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Glossary
5536 PRI RAS Communications Controller Users Guide 209
LAP-D (Link Access Procedure-D) For ISDN, Data Link layer pro-
cedure using D channel communications. For Frame relay, a protocol
that operates at the data link layer (layer 2) of the OSI architecture.
LAPD is used to convey information between layer 3 entities across
the frame relay network.
LATA (Local Area Transport Area) The territory covered by an
individual local telephone operating company.
LEC (Local Exchange Carrier) The local phone companies—either
a Regional Bell Operating Company (RBOC) or an independent phone
company—that provide local transmission services.
LED (Light Emitting Diode) Semiconductor device used for display
purposes in electronic equipment.
LLC (Logical Link Control) The upper half of the Data Link layer in
LANs. Performs error control, broadcasting, multiplexing, and flow
control functions. See MAC (Medium Access Control).
Leased Line Telephone line reserved for the exclusive use of a leas-
ing customer without interexchange switching arrangements. A leased
line may be point-to-point or multipoint. Also called dedicated or pri-
vate line.
LLC/SNAP Logical Link Control/SubNetwork Attachment Point
Local Describes files and devices, such as disk drives, that are
attached to your machine.
Logical unit (LU) A type of network accessible unit that enables
users to gain access to network resources and communicate with each
other.
Loop Qualification This is a test done by the phone company to
make sure the customer is within the maximum distance of 18,000 feet
from the central office that services that customer. Note, however, that
ISDN service could be available at a longer distance than that with a
repeater.
LOS (Lost Of Signal) PRI alarm.
LT (Line termination) The equivalent of the NT1 function at the
CO.
LU See logical unit.
MAC (Medium Access Control) A set of protocols that are the
lower part of the Data Link layer and comprise the basis of the IEEE
LAN specifications. In general, MAC determines the way devices can
transmit in a broadcast network. See LLC (Logical Link Control).