Multitech ProxyServer MTPSR3-100, User Manual

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Glossary

L

LAPB: Link Access Procedure Balanced; based on the X.25
Layer 2 specification. A full-duplex point-to-point, bit-synchronous
protocol commonly used as a data link control protocol to
interface X.25 DTEs. LAPB is the link initialization procedure that
establishes and maintains communications between the DTE
and the DCE.

LAPD: Link Access Protocol for the D-Channel; based on the
ISDN Q.921 specification. A full-duplex, point-to-point bit-
synchronous link-level protocol for ISDN connections; different
from LAPB in its framing sequence. Transmission is in units
called “frames”, and a frame may contain one or more X.25
packets.

Line Coding: The representation of 1s and 0s on a T1 line. The
two methods of line coding commonly used, B8ZS and AMI,
differ in the restrictions placed on user data. T1 line coding
ensures that sufficient timing information is sent with the digital
signal to ensure recovery of all the bits at the far end. Timing
information on the T1 line is included in the form of 1s in the data
stream; a long string of 0s in the data stream could cause
problems recovering the data.

Line Termination (LT): The electronics at the ISDN network side
of the user/network interface that complements the NT1 at the
user side. The LT and the NT1 together provide the high-speed
digital line signals required for BRI access.

Listed Directory Number (LDN): The main number assigned by
the telco; the number listed in the telephone directory and also
provided by Directory Assistance. Some devices can have more
than one LDN, such as ISDN devices that have one LDN for
voice and another LDN for data.

Local Area Network (LAN): 1. A computer network located on a
user’s premises within a limited geographical area.
Communication within a local area network is not subject to
external regulations; however, communication across the LAN
boundary may be subject to some form of regulation. 2. A LAN
does not use store-and-forward techniques. 3. A network in
which a set of devices are connected to one another for a
communication and that can be connected to a larger network.

Local Access and Transport Area (LATA): A post-divestiture
geographical area generally equivalent to a Standard
Metropolitan Statistical Area. At divestiture, the territory served
by the Bell system was divided into approximately 161 LATAs.
The Bell Operating Companies (BOCs) provide Intra-LATA
services.

Local Exchange Carrier (LEC): The local phone company
which provides local (i.e., not long distance) transmission
services. AKA “telco”. LECs provide T1 or FT1 access to LDCs
(unless the T1 circuit is completely intra-LATA). Inter-LATA T1
circuits are made up of a combination of Access and Long Haul
facilities.

Local Management Interface (LMI): A specification for frame
relay equipment that defines status information exchange.

Local Loop: A transmission path, typically twisted-pair wire,
between an individual subscriber and the nearest public
telecommunications network switching center. The wires provide
ISDN service, but require an NT1 at the user end and an LT at
the network end. (AKA, “loop” or “subscriber loop”.)

Logical Link Control (LLC2): In a local area network, the
protocol that governs the exchange of transmission frames
between data stations independently of how the transmission
medium is shared. The LLC2 protocol was developed by the
IEEE 802 commitee and is common to all LAN standards.

Logical Unit (LU): A type of network accessible unit that enables
end users to gain access to network resources and communicate
with each other.

Long Haul: The T1 element that connects to the Access portion
of the long distance company’s (LDC’s) central office. The LDC is
commonly called the point of presence (POP). Each LDC has a
number of POPs, located throughout the country. The LDC is
also called an IEC (Inter Exchange Carrier).

Long Haul Communications: The type of phone call reaching
outside of a local exchange (LE).

M

Management Information Base (MIB): A database of network
management information used by the Common Management
Information Protocol (CMIP) and the Simple Network
Management Protocol (SNMP).

Megacom: An AT&T service with a normal WATS line (typically
T1) between the customer premise and the AT&T serving class 4
CO are the customer’s responsibility.

MegaLink: BellSouth’s leased T1 service.

Message: Associated with such terms as packet, frame, and
segment. 1. In information theory, an ordered series of
characters intended to convey information. 2. An assembly of
characters and sometimes control codes that is transferred as an
entry from an originator to one or more recipients.

Modem: A communications device that enables a computer to
transmit information over a telephone line. It converts the
computer’s digital signals into analog signals to send over a
telephone line and converts them back to digital signals at the
receiving end. Modems can be internal and fit into an expansion
slot, or external and connect to a serial port.

Multiplexer (Mux): 1. A device that takes several input signals
and combines them into a single output signal in such a manner
that each of the input signals can be recovered. 2. A device
capable of interleaving the events of two or more activities or
capable of distributing the events of an interleaved sequence to
the respective activities. 3. Putting multiple signals on a single
channel.

Multiprotocol: A device that can interoperate with devices
utilizing different network protocols.

Multithreading: The ability of a software system to be able to
handle more than one transaction concurrently. This is
contrasted to the case where a single transaction is accepted
and completely processed before the next transaction processing
is started.

N

Nailed Connection: A permanent or dedicated circuit of a
previously switched circuit or circuits.

Nailed-up Circuit: A semi-permanent circuit established through
a circuit-switching facility for point-to-point connectivity.

NAK (Negative Acknowledgment): Communications code used
to indicate that a message was not properly received, or that a
terminal does not wish to transmit. Contrast with ACK.

Network: A group of computers connected by cables or other
means and using software that enables them to share
equipment, such as printers and disk drives to exchange
information.

Node: Any point within a network which has been assigned an
address.