AT&T 7400 series manual Listed directory number, Local area network LAN, Also wide area network

GL-16GLOSSARY

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listed directory number	The listed number in a public directory for a communications system. An
(LDN)	incoming call to an LDN is usually answered by an attendant.
local area network (LAN)	A networking arrangement specifically designed for a limited geographical
	area. Generally, a LAN is limited in range to a maximum of 6.2 miles and
	provides high-speed carrier service with low error rates. Common
	configurations include star (including circuit switched), ring, and bus. See
	also wide area network.
local exchange company	A company franchised to provide public intra-LATA (local access and
(LEC)	transport area) telephone service to subscribers within a defined
	geographical area. Also called a local exchange carrier or local telephone
	company.
logical channel (or	A message slot on a digital communications link. A logical channel is one
circuit)	of the logically independent elements of a data stream that is multiplexed
	onto a single communications carrier.
manual dialing	Use of the dialing pad on a telephone to place a call by dialing each digit
	individually.
MEGACOM®	AT&T’s tariffed digital WATS offering for outward calling. See also 800
	Service.
MEGACOM® 800	AT&T’s tariffed digital 800-service offering for inward calling.
message-oriented	See DMI with message-oriented signaling.
signaling (MOS)
modem	A device that converts digital data signals to analog signals for
	transmission over telephone circuits. The analog signals are converted
	back to the original digital data signals by another modem at the other end
	of the circuit.
modem pooling	A capability that provides shared conversion resources (modems and data
	modules) for cost-effective access to analog facilities by data terminals.
	When needed, modem pooling inserts a conversion resource into the path
	of a data call. Modem pooling serves both outgoing and incoming calls.
modular asynchronous	A rack-mounted equipment unit housing up to eight plug-in asynchronous
data unit (MADU)	data units (ADUs).
modular processor data	A processor data module (PDM) that can be configured to provide several
module (MPDM)	kinds of interfaces (RS-232C, RS-449, and V.35) to customer-provided
	data terminal equipment (DTE). See also processor data module.
modular trunk data	A trunk data module (TDM) that can be configured to provide several
module (MTDM)	kinds of interfaces (RS-232C, RS-449, and V.35) to customer-provided
	data terminal equipment (DTE).