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Glossary

LAN switch

A high-speed, multiple-interface transparent bridging mecha-

nism, transmitting packets between segments of data links, usually referred
to specifically as an Ethernet switch. LAN switches transfer traffic based
on MAC addresses. Multilayer switches are a type of high-speed, special-
purpose, hardware-based router. See also: multilayer switch and store-and-
forward packet switching.

LAPB

Link Accessed Procedure, Balanced: A bit-oriented data-link layer

protocol that is part of the X.25 stack and has its origin in SDLC. See also:
SDLC and X.25.

LAPD

Link Access Procedure on the D channel. The ISDN data-link layer

protocol used specifically for the D channel and defined by ITU-T Recom-
mendations Q.920 and Q.921. LAPD evolved from LAPB and is created to
comply with the signaling requirements of ISDN basic access.

latency

Broadly, the time it takes a data packet to get from one location to

another. In specific networking contexts, it can mean either 1) the time
elapsed (delay) between the execution of a request for access to a network by
a device and the time the mechanism actually is permitted transmission, or 2) the
time elapsed between when a mechanism receives a frame and the time that
frame is forwarded out of the destination port.

layer 2 switching

Layer 2 switching is hardware based, which means it

uses the MAC address from the hosts' NIC cards to filter the network.
Switches use Application-Specific Integrated Circuits (ASICs) to build and
maintain filter tables. It is OK to think of a layer 2 switch as a multiport
bridge

layer 3 switch

See: multilayer switch.

layered architecture

Industry standard way of creating applications to

work on a network. Layered architecture allows the application developer to
make changes in only one layer instead of the whole program.

LCP

Link Control Protocol: The protocol designed to establish, configure,

and test data link connections for use by PPP. See also: PPP.

leaky bucket

An analogy for the basic cell rate algorithm (GCRA) used in

ATM networks for checking the conformance of cell flows from a user or
network. The bucket's "hole" is understood to be the prolonged rate at
which cells can be accommodated, and the "depth" is the tolerance for cell
bursts over a certain time period.

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