0-9  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 lambda An optical wavelength. large effective area fiber (LEAF) Corning's high-end optical fiber. laser Light amplification by stimulated emission of radiation. This is an analog transmission device that produces highly coherent light using light amplification through the stimulated emission of radiation. Lasers are used in fiber-optic communications systems as a light source. laser diode A semiconductor that emits coherent light. last mile A popular term for the last segment of the connection between a communications provider and the customer. See also local loop or on ramp. latency Delay between transmission and reception in communications circuit. "Totally latency equals the sum of compression/ decompression delays at the two endpoints and server router delays for every network node between endpoints. Fifty milliseconds delay unnoticeable, 250-300 milliseconds annoying, 600 milliseconds unbearable." -- Network Magazine layering A technique to write complex software faster and more easily. Layering is often used with public, open software. The idea is to have layers of software on top of other layers. Each performs a specific task. The idea is that if your software works at one layer, it should be compatible with the layers of software above and below it. The most famous layered software is the seven-layer open systems interconnection (OSI) model. It breaks each step of a transmission between two devices into a discrete set of functions. These functions are grouped within a layer according to what they are meant to accomplish. Accomodating changes are made at the layer level rather than by reworking the entire OSI model. leverage The degree to which an investor or business is utilizing borrowed money to increase purchasing power. Leverage is often used to attempt to increase the rate of return from an investment and can be referred to as "using margin." The extent of an individual's or company's leverage can be determined through interest and debt ratios. Shareholders may prefer highly leveraged companies when the return on investment outpaces the interest payments on the debt, since their returns will be greater than an unleveraged company. However, over-leveraged companies (e.g., companies with high debt-to-capital ratios) face greater risk in their ability to meet scheduled interest and principal payments. license and maintenance model This is the model that has been the most popular with business software companies. The purchaser is granted a perpetual right to use the software. In addition the purchaser pays a maintenance fee that is usually between 18% and 20% of the purchase price annually. The maintenance contract gives the purchaser access to support and the right to receive upgrades. light-emitting diode (LED) A semiconductor that gives off light. light wave CDMA (LCDMA) Templex Technology¹s implementation of code division multiple access (CDMA) on an optical network. lightpath Analogous to virtual circuits in the ATM domain, a lightpath is a virtual circuit in the optical domain that could consist of multiple spans, each using a difference physical wavelength for the transmission of information across an optical network. lightweight directory access protocol (LDAP) A protocol for accessing online directory services. line overhead Eighteen bytes of overhead accessed, generated and processed by line-terminating equipment. This overhead supports functions such as locating the SPE in the frame, multiplexing or concatenating signals, performance monitoring, Automatic Protection Switching, and line maintenance. line sharing (DSL) Refers to an FCC mandate that allows facilities-based DSL providers to share the existing voice line for the provisioning of DSL providers service. Currently, facilities-based DSL providers must lease a second copper line from the ILEC at approximately $20 per month to provide DSL service. With Line Shares, these providers will pay a reduced leasing fee, thus greatly increasing these service providers' ability to compete with ILECs within the residential market where Line Sharing will have its greatest impact. line-terminating equipment Network elements such as add/drop multiplexers or digital cross-connect systems that can access, generate, and process line overhead. link extender A product used to extend the distance of a high-speed multi-mode data link. liquid crystal display (LCD) A display technology that uses rod-shaped molecules (liquid crystals) that flow like liquid and bend light. Unenergized, the crystals direct light through two polarizing filters, allowing a natural background color to show. When energized, they redirect the light to be absorbed in one of the polarizers, causing the dark appearance of crossed polarizers to show. The more the molecules are twisted, the better the contrast and viewing angle. Because it takes less power to move molecules than to energize a light-emitting device, LCDs replaced LEDs in digital watches years ago. The LCD was developed in 1963 at RCA's Sarnoff Research Center in Princeton, NJ. lit fiber A fiber optical cable that is transmitting an optical signal. The opposite of dark fiber. lithium niobate (LiNbO3) A crystal with unique electro-optical properties that is useful in fiber optics. local area network (LAN) A data communications system that (a) lies within a limited spatial area, (b) has a specific user group, (c) has a specific topology, and (d) is not a public switched telecommunications network, but may be connected to one. (188) Note 1 LANs are usually restricted to relatively small areas, such as rooms, buildings, ships, and aircraft local loop A communication circuit connecting the telephone company central office with a subscriber's instrument. Also see last mile and on ramps. location-based services Applications that utilize the geographic position of a mobile device. logical topology The set of lightpath that are embedded on a physical fiber network are said to form a multi-hop logical topology, sometimes referred to as virtual topology. long-haul communication A type of phone call that reaches outside a local exchange or serving area. long-haul DWDM Optical transport hardware using dense wave division multiplexing (DWDM) technology that can transfer optical signals at distances over 500 km without electrical regeneration. Ultra-long-haul transmission spans have reached 6,400 km. long-haul SONET (LH SONET) Long-haul (LH) transmission equipment (digital cross connects, add/drop multiplexers), used in SONET rings in core networks, that interconnect disparate metro rings. long reach Single-mode fiber sections of up to 40 kilometers, with a signal loss in the range of 10 to 28 dB. Transmission is via high-power, single longitudinal mode (SLM) or multi-longitudinal mode (MLM) at either 1310 or 1550 nm. loopback A method of performing transmission tests on a circuit not requiring the assistance of personnel at the distant end. loss (dB) Identifies in decibels the drop in signal level between nodes at a given point in time. loss budget An accounting of the overall attenuation in a system. loss carryforward Refers to the ability under the tax code of a corporation to carry present operating losses forward so as to offset future taxable income. A company with significant loss carryforwards may be an acquisition target for a profitable acquirer looking to minimize its own tax burden, since the carryforwards are sometimes transferable to a new corporate owner.