shared. (T) The LLC protocol was developed by the
IEEE 802 committee and is common to all LAN
standards.
logical link control (LLC) protocol data unit. Aunit
of information exchanged between link stations in
different nodes. The LLC protocol data unit contains a
destination service access point (DSAP), a source
service access point (SSAP), a control field, and user
data.
logical unit (LU). A type of network accessible unit
that enables users to gain access to network resources
and communicate with each other.
loopback test. A test in which signals from a tester
are looped at a modem or other network element back
to the tester for measurements that determine or verify
the quality of the communications path.
low-entry networking (LEN). Acapability of nodes to
attach directly to one another using basic peer-to-peer
protocols to support multiple and parallel sessions
between logical units.
low-entry networking (LEN) end node. ALEN node
receiving network services from an adjacentAPPN
network node.
low-entry networking (LEN) node. Anode that
provides a range of end-user services, attaches directly
to other nodes using peer protocols, and derives
network services implicitly from an adjacentAPPN
network node, that is, without the direct use of CP-CP
sessions.
M
Management Information Base (MIB). (1)A collection
of objects that can be accessed by means of a network
management protocol. (2)A definition for management
information that specifies the information available from
a host or gateway and the operations allowed. (3) In
OSI, the conceptual repository of management
information within an open system.
management station. In Internet communications, the
system responsible for managing all, or a portion of, a
network. The management station communicates with
network management agents that reside in the
managed node by means of a network management
protocol, such as the Simple Network Management
Protocol (SNMP).
mapping. The process of converting data that is
transmitted in one format by the sender into the data
format that can be accepted by the receiver.
mask. (1)A pattern of characters used to control
retention or elimination of portions of another pattern of
characters. (I) (A)(2) To use a pattern of characters to
control retention or elimination of portions of another
pattern of characters. (I) (A)
maximum transmission unit (MTU). In LANs, the
largest possible unit of data that can be sent on a given
physical medium in a single frame. For example, the
MTU for Ethernet is 1500 bytes.
medium access control (MAC). In LANs, the
sublayer of the data link control layer that supports
medium-dependent functions and uses the services of
the physical layer to provide services to the logical link
control (LLC) sublayer.The MAC sublayer includes the
method of determining when a device has access to the
transmission medium.
medium access control (MAC) protocol. In a local
area network, the protocol that governs access to the
transmission medium, taking into account the
topological aspects of the network, in order to enable
the exchange of data between data stations. (T)
medium access control (MAC) sublayer. Ina local
area network, the part of the data link layer that applies
a medium access method. The MAC sublayer supports
topology-dependent functions and uses the services of
the physical layer to provide services to the logical link
control sublayer. (T)
metric. In Internet communications, a value,
associated with a route, which is used to discriminate
between multiple exit or entry points to the same
autonomous system. The route with the lowest metric is
preferred.
metropolitan area network (MAN). Anetwork formed
by the interconnection of two or more networks which
may operate at higher speed than those networks, may
cross administrative boundaries, and may use multiple
access methods. (T) Contrast with
local area network
(LAN)
and

wide area network (WAN)

.
MIB. (1) MIB module. (2) Management Information
Base.
MIB object. Synonym for

MIB variable

.
MIB variable. In the Simple Network Management
Protocol (SNMP), a specific instance of data defined in
a MIB module. Synonymous with

MIB object

.
MIB view. In the Simple Network Management
Protocol (SNMP), the collection of managed objects,
known to the agent, that is visible to a particular
community.
MILNET. Themilitary network that was originally part
ofARPANET. It was partitioned from ARPANET in 1984.
MILNET provides a reliable network service for military
installations.
modem (modulator/demodulator). (1)A functional
unit that modulates and demodulates signals. One of
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