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LAN (Local Area Network): A data-communications system confined to a limited geographic area with moderate to high data rates. The area served may consist of a single building, a cluster of buildings, or a campus type of arrangement. The network uses some type of switching technology and does not use common-carrier circuits, although it may have gateways or bridges to other public or private networks. 

LAP (Link Access Procedure): A bit-oriented data link protocol derived from the HDLC. It is an earlier version of LAPB and is seldom used today.

LAPB (Link Access Procedure for B channel): A LAP protocol used in ISDN for the B channel.

LAPB (Link Access Procedure, Balanced): A LAP protocol in which stations can only function in balanced mode.

LAPD (Link Access Procedure for D channel): A LAP protocol used in ISDN for the D channel.

LAPM (Link Access Procedure for Modems): A LAP protocol defined for modems.

Last Mile: Expression used to describe the end-user connection to a WAN; i.e., between an ISP and the end-user. Traditionally this has been the main bottleneck when using modems. With newer broadband technology, it is becoming less of an issue.

LATA (Local Access and Transport Area): Under the terms of the Modification of Final Judgment (MFJ), a geographical area within which a divested Bell Operating Company (BOC) is permitted to offer exchange telecommunications and exchange access services. 

Latency: The amount of time it takes for a packet to travel across a network and reach its destination. Together, latency and bandwidth define the speed and capacity of a network.

Launch: To open and run an application. You launch your web browser to view a web page.

LCP (Link Control Protocol): LCP is a PPP protocol used to negotiate the encapsulation format options, handle varying limits on sizes of packets, authenticate the identity of its peer on the link, determine when a link is functioning properly and when it is defunct, detect a looped-back link and other common misconfiguration errors, and terminate the link.

LDAP (Lightweight Directory Access Protocol): is a technology for accessing common directory information. LDAP provides an extendable architecture for centralized storage and management of information that needs to be available for today's distributed systems and service

Leased Line: A permanently connected private telephone line between two locations. Leased lines are typically used to connect a moderate-sized local network to an Internet service provider.

Line Layer: A SONET layer responsible for the movement of a signal across a physical line.

Line Losses - marginal energy costs are estimated at the busbar, where the generation unit first connects to the transmission system. Customers take delivery at various points on the transmission and distribution system. Losses reflect energy dissipation as electricity flows through the wires, and through its transformation down to lower delivery levels. Standard rates include loss factors applicable to the various levels of delivery, transmission, subtransmission, and distribution, and for transformation losses when the customer is metered on the low voltage side of a utility owned transformer. These factors are used to mark off wholesale RTP prices to reflect the higher generation output required to delivery energy to the end-use customer.

Link Layer: Layer Two of the OSI reference model; also known as the Data Link Layer. 

Link State Routing: This type of routing requires each router to maintain at least a partial map of the network. When a network link changes state (up to down, or vice versa), a notification, called a link state advertisement (LSA) is flooded throughout the network. All the routers note the change, and recompute their routing table accordingly. The cost/metric is based on number of hops, link speeds, traffic congestion, and other factors as determined by the network designer. Link state routers use Dijkstra's algorithm to calculate shortest (lowest cost) paths. Link state routing is an improvement over distance-vector routing protocols such as RIP which normally use only a single metric (such as hop count) and which exchange all of their table information with all other routers on a regular schedule. Link state routing normally requires more processing but less transmission overhead. See also BGP.

Link: A text or image within a Web page that causes the browser to open another web page when you click it.

Links: See hyperlink.

Listserv: A program that allows groups to have discussions through e-mail, called mailing lists.

LLC (Logical Link Control): The upper sublayer of the data link layer as defined by IEEE 802.2. See also MAC.

Load (Electric): The amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy-consuming equipment of the consumers.  [DOE Glossary of Electricity Terms]

Load Curve - Graphic presentation of the variation of load versus time. Often aggregations of similar customers are used to estimate energy usage.

Load Schedule - Periodic sets of generation and corresponding loads.

Load-Serving Entity: an entity that provides or arranges for serving the electrical demand and energy requirements of its customers.  (NERC "Terms and Their Definitions As Used in the NERC Planning Standards")

Load Shedding - Manual or automatic shedding of customer loads, usually triggered by emergency conditions, such as when the frequency has dropped below a specific percentage of nominal, resulting from the capacity deficit in the power system.

LocalTalk: Is a cabling scheme offering a plug-and-play network solution that could transmit data at 234 kb/s. Compare with Ethernet.

Logging: The process of storing information about events that occurred on the firewall or network.

Logical Device Model: A Logical Device model is the entity which is connected to the communications network. It contains one or more Physical Device models.

Logical Unit: concept used in IEC 61850 for grouping object models into useful blocks. In UCA, Logical Units were referred to as Bricks.

Login: An opening procedure to identify yourself to a system as a legitimate user and begin a session. To log in you usually need a valid user name and password that were preassigned by the system administrator of the system.

Logout: A closing procedure to formally end a session with a system.

Loopback: A diagnostic procedure used for transmission devices. A test message is sent to a device being tested. The message is then sent back to the originator and compared with the original transmission. Loopback testing may be performed with a locally attached device or conducted remotely over a communications circuit.