Browsing: L
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label
swapping |
Routing algorithm
used by APPN in which each router that a message passes
through on its way to its destination independently
determines the best path to the next router.
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LAN |
Local-area
network. High-speed, low-error data network
covering a relatively small geographic area (up to a few
thousand meters). LANs connect workstations, peripherals,
terminals, and other devices in a single building or other
geographically limited area. LAN standards specify cabling
and signaling at the physical and data link layers of the
OSI model. Ethernet, FDDI, and Token Ring are widely used
LAN technologies. Compare with
MAN
and
WAN.
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LANE |
LAN
emulation. Technology that allows an ATM network to
function as a LAN backbone. The ATM network must provide
multicast and broadcast support, address mapping
(MAC-to-ATM), SVC management, and a usable packet format.
LANE also defines Ethernet and Token Ring ELANs. See also
ELAN.
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LAN emulation |
See
LANE.
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LAN Emulation Client |
See
LEC.
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LAN Emulation
Configuration Server |
See
LECS.
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LAN Emulation Server |
See
LES.
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LAN
Extender |
Any of the products
in the Cisco 1000 series. Cisco LAN Extenders provide a
transparent connection between a central site and a remote
site, logically extending the central network to include the
remote LAN. LAN Extender products support all standard
network protocols and are configured and managed through a
host router at the central site, requiring no technical
expertise at the remote end. See also
Cisco
1000.
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LAN Manager |
Distributed NOS,
developed by Microsoft, that supports a variety of protocols
and platforms.
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LAN Manager for UNIX |
See
LM/X.
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LAN Network Manager |
See
LNM.
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LAN Server |
Server-based NOS
developed by IBM and derived from LNM. See also
LNM.
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LAN
switch |
High-speed switch
that forwards packets between data-link segments. Most LAN
switches forward traffic based on MAC addresses. This
variety of LAN switch is sometimes called a frame switch.
LAN switches are often categorized according to the method
they use to forward traffic: cut-through packet switching or
store-and-forward packet switching. Multilayer switches are
an intelligent subset of LAN switches. An example of a LAN
switch is the Cisco Catalyst 5000. Compare with
multilayer
switch. See also
cut-through
packet switching and
store
and forward packet switching.
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LAPB |
Link Access
Procedure, Balanced. Data link layer protocol in
the X.25 protocol stack. LAPB is a bit-oriented protocol
derived from HDLC. See also
HDLC
and
X.25.
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LAPD |
Link Access
Procedure on the D channel. ISDN data link layer
protocol for the D channel. LAPD was derived from the LAPB
protocol and is designed primarily to satisfy the signaling
requirements of ISDN basic access. Defined by ITU-T
Recommendations Q.920 and Q.921.
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LAPM |
Link Access
Procedure for Modems. ARQ used by modems
implementing the V.42 protocol for error correction. See
also
ARQ
and
V.42.
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laser |
Light
amplification by stimulated emission of radiation.
Analog transmission device in which a suitable active
material is excited by an external stimulus to produce a
narrow beam of coherent light that can be modulated into
pulses to carry data. Networks based on laser technology are
sometimes run over SONET.
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LAT |
Local-area
transport. A network virtual terminal protocol
developed by Digital Equipment Corporation.
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LATA |
Local access
and transport area. Geographic telephone dialing
area serviced by a single local telephone company. Calls
within LATAs are called "local calls." There are
well over 100 LATAs in the United States.
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latency |
1. Delay between the
time a device requests access to a network and the time it
is granted permission to transmit.
2. Delay between the time when a device receives a frame and
the time that frame is forwarded out the destination port.
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LCC |
Line card
control. Process that runs on the NP for each CLC,
LSC, and MSC of a LightStream 2020 ATM switch. LCC
establishes VCCs, maintains the link management protocol for
the line card, continually monitors line quality on each
trunk using TUD, and performs other functions. See also
ECC.
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LCI |
Logical
channel identifier. See
VCN.
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LCN |
Logical channel number. See
VCN.
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leaf internetwork |
In a star topology,
an internetwork whose sole access to other internetworks in
the star is through a core router.
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learning
bridge |
Bridge that performs
MAC address learning to reduce traffic on the network.
Learning bridges manage a database of MAC addresses and the
interfaces associated with each address. See also
MAC
address learning.
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leased
line
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Transmission line
reserved by a communications carrier for the private use of
a customer. A leased line is a type of dedicated line. See
also
dedicated
line.
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LEC |
1.) LAN Emulation Client. Entity in an end system
that performs data forwarding, address resolution, and other control
functions for a single ES within a single ELAN. A LEC also provides
a standard LAN service interface to any higher-layer entity that
interfaces to the LEC. Each LEC is identified by a unique ATM
address, and is associated with one or more MAC addresses reachable
through that ATM address. See also
ELAN and
LES.
2.) Local exchange carrier. Local or
regional telephone company that owns and operates a telephone
network and the customer lines that connect to it.
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LECS |
LAN
Emulation Configuration Server. Entity that assigns
individual LANE clients to particular ELANs by directing
them to the LES that corresponds to the ELAN. There is
logically one LECS per administrative domain, and this
serves all ELANs within that domain. See also
ELAN.
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LED |
Light
emitting diode. Semiconductor device that emits
light produced by converting electrical energy. Status
lights on hardware devices are typically LEDs.
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LEN
node |
Low-entry
networking node. In SNA, a PU 2.1 that supports LU
protocols, but whose CP cannot communicate with other nodes.
Because there is no CP-to-CP session between a LEN node and
its NN, the LEN node must have a statically defined image of
the APPN network.
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LES |
LAN
Emulation Server. Entity that implements the
control function for a particular ELAN. There is only one
logical LES per ELAN, and it is identified by a unique ATM
address. See also
ELAN.
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Level 1 IS |
Level 1 IS provides routing within an
area. It keeps track of the routing within its own area. For a
packet destined for another area, a Level 1 IS sends the packet to
the nearest Level 2 IS in its own area, regardless of what the
destination area is.
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Level 2 IS |
Level 2 IS provides routing between
Level 1 areas and form an intradomain routing backbone. It keeps
track of the paths to destination areas. A level 1 must go through a
level 2 IS to communicate with another area. See also
Level 1 IS, Level 3 IS.
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Level 3 IS |
Level 3 IS provides routing between
separate domains. See also Level 1 IS,
Level 2 IS.
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Level 1 router |
Device that routes
traffic within a single DECnet or OSI area.
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Level 2 router |
Device that routes
traffic between DECnet or OSI areas. All Level 2 routers
must form a contiguous network.
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light amplification
by stimulated emission of radiation |
See
laser.
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light emitting diode
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See
LED.
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limited resource
link
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Resource defined by
a device operator to remain active only when being used.
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limited-route explorer packet |
See
spanning
explorer packet.
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line |
1. In SNA, a
connection to the network.
2. See
link.
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line card |
Card on a
LightStream 2020 ATM switch that, together with its access
card, provides I/O services for the switch. There are four
types of line cards:
CLC,
LSC,
MSC,
and
PLC.
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line card control |
See
LCC. |
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line code type |
One of a number of
coding schemes used on serial lines to maintain data
integrity and reliability. The line code type used is
determined by the carrier service provider. See also
AMI,
B8ZS,
and
HBD3.
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line conditioning |
Use of equipment on
leased voice-grade channels to improve analog
characteristics, thereby allowing higher transmission rates.
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line console 0 |
Command used to
establish a password on the console terminal.
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line driver |
Inexpensive
amplifier and signal converter that conditions digital
signals to ensure reliable transmissions over extended
distances.
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Line Interface
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See
LINF.
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line of sight |
Characteristic of
certain transmission systems such as laser, microwave, and
infrared systems in which no obstructions in a direct path
between transmitter and receiver can exist.
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line printer daemon |
See
LPD.
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line turnaround
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Time required to
change data transmission direction on a telephone line.
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line vty 0
4 |
Command used to
establish password protection on incoming Telnet sessions.
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LINF |
Line
Interface. Interface card used on the LightStream
100 ATM switch. The LINF receives cells sent over a line,
checks them for errors, and forwards them toward their
destination.
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link |
Network
communications channel consisting of a circuit or
transmission path and all related equipment between a sender
and a receiver. Most often used to refer to a WAN
connection. Sometimes referred to as a line or a transmission
link.
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Link Access
Procedure, Balanced |
See
LAPB.
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Link Access
Procedure for Modems |
See
LAPM.
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Link Access
Procedure on the D channel |
See
LAPD.
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link layer |
See
data
link layer.
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link-layer address |
See
MAC
address.
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link-state
advertisement |
See
LSA.
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link-state packet |
See
LSA.
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link
state routing algorithm |
Routing algorithm in
which each router broadcasts or multicasts information
regarding the cost of reaching each of its neighbors to all
nodes in the internetwork. Link state algorithms create a
consistent view of the network and are therefore not prone
to routing loops, but they achieve this at the cost of
relatively greater computational difficulty and more
widespread traffic (compared with distance vector routing
algorithms). Compare with
distance
vector routing algorithm. See also
Dijkstra's
algorithm.
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little-endian |
Method of storing or
transmitting data in which the least significant bit or byte
is presented first. Compare with
big-endian.
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LLC |
Logical Link
Control. Higher of the two data link layer
sublayers defined by the IEEE. The LLC sublayer handles
error control, flow control, framing, and MAC-sublayer
addressing. The most prevalent LLC protocol is IEEE 802.2,
which includes both connectionless and connection-oriented
variants. See also
data
link layer and
MAC.
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LLC2 |
Logical Link
Control, type 2. Connection-oriented OSI
LLC-sublayer protocol. See also
LLC.
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LMI |
Local
Management Interface. Set of enhancements to the
basic Frame Relay specification. LMI includes support for a
keepalive mechanism, which verifies that data is flowing; a
multicast mechanism, which provides the network server with
its local DLCI and the multicast DLCI; global addressing,
which gives DLCIs global rather than local significance in
Frame Relay networks; and a status mechanism, which provides
an on-going status report on the DLCIs known to the switch.
Known as LMT in ANSI terminology.
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LMT |
See
LMI.
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LM/X |
LAN Manager
for UNIX. Monitors LAN devices in UNIX
environments.
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LNM |
LAN Network
Manager. SRB and Token Ring management package
provided by IBM. Typically running on a PC, it monitors SRB
and Token Ring devices, and can pass alerts up to NetView.
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load balancing |
In routing, the
ability of a router to distribute traffic over all its
network ports that are the same distance from the
destination address. Good load-balancing algorithms use both
line speed and reliability information. Load balancing
increases the utilization of network segments, thus
increasing effective network bandwidth.
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local access and
transport area
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See
LATA.
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local
acknowledgment |
Method whereby an
intermediate network node, such as a router, responds to
acknowledgments for a remote end host. Use of local
acknowledgments reduces network overhead and, therefore, the
risk of time-outs. Also known as local termination.
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local-area network |
See
LAN.
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local-area transport |
See
LAT.
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local bridge |
Bridge that directly
interconnects networks in the same geographic area.
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local database |
See
configuration
database.
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local exchange
carrier
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See
LEC.
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local
explorer packet |
Generated by an end
system in an SRB network to find a host connected to the
local ring. If the local explorer packet fails to find a
local host, the end system produces either a spanning
explorer packet or an all-routes explorer packet. See also
all-routes
explorer packet,
explorer
packet, and
spanning
explorer packet.
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local loop |
Line from the
premises of a telephone subscriber to the telephone company
CO.
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Local Management
Interface |
See
LMI.
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LocalTalk |
Apple proprietary
baseband protocol that operates at the data link and
physical layers of the OSI reference model. LocalTalk uses
CSMA/CD media access scheme and supports transmissions at
speeds of 230 Kbps.
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local termination |
See
local
acknowledgment.
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local traffic filtering |
Process by which a
bridge filters out (drops) frames whose source and
destination MAC addresses are located on the same interface
on the bridge, thus preventing unnecessary traffic from
being forwarded across the bridge. Defined in the IEEE 802.1
standard. See also
IEEE
802.1.
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logical address |
See
network
address.
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logical channel |
Nondedicated,
packet-switched communications path between two or more
network nodes. Packet switching allows many logical channels
to exist simultaneously on a single physical channel.
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logical channel
identifier |
See
LCI.
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logical channel
number |
See
LCN.
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Logical Link Control |
See
LLC.
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Logical Link
Control, type 2 |
See
LLC2.
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logical unit |
See
LU.
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Logical Unit 6.2 |
See
LU
6.2.
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loop |
Route where packets
never reach their destination, but simply cycle repeatedly
through a constant series of network nodes.
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loopback test |
Test in which
signals are sent and then directed back toward their source
from some point along the communications path. Loopback
tests are often used to test network interface usability.
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lossy |
Characteristic of a
network that is prone to lose packets when it becomes highly
loaded.
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low-entry networking
node |
See
LEN
node.
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low-speed line card |
See
LSC.
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LPD |
Line printer
daemon. Protocol used to send print jobs between
UNIX systems.
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LSA |
Link-state
advertisement. Broadcast packet used by link-state
protocols that contains information about neighbors and path
costs. LSAs are used by the receiving routers to maintain
their routing tables. Sometimes called a link-state
packet (LSP).
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LSC |
Low-speed
line card. Card on the LightStream 2020 ATM switch
that can be configured as an edge or a trunk card. An LSC,
in conjunction with an access card, supports eight trunk or
edge ports (Frame Relay or frame forwarding) at individual
port speeds up to 3.584 Mbps, or an aggregate rate of 6 Mbps
per line card. See also
edge
card,
MSC,
and
trunk
card.
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LSP |
Link-state
packet. See
LSA.
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LSPD |
link-state PDU database (LSPD) is the
database maintained each router running a link-state routing
protocol. It provides a global view of the area itself and the exit
points to neighboring areas.
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LU |
Logical unit.
Primary component of SNA, an LU is an NAU that enables end
users to communicate with each other and gain access to SNA
network resources.
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LU 6.2 |
Logical Unit
6.2. IN SNA, an LU that provides peer-to-peer
communication between programs in a distributed computing
environment. APPC runs on LU 6.2 devices. See also
APPC.
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LynxOS |
Real-time, UNIX-like
operating system that runs on the NP of a LightStream 2020
ATM switch. |
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