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) ◆ Thelocalphonecompanies—either a Regional Bell Operating Company (RBOC) or an independent phone company—that provide local transmission services.

LED (Light Emitting Diode) ◆ Semiconductordeviceusedfordisplay 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 leasing customer without interexchange switching arrangements. A leased line may be point-to-point or multipoint. Also called dedicated or private 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 (LU).

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).

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