Layer 2 Forwarding Protocol

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

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.

Local Area Network

A network that uses dedicated in-house links to connect a group of organizational users within an office, a building, or a campus without using facilities from a telephone company or other outside carrier.

High-speed switch that forwards packets between data-link segments. Most LAN switches forward traffic based on MAC addresses. This variety of LAN switch is sometimes called a frame switch. LAN switches are often 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.

This is the practical set of tools, from OS layer protocols to support services that make a remote access device an effective link between LANs and WANs. An effective remote access server must include a host of communications and translation protocols to fulfil this function.

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 ELANs.

LANE User-Network Interface

Link Access Procedure, Balanced

Data link layer protocol in the X.25 protocol stack. LAPB is a bit-oriented protocol derived from HDLC.

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 signalling requirements of ISDN basic access.

Link Access Procedure for Modems

Light Amplification by Stimulated Emission of Radiation

Analogue transmission device in which a suitable active material is excited by an external stimulus to produce a narrow beam of coherent light that can be modulated into pulses to carry data. Networks based on laser technology are sometimes run over SONET

Local-Area Transport

A network virtual terminal protocol developed by Digital Equipment Corporation.

Local Access and Transport Area

LATAs are geographic regions within the United States that define areas within which Bell operating companies can offer exchange and exchange-access services.

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

Loop Access Test System

A relay connection matrix that provides access to individual customer four-wire local loops and/or to DS0 (64 kbps) circuits. The matrix is only at DDS hub offices.

Emerging 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 are functionally equivalent to bridges. These downsides for a large, flat network include being subject to broadcast storms, spanning tree loops, and address limitations.

Logical Channel Identifier

Logical Channel Number

Link Control Protocol

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

Least Cost Routing

Line Code Violation

Lightweight Directory Access Protocol

Directories containing information such as names, phone numbers, and addresses are often stored on a variety of incompatible systems. LDAP provides a simple protocol that allows you to access and search these disparate directories over the Internet.

Long Distance Carrier

Low-Delay CELP

CELP voice compression algorithm providing 16 Kbps, or 4:1 compression.

LAN Emulation Address Resolution Protocol

Protocol that provides the ATM address that corresponds to a MAC address.

A transmission facility which is leased by an end user from a public carrier, and which is dedicated to that user's traffic. Typically, frequency synchronization is maintained from one end of the circuit to the other. Leased line circuits are generally used less in recent times, while public data networks are more common.

Local Exchange Carrier

Local telephone company, providing connections between local points or to long distance carriers for extended connections.

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.

LAN Emulation Configuration Server

Entity that assigns individual LANE clients to particular ELANs by directing them to the LES that corresponds to the ELAN. There is logically one LECS per administrative domain, and this serves all ELANs within that domain.

Low Earth Orbit satellite

Satellites that are not stationary from a fixed point on earth and have the lowest orbit of all communication satellites. Must either be tracked or use a frequency band and access methodology that allows access to the satellite with a non-directional antenna. Most handset-to-satellite systems are based on LEO satellites using L-Band.

LAN Emulation Server

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

Characteristic of certain transmission systems such as laser, microwave, and infrared systems in which no obstructions in a direct path between transmitter and receiver can exist.

The speed of the physical wire attached to the interface or interface hardware. The line speed is 10Mbps for Ethernet and 1.544Mbps for T1.

Logical IP Subnet

A group of IP nodes (such as hosts and routers) that connects to a single ATM network and belongs to the same IP subnet

Line LoopBack

Logical Link Control

Higher of the two data link layer sublayers 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.

Logical Link Control, Type 2

Connection-oriented OSI LLC-sub-layer protocol

Local Multipoint Distribution Services

A digital wireless cable system that provides two-way transmission in the 28 gigahertz range of the spectrum. It depends on line of sight and requires a transmitter every few miles.

Local Management Interface set

Set of enhancements to the basic Frame Relay specification. LMI includes support for a keepalive 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 DLCIs global rather than local significance in Frame Relay networks; and a status mechanism, which provides an on-going status report on the DLCIs known to the switch. Known as LMT in ANSI terminology.

Loop Maintenance Operations System

A testing system for voice grade telephone service that records customer trouble reports and tracks subsequent maintenance activities.

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 NetView.

In routing, the ability 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.

Bridge that directly interconnects networks in the same geographic area.

The physical wires that run from the subscriber's telephone set, PBX, or key telephone system, to the telephone company central office. Increasingly, the local loop now goes from the main distribution frame in the basement to the telephone company. The subscriber is responsible for getting his wires from the box in the basement to this phone, PBX, or key system.

Apple Computer's proprietary baseband protocol that operates at the data link and physical layers of the OSI reference model. LocalTalk uses CSMA/CD and supports transmissions at speeds of 230.4 Kbps.

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.

A test procedure in which the received signal returns to its source.

Loss Of Signal

The absence of pulses lasting for one millisecond or more.

Link-State Routing Protocol

A sophisticated method of determining the shortest paths through the network.

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.