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Glossary Section "M" ( Definitions )

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0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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 Exchange

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., sherylrice@bestdatasource.com) 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.

Mbps  Millions Bits of information transmitted Per Second.

MDU Multiple Dwelling Unit

MEF Metro Ethernet Forum. The defining body for carrier Ethernet.

megabit 1,000,000 bits

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 protocols.

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 Shortest-Path first.

MoU Memorandum of Understanding.

MP Multilink Protocol

MPEG  Moving Picture Experts Group. Commonly refers to the international standard for digital video and audio compression.

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 Reconstructable Unit

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 destinations.

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. 

Multiplexer 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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