labeling system - See ANSI/TIA/EIA-606-A, Administration Standard for Commercial Telecommunications Infrastructure.

labor list - A complete list of all major units of labor to be employed on the project.

ladder cable tray - A prefabricated structure consisting of side rails connected at the bottom by transverse members (rungs) for supporting and routing cables or conductors within the structure.

ladder rack - A device similar to a cable tray but more closely resembles a single section of a ladder. It is constructed of metal with two sides affixed to horizontal cross members.

ladder tray - See ladder cable tray and cable tray.

LAN address - See local area network (LAN) address and medium access control (MAC) address.

LAN emulation (LAN-E or LANE) - 1. A set of specifications for the translation process allowing the operation of LAN-toLAN bridged connectivity over an asynchronous transfer mode (ATM) network allowing ATM to be deployed on a legacy LAN or legacy LAN applications. 2. The method used by ATM switching equipment to emulate the characteristics of shared-media LANs.

laser - See light amplification by stimulated emission of radiation.

laser diode - A laser for optical fiber applications, usually made from a p-n junction in a semiconductor material. Laser diodes give higher performance at higher cost than light-emitting diodes. Laser diodes are commonly used with singlemode optical fiber.

laser launch bandwidth - The effective bandwidth of a fiber when a laser is launched into it.

lashing - Attachment of cable to another cable or support strand by wrapping thin metallic or dielectric strands around them.

last mile - Generally referred to as the last leg of network transport from the point of presence or local exchange switch to a home or business.

latency - The time it takes for a signal to pass through a device or network (e.g., the delay between the time a switch receives a message on an input port and forwards it to an output port).

lateral conduit - A conduit placed from the sidewall of a maintenance hole to the structure.

launch cable - The length of optical fiber cable used to condition the launch of the optical time domain reflectometer test signal so that the correct results will be obtained.

lay - The length measured along the axis of a wire or cable required for a single strand (in stranded wire) or conductor (in cable) to make one complete turn about the axis of the conductor or cable. In a twisted-pair cable, the lay length is the distance it takes for the two wires to completely twist around each other.

lay direction - The direction of the progressing spiral twist in a cable while looking along the axis of the cable away from the observer. The lay direction can be either clockwise or counter clockwise.

Layer 1 - See Physical layer

Layer 2 - See Data Link layer

Layer 3 - See Network layer

Layer 4 - See Transport layer

Layer 5 - See Session layer

Layer 6 - See Presentation layer

Layer 7 - See Application layer

Layer 2 address - See device address.

Layer 2 switching - A technology that is functionally equivalent to bridging.

Layer 3 switching - A combination of Layer 2 switching and Layer 3 routing that integrates routing with switching, resulting in high data transfer rates.

Layer 4 switching - A technology that enables routing decisions to be made on the basis of application-related information to determine priorities and allocate bandwidth.

LC connector - A small form factor (SFF) single fiber, optical fiber connector used for the termination of both multimode and singlemode optical fiber cables. A two-fiber, duplex connector option is also available. The housing mechanism of the LC connector (simplex and duplex) is a push-pull type connection.

leaky coax - A colloquial term for radiating cable. See also radiating cable/leaky coaxial cable (LCX).

learning - The process of associating port numbers with media access control addresses.

lease - A contract that grants the lessee (tenant) the right to occupy the property of the lessor (landlord) for a specified period of time.

least squares averaging (LSA) - A mathematical technique utilized in the measurement of optical fiber that allows the detection and evaluation of certain characteristics. Typically applies to the use of optical test equipment.

leg - 1. The portion of the conduit elbow that is straight. 2. A segment of an end-to-end route or path (e.g., a path from user to user via several networks and nodes within networks).

legend - A list of symbols and abbreviations on construction documents.

lens antenna - Antennas that consist of lenses that are fed by a specially designed feed horn to focus the radio frequency energy.

license - An interest in property for a limited time and purpose.

lien - A legal right of a party or claimant, such as a subcontractor, to control the improved property of another or have it sold for payment of a claim. (CSI)

lifting belt - Safety device designed to be warn around the abdomen to help support the stomach muscles while encouraging proper posture.

light amplification by stimulated emission of radiation (laser) - A device that produces coherent, highly directional light with a narrow range of wavelengths used in a transmitter to convert information from electric to optical form.

light commercial building - A building or portion thereof that is intended for use with one to four nonresidential exchange access lines per tenant. (TIA)

light-emitting diode (LED) - A semiconductor diode that spontaneously emits incoherent light from the PN junction when forward current is applied. It converts information from electrical to optical form. An LED typically has a large spectral width.

lightning down conductor - A metallic conductor running vertically down a building, connecting the air terminals, and equalizing conductorstothe lightning ground terminals.

lightning equalizing conductor - A closed metallic loop around the top and bottom of a building that aids in equalizing the potential of a lightning strike over the entire building and offers multiple connection points to the ground terminals.

lightning ground terminal - A grounded metallic conductor installed for lightning protection.

lightning rod - See air terminal.

light source - Used in conjunction with a power meter, the test equipment unit that normally contains a light-emitting diode or laser used t~ create a light wavelength for testing optical fiber cable attenuation or continuity.

lightwave - An electromagnetic wave in the optical spectrum of frequencies.

lightweight access point protocol (LWAPP) - Not a current IEEE standard, though the intention is for LWAPP to standardize how switcheslrouters communicate with access providers.

limited common element (LCE) - A portion of a dock that is accessible only to those boat slips that it serves on either side.

linearity - A signal output voltage directly proportional to the signal input voltage.

line cord - Telecommunications equipment cord typically using stranded or tinsel conductor. See also work area cable (cord).

line-of-sight (LoS) - The imaginary line that connects the observer's eye with the object the observer is looking at. See also Fresnel zone.

line supervision - The electrical supervision of a monitoring loop to detect for tampering (a cut or shorted wire). Line supervision usually requires a terminating element at the end of the monitoring loop (i.e., resistor, diode).

linewidth - The spread of wavelengths around the central wavelength of a signal source (e.g., laser).

link - A transmission path between two points, not including terminal equipment, work area cables, and equipment cables. Can be up to 90 m (295 ft) in length for horizontal cabling. See also permanent link test configuration.

link access device (LAD) - An internetworking device used to convert LAN signals into a format suitable for transmission over a wide area internetwork link.

linkage - A connection between a record and an identifier or between records. (TIA)

link aggregation - A mechanism that combines multiple network communications channels into a single large channel to improve data transfer efficiency. Also called trunking. See also port aggregation.

linked cells - Contiguous cells in a wireless LAN that are interconnected to provide seamless interoperability.

link loss budget - The maximum allowable loss for the end-to-end cable system.

link margin - The amount of available signal level (in dB) between the normal receive level and the point at which the signal is too weak to be received.

link pulse - A communications signal used in 10BASE-T LANs to indicate link status and in auto-negotiation-equipped devices to communicate information about abilities and negotiate communications methods. A continuity test pulse sent between media attachment units on a twisted-pair link on an Ethernet network. Used to test the integrity of the link.

link reliability - A calculation of how much of the time a system is expected to be functional (expressed in percent or time).

link segment - 1. A point-to-point Ethernet segment connecting two medium dependent interfaces (MDIs). 2. In 100VG-AnyLAN (IEEE 802.12) demand priority access method, the physical interconnection of two repeaters or a repeater and an end node. It includes the medium and its two attached MDI connectors.

link state algorithm (LSA) - A method of computation used to determine efficient routing in networks, based on Dijkstra's algorithm.

list of materials - Bidding document containing all of the items to be installed by description, catalog number, quantity, unit price, and total price. See also bill of materials.

listed - 1. Equipment included in a list published by an organization, acceptable to the authority having jurisdiction (AHJ), that maintains periodic inspection of production of listed equipment, and whose listing states either that the equipment or material meets appropriate standards or has been tested and found suitable for use in a specified manner. (T(A) 2. Buildings of historic/public interest that structurally cannot be altered or can only be altered with approval of the AHJ. 3. A product listed after it successfully completes a series of mechanical, electrical, and thermal characteristic tests that simulate all reasonable, foreseeable hazards.

load balancing - A mechanism for distributing incoming requests among a collection of devices or circuits to reduce response times. A technology that complements server clustering. See cluster.

loaded pair - A pair in an outside plant cable that has been conditioned for use at voice frequency by the use of loading coils. Loaded pairs are typically not desirable for high-speed data communications since the loading coils tend to inhibit signals operating at frequencies above voice frequency (4000 Hz).

loading coil - A low-resistance, high-inductance coil inserted in a voice copper circuit to increase its inductance in order to compensate for the buildup of capacitance in a cable pair.

load point - The point at which loading coils are attached.

lobby network - A LAN, protected by firewalls, that can be used to connect servers providing Internet content. Also called a demilitarized zone network, perimeter network, and screened subnet.

lobe - The connection between a network device and a token ring concentrator (e.g., multistation access unit). . lobe cabling In token ring, the cabling used to connect the network device to the concentrator. This includes all work area cabling, horizontal cabling, and patch cables.

local - A geographic zone large enough to encompass a multibuilding campus. See also metropolitan.

local alarm - A visual or audible signaling device located at a monitored door, window, or other opening. It is used to pinpoint a violation by sounding a distinctive alarm at an opening and to frighten away the would-be intruder.

local area network (LAN) - The standard industry term for a network installation that serves a relatively small area (e.g., structured cabling installation serving a building).

local area network (LAN) address - Any network client's (e.g., personal computer, laptop, server) address within the LAN. Networking addresses are protocol dependent. See also medium access control (MAC) address.

local exchange carrier (LEC) - A telecommunications company that provides public switched network access service. (TIA). Can be referred to as incumbent local exchange carrier (ILEC) and competitive local exchange carrier (CLEC).

local multipoint distribution services (LMDS) - A fixed wireless technology that operates in the 28 GHz band and offers line-of-sight coverage over distances up to 3.0 km to 5.0 km (1.9 mi to 3.1 mi). It can deliver data and telephony services to 80,000 customers from a single node.

local station - A station that is directly connected to the network over cabling or wireless media. See also remote station and station.

logging - Creating and storing a permanent record of events that can be reviewed, printed, and analyzed.

logical link control (LLC) - The upper sublayer of the Open Systems Interconnection Data Link layer. The LLC provides direct interfacing (bridging) of medium access control (MAC) addresses for all Institute of Electrical and Electronics Engineers, Inc.® LAN designs. MAC devices can only access the network layer through the LLC.

logical topology - 1. The path taken by messages as they travel from one device to another on a network. 2. The actual method (ring, bus, star) by which different nodes in a network communicate with one another as compared to the physical connections. Contrast with physical topology.

log-periodic dipole array (LPDA) - Consists of a system of driven elements, but not all elements in the system are active on a single frequency of operation.

long wavelength (LW) - See wavelength.

longitudinal noise - Noise coupled due to electrostatic or electromagnetic fields that induces longitudinal currents into the disturbed circuit. See also common-mode voltage.

LonMark International - A global membership organization created to promote and advance the business of efficient and effective integration of open, multivendor control systems utilizing ANSI/EIA/CEA 709.1 and related standards. (LonMark)

LonTalk* (Local Operating Network Talk) - A protocol developed by the Echelon Corporation for interoperable control networks using the LonWorks~ technology. LonWorks is used for processing and communicating signals in distributed control networks consisting of intelligent devices (i.e., NeurWl chips).

loop - 1. In telephone systems, the wire pair that connects the customer to the switching center. This path is called a loop because it is generally two wires electrically tied together through the customer terminal set when the customer goes off hook. 2. The outside plant facilities that extend from a serving main entrance facility or remote site to the exchange boundary. 3. A communications channel from a switching center or an individual message distribution point to the user terminal.

loop diversity - The placing of alternate facilities to back up the main system in case of failure. See also alternate entrance.

loop resistance - A measurement of the resistance of both conductors in a pair of conductors connected in series.

loose tube - A type of optical fiber cable construction where one or more fibers are laid loosely in a protective tube often filled with gel. Also called loose tube fiber.

loss - Attenuation of a signal, usually measured and expressed in dB.

loss budget - The total allowable loss between source and detector allocated among optical fiber, connectors, splices, and safety margin.

loss level - A change or sudden spike up from the backscatter that indicates Fresnel reflections.

loss resolution - Setting on an optical time domain reflectometer to determine data points.

low frequency (LF) - Frequencies in the range of 30 kHz to 300 kHz.

low-intensity laser - This device operates in the visible light range and is used to identify individual fibers that glow red at the point of a fiber break. Also called a hot red light.

low-smoke halogen free-flame retardant (LSHF-FR) - LSHF cables produce little smoke, which is nontoxic relative to cables produced with other dielectric materials. The LSHF-FR cables are also flame retardant.

low-voltage cabling/low-voltage cabling system - Telecommunications signaling (includes building automation signaling) voltage levels are typically power-limited when compared to electrical power circuits that can vary from 100 volts alternating current (ac) to 240 volts ac in commercial buildings. Circuits typically use an inherently limited power source without overcurrent protection or a noninherently limited power source where overcurrent protection is required. Electrical power may consist of direct current (dc) or ac sources and levels may vary by country. Since telecommunications cabling systems are not used to distribute electrical power, the signaling that occurs on these copper-based cabling components (cables, connecting hardware, and patch cords) is generally described as low voltage.

low-voltage disconnect (LVD) - An electromechanical device designed to disconnect a battery from the load at a predetermined voltage.

low-voltage mounting bracket - A device that may be inserted in or on a nonfire-rated finished wall allowing the mounting of a faceplate that may hold telecommunications outlet/connectors.

low-voltage ring - See low-voltage mounting bracket.

low-wide building - A building (e.g., large shopping mall, factory, warehouse). The private branch exchange and key systems may be remotely located from the entrance facility protector, creating the need for special attention to grounding and bonding.

lump sum - Payment method for a telecommunications project in which the contractor is paid the full amount upon completion and acceptance of the work.