LAN: Local Area Network
LAN switch: High-speed switch that forwardspackets between data-link segments. Most LAN switchesforward traffic based on MAC addresses. Thisvariety of LAN switch is sometimes called a frame switch.LAN switches are often categorized according to themethod they use to forward traffic: cut-through packet switching or store-and-forwardpacket switching. Multilayer switches are an intelligent subset of LANswitches. Compare with multilayer switch.See also cut-through packet switchingand store and forward packetswitching.
LANE: LAN Emulation
LAP-B: Link Access Protocol, Balanced; Datalink layer protocol in the X.25 protocol stack.LAP-B is a bit-oriented protocol derived from HDLC.See also HDLC and X.25.
LAPD: Link Access Procedure on the D channel;ISDN datalink layer protocol for the D channel. LAPDwas derived from the LAPB protocol and is designedprimarily to satisfy the signaling requirements of ISDNbasic access. Defined by ITU-T Recommendations Q.920and Q.921.
LATA: Local Access and Transport Area; isa term in the U.S. for a geographic area covered by one or more local telephonecompanies, which are legally referred to as local exchange carriers (LECs).A connection between two local exchanges within the LATA is referred toas intraLATA. A connection between a carrier in one LATA to a carrier inanother LATA is referred to as interLATA. InterLATA is long-distance service.The current rules for permitting a company to provide intraLATA or interLATAservice (or both) are based on the Telecommunications Act of 1996.
LaTeX: Additions to 'TeX'written by Leslie Lamport at DEC.
LCD: Liquid-Crystal Display
LCN: Logical Channel Number
LDAP: Lightweight Directory Access Protocol
LEC: Local Exchange Carrier; is the term fora public telephone company in the U.S. that provides local service. Someof the largest LECs are the Bell operating companies (BOCs)which were grouped into holding companies known collectively as the regionalBell operating companies (RBOCs) when the Bell Systemwas broken up by a 1983 consent decree. In addition to the Bell companies,there are a number of independent LECs, such as GTE.
LEC companies are also sometimes referred to as "telcos." A "local exchange"is the local "central office" of an LEC. Lines from homes and businessesterminate at a local exchange. Local exchanges connect to other local exchangeswithin a local access and transport area (LATA) orto interexchange carriers (IXCs) such as long-distancecarriers AT&T, MCI, and Sprint.
LED: Light-Emitting Diode(s)
LEO: Low Earth Orbit; used to describe satellitesorbiting between 600 and 1000 miles above the Earth. A low-earth-orbit(LEO) satellite system employs a large fleet of "birds," each in a circularorbit at a constant altitude of a few hundred miles. The orbits take thesatellites over, or nearly over, the geographic poles. Each revolutiontakes approximately 90 minutes to a few hours. The fleet is arranged insuch a way that, from any point on the surface at any time, at least onesatellite is on a line of sight. The entire system operates in a mannersimilar to the way a cellular telephone network functions. The main differenceis that the transponders, or wireless receiver/transmitters, are movingrather than fixed, and are in space rather than on the earth. A well-designedLEO system makes it possible for anyone to access the Internet via wirelessfrom any point on the planet, using
an antenna no more sophisticated than old-fashioned television "rabbitears."
Some satellites revolve around the earth in elliptical orbits. Thesesatellites move rapidly when they are near perigee, or their lowest altitude;they move slowly when they are near apogee, or their highest altitude.Such "birds" are used by amateur radio operators, and by some commercialand government services. They require directional antennas whose orientationmust be constantly adjusted to follow the satellite's path across the sky.
link-state routing algorithm:Routing algorithm in which each router broadcastsor multicasts information regarding the cost ofreaching each of its neighbors to all nodes in the internetwork. Link statealgorithms create a consistent view of the network and are therefore notprone to routing loops, but they achieve this at the cost of relativelygreater computational difficulty and more widespread traffic (comparedwith distance vector routing algorithms). Compare with distancevector routing algorithm.
LLC: Logical Link Control
LMDS: Local Multipoint Distribution System;Wireless technology operating between 22 and 29 GHz,with a range of approximately 2-5 miles. Currently being used for wirelessTV and 'wireless cable'. LMDS has a similar architecture to cellular technology.Future LMDS modems will offer approximately 54 Mbps. Current data throughputservices are only around 550 Kbps.
LTC: Longitudinal timecode. Timecode recordedon linear track on tape and read by a static head. This can be easily readwhen the tape is moving forwards or backwards but not at freeze frame,when VITC, timecode recorded with the picture material,can be used. See also: VITC.