- Media Access Control.
Lower of the two sublayers of the data link layer defined by the
IEEE. The MAC sublayer handles access to shared media, such as
whether token passing or contention will be used. See also data
link layer and LLC.
- Standardized data link layer
address that is required for every port or device that connects to a
LAN. Other devices in the network use these addresses to locate
specific ports in the network and to create and update routing
tables and data structures. MAC addresses are 6 bytes long and are
controlled by the IEEE. Also known as a hardware address, a MAC-layer
address, or a physical address. Compare with network
address.
- Service that characterizes a
learning bridge, in which the source MAC address of each received
packet is stored so that future packets destined for that address
can be forwarded only to the bridge interface on which that address
is located. Packets destined for unrecognized addresses are
forwarded out every bridge interface. This scheme helps minimize
traffic on the attached LANs. MAC address learning is defined in the
IEEE 802.1 standard. See also learning
bridge and MAC
address.
MacIP
- Network layer protocol that
encapsulates IP packets in DDS or transmission over AppleTalk. MacIP
also provides proxy ARP services.
MAC-layer address
- See MAC
address.
Main cross connect
- See MCC.
Main distribution facility
- See MDF.
Maintenance Operation
Protocol
- See MOP.
- Metropolitan-area
network. Network that spans a metropolitan area. Generally,
a MAN spans a larger geographic area than a LAN, but a smaller
geographic area than a WAN. Compare with LAN
and WAN.
managed object
- In network management, a
network device that can be managed by a network management protocol.
Management Information Base
- See MIB.
management services
- SNA functions distributed
among network components to manage and control an SNA network.
Manchester encoding
- Digital coding scheme, used
by IEEE 802.3 and Ethernet, in which a mid-bit-time transition is
used for clocking, and a 1 is denoted by a high level during the
first half of the bit time.
Manufacturing Automation
Protocol
- See MAP.
- Manufacturing
Automation Protocol. Network architecture created by
General Motors to satisfy the specific needs of the factory floor.
MAP specifies a token-passing LAN similar to IEEE 802.4. See also IEEE
802.4.
mask
- See address
mask and subnet
mask.
master management agent
- See MMA.
- Media attachment
unit. Device used in Ethernet and IEEE 802.3 networks that
provides the interface between the AUI port of a station and the
common medium of the Ethernet. The MAU, which can be built into a
station or can be a separate device, performs physical layer
functions including the conversion of digital data from the Ethernet
interface, collision detection, and injection of bits onto the
network. Sometimes referred to as a media access unit, also
abbreviated MAU, or as a transceiver. In Token Ring, a
MAU is known as a multistation access unit and is usually
abbreviated MSAU to avoid confusion. See also AUI
and MSAU.
- Specifies the largest burst
of data above the insured rate that will be allowed temporarily on
an ATM PVC, but will not be dropped at the edge by the traffic
policing function, even if it exceeds the maximum rate. This amount
of traffic will be allowed only temporarily; on average, the traffic
source needs to be within the maximum rate. Specified in bytes or
cells. Compare with insured
burst. See also maximum
rate.
- Maximum total data
throughput allowed on a given virtual circuit, equal to the sum of
the insured and uninsured traffic from the traffic source. The
uninsured data might be dropped if the network becomes congested.
The maximum rate, which cannot exceed the media rate, represents the
highest data throughput the virtual circuit will ever deliver,
measured in bits or cells per second. Compare with excess
rate and insured
rate. See also maximum
burst.
- See MTU.
MB
- megabyte.
Mb
- megabit.
- Multicast backbone.
The multicast backbone of the Internet. MBONE is a virtual multicast
network composed of multicast LANs and the point-to-point tunnels
that interconnect them.
Mbps
- megabits per second.
- Micro channel
architecture. Bus interface commonly used in PCs and some
UNIX workstations and servers.
- Main cross-connect.
Wiring closet that serves as the most central point in a star
topology and where LAN backbone cabling connects to the Internet.
- Multiport
Communications Interface. Card on the AGS+ that provides
two Ethernet interfaces and up to two synchronous serial interfaces.
The MCI processes packets rapidly, without the interframe delays
typical of other Ethernet interfaces.
- Minimum cell rate.
Parameter defined by the ATM Forum for ATM traffic management. MCR
is defined only for ABR transmissions, and specifies the minimum
value for the ACR. See also ABR
(available bit rate), ACR,
and PCR.
- Message Digest 5.
Algorithm used for message authentication in SNMP v.2. MD5 verifies
the integrity of the communication, authenticates the origin, and
checks for timeliness. See also SNMP2.
- Main distribution
facility. Primary communications room for a building.
Central point of a star networking topology where patch panels, hub,
and router are located. See also IDF
- Plural of medium. The
various physical environments through which transmission signals
pass. Common network media include twisted-pair, coaxial and
fiber-optic cable, and the atmosphere (through which microwave,
laser, and infrared transmission occurs). Sometimes called physical
media.
Media Access Control
- See MAC.
Media Access Control Address
- See MAC
address.
media access unit
- See MAU.
media attachment unit
- See MAU.
media interface connector
- See MIC.
media rate
- Maximum traffic throughput
for a particular media type.
medium
- See media.
medium-speed line card
- See MSC.
megabit
- Abbreviated Mb.
megabits per second
- Abbreviated Mbps.
megabyte
- Abbreviated MB.
- Network topology in which
devices are organized in a manageable, segmented manner with many,
often redundant, interconnections strategically placed between
network nodes. See also full
mesh and partial
mesh.
- Application layer (Layer 7)
logical grouping of information, often composed of a number of
lower-layer logical groupings such as packets. The terms datagram,
frame,
packet,
and segment
are also used to describe logical information groupings at
various layers of the OSI reference model and in various technology
circles.
message handling system
- See MHS.
Message Digest 5
- See MD5.
Message Queuing Interface
- See MQI.
- Switching technique
involving transmission of messages from node to node through a
network. The message is stored at each node until such time as a
forwarding path is available. Contrast with circuit
switching and packet
switching.
message unit
- Unit of data processed by
any network layer.
Metal oxide varister
- See MOV.
metasignaling
- Process running at the ATM
layer that manages signaling types and virtual circuits.
metering
- See traffic
shaping.
metric
- See routing
metric.
metropolitan-area network
- See MAN.
MGS
- Cisco midrange multiprotocol
router designed for medium to small regional and district
environments. The MGS is a 4-slot router that can handle up to 11
interfaces of different types.
- Message handling
system. ITU-T X.400 recommendations that provide message
handling services for communications between distributed
applications. NetWare MHS is a different (though similar) entity
that also provides message-handling services. See also IFIP.
- Management
Information Base. Database of network management
information that is used and maintained by a network management
protocol such as SNMP or CMIP. The value of a MIB object can be
changed or retrieved using SNMP or CMIP commands. MIB objects are
organized in a tree structure that includes public (standard) and
private (proprietary) branches.
- Polling technique used by
the SNMP protocol to gather information needed to monitor the
network.
- Technique used by the CMIP
protocol to obtain information needed to monitor the network. It is
dependent upon network devices to initiate reports regarding their
status to a central monitoring station on the network.
- Media interface
connector. FDDI de facto standard connector.
micro channel architecture
- See MCA.
microcode
- Translation layer between
machine instructions and the elementary operations of a computer.
Microcode is stored in ROM and allows the addition of new machine
instructions without requiring that they be designed into electronic
circuits when new instructions are needed.
microsegmentation
- Division of a network into
smaller segments, usually with the intention of increasing aggregate
bandwidth to network devices.
- Unit of measure equal to one
millionth of a meter or one thousandth of a millimeter. Sometimes
the symbol µ is used instead of the word micron.
microwave
- Electromagnetic waves in the
range 1 to 30 GHz. Microwave-based networks are an evolving
technology gaining favor due to high bandwidth and relatively low
cost.
midsplit
- Broadband cable system in
which the available frequencies are split into two groups: one for
transmission and one for reception.
Military Network
- See MILNET.
millions of instructions per
second
- See mips.
- Military Network.
Unclassified portion of the DDN. Operated and maintained by the DISA.
See also DDN
and DISA.
minimum cell rate
- See MCR.
- MultiChannel
Interface Processor. Interface processor on the Cisco 7000
series routers that provides up to two channelized T1 or E1
connections via serial cables to a CSU. The two controllers on the
MIP can each provide up to 24 T1 or 30 E1 channel-groups, with each
channel-group presented to the system as a serial interface that can
be configured individually.
- Millions of
instructions per second. Number of instructions executed by
a processor per second.
- Master management
agent. SNMP agent that runs on the NP of a LightStream 2020
ATM switch. MMA translates between an external network manager using
SNMP and the internal switch management mechanisms.
- Modulator-demodulator.
Device that converts digital and analog signals. At the source, a
modem converts digital signals to a form suitable for transmission
over analog communication facilities. At the destination, the analog
signals are returned to their digital form. Modems allow data to be
transmitted over voice-grade telephone lines.
modem eliminator
- Device allowing connection
of two DTE devices without modems.
- Process by which the
characteristics of electrical signals are transformed to represent
information. Types of modulation include AM, FM, and PAM. See also AM,
FM,
and PAM.
modulator-demodulator
- See modem.
- Management tool on the
LightStream 2020 ATM switch that allows a user to examine individual
nodes in the network and learn the status of interface modules and
power supplies. The monitor is an HP OpenView-based application that
runs on an NMS.
monomode fiber
- See single-mode
fiber.
- Maintenance
Operation Protocol. Digital Equipment Corporation protocol,
a subset of which is supported by Cisco, that provides a way to
perform primitive maintenance operations on DECnet systems. For
example, MOP can be used to download a system image to a diskless
station.
- Public-domain WWW browser,
developed at the National Center for Supercomputing Applications
(NCSA). See also WWW
browser.
- Multicast OSPF.
Intradomain multicast routing protocol used in OSPF networks.
Extensions are applied to the base OSPF unicast protocol to support
IP multicast routing.
- Metal oxide varistor.
Voltage clamping surge suppressor capable of absorbing large
currents without damage.
- Message Queuing
Interface. International standard API that provides
functionality similar to that of the RPC interface. In contrast to
RPC, MQI is implemented strictly at the application layer. See also RPC.
- Multistation access
unit. Wiring concentrator to which all end stations in a
Token Ring network connect. The MSAU provides an interface between
these devices and the Token Ring interface of, for example, a Cisco
7000 TRIP. Sometimes abbreviated MAU.
- Medium-speed line
card. Card on the LightStream 2020 ATM switch that can be
configured as an edge or a trunk card. The MSC, in conjunction with
an access card, supports two trunk or edge (UNI) ports at data rates
up to T3 or E3.
- Maximum transmission
unit. Maximum packet size, in bytes, that a particular
interface can handle.
- North American companding
standard used in conversion between analog and digital signals in
PCM systems. Similar to the European alaw. See also a-law
and companding.
- Network that allows multiple
devices to connect and communicate simultaneously.
- Single packets copied by the
network and sent to a specific subset of network addresses. These
addresses are specified in the destination address field. Compare
with broadcast
and unicast.
- Single address that refers
to multiple network devices. Synonymous with group address.
Compare with broadcast
address and unicast
address. See also multicast.
multicast backbone
- See MBONE.
multicast group
- Dynamically determined group
of IP hosts identified by a single IP multicast address.
Multicast OSPF
- See MOSPF.
- Router used to send IGMP
query messages on their attached local networks. Host members of a
multicast group respond to a query by sending IGMP reports noting
the multicast groups to which they belong. The multicast router
takes responsibility for forwarding multicast datagrams from one
multicast group to all other networks that have members in the
group. See also IGMP.
multicast server
- Establishes a one-to-many
connection to each device in a VLAN, thus establishing a broadcast
domain for each VLAN segment. The multicast server forwards incoming
broadcasts only to the multicast address that maps to the broadcast
address.
MultiChannel Interface
Processor
- See MIP.
- Communications line having
multiple cable access points. Sometimes called a multipoint line.
multihomed host
- Host attached to multiple
physical network segments in an OSI CLNS network.
multihoming
- Addressing scheme in IS-IS
routing that supports assignment of multiple area addresses.
- Switch that filters and
forwards packets based on MAC addresses and network addresses. A
subset of LAN switch. The Catalyst 5000 is an example of a
multilayer switch. Compare with LAN
switch.
- Optical fiber supporting
propagation of multiple frequencies of light. See also single-mode
fiber.
multiple domain network
- SNA network with multiple
SSCPs. See also SSCP.
- Scheme that allows multiple
logical signals to be transmitted simultaneously across a single
physical channel. Compare with demultiplexing.
multipoint line
- See multidrop
line.
Multiport Communications
Interface
- See MCI.
multistation access unit
- See MSAU.
- Network using equipment from more than one vendor. Multivendor networks pose many more compatibility problems than single-vendor networks. Compare with single-vendor network.