Glossary Section "M" ( Definitions )
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MAC Media Access Control. The
lower portion of the datalink layer. As defined by the IEEE, the lower of the two
sublayers of the OSI reference model data link layer. The MAC sub-layer is concerned with
media access issues, such as whether token passing or contention is used
MAC address The hardware
address of a device connected to a shared media.
MAE Metropolitan Access
mail bridge A mail gateway
that forwards electronic mail between two or more networks while ensuring that the
messages it forwards meet certain administrative criteria. A mail bridge is simply a
specialized form of mail gateway that enforces an administrative policy with regard to
what mail it forwards.
mail exploder Part of an
electronic mail delivery system which allows a message to be delivered to a list of
addressees. Mail exploders are used to implement mailing lists. Users send messages to a
single address (e.g., firstname.lastname@example.org) and the mail exploder takes care of
delivery to the individual mailboxes in the list.
mail gateway A machine that
connects two or more electronic mail systems (especially dissimilar mail systems on two
different networks) and transfers messages between them. Sometimes the mapping and
translation can be quite complex, and generally it requires a store-and-forward scheme
whereby the message is received from one system completely before it is transmitted to the
next system after suitable translations.
Majordomo A program which
handles mailing list maintenance such as adding and removing addresses from mailing lists.
MAN Metropolitan Area Network.
A data network intended to serve an area approximating that of a large city.
MANO Magagement and Orchestration
Martian Humorous term applied
to packets that turn up unexpectedly on the wrong network because of bogus routing
entries. Also used as a name for a packet which has an altogether bogus (non-registered or
ill-formed) Internet address.
MAU Media Attachment
Unit. This is the device that connects the AUI port on a host system to the rest
of the Ethernet network medium
MBONE Multicast Backbone. A
collection of Internet routers that support IP multicasting. The MBONE is used as a
"broadcast (actually multi-cast) channel" on which various public and private
audio and video programs are sent.
Bits of information transmitted Per Second.
MDU Multiple Dwelling Unit
MEF Metro Ethernet Forum. The defining body for carrier Ethernet.
MEP Maintenance End Point
message The Layer 3
information that is passed between the CPE and SPCS for signalling.
Message Digest (MD-2, MD-4,
MD-5) Message digests are algorithmic operations, generally performed on text, which
produce a unique signature for that text. MD-2, described in RFC 1319; MD-4, described in
RFC 1320; and MD-5, described in RFC 1321 all produce a 128-bit signature. They differ in
their operating speed and resistance to crypto-analytic attack. Generally, one must be
traded off for the other. See PGP, DES, RSA.
meter A unit of measure in the metric system
which equals 39.37 inches.
MHS Message Handling System.
The system of message user agents, message transfer agents, message stores, and access
units which together provide OSI electronic mail. MHS is specified in the CCITT X.400
series of Recommendations.
MIB Management Information
Base. A collection of objects that can be accessed via a network management protocol.
Both SNMP and RMON use standardized MIB formats that allows any SNMP and RMON tools to monitor any device defined by a MIB.
Mid-level network Mid-level
networks (a.k.a. regionals) make up the second level of the Internet hierarchy. They are
the transit networks which connect the stub networks to the backbone networks.
MILNET MILitary NETwork.
Originally part of the ARPANET, MILNET was partitioned in 1984 to make it possible for
military installations to have reliable network service, while the ARPANET continued to be
used for research.
MIME Multi-purpose Internet
Mail Extensions. The standard for multimedia mail contents in the Internet suite of
MIMO - Multiple-Input and Multiple-Output refers to the use of multiple antennas to improve performance of a radio link.
MIP Maintenance Intermediate Point
Modem stands for
Modulator/Demodulator. A modem transmits computer data over the telephone
network. On the sending sided it converts digital data to analog for
transmission over an analog line (such as the telephone network). On the
receiving side it converts the analog transmission back to digital data.
Modbus is a serial communications protocol. It was developed with industrial
applications mind. Modbus is frequently used in oil and gas SCADA applications.
MOS Mean Opinion
Score is score given by human listeners. The values range from 1 to 5, where 5
is the highest quality level.
MOSPF Multicast Open
MoU Memorandum of
MP Multilink Protocol
MPEG Moving Picture
Experts Group. Commonly refers to the international standard for digital video and audio
MPLS Multiprotocol Label
Switching integrates Layer 2 information about network links such as
bandwidth, utilization and latency into Layer 3 (IP). This gives network
operators flexibility to divert and route traffic around link
failures, congestion, and bottlenecks.
MPOA Multiprotocol Over ATM.
An ATM Forum specification that defines how ATM traffic is routed from one virtual LAN to
another. MPOA is key to making LAN emulation, Classical IP over ATM, and proprietary
virtual LAN schemes inter-operate in a multi-protocol environment.
MRU Maximum Receivable Unit
MRRU Maximum Receivable
MTA Message Transfer Agent. An
OSI application process used to store and forward messages in the X.400 Message Handling
System. Equivalent to Internet mail agent.
MT-RJ Mechanical Transfer Registered Jack. This is a fiber-optic Cable Connector found on some small form factor devices. It is smaller than an SC connector but houses two fibers.
MTTR Mean Time To Repair
MTU Maximum Transmission Unit.
The largest possible unit of data that can be sent on a given physical medium. Example:
The MW of Ethernet is 1500 bytes.
multicast A special form of
broadcast where copies of the packet are delivered to only a subset of all possible
multi-homed host A computer
connected to more than one physical datalink. The data links may or may not be attached to
the same network.
Multi Mode Fiber An optical
fiber which allows several rays of light to pass. It is less expensive than single mode
fiber but it has less capacity and a shorter range.
aka MUX This equipment allows multiple signals to be transmitted over the same physical
media. There are Time Division Multiplexers and Frequency Division Multiplexers.
Multipoint line A
communications line having multiple cable access points.
MX Mail Exchange Record A DNS
resource record type indicating which host can handle mail for a particular domain.
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