L L Light lens; a photocopier term. L-Band That part of the electromagnetic spectrum usually applied to satellite and microwave communications. LAB Line attachment base. LAMA See local automatic message accounting. LAN See local area network. LAN Manager Local area network management software jointly developed by Microsoft and 3Com that runs under MS-DOS and OS/2. land The flat, unmarked area between the marks on an optical disk. land and groove A physical feature of optical disks, applied during manufacture, which defines track locations. The groove is recordable, the land separates the grooves and is not recordable. land mobile service Two-way radio service in the 44-50 MHz band. landline The traditional telephone services and/or companies. landscape Page or monitor orientation in which the page width exceeds the page length. LAP Link Access Protocol. LAP-B link access procedure-balanced. CCITT-compatible protocolthat provides error-controlled access to packet-switched networks. LAP-D See link access procedure. LAP-M Link access pocedure for modems protocol. large scale integration (LSI) Depositing many electronic circuits, including transistors, on a small silicon chip in a single manufacturing process. laser Light Amplification by Stimulated Emission of Radiation. A very narrow beam of intense, single-wavelength light used to read and write data on an optical disk. laser disk Storage means written and read by laser. See also optical disk and video disk. laser fax A conventional laser printer that also can be used as a fax machine when combined with an optional plug-in cartridge and used with a personal computer. laser optical System of recording on grooveless disks using a laser-optical-tracking pickup. laser printer Printer that uses a beam of light to elecrostatically change a drum so that it attracts toner, which is transferred to heated paper. laser servo Using a laser-readable tracking technique for magnetic recording. Results in greater data capacities. This is the basis of floptical. LaserJet Hewlett-Packard (HP)'s desktop printer that has set the industry standard. last in/first out (LIFO) A queuing technique in which the newest entry in a queue or file is the first to be removed. last number redial A PBX/electronic key telephone feature in which the last number dialed can be automatically redialed at the touch of a preprogrammed button. LAT Local Area Transport; Digital Equipment's DECnet protocol that controls micro-host links. LATA See local access and transport area. latency Akin to waiting time, it is the time interval between a network station seeking access to a transmission channel and that access being granted or received. latent image A residual image on the drum of a electrostatic printer or copier caused by incomplete removal of the static charge from the previous image. lathe In graphic design, it's a way to create a three-dimensional shape by rotating a two-dimensional shape around a central axis. LAWN (Local Area Wireless Network) O'Neill Communications' wireless local area network unit designed to allow PC users to transfer files, exchange messages, and share peripherals. layer A group of functions that provide a defined set of communications services to a specific user. See also OpenSystems Interconnection model. LCD See liquid crystal display. LCMD See logarithmic companded delta modulation. LCN Logically connected node. LCP Language Conversion Program. LCR Least cost routing.See also automatic route selection. LCU See line control unit. LD See long-distance. LDM See limited distance modem. LDN See listed directory number. lead screw A highly accurate screw which is turned at a constant rate to move the optical heads of some laser disk and CD recording machines to produce uniformly spaced spiral tracks. leading The vertical spacing between lines of type (between baselines). learning bridge See smart bridges. leased line A communications line that a user leases from a common carrier (public utility company) for exclusive use. least cost routing (LCR) A method of automatically selecting the least costly facility for transmitting a call. Synonym: MERS (most economical route selection); route optimization; ARS (automatic route selection); flexible route selection. LEC See local exchange carrier; see local exchange. LED See light-emitting diode. LEN Low-Entry Networking. letter quality Printer output that resembles typewritten text. letters shift A teleprinter function initiated by the letters-shift character, causing the machine to shift from upper-to lowercase. level The strength of an audio or video signal. LF See see low frequency. Library A device that automatically handles and stores media and can randomly load and unload individual tapes or disks to and from a drive. library routine A proven routine that is stored in a program library. LIFO See last in/first out. ligature Certain letter combinations that appear frequently together are combined as one character for aesthetic purposes. light Technically, light is electromagnetic radiation visible to the human eye. Light usually means the electromagnetic waves with a wavelength from .000075 cm. (red) to .000038 cm. (violet). light pen A CRT input device that is a light-sensitive stylus connected by cable to a video terminal. The user brings it to a spot on the screen (i.e., to edit text, choose from a menu, or draw an image), then presses a button to initiate the computer's response. light-emitting diode (LED) A small solid-state device that emits light when a current is applied. lightguide A transmission channel that contains a number of optical fibers packaged together. lightwave transmissions Laser communication systems transmitted through the air rather than through fiber optic cable. LILO Last In, Last Out. LIM/EMS Lotus Intel Microsoft Extended Memory Specification. limited-distance modem (LDM) A modem that operates on lines of up to approximately 6 miles. LINC Logic Information Network Compiler (Unisys.) line The transmission path from a nonswitching subscriber terminal to a switching center. line art An image with no grayscale - only black and white. A pen-and-ink drawing is line art. Text is also a kind of line art. line conditioning Telephone company service that reduces envelope delay, noise, and amplitude distortion, enabling the subscriber to transmit higher speed data than over traditional phone lines. line control block (LCB) A storage area containing control information required for managing and scheduling line operations. line control unit A synonym for datalink control protocol. line driver An amplifier that increases a signal's strength before the signal is placed on the address or data bus, or transmitted. line hit Interference that causes a loss or an insertion of spurious bits (unwanted signals) into a data path. line load control Attendant's ability to temporarily restrict least-important stations from initiating outbound calls during excessive traffic load or emergency conditions. line loading A method of minimizing amplitude distortion by equipping a telephone line with loading (inductor) coils. line lockout See lockout. line preference The ability to program a PBX to accept calls on a certain line. line ringing A multibutton telephone can receive ringing signals for incoming calls on specific lines. line screen The resolution of a halftone expressed in lines per inch. Usually between 53 lpi and 150 lpi. line segment In vector graphics, same as vector. line speed The maximum transmission rate of signals over a circuit, usually expressed as baud, or bits per second (bps). line status indication A visual indication of such line conditions as busy, idle, on hold, or ringing. line switching A technique that establishes a connection between incoming and outgoing lines. See also message-switching. line turnaround Action required in a communications system after receiving a data block to reverse the direction of transmission so that the receiving device can send data. Line turnaround time in a half-duplex system is usually much longer than in a full-duplex system. linear distortion Monitor problem, caused by misalignment of the electron guns that illuminate the color screen pixels. link A communications path between two devices or nodes in a network. See also bridge or gateway. Link Access Procedure (LAP-D) A member of the HDLC (High LevelData Link Control) protocol family, provides reliable signaling on anISDN-D channel. link layer The layer in the OSI model relating to data transmission between network nodes. linotronic A brand of photographic imagesetters made by Allied Linotype Company that are PostScript compatible and have a resolutions up to 2400 dpi. liquid crystal display (LCD) Liquid crystals are low power consumption devices that produce a non-emissive display system (i.e., modulate ambient light rather than emit light) with good visibility even in sunlight. LISP List Processing (programming language). list processing Method of processing data in list form. A list processing language is used primarily for research (such as in mathematical and arithmetic logic) rather than for production programming. listed directory number (LDN) Incoming network calls to the PBX via telephone directory numbers are routed to the attendant. listserver A file server that automatically mails information to mailing-list subscribers. lithography Common type of printing where the image is etched into a plate, onto which ink is applied and put in contact with the paper. LLAPI Low Level Application Programming Interface (IBM). LLC See logical link control. LM 1. Link Manager. 2. Load Module. LMDS See local multipoint distribution service. LMI See local management interface. lo-res See low resolution. load To enter data from external storage, (i.e., a diskette) to computer memory. load balancing for station/trunk lines PBX feature that permits the subscriber to change phone and trunk terminations on the PBX so that traffic on the network flows more smoothly. load sharing A two- or multiple-computer system that shares the load during peak hours. During nonpeak periods or normal operation, one computer manages the entire load with the other(s) acting as fallback. lobe The angular region over which an antenna or aerial experiences strong reception. local access and transport area (LATA) Defines the local calling area of responsibility for call handling by the BOC's as established by the court-ordered AT&T divesture plan. local area network (LAN) An environment in which multiple workstations, printers, and other devices are connected via cabling to allow users to share resources. local area transport (LAT) A communications protocol used in a local area network. local automatic message accounting (LAMA) Central office equipment that records the information required for billing a subscriber's local phone calls by the local phone company. A local call is a call within the local service area of the calling phone. local call billing In hotel applications, local call billing computes the dollar amount for local calls placed by guests based on total message units. local exchange Switching center where a subscriber's lines terminate. Also called end office. Local exchange carrier (LEC) A local telephone company. local line A channel connecting the subscriber's equipment to the line-terminating equipment in the central office exchange. Usually a two- or four-wire metallic circuit. local loop The local connection between the end user and the Class 5 central office. local management interface (LMI) A specification for use by frame relay products that defines a method of exchanging status information between the user device and the network. local multipoint distribution service Two sets of 50 channels in the 28 GHz band. local regulation When objects on a monitor change size in proportion to their brightness. local service area Area in which calls may be placed without contracting toll charges. local trunk Trunks between local central offices (class 5 offices). LocalTalk Apple's 230K-bps baseband network technology that uses the CSMA/CA media access method. lockout To ensure privacy, the attendant and executive override capabilities are not allowed to function on a station line. See also privacy and lockout. log in See log on. log off Procedure which ends a terminal session. log on Procedure which initiates a terminal session. log out See log off. logarithmic The exponent (power) to which a number (the base) must be raised to yield the original number. logarithmic companded delta modulation (LCDM) A refined delta modulation (DM) technique that logarithmically scales the input amplitude to increase the dynamic range of coding analog signals into digital signals. logic circuit An electronic circuit that is used to complete a logical function and is usually encoded on a chip. logic gate Basic decision-making circuits in digital equipment, usually having two or more binary inputs, and one binary output. logic-seeking printer Printer that skips over blank spaces to speed-printing. logical channel In a packet mode operation, a method of two-way simultaneous transmission across a data link comprising associated send and receive channels. In data communications, an electrical path connecting a station and a channel. logical link control Protocol created by the IEEE 802 committee, common to all of its LAN standards for data link-level transmission control; the upper sublayer of the OSI protocol. logical link control sublayer See LLC sublayer. logical page The area in desktop publishing documents where the text and art appears. May not be the same as the physical size of the page. logical record A record separate from its physical environment (i.e., parts of the same record can be located in different locations). long haul Circuits spanning considerable distances. long-distance Any telephone call outside the local service area. Also called toll call or trunk call. longitudinal balance A measure of the electrical balance between the two conductors (tip and ring) of a telephone circuit; specifically, the difference between the tip-to-ground and ring- to-ground AC signal voltages, expressed in decibels. If the longitudinal balance of a circuit is insufficient, cross talk, electronic chatter, and miscellaneous noises can occur. longitudinal redundancy check (LRC) A block-checking procedure in which each bit of the check character depends only on bits of corresponding positions in the data characters. lookahead routing A switching system feature that uses a dedicated communications channel to verify the availability of all links required to switch the call. loop 1. A short transmission line connecting the user and the switchboard. 2. A closed path in which a signal can circulate; may be within a piece of equipment (e.g., a repeater or carrier terminal) or it may be a complete carrier circuit. loop checking A technique of checking the accuracy of transmission of data in which the received data is returned to the sender for comparison with the original data. loop circuit Circuit linking a subscriber's telephone with the local switching equipment. loop network A central network topology that includes a continuous circuit connecting all nodes in which messages are routed around the loop to and through a central controller. loop signaling Any of the three signaling methods that use the metallic loop formed by the trunk conductors and the terminating equipment bridges. loop-start Supervisory signal, initiated by an off-hook telephone, received at the PBX or local exchange that closes a DC loop and initiates service. loopback Diagnostic test in which a signal is returned to the sending device after passing through a data communications link or network. By comparing the transmitted signal to the received signal, a technician can determine the source of a problem. lossless compression Compression techniques that do not decompress data 100 percent back to original. lossy Methods of image compression, such as JPEG, that reduce the size of an image by disregarding, and losing forever, some of its original data. loudspeaker paging access See paging. low frequency (LF) Band of frequencies between 30 and 300 kilohertz. low level language Languages such as Assembler and C that use symbols which are converted directly into machine code. lpi Lines per inch. lpm Lines per minute. LQ Letter quality. LRC See longitudinal redundancy check. LSI See large-scale integration. LTAB Line and token ring attachment base. LU Logical Unit. LU6.2 Protocol also referred to as APPC, advanced peer-to-peer communications, as defined in the IBM SNA environment. See peer communications. luminance The amount of brightness, measured in lumens, that is given off by a pixel or area on a screen.