Glossary - L
Local Area Network
A network that interconnects PCs, terminals, workstations, servers, printers and other peripherals at a high speed
over short distances (usually within the same floor or building). Various LAN standards have been developed, with
Ethernet as the most widely used.
LAN Emulation (ATM)
A way for legacy LAN MAC-layer protocols like
Ethernet and token ring, and all
higher-layer protocols and applications, to access work transparently across an
ATM network. LAN emulation retains all Ethernet and token ring drivers and adapters;
no modifications need to be made to Ethernet or token ring end-stations. A technique that specifies the interfaces and
protocols needed for providing LAN-supported functionality and connectivity in an ATM
environment, so that legacy protocols can be interoperable with the ATM protocols, interfaces and devices.
Set of ATM Forum-developed specifications for the operation of LAN-to-LAN bridged
connectivity over an ATM network.
- LAN Emulation Services (ATM)
Link Acces Protocol (ATM)
Subset of protocols used to manage a transmission. Usually, LAP refers to protocol classes used by
HDLC (High Level Data Link Control).
- Link Access Procedure, Balanced (data-link layer)
Local Access and Transport Area
Geographically defined telecommunication areas, within which a local carrier can provide communications services.
With the divestiture and deregulation actions of 1984, the domestic U.S. was divided into over a hundred small
geographic areas, called LATAs. LECs were permitted to retain a monopoly on the provision of services
within each LATA but were excluded from providing inter-LATA services. IXCs were given the
freedom to compete for communications services between LATAs but were excluded from providing intra-LATA services.
Some of these restrictions are beginning to be eased by additional legislation.
Time interval between when a network station seeks access to a transmission channel and when access is granted
or received. In a bridge or router, the amount
of time elapsed between receiving and retransmitting the LAN packet.
- Line Build Out (physical layer, T1)
- Line Code Violation (physical layer, error)
Link Control Protocol (protocol)
A protocol used to automatically agree upon encapsulation format options, handle varying packet size limits,
authenticate the identity of its peer on the link, determine when a link is functioning properly and when it
is defunct, detect a looped-back link and other common misconfiguration errors, and terminate the link (RFC 1570).
Leightweight Directory Access Protocol (standard, X.500)
An IETF standard based on X.500; it permits users to create and query network
directories from a PC or web browser. It provides read/write interactive access to the X.500 Directory.
See also DAP.
- Same as LAN Emulation.
- Leaky bucket
A method of data traffic flow regulation using a buffer (bucket) and a regulator to present the data to the network
at a specific rate. A flow control algorithm, where cells are monitored to
check whether they comply with the connection parameters. Non-conforming cells are either tagged (as violators) or
dropped from the network. The analogy is taken from a bucket (memory buffer) with a hole in its bottom that allows
the fluid (cells) to flow out at a certain rate. See also GCRA,
traffic contract, UPC.
LAN Emulation ARP (ATM)
The ARP used in LAN Emulation for binding a
requested ATM address to the MACaddress.
- leased line (communications)
- A private telephone circuit permanently connecting two points, normally provided on a lease by a local PTT.
LAN Emulation Client (ATM)
ATM Forum-defined specifications in support of LAN-to-LAN connectivity, called
LAN Emulation. Typically located in an ATM end system (i.e. ATM host, LAN switch), its task is
to maintain address resolution tables and forward data traffic. It is uniquely associated with an
ATM address. LEC defines that set of functions implemented in a LAN
DTE to interface with an ATM network in support of LAN Emulation. See
Local Exchange Carrier (network)
An intra-LATAcommunication services provider.
The local or regional telephone company providing connections between local points or to long distance carriers
for extended connections. LEC owns and operates lines to customer locations and Class 5 Central Office Switches and
have connections to other COs, Tandem (Class 4 Toll) offices and may connect directly to
IECs like LDDS WorldCom, AT&T, MCI, Sprint, etc. Depending on the location, the LEC may be part of an
RBOC (Regional Bell Operating Company) or an independent telephone company, such as
GTE or United Telephone.
LAN Emulation Configuration Server (ATM)
A server whose main function is to provide configuration information to a LEC (such as the
ELAN it belongs to or its LES).
LAN Emulation Network Node Interface (ATM)
Same as LNNI.
Low Earth Orbit[ing satellite [system]] (communications)
The kind of orbit used by communications satellites that will offer high bandwidth
for video on demand, television and other Internet communications.
In LEO, Communications satellites have an orbit near the earth relative to geostationary satellites (36 000 km) and this
orbit, is not in a fixed position relative the the Earth's surface so several satellites are required to provide continuous
LAN Emulation Server (ATM)
A server which provides support for the LAN emulation address resolution protocol
(LE-ARP). The LECs register their own ATM and
MACaddresses with the LES. A LES is uniquely identified by an ATM address
(ATM Forum-defined specifications).
LAN Emulation Service (ATM)
An ATM Forum appointed technical workgroup to address LAN Emulation.
LEarn from Video Extensive Real Atm Gigabit Experiment
The LEVERAGE project builds on HIPERNET (High Performance Networked Multimedia for Distributed Language Training),
a three year project (1996-1998) funded by the European Commission within RACE (Research in Advanced Communications in Europe)
which ran from January 1994 to December 1995.
The main goals of the LEVERAGE project are:
ACTS Project AC109.
- To demonstrate how communication between learners in cross-linguistic situations can be supported and improved
very effectively by multimedia broadband technology.
- To develop, implement and field trial a complete multimedia network infrastructure to support joint work between
and on the sites of three of the partners:
- University of Cambridge
- Institut National des Télécommunications (Paris)
- Universidad PolitÈcnica de Madrid
Web site: http://www.dit.upm.es/~leverage/.
- LI (ATM)
A 6-bit field in the AAL3/4 SAR-PDU trailer that
indicates the number of bytes in the SAR-PDU that contain CPCS information.
Also field in the AAL2 headers.
Logical IP Subnetwork (ATM)
An IP subnetwork is a single network on which all devices have a direct communications path to all other devices.
Examples would be a LAN or a point-to-point circuit (two devices). A LIS is a network in which the
IP protocol can operate as if all devices are directly connected, even if they are not, such as in a virtual
circuit-based network. See Classical IP, LAN.
Logical Link Control
IEEE specifications for the upper half of the data link layer (layer 2) in a
LAN that provides common addressing, error checking, broadcasting, multiplexing,
flow control and access control procedures independent of the physical
transmission methodology. See also MAC.
- LLC Encapsulation
Logical Link Control Encapsulation
A method of adding headers to AAL5 CPCS-PDU's to allow several protocols to be carried over the same
VC. The header allows the receiver to identify the protocol of the routed or bridged
Local Multipoint Distribution Service (network)
A broadband wireless technology, a form of cellular radio that operate at frequencies of 28 and 40 GHz. LMDS can be an
alternative to the local loop and permits a high bandwith traffics up to 36 Mbis/s within a maximum radius of 3 km
from an antenna. One of the technologies used to bypass the bottleneck of "the last mile" (local loop). Others
technologies to solve this problem are DSL and cable modem.
Local Management Interface (ATM)
An ITU-T-defined interface to provide an ATM end-system user with network management
information. See also ILMI.
LAN emulation network-to-network interface - LAN Emulation Network Node Interface (ATM)
Specifies the NNI operation between the LANE servers
(LES, LECS, BUS).
Enables one vendor's implementation of LAN emulation to work with another's. This specification is
essential for building multivendor ATM networks and is currently under development at the
- Load Balancing (communications)
The practice of splitting communication into two (or more) routes. By balancing the traffic on each route, communication
is made faster and more reliable. In remote internetworking bridges and
routers perform load balancing by splitting LAN-to-LAN traffic among
two or more WAN links. This allows for the combination of several lower speed lines to
transmit LAN data simultaneously.
- Local Loop - Local Access (network)
The connection from a subscriber to the Central Office. The portion of a circuit connecting the
LEC's CO with the customer's premise equipment across
the local network.
- LocalTalk (hardware, network)
An Apple Computer network standard using Apple Computer's own networking hardware. See also
- Loss Of Frame (network, control)
- Log In - Log On (communications)
The way by which a user starts an interaction procedure with a computer system. Usually, the user begins by
- Loss Of Pointer (network, control)
- Loss Of Signal (error, network, control)
Longitudinal Redundancy Check (ATM)
Parity error detection system that consists in checking the whole block of words, contrary to the vertical redundancy check
that consists in checking every word of the block.
Least Significant Bit
In a binary word, this is the bit that represents the value "1" (usually it is the bit located on the right). This means that
if we lose this bit, the global value of the word is not really "affected".
- Line Termination (network, communications)
- L-UNI - LUNI
LAN emulation user network interface (ATM)
Specifies the UNI between a LEC and the network providing
the LAN Emulation.
Defines how legacy LAN applications and protocols work with ATM. Currently in development at the
ATM Forum, L-UNI adapts Layer 2 LAN packets to AAL 5
PDUs,which can then be divided into cells.
L-UNI uses a client-server architecture to resolve LAN-to-ATM addresses, the most complex aspect of
LAN emulation. A LAN emulation client (LEC) resides in each ATM-attached device;
a LAN emulation server (LES) and broadcast and unknown server (BUS)
reside anywhere on the ATM network. When a legacy LAN end-station sends a message across the ATM network to another
legacy end-station, the LEC requests ATM address and routing information from the LES and BUS, which
correlate the MAC-layer LAN address of the destination with the ATM addresses needed
to traverse the backbone.