L

LAN

Local Area Network: Broadly, any network linking two or more computers and related devices within a limited geographical area (up to a few kilometers). LANs are typically high-speed, low-error networks within a company. Cabling and signaling at the physical and Data Link layers of the OSI are dictated by LAN standards. Ethernet, FDDI, and Token Ring are among the most popular LAN technologies. Compare with: MAN and WAN.

LANE

LAN emulation: The technology that allows an ATM network to operate as a LAN backbone. To do so, the ATM network is required to provide multicast and broadcast support, address mapping (MAC-to-ATM), and SVC management, in addition to an operable packet format. Additionally, LANE defines Ethernet and Token Ring ELANs. See also: ELAN.

LAN switch

A high-speed switching mechanism, transmitting packets between segments of data links, occasionally referred to as a frame switch. LAN switches transfer traffic based on MAC addresses. Multilayer switches are a type of LAN switch. See also: multilayer switch, cut-through packet switching, and store-and-forward packet switching.

LAPB

Link Accessed Procedure, Balanced: A bit-oriented Data Link layer protocol that is part of the X.25 stack and has its origin in SDLC. See also: SDLC and X.25.

LAPD

Link Access Procedure on the D channel. The ISDN Data Link layer protocol used specifically for the D channel and defined by ITU-T Recommendations Q.920 and Q.921. LAPD evolved from LAPB and is created to comply with the signaling requirements of ISDN basic access.

latency

Broadly, the time it takes a data packet to get from one location to another. In specific networking contexts, it can mean either 1) the time elapsed (delay) between the execution of a request for access to a network by a device and the time the mechanism actually is permitted transmission, or 2) the time elapsed between when a mechanism receives a frame and the time that frame is forwarded out of the destination port.

LCP

Link Control Protocol: The protocol designed to establish, configure, and test data link connections for use by PPP. See also: PPP.

leaky bucket

An analogy for the basic cell rate algorithm (GCRA) used in ATM networks for checking the conformance of cell flows from a user or network. The bucket’s “hole” is understood to be the prolonged rate at which cells can be accommodated, and the “depth” is the tolerance for cell bursts over a certain time period. See also: GCRA.

learning bridge

A bridge that builds a dynamic database of MAC addresses and the interfaces associated with each address to reduce traffic on the network.

LE ARP

LAN Emulation Address Resolution Protocol: The protocol providing the ATM address that corresponds to a MAC address.

LEC

LAN Emulation Client: Software providing the emulation of the Link Layer interface that allows the operation and communication of all higher- level protocols and applications to continue. The LEC client runs in all ATM devices, which include hosts, servers, bridges, and routers. The LANE client is responsible for address resolution, data transfer, address caching, interfacing to the emulated LAN, and driver support for higher-level services. See also: ELAN and LES.

LECS

LAN Emulation Configuration Server: An important part of emulated LAN services, providing the configuration data that is furnished upon request from the LES. These services include address registration for Integrated Local Management Interface (ILMI) support, configuration support for the LES addresses and their corresponding emulated LAN identifiers, and an interface to the emulated LAN. See also: LES and ELAN.

LES

LAN Emulation Server: The central LANE component that provides the initial configuration data for each connecting LEC. The LES typically is located on either an ATM-integrated router or a switch. Responsibilities of the LES include configuration and support for the LEC, address registration for the LEC, database storage and response concerning ATM addresses, and interfacing to the emulated LAN See also: ELAN, LEC, and LECS.

Level 1 routing

Used by the IS-IS routing protocol. An area is a group of contiguous networks and attached hosts that is specified to be an area by a network administrator or manager. A domain is a collection of connected areas. Routing domains provide full connectivity to all end systems within them. Level 1 routing is routing within a Level 1 area.

Level 2 routing

Used by the IS-IS routing protocol. An area is a group of contiguous networks and attached hosts that is specified to be an area by a network administrator or manager. A domain is a collection of connected areas. Routing domains provide full connectivity to all end systems within them. Level 1 routing is routing within a Level 1 area while Level 2 routing is routing between Level 1 areas.

link-state routing algorithm

A routing algorithm that allows each router to broadcast or multicast information regarding the cost of reaching all its neighbors to every node in the internetwork. Link-state algorithms provide a consistent view of the network and are therefore not vulnerable to routing loops. However, this is achieved at the cost of somewhat greater difficulty in computation and more widespread traffic (compared with distance vector routing algorithms). See also: distance vector routing algorithm.

listening

One of the five states of a network switch is listening. The others are blocking, learning, forwarding, and filtering.

LLAP

LocalTalk Link Access Protocol: In a LocalTalk environment, the Data Link–level protocol that manages node-to-node delivery of data. This protocol provides node addressing and management of bus access, and it also controls data sending and receiving to assure packet length and integrity.

LLC

Logical Link Control: Defined by the IEEE, the higher of two Data Link layer sublayers. LLC is responsible for error control, flow control, framing, and MAC-sublayer addressing. The predominant LLC protocol, IEEE 802.2, defines both connectionless and connection-oriented operations. See also: Data Link layer and MAC.

LLQ

LLQ is a feature that provides a PQ to CBWFQ. LLQ enables a single PQ within CBWFQ at the class level. With LLQ, delay-sensitive data in the PQ is dequeued and sent first. In a VoIP network with LLQ implementation, voice traffic is placed in the PQ.

LMI

An enhancement to the original Frame Relay specification. Among the features it provides are a keep-alive mechanism, a multicast mechanism, global addressing, and a status mechanism.

LNNI

LAN Emulation Network-to-Network Interface: In the Phase 2 LANE specification, an interface that supports communication between the server components within one ELAN.

load balancing

A technique that distributes network traffic along parallel paths to make the most efficient use of the available bandwidth while also providing redundancy. Load balancing will automatically move a user’s job from a heavily loaded network resource to a less-loaded resource.

local explorer packet

In an SRB network, a packet generated by an end system to find a host linked to the local ring. If no local host can be found, the end system will produce one of two solutions: a spanning explorer packet or an all-routes explorer packet.

LocalTalk

Utilizing CSMA/CD, in addition to supporting data transmission at speeds of 230.4Kbps, LocalTalk is Apple Computer’s proprietary baseband protocol, operating at the Data Link and Physical layers of the OSI reference model.

Logical Address

A logical address is usually assigned by the administrator and is subject to change. IP and IPX addresses are examples of logical addresses.

LPD

LPD is the line printer daemon. It uses the system calls listen and accept to receive requests to print files in the queue, transfer files to the spooling area, display the queue, or remove jobs from the queue. In each case, it forks a child to handle the request so the parent can continue to listen for more requests.

LSA

Link-State Advertisement: Occasionally referred to as link-state packets (LSPs), these advertisements are broadcast packets, containing information about neighbors and path costs, that are employed by link-state protocols. Receiving routers use LSAs to maintain their routing tables.

LSU

(Link State Update) OSPF uses IP multicast to exchange Hello packets and Link State Update packets or routing updates.

LUNI

LAN Emulation User–to–Network Interface: Defining the interface between the LAN Emulation Client (LEC) and the LAN Emulation Server, LUNI is the ATM Forum’s standard for LAN Emulation on ATM networks. See also: LES and LECS.