have a problem keeping up with the changes. URLs change frequently because the documents are moved to new computers, the file structure on the computer is reorganized, or sites are discontinued. Many times there isn’t a reference to a new link (URL).

LINK-STATE ROUTING ALGORITHM:

Routing algorithm in which each router broadcasts or multicasts information to all nodes in the inter-network regarding the cost for reaching each of its neighbors: Link state algorithms create a consistent view of the network and therefore are not prone to routing loops; however, they achieve this at the cost of relatively greater computational difficulty and more widespread traffic.

LINKED ARRAY:

A data structure media designed to allow the joining of various sized lists in a manner that allows the inserting and deleting of the list elements, in parallel, without contention.

LINKED CHANNELS:

A term used when two or more channels are used between Communications Switching Centers (AUTODIN ASC) in order to provide adequate service. When a single channel cannot provide adequate service, without delays, additional channels, linked to the first, are provided. This linking is accomplished within the system program.

LINKED OBJECT:

An object that is inserted into a document but still exists in the source file: When information is linked, the new document is updated automatically if the information in the original document changes.

LINUX:

A widely used Open Source Unix-like operating system: Linux was first released in 1991. There are versions of Linux for almost every available type of computer hardware from desktop machines to large mainframes. The inner workings of Linux are open and available for anyone to examine and change as long as they make their changes available to the public.

LIQUID CRYSTAL DISPLAY (LCD):

A type of display used in digital watches and many portable computers. LCD displays utilize two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light.

LIS:

Logical IP Subnet: A group of IP nodes (hosts and/or routers) that connects to a single ATM network and belongs to the same IP subnet.

LISTPROC:

One of the common types of E-mail discussion lists.

LISTSERV ®:

The most common kind of mail-list: Listserv is a registered trademark of L-Soft international, Inc. Listserv(s) originated on BITNET (‘Because It's Time NETwork’ or ‘Because It's There NETwork’), but Listserv(s) are now common on the Internet.

Automated mailing list distribution system originally designed for the Bitnet/EARN network. Allows users to add or delete themselves from mailing lists without any other human intervention.

LITERATI:

Since 1992, Literati information technology has provided comprehensive Information Technology and Web Development consulting services to businesses throughout north central West Virginia and the tri-state area.

Literati information technology provides a resource for all current author-related information, as provided directly by authors or their publishers, or as researched by the Literati staff.

LITTLE-ENDIAN:

Method of storing or transmitting data in which the least significant bit or byte is presented first

LLAP:

Local-Talk Link Access Protocol: Link-level protocol that manages node-to-node delivery of data on a Local-Talk network. LLAP manages bus access, provides a node-addressing mechanism, and controls data transmission and reception, ensuring packet length and integrity.

LLC:

Logical Link Control: The higher of the two data link layer sub-layers defined by the IEEE. The LLC sub-layer handles error control, flow control, framing, and MAC-sub-layer addressing. The most prevalent LLC protocol is IEEE 802.2, which includes both connectionless and connection-oriented variants.

LLC2:

Logical Link Control, type 2: Connection-oriented OSI LLC-sub-layer protocol

LMDS:

1) Local Multipoint Distribution System: A fixed broadband wireless system used for voice and interactive data. Generally used as a lower cost alternative to landline connections for businesses and others requiring high bandwidth connections to public networks.

2) Local Multipoint Distribution Service: A relatively low power license for broadcasting voice, video, and data. There are typically two licenses granted in three frequencies, each to separate entities within a BTA. These licenses are known as Block A or Block B licenses. Block A licenses operate from 27.5 to 28.35 GHz, 29.10 to 29.25 GHz, and 31.075 to 31.225 GHz for a total of 1.159 MHz of bandwidth. Block B licenses operate from 31.00 to 31.075 GHz and 31.225 to 31.300 for a total of 150 MHz of bandwidth. LMDS systems have a typical maximum transmission range of approximately 3 miles as opposed to the transmission range of an MMDS system, which is typically 25 miles. This difference in range is primarily a function of physics and FCC allocated output power rates.

LMF:

Language Media Format: Message (data) code set and protocol indicator; a two-character field included in the header portion of the message.

LMFS:

Lockheed Martin Federal Systems

LMI:

Local Management Interface: Set of enhancements to the basic Frame Relay specification. LMI includes support for a keep-alive mechanism, which verifies that data is flowing; a multicast mechanism, which provides the network server with its local DLCI and the multicast DLCI; global addressing, which gives DLCI(s) global rather than local significance in Frame Relay networks; and a status mechanism, which provides an on-going status report on the DLCI(s) known to the switch.

LMT:

Cisco's Last Mile Technology

LM/X:

LAN Manager for UNIX: Monitors LAN devices in UNIX environments

LNM:

LAN Network Manager: SRB and Token Ring management package provided by IBM. Typically running on a PC, it monitors SRB and Token Ring devices, and can pass alerts up to Net-View

LNNI:

LAN Emulation Network-to-Network Interface: Supports communication between the server components within a single ELAN

LNS:

L2TP Network Server: A node that acts as one side of an L2TP tunnel endpoint and is a peer to the L2TP Access Concentrator (LAC). The LNS is the logical termination point of a PPP session that is being tunneled from the remote system by the LAC.

LOAD BALANCING:

1) A technique used by Windows Clustering to improve the performance of a server-based program (Web server) by distributing its client requests across multiple servers within the cluster. Each host can specify the load percentage that it will handle, or the load can be equally distributed across all the hosts. If a host fails, Windows Clustering dynamically redistributes the load among the remaining hosts.

2) In routing, the capability of a router to distribute traffic over all its network ports that are the same distance from the destination address. Good load-balancing algorithms use both line speed and reliability information. Load balancing increases the use of network segments, thus increasing effective network bandwidth.

LOAD FACTOR:

A ratio of the Peak to Average data transmission load over a designated time period

LOADING:

A method of adding regularly spaced inductance coils to a physical wire circuit to improve its transmission characteristics.

LOADING COIL (Induction Coil):

Refers to a coil that is used to compensate for wire (channel) capacitance and is used to boost the quality level and extend the usable distance on voice-grade lines (channels).

They are added in series with the telephone line, which compensates for the parallel capacitance of the line.

LOCAL ACCESS TRANSPORT AREA:

See LATA

LOCAL ACKNOWLEDGEMENT:

Method where an intermediate network node, such as a router, responds to acknowledgments for a remote end host: Use of local acknowledgments reduces network overhead and, therefore, the risk of time-outs.

LOCAL ADJACENCY:

Two VNS(s) that control different VSN areas but communicate with one another through a Frame Relay PVC; considered being locally adjacent.

LOCAL ANALOG LOOP-BACK:

A loop-back at the line (analog) side of the local MODEM in order to test the analog (AC) output and input circuitry

LOCAL AREA DATASET:

A device designed to perform circuit conditioning of an RS-232 signal over a DC circuit in order to avoid interference from the adjacent circuits.

LOCAL AREA DATA TRANSPORT:

See LADT

LOCAL AREA NETWORK:

See LAN

LOCAL ATTACHMENT:

Refers to the connection of a control unit or peripheral device directly to an IBM host channel; other individuals may also use the term for other systems.

LOCAL BRIDGE:

Bridge that directly interconnects networks in the same geographic area

LOCAL CENTRAL OFFICE / LOCAL EXCHANGE:

See End Office.

LOCAL CHANNEL LOOP-BACK:

A channel loop-back at the channel (line) side of a local MODEM or concentrator / multiplexer for diagnostic testing; input looped back to output.

LOCAL COMPOSITE LOOP-BACK:

Performing a composite loop-back at the output or composite end of the local concentrator/multiplexer for diagnostic testing. Output looped back to Input.

LOCAL DIGITAL LOOP-BACK:

A digital loop-back at the Data Terminal Equipment (DTE) side of a local MODEM; this may apply to a DTE send looped-back to DTE receive or MODEM receive (DC side) loop-back to MODEM send, depending on what is being tested.

LOCAL EXPLORER PACKET:

Packet generated by an end system in an SRB network to find a host connected to the local ring. If the local explorer packet fails to find a local host, the end system produces either a spanning explorer packet or an all-routes explorer packet.

LOCAL LOOP:

The local circuit connection between the end-user and the user's nearest telephone exchange office or computer system.

LOCAL MEASURED SERVICE (LMS); MESSAGE RATE SERVICE:

A pricing system used by LEC(s) (Local Exchange Carrier) to charge users for local exchange telephone usage, in addition to a basically low monthly fee for telephone service.

LOCAL TALK:

Apple Computers proprietary base-band protocol that operates at the data link and physical layers of the OSI reference model: Local-Talk uses CSMA/CD and supports transmissions at speeds of 230.4 kbps.

LOCAL TRAFFIC FILTERING:

Process in which a bridge filters out (drops) frames whose source and destination MAC addresses are located on the same interface on the bridge, thus preventing unnecessary traffic from being forwarded across the bridge.

LOCATION SERVER:

A SIP redirect or proxy server that uses a location service to get information about the location of a caller: Location services are offered by location servers.

LOCD:

Loss of Cell Delineation: A SONET port status indicator that activates when an LOCD defect occurs and does not clear for an interval of time equal to the alarm integration period, which is typically 2.5 seconds.

LOCK-AND-KEY:

Lock-and-key is a traffic filtering security feature that dynamically filters IP protocol traffic

LOF:

Loss of Frame: LOF is a generic term with various meanings depending on the signal standards domain in which it's being used.

A SONET port status indicator that activates when an LOF defect occurs and does not clear for an interval of time equal to the alarm integration period, which is typically 2.5 seconds.

LOGICAL CHANNEL / LOGICAL CONNECTION:

Virtual Circuit: Which is a packet switching environment providing network facilities with the appearance of a dedicated private line, even though the individual packets may be using various communication routes!

LOCAL GROUP:

For computers running Windows and member servers: A group that can be granted permissions and rights from its own computer domain and also from other trusted domains

LOCAL LOOPBACK:

RS-449 signal (Pin 10) – A control signal from the Data Terminal Equipment (DTE) to the Data Communication Equipment (DTE) that causes the analog signal output to be connected to the analog signal receiver input.

LOG FILE:

A file that stores messages generated by an application, service, or operating system: These messages are used to track the operations performed. For example: Web servers maintain log files listing every request made to the server. Log files are usually plain text (ASCII) files and often have a .log extension.

In Backup: A file that contains a record of the date the tapes (discs) were created and the names of files and directories successfully backed up and restored. The Performance Logs and Alerts service also creates log files.

LOGIC BOMB:

A logic bomb is a type of Trojan horse (malicious logic) that executes when specific conditions occur. Triggers for logic bombs can include a change in a file, a particular series of keystrokes, or a specific time or date.

LOGICAL ADDRESS:

Network layer address referring to a logical, rather than a physical network device; also called a Network Address.

LOGICAL CHANNEL:

Non-dedicated, packet-switched communications path between two or more network nodes. Packet switching allows many logical channels to exist simultaneously on a single physical channel.

LOGICAL CHANNEL NUMBER:

A number assigned in packet switching networks whenever a virtual call is placed.

LOGICAL DIAGRAM:

Refers to an equipment design diagram representing the logical (electrical) elements and their interconnections and usually does not express construction or engineering details.

LOGICAL DRIVE:

A volume created within an extended partition on a basic Master Boot Record (MBR) disk. Logical drives are similar to primary partitions, except that primary partitions are limited to four primary partitions per disk, where a user can create an unlimited number of logical drives per disk. A logical drive can be formatted and assigned a drive letter.

LOGICAL GROUP / LOGICAL GROUP NUMBER:

The process of dividing logical channels in packet-switched networks into one of 16 logical groups

LOGICAL PRINTER:

The software interface between the operating system and the printer in Windows: While a printer is the device that does the actual printing, a logical printer is its software interface on the print server. This software interface determines how a print job is processed and how it is routed to a local or network port, to a file, to a remote print share, etc. When a user prints a document, it is spooled (or stored) on the logical printer before it is sent to the printer itself.

LOGIN:

1) The account name used to gain access to a computer system (Not a Password).

2) The act of connecting to a computer system by giving a User Name and Password.

LOGON SCRIPT:

Files that can be assigned to user accounts: Typically a batch file, a logon script runs automatically every time the user logs on. It can be used to configure a user's working environment at every logon, and it allows an administrator to influence a user's environment without managing all aspects of it. A logon script can be assigned to one or more user accounts.

LOGON SCRIPT PATH:

A sequence of directory names that specifies the location of the logon script: When a user logs on, the authenticating computer locates the specified logon script by following that computers local logon script path.

LONG NAME:

A folder name or file name longer than the 8.3 file name standard of the FAT file system, which can be up to eight characters followed by a period and an extension of up to three characters. The long name version of Windows supports long file names up to 255 characters. This version of Windows automatically translates long names of files and folders to 8.3 names for MS-DOS and Windows 3.x users.

In a Macintosh environment, users can assign long names to files and folders on the server and, using AppleTalk network integration, can assign long names to Macintosh-accessible volumes when they are created.

LONG SPACE DISCONNECT:

A MODEM function, which causes a connection termination in response to an extended space signal (open line condition).

LONGITUDINAL BALANCE:

A measurement of the electrical balance between the two conductors (tip and ring) of a telephone circuit (or other circuit): specifically, the difference between the tip-to-ground and ring-to-ground. If the longitudinal balance of a circuit is insufficient, cross talk, electronic chatter, and miscellaneous noises can occur. The term Tip and Ring refers to a ‘plug’ (connector) that is inserted into a ‘Jack’, one wire of the circuit connected to the plug tip and the other wire connected to the ring of the plug, with insulation between. This allows for rerouting and testing circuits.

LONGITUDINAL CURRENTS:

A term used to identify a line condition where current flows in the same direction in the two conductors of a cable pair (pair of wires).

LONGITUDINAL REDUNDANCY CHECK (LRC):

A parity error detection method often called Horizontal Parity Checking, where the Block Check Character (BCC) consists of bits calculated on either odd or even parity for all the characters in the transmitted block.

LONGITUDINAL REDUNDANCY CHECK BIT (LRC):

A block checking procedure in which the check characters depend only on bits of corresponding positions in the data characters. See Longitudinal Redundancy Check

LOOP:

1) A coding technique in computers where the same group of instructions are continuously reused, with modifications to the data being manipulated.

2) A circuit between the user and the central office. See Local Loop

3) Route where packets never reach their destination, but simply cycle repeatedly through a constant series of network nodes.

LOOP-BACK TEST, LOOP-BACK:

Diagnostic tests used to evaluate and compare the signal transmitted with the returned signal, which helps determine the operational status of the equipment and related transmission paths. For instance, this could be accomplished on the dc or ac side of a MODEM, which would allow the testing of the local equipment or the line (channel)

LOOP START:

1) A signal that indicates an off-hook condition between an analog telephone set and a switch; by picking up the receiver, the loop will close and will allow DC current to flow.

2) A method of signaling where a DC closure is applied to a phone line (loop) and the start of DC current flow indicates a change from on-hook to off-hook.

LOOP START TRUNK:

A two-wire central-office trunk or dial-tone line that recognizes off-hook status when a telephone switch hook puts a 1000-ohm short across the tip and ring as the handset is lifted.

LOP:

Loss of Pointer: Failure state in the SONET signal where a receiving network cannot identify/lock on the pointer value of the H1 and H2 bytes to show the location of SPE.

LOS / LOSS:

1) A reduction in a signals level as expressed in decibels

2) Loss of Signal: Occurs when ‘n’ consecutive zeros is detected on an incoming signal.

3) Line of Sight: Refers to the fact that there must be a clear, unobstructed path between the transmitters and receivers. See Loss of Signal. Also see attenuation.

LOSS OF SIGNAL (LOS):

The absence of data pulses for one millisecond or more.

LOSSY:

Characteristic of a network that is prone to lose packets when it becomes highly loaded; low-entry networking node

LOW FREQUENCY (LF):

Normally refers to frequencies in the 30 to 300 kHz range.

LOW PASS:

Usually refers to a filtering device passes (allows) only frequencies below a predetermined level.

LPD SERVER:

See Line Printer Daemon

LPD:

Line Printer Daemon: Protocol used to send print jobs between UNIX systems

LR:

Long Reach: The distance specification for optical systems that operate effectively from 20 to 100 km (12.5 to 62 mi).

LRC:

See Longitudinal Redundancy Check

LRM:

Low Rate Multiplexer

LSA:

Link-State Advertisement: Broadcast packet used by link-state protocols that contains information about neighbors and path costs. LSA(s) are used by the receiving routers to maintain their routing tables.

LSB:

Least Significant Bit: Bit zero

LSC:

1) Label Switch Controller: Controller that creates cross-connects in an ATM switch so that labeled packets are forwarded through the switch; formerly referred to as Tag Switch Controller (TSC).

2) Link State Control: SS7 MTP 2 function that provides the overall coordination of a session

LSCDM:

Low Speed Cable Driver MODE:

LSI:

Large Scale Integrated (chip or circuit)

LSP:

Link-State Packet

LSP TUNNEL:

Label Switched Path Tunnel: A configured connection between two routers that uses MPLS to carry the packets.

LSR:

Label Switch Router: The role of an LSR is to forward packets in a MPLS network by looking only at the fixed-length label.

LSSU:

Link Status Signal Unit: SS7 message that carries one or two octets (8-bit bytes) of link status information between signaling points at either end of a link. It is used to control link alignment and to provide the status of a signaling point, such as a local processor outage, to the remote signaling point.

LTC:

1) Line Traffic Controller - 96 channels (ADU/ATC)

2) Line Termination Coordinator: The LTC was the front-end unit used in overseas AUTODIN systems. The multi-purpose overseas computers were capable of being assigned to the CM (Communication Processor) or LTC function by loading the appropriate program.

LTE:

Line-Terminating Equipment: Network elements that originate and/or terminate line (OC-n) signals. LTE(s) originate, provide access, modify, and/or terminate the transport overhead.

LTRS:

See Letters Shift

L2F PROTOCOL:

Layer 2 Forwarding Protocol: Protocol that supports the creation of secure virtual private dial-up networks over the Internet.

L2TP:

Layer 2 Tunneling Protocol: An industry-standard Internet tunneling protocol. Unlike Point-to-Point Tunneling Protocol (PPTP), L2TP does not require IP (Internet Protocol) connectivity between the client workstation and the server. L2TP requires only that the tunnel medium provide packet-oriented point-to-point connectivity. The protocol can be used over media such as ATM, Frame Relay, and X.25. L2TP provides the same functionality as PPTP. Based on Layer 2 Forwarding (L2F) and PPTP specifications, L2TP allows clients to set up tunnels across intervening networks.

L2TP SESSION:

Communications transactions between the LAC and the LNS that support tunneling of a single PPP connection: There is a one-to-one relationship among the PPP connection, L2TP Session, and L2TP call.

LU:

Logical Unit: Primary component of SNA; an NAU that enables end users to communicate with each other and to gain access to SNA network resources.

LU 6.2:

Logical Unit 6.2: In SNA, a LU that provides peer-to-peer communication between programs in a distributed computing environment. APPC runs on LU 6.2 devices.

LUN:

Logical Unit Number: An encoded 3-bit identifier used on an SCSI (Small Computer System Interface) bus to distinguish among up to eight devices (logical units) with the same SCSI ID. A LUN is an indivisible unit presented by a storage device to its host. LUN are assigned to each disk drive in an array so the host can address and access the data on those devices.

LUN MASKING:

An array security feature that lets a server access only its own and no other LUN (Logical Unit Number) on a Fiber Channel; each LUN can specify what host or combination of hosts has access to that LUN.

LUNI:

LAN Emulation User-to-Network Interface: The ATM Forum standard for LAN emulation on ATM networks; defines the interface between the LEC and the LAN Emulation Server components.

LURK:

The term refers to individuals that listen to chat room or newsgroup discussions without participating: Newcomers are encouraged to lurk for a while until they get the feel of things. The term ‘lurker’ is sometimes used negatively to refer to people who take from discussions, but never give.

LVC:

Label Switched Controlled Virtual Circuit: A Virtual Circuit (VC) established under the control of MPLS. The LVC is not a PVC or SVC. The LVC must traverse only a single hop in a Label-Switched Path (LSP) but the LVC can traverse several ATM hops if it exists within a VP tunnel.