Index - A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z
LADT (LOCAL AREA DATA TRANSPORT) - 1.) One of a number of similar names for LEC service offerings of in-city data transport using baseband (short haul) modems rented from the LEC, with names such as LADS ( Local Area Data Service ) being typical; 2.) AT&T's product name for providing simultaneous voice and data (see SVD) by Frequency Division Multiplexing 4800 bps data above speech signals on a two-wire voice telephone exchange line; when used in combination with Centrex and a data PBX in the LEC's exchange building, the resultant data operation is called Datakit.
LASER - Acronym for: Light Amplification by Stimulated Emission of Radiation; converters of electrical energy into light of great purity and thus controllability adequate for telecommunications by guiding the energy along glass waveguides; used more commonly for high- capacity, long-haul fiberoptic links of common carriers; the fiber links of end users most commonly employ less expensive Light Emitting Diodes ( LED ) for shorter distances and lower capacities.
LATENCY - Used by some to describe the time delay from the point when a network station seeks access to a transmission channel and the time access is granted by the network; an evolving term unique to certain LANs.
LAYER; LAYERING; LAYERED ARCHITECTURE - Nomenclature of the OSI Reference Model for data transport that defines the functions in each step of a hierarchy of operations that must occur in order to transfer information between points.
LEASED LINES - Any circuit or combination of circuits designated to be at the exclusive disposal of a given user. - Synonym: Private line; Full Period Line; Dedicated Line, Tie Line (colloquial).
LEAST COST ROUTING (LCR) - The function of automatically selecting the least expensive means for connection of a given call. - Synonym: Most Economical Route Selection (MERS); Automatic Route Selection (ARS); Flexible Route Selection. Typically a feature of electronic PBXs, which vary widely in their approach and abilities to perform the task; requires custom loading of a table of the services available, class-marking of each station on the PBX and maintenance of the tables with changes. LED (LIGHT EMITTING DIODE) - A semiconductor device that emits light under proper electrical conditions. Used both for simple indicators on electronic equipment and (with proper selection and use)as the source of signals for short-range (multimode) fiber optic transmission systems. LEVEL - An expression of the relative signal strength at a point in a communications circuit compared to a standard; the standard is most often 1 milliwatt of power at a frequency of 1000 Hertz in a 600 Ohm circuit for 4 wire circuits and 900 Ohms for 2 wire circuits. Internationally, the frequency is 800 Hertz per CCITT standards.
LIGHTWAVE COMMUNICATIONS (LIGHTGUIDE COMMUNICATIONS, OPTICAL COMMUNICATIONS, FIBEROPTIC COMMUNICATIONS) - Descriptive of the use of frequencies in the visible light portion of the electromagnetic spectrum for the transmission of information. "Optical communications" may also mean use of lightwaves in free space. LIMITED DISTANCE MODEM (LDM); SHORT-HAUL MODEM; SHORT-
RANGE MODEM (SRM); BASEBAND MODEM - Descriptive of a wide variety of data modems that take advantage of the wide bandwidth available for, in some cases, up to 20 miles in non-loaded local telephone cable; there are no standards as to how these modems do their job, but there are LEC restrictions on use of certain types on LEC cable facilities. A class of these devices with names like "cable line driver" imply the most minimal of modulation processes; confusion abounds in the descriptive names of this class of devices.
LINE - A widely-variable term for may sorts of transmission paths in telecommunications work.
LINE CONTROL UNIT (LCU) - A data communications term used by some vendors for hardware that controls polling and access by remote terminals; most commonly found in minicomputer networks, LCU capability ranges from simple hardware to processor-based devices with a history dating to telegraph networks.
LINE HIT - Descriptive of short, random disturbances to transmission facilities that cause errors in transmission; non-specific as to the cause or remedy for them.
LINE PRINTER - Descriptive of computer printers that set and print an entire line of data at a time; often indicative of a high-speed, high volume printer.
LINE SIDE - Descriptive of observing from or sending into the transmission path. Antonym: Equipment Side; Drop Side; Terminal Side.
LINE SIGNALS - 1.) In the CCITT sense, equivalent to "supervisory signaling" in Bell network language; 2.) In North American colloquial use, any of a wide variety of communications signals as found transiting a physical transmission medium..
LINE UP - Plant technician colloquialism for testing and adjusting transmission performance of a circuit to specified levels and losses at various points along the circuit.
LINK - 1.) Non-specific term for any sort of communications facilities; 2.) A portion of a circuit intended to connect two points in tandem.
LINK LAYER - The logical second layer of the OSI Reference Model for Open Systems Interconnection, located between the Physical and Network layers.
LOAD FACTOR - Ratio of the Peak to Average ratio over a designated time period; has meaning in both traffic engineering and in transmission technology, particularly for data transmission.
LOADING - A method of adding regularly spaced inductance coils to a physical wire circuit to improve its transmission characteristics for speech; may cause adverse effects to baseband digital transmission. Internationally called "Pupinisation," honoring its Polish developer, the physicist Pupin.
LOCAL ACCESS AND TRANSPORT AREA (LATA) - A geographic area (called "exchange" or "exchange area" in the MFJ) within each LEC's franchised territory established in accordance with the provisions of the MFJ; its purpose is to define the territory within which a LEC may offer its telecommunications services. Transportation of information beyond the LATA must be accomplished by an IEC.
LOCAL AREA NETWORK (LAN) - Intraoffice communication system usually used to provide high-speed data transmission within a limited area. Definitions of the geographic scope of a LAN are fuzzy, as are definitions of its precise capability and capacity.
LOCAL EXCHANGE CARRIER (LEC) - A local telephone company, either one of the 23 Bell Operating Companies (BOC) or one of the 1400+ independent local (non-Bell) telephone companies; their scope of total service offerings is now restricted to within their LATA, with transport beyond their LATA mandated to an IEC.
LOCAL MEASURED SERVICE (LMS, MEASURED SERVICE, MESSAGE RATE SERVICE) - A pricing system used by LECs to charge users ( in the form of " message units ") for local exchange telephone usage, in addition to a basically low monthly fee for telephone service. Widely used since the 19-teens in established, dense telephone markets as a basis for local telephone service. Also rather common in European cities, where users are charged for "pulses" that represent some number of seconds of usage that vary with the distance of individual calls, even on long distance calls extending to intercontinental lengths. Alternatives are " Flat Rate " pricing and " Call Detail Billing ," both seen more frequently in North America, particularly in non-Bell areas.
LOCAL LOOP - The local circuit connection between the end user and the user's nearest telephone exchange office; notorious for being the poorest, weakest link in data circuits.
LOGICAL LINK CONTROL (LLC) - a protocol standardized by the IEEE for use in 802-type LAN, for data link level transmission control; the upper sublayer of Layer 2 of IEEE's OSI equivalent model, complementing Medium Access Control (MAC) in IEEE 802.2.
LONG HAUL (LONG-HAUL) - Descriptive of communications circuits spanning considerable distances; ranging from inter-LATA to intercontinental.
LOOP BACK (LOOPBACK; LOOP-BACK) - A transmission testing method of simply having the distant end on a circuit send back the signals it receives for evaluation at the transmitting end; subject to a variety of ambiguities, even false affirmatives in certain situations. Historical synonyms: Busback; Bus Back; Bust-back.
LOOP SIGNALING - Any of several supervisory signaling methods which use the metallic loop formed by cable wire conductors and terminating equipment; in historic toll cable working, the terms Simplex (SX), DX (DUPLEX) and EMX describe several Bell methods. LOS (LINE OF SIGHT; LOSS OF SIGNAL) -1.) Descriptive of the use of free-space communications technologies requiring an unobstructed path between transmitter and receiver, as in microwave radio, satellite communications, and infrared optical communications links; 2.) NASA operating term for interruption of communications with a given ground station from a space vehicle as it passes rapidly over the Earth's surface.