Glossary - M

M13

DS-1/DS-3 multiplexer (network)
Device which multiplexes 28 DS-1 signals into a single DS-3 signal and vice versa. See TDM.

MAC

Media Access Control (network)
IEEE specifications for the lower half of the data link layer (layer 2) that defines topology-dependent access control protocols for IEEE LAN specifications. See LLC, PMD.

MAC Address

The hardware address of a device connected to a shared media. See also Media Access Control, Ethernet, token ring.

Mainframe (computer)

A powerful computer that contains all of the processing capability for a group of users (i.e. comprehensive software and several peripherals). Mainframe access is accomplished through terminals or other networked devices.

MAN

Metropolitan Area Network (network)
A term to describe a network that provides regional connectivity within a metropolitan area (such as a city). MANs are classified to be between LANs and WANs.

MAPI

Microsoft Mail Application Program Interface (messaging)
Microsoft's system for sending e-mail across a local area network.

Mapping (network)

In a network, the logical association of one set of values (like addresses) with values of another set, such as devices on another network.

MAU

Media Access Unit - Media attachment Unit (network)
A device that allows conversion between the AUI and various cable types such as Thick, Thin and twisted Pair. Used in Ethernet and IEEE networks. The MAU, which can be buit into a station or can be a separated device, performs physical layer functions including conversion of the digital data from the Ethernet interface, collision detection, and injection of bits onto the network.

Multistation Access Unit (network)

MBONE

Multicast BackbONE (network, Internet)
A virtual network on top of the Internet which supports routing of IP multicast packets, intended for multimedia transmission. MBONE gives public access desktop video communications. The quality is poor with only 3-5 frames per second instead of the 30 frames per second of commercial television. Its advantage is that it avoids all telecommunications costs normally associated with teleconferencing. An interesting innovation is the use of MBONE for audio communications and an electronic "whiteboard" where the computer screen becomes a shared workspace where two physically remote parties can draw on and edit shared documents in real-time.

Mbps (unit, communications)

Megabits per second
Transmission speed or rate of one million bits per second. See Kbps, Gbps.

MBS

Maximum Burst Size (ATM)
A traffic parameter that specifies the maximum number of cells that can be transmitted at the peak rate (PCR). In a other way, ATM performance parameter defining the duration of transmission at peak rate that would be accepted on a given ATM virtual circuit.

MCA

Micro Channel Architecture (hardware)
16/32 bits bus developed by IBM in 1986 for its PS/2 machines. It is not successful at all and IBM even uses it only for its high level systems.

MCDV

Maximum Cell Delay Variation (ATM)
Maximum CDV over a given QoS class.

MCLR

Maximum Cell Loss Ratio (ATM)
Maximum CTD over a given QoS class, defined for CBR and VBR traffic and for cells with CLP = 0.

MCR

Minimum Cell Rate (ATM)
ATM performance parameter which specifies the minimum rate for cell transmission that a network must guarantee to a user on a given virtual circuit. Also, a field in an RM cell specifying the smallest value to which the ER field can be set.

MCTD

Maximum Cell Transfer Delay
The maximum CTD over a given QoS class.

MDI

Medium-Dependent Interface (network, ethernet)
The mechanical and electrical interface between the trunk cable medium and the MAU. It is used mostly to caracterize a type of Ethernet twisted pair port connection: MDI ports connect to MDIX (cross-over) ports using straight-through twisted pair cabling. See also MDI-X.

MDIX - MDI-X

Medium-Dependent Interface-X (network, ethernet)
MDI-X is another version of the MDI interface that enables like devices to connect, using different pin-outs, avoiding conflicts that occur when receiving and transmitting packets use the same pin-out. MDI-to-MDI and MDIX-to-MDIX links use cross-over twisted pair cabling.

Mean Cell Transfer Delay

The average of the processing, queueing and propagation delays.

Messaging Directory (messaging, network, X.400)

A directory service based on X.400 messaging to keep various E.Mail based directories apprised of changes.

Meta Directory (messaging, network, X.400)

A directory service which permits management of multiples directories from various origin as if they were single, unified entity.

MHS

Message Handling System(messaging, standard, network)
The standard defined by ITU-T as X.400 and by ISO as Message-Oriented Text Interchange Standard (MOTIS). MHS is the X.400 family of services and protocols that provides the functions for global electronic mail transfer among local mail systems and MTAs. It is used by CompuServe, among others.

MIB

Management Information Base (network)
A data structure that defines objects for referencing variables such as integers and strings. In general, it contains information regarding network's management and performance, i.e.traffic parameters. See also ILMI, ATM MIB.

MIC

Media Interface Connector (cable)

MID

Message IDentifier

Multiplex IDentification (ATM)
A 10-bit field in the AAL3/4 SAR-PDU header for identifying the different CPCS-PDUs multiplexed over the same VCC.

Middleware (communications)

Software layer used to integrate an application in a specific environment. It is a kind of API that handles an application environment, not a hardware environment. It is especially used in distributed environments.

MIDI

Musical Instrument Digital interface
Exchange data format used between a computer and musical instruments.

MIF

Management Information Format (network, management, web)
Source of management information data for CIM compliant software.

MIME

Multipurpose Internet Mail Extension (file format, multimedia, messaging)
A standard for multi-part, multimedia electronic mail messages and World-Wide Web hypertext documents on the Internet. MIME provides the ability to transfer non-textual data, such as graphics, audio and fax. It is defined in RFC 1341. It uses mimencode to encode binary data into base 64 using a subset of ASCII.
FAQ.

MIN

Multistage Interconnection Network
A switch fabric built from switching elements organized in series and/or in parallel, for providing physical connections between the inputs and the outputs of a switch.

Mips

Million instructions per second (unit)
A measure of a computer's speed or power.

Mirror

1. hardware, storage: writing duplicate data to more than one device (usually two hard disks), in order to protect against loss of data in the event of device failure. This technique may be implemented in either hardware (sharing a disk controller and cables) or in software. It is a common feature of RAID systems. Several operating systems support software disk mirroring or disk duplexing, e.g. Novell NetWare. See also Redundant Array of Independent Disks(RAID). Interestingly, when this technique is used with magnetic tape storage systems, it is usually called "twinning". A less expensive alternative, which only limits the amount of data loss, is to make regular backups from a single disk to magnetic tape.
2. networking: an archive site which keeps a copy of some or all files at another site so as to make them more quickly available to local users and to reduce the load on the source site. Such mirroring is usually done for specific whole directories or files on a specific remote server as opposed to a cache or proxy server which keeps copies of everything that is requested via it. For example, src.doc.ic.ac.uk is the main UK mirror for the GNU archive at prep.ai.mit.edu.

MMDS

Multichannel Multipoint Distribution Service (network)
A broadband wireless technology, a form of cellular radio that operate at frequencies of 2 GHz. MMDS can be an alternative to the local loop and permits a high bandwith traffics up to 10 Mbis/s. One of the technologies used to bypass the bottleneck of "the last mile" (local loop). Others technologies to solve this problem are DSL and cable modem.

MMF

MultiMode Fiber Optic Cable (physical layer)

MNP

Microcom Network Protocols (communications, network)
Protocols used to improve the transmission quality between 2 modems. They have been initialy developed by the American company Microcom. They are now a standard. They are organised in 10 classes.

Modem

Modulator/demodulator (hardware, communications)
An electronic device for converting between serial data (typically RS-232) from a computer and an audio signal suitable for transmission over telephone lines. In one scheme the audio signal is composed of silence (no data) or one of two frequencies representing 0 and 1.
Modems are distinguished primarily by the maximum baud rate they support. Baud rates can range from 75 baud up to 28800 and beyond. Data to the computer is sometimes at a lower rate than data from the computer on the assumption that the user cannot type more than a few characters per second.
Various data compression and error correction algorithms are required to support the highest speeds. Other optional features are auto-dial (auto-call) and auto-answer which allow the computer to initiate and accept calls without human intervention. Most modern modems support a number of different protocols and two modems, when first connected will automatically negotiate to find a common protocol. Some modem protocols allow the two modems to renegotiate ("retrain") if the initial choice of data rate is too high and gives too many transmission errors.
A modem may either be internal, connected to the computer's bus or external ("stand-alone"), connected to one of the computer's serial ports. The actual speed of transmission in characters per second depends not just the modem-to-modem data rate, but also on the speed with which the processor can transfer data to and from the modem, the kind of compression used andwhether the data is compressed by the processor or the modem, the amount of noise on the telephone line (which causes retransmissions), the serial character format (typically 8N1: one start bit, eight data bits, no parity, one stop bit).

MOF

Managed Object Format (network, management, web)
Data structure used by CIM to describe all managed element on the network.

Mosaic (network, Internet)

First graphical Web browser developped by the student Mark Andresseen at NCSA of Illinois University. For more information: http://www.ncsa.uiuc.edu/SDG/Software/Mosaic/Docs/help-about.html.

MPEG

Motion Picture Experts Group (compression, standard, algorithm, file format, body)
One of three industry organizations developing standards and specifications for the transmission of video information over various media and network technologies. (see JPEG, Px64). By extension, a video technology standard that specifies the digital encoding, transmission and decoding protocols, capable of presenting VCR quality motion video.

MPOA

Multiprotocol Over ATM (ATM)
A set of standards to support, other than IP, (distributed) routing protocols. Developed on top of LANE and NHRP it willl support switches, route servers and hosts all attached to an ATM network.

MR

Mean Rate (ATM)
Same as Average Cell Rate.

MSB

Most Significant Bit
Bit n-1 in an n bit binary number, the bit with the greatest weight (2^(n-1)). The first or leftmost bit when the number is written in the usual way.

MSP

Maintenance Service Provider (network)

MTA

Message Transfer Agent (messaging)
The X.400 equivalent of Mail Transfer Agent.

Mail Transfer Agent (messaging)
The program responsible for delivering e-mail messages. Upon receiving a message from a Mail User Agent or another MTA it analyses the recipients and either delivers it (local addressee) or forwards it to another MTA (routing). In either cases, it may edit and/or add to the message headers.
The most widely used MTA for Unix is sendmail.

MTS

Message Transfer System (messaging)
The collection of Message transfer Agents providing the Message Transfer service Elements.

MTU

Maximum Transmission Unit
Maximum allowable size of a PDU. For instance, MTU size for Ethernet is 1500 octets.

MUA

Mail User Agent (messaging)
User program to read and write mails.

Multicast

Single packets copied to a specific subset of network addresses (it is not limited to the local network). These addresses are specified in the destination-address field of the packet. It is different from broadcast where a message is sent to every station on a local network.

Multicast Addressing

Ethernet addressing scheme used to send packets to devices of a certain type or for broadcasting to all nodes. The least significant bit of the most significant byte of a multi-cast address is one.

Multicast Packets (network)

Multicast packets are addressed to a group of devices on a LAN. LAN stations use multicast packets to deliver information to a specific set of devices such as routers, file servers, and hosts.

Multimedia

A way of presenting to the user a combination of different forms of information such as text, data, images, video, audio, graphics (i.e. videoconference).

Multiplex (communications)

Multiplexer (communications)

A networking local device where multiple streams of information are combined so they can share a common physical medium. They are then separated by a similar device at the other end of the link. This can be done in a variety of ways: time division multiplexing, frequency division multiplexing and statistical multiplexing.
Multiplexers are also becoming increasingly efficient in terms of data compression, error correction, transmission speed and multi-drop capabilities. For example, an M1-3 MUX combines 28 DS-1s into a DS-3.
See TDM.

Multiplexing - Multiplex Operation - Multiple access

Combining several signals for transmission on some shared medium (e.g. a telephone wire). The signals are combined at the transmitter by a multiplexor (a "mux") and split up at the receiver by a demultiplexor. The communications channel may be shared between the independent signals in one of several different ways: time division multiplexing, frequency division multiplexing or code division multiplexing.
If the inputs take turns to use the output channel (time division multiplexing) then the output bandwidth need be no greater than the maximum bandwidth of any input. If many inputs may be active simultaneously then the output bandwidth must be at least as great as the total bandwidth of all simultaneously active inputs. In this case the multiplexor is also known as a concentrator.
The converse equipment or process for separating a multiplexed stream into individual channels is called demultiplexer. In a layer: A function that interleaves the information from multiple connections into one connection.

Multiplexor

See Multiplexer.

Multiprotocol encapsulation over ATM

Allows higher-layer protocols, such as IP or IPX, to be routed over ATM by enabling an ATM-aware device or application to add a standard protocol identifier to LAN data.

Mux

MUltipleXer
See multiplexer.

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