The Cable Center

This glossary of cable and telecommunications terms is intended to enhance your understanding of this dynamic industry. We are able to present this information with the generous help of CableLabs - consult their website for the most up-to-date information about cable technology.

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

Laser
A device that generates coherent electromagnetic radiation in, or near, the visible part of the spectrum.

Last mile
Refers to the last “mile” between a central office and a customer in a telephone network or a node and a customer in a cable television network. Last-mile distances generally range from 0 miles to 3 miles.

Last Mile Framing
The data encapsulation and transmission protocols used between the consumer premises and the headend. Framing techniques include ATM, MPEG and IP.

Latency
The time taken for a signal element to pass through a device or system.

Layer
In networks, layers refer to software protocol levels comprising the architecture, with each layer performing functions for the layers above it. Or a subdivision of the Open System Interconnection (OSI) architecture, constituted by subsystems of the same rank.

Leapfrogging
Cable television operators’ practice of skipping over one or more of the nearest TV stations to bring in a further signal for more program diversity. FCC rules establish priority for carrying stations that lie outside the cable systems service area.

Leaseback
The practice by telephone companies of installing and maintaining cable television distribution systems, and leasing the facilities back to separate contractors for operation of the system.

Leased Access
On some systems, a public access channel for which programmers pay a fee for use and are permitted to sell commercial time in their programming. Also known as Leased Channel.

Level Diagram
A graphic diagram indicating the signal level at any point in the system.

Lifetime of an application
The lifetime of an application characterizes the time from which the application is loaded to the time the application is destroyed.

Line or Loop
An analog or digital access connection from a user terminal which carries user media content and telephony access signaling (DP, DTMF, BRI, proprietary business set).

Line Extender
Types of amplifiers used in the feeder system. Also known as Distribution Amplifier.

Line Frequency
The number of horizontal scans per second, nominally 15,750 times per second.

Line Information Database (LIDB)
Contains information on customers required for real-time access such as calling card personal identification numbers (PIN) for real-time validation.

Line Speed
The rate at which individual bits are transmitted on a telephone connection. A modem’s line speed may be set at 14,400 bits per second, an ISDN line at 64,000 bits per second. Line speed does not take into account whether the data it is sending has been compressed to increase actual throughput.

Link Encryption
Cryptography applied to data as it travels on data links between the network devices.

Local Access and Transport Area (LATA)
A geographical area used for regulatory, pricing, and network organization purposes to partition the public switched telephone network into distinct regions. Or a geographical area designated by the telephone company. Frequently, but not always, corresponds to an area code.

Local Access and Transport Area Switching Systems Generic Requirements (LSSGR)
A very large set of documents published by Telcordia (formerly Bellcore) that describes the local telephone network.

Local Area Network (LAN)
A LAN is a collection of computing equipment at a single location (e.g., an office building or campus) that communicate with each other to share resources and information, such as disk storage and files, printers, and email. See also WAN. Or a non-public data network in which serial transmission is used for direct data communication among data stations located on the user’s premises.

Local Distribution System (LDS)
A wide band microwave system or cable system which is capable of transporting a number of television signals simultaneously. Used to interconnect cable system headends.

Local Exchange
An exchange where telephone subscriber lines connect.

Local Exchange Carrier (LEC)
Telephone company lingo for your local telephone company. See also RBOC.

Local Loop
This portion of the telecommunications network physically connects end users to the central office network facilities and generally is dedicated to that particular user. Twisted pairs of copper wire form the traditional medium of the telephone network local loop, although other connections now are used in some cases.

Local Multipoint Distribution System (LMDS)
A fixed wireless technology that is one solution for bringing high-bandwidth services to homes and offices within the “last mile” of connectivity.

Local Number Portability (LNP)
A system that allows local telephone numbers to be transferred to competitive local exchange carriers. This allows the subscriber to change local phone companies without experiencing a change in phone numbers.

Local Origination
Programming developed by an individual cable TV system specifically for the community it serves.

Local Signals
Television signals that are received at locations that are within the station’s Predicted Grade B Contour. Cable systems must carry all commercial local signals in their areas.

Locator
This term has different definitions depending on the application format: A DVB-HTML locator is a link, expressed in the syntax in IETF RFC 2396 [40], which provides an unambiguous pointer to a DVB-HTML document accessible to the MHP in a specific transport stream. The schemed specified should resolve to one of the available transports signalled for the DVB-HTML application. For signed DVB-HTML applications, the schemes HTTP and HTTPS may use the return channel. This version of the specification does not include a scheme for transport independent locators; future versions are expected to do so. This term in the DVB-HTML context should not be confused with the DVB-J class of the same name.

Logical Link Control (LLC)
The LLC network protocol sublayer is the part of the data link layer that uses the services of the Medium Access Control (MAC) Layer to provide services to the Network Layer. See Logical Link Control Procedure.

Logical Link Control (LLC) procedure
In a local area network (LAN), or a metropolitan area network (MAN), that part of the protocol that governs the assembling of data link layer frames and their exchange between data stations, independent of how the transmission medium is shared.
Long-Distance Service This term refers to a communication terminating outside the local telephone service area of the originating party. Since 1984 in the U.S., the term generally has meant service across local access and transport areas (LATAs).

Low Band
TV channels 2 through 6.

Low Noise Amplifier (LNA)
A low noise signal booster used to amplify the weak signals received on a satellite antenna. Usually found in the receiver front ends.

Low Pass Filter (LPF)
Replaces the regular filter (used for one-way transmission) on a drop, and enables a subscriber to have 2-way service. The LPF allows low frequencies to pass, but blocks out higher frequencies.

Low Power Television
Broadcast medium that is similar to commercial TV but limited in broadcast coverage area by its low power signal.

Low Split
When upstream frequencies are assigned below 54MHz.

Low VHF Band
The part of the frequency band allocated by the FCC for VHF broadcast television, including television channels 2 through 6, or 54 through 108 MHz.

Luminance Signal
That portion of the NTSC color television signal which contains the luminance or brightness information.