MAC address
Media Access Control address (MAC address) is a unique identifier attached to most forms of networking equipment. A MAC address is 48 bits long. The MAC address is commonly written as a sequence of 12 hexadecimal digits as follows: 48-3F-0A-91-00-BC. Most layer 2 network protocols use one of three numbering spaces managed by the IEEE: MAC-48, EUI-48, and EUI-64, which are designed to be globally unique.

MAC address learning
MAC address learning is a 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.

MAC Layer
Media Access Control Layer (MAC Layer) is one of two sublayers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one Network Interface Card (NIC card) to another across a shared channel.

MAC: Media Access Control
The Media Access Control (MAC) is a sublayer in data link layer of the OSI network model that determines who is allowed to access the physical media at any one time. It acts as an interface between the Logical Link Control sublayer and the network's physical layer. The MAC sublayer is primarily concerned with the control of access to the physical transmission medium (i.e. which of the stations attached to the wire or frequency range has the right to transmit) or low-level media-sharing protocols like CSMA/CD. MAC provides unique identification and access control for computers on an Internet Protocol (IP) network. MAC assigns a unique number to each IP network adapter called the MAC address.

MADI: Multi-channel Audio Digital Interface
Multi-channel Audio Digital Interface (MADI) is an interface standard described by the Audio Engineering Society (AES) standards AES-10 and AES-10id. It was developed by Neve, Sony, and SSL as an easy way to interface digital multitrack tape recorders to mixing consoles.

MAE: Metropolitan Access Exchange
Metropolitan Access Exchange(MAE), also known as Metropolitan Area Exchange, is one type of a number of Internet exchange points, that are implemented as metropolitan area networks. A MAEs allow Internet backbone operators and/or regional network operators peer with one another, in which in which different network authorities agree to exchange route advertisements and traffic. MAE-West is in California's Silicon Valley and MAE-East is in the Washington, DC, area. MAE is a trademark of MCI Worldcom, which acquired the MAEs in its purchase of MFS (Metropolitan Fiber Systems) Communications.

Mail Bridge
Mail Bridge is a gateway that forwards e-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
Mail Exploder is part of an e-mail delivery system that 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 (for example, list@somehost.com), and the mail exploder takes care of delivery to the individual mailboxes in the list.

Mail Gateway
Mail Gateway is a machine that connects two or more e-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.

MAN: Metropolitan-area Network
Metropolitan Area Network (MAN) is a computer networks usually spanning a campus or a city, which typically connect a few local area networks using high speed backbone technologies. A MAN often provides efficient connections to a wide area network (WAN). Generally, a MAN spans a larger geographic area than a LAN, but a smaller geographic area than a WAN.

Managed FRAD
Managed Frame Relay Access Device (Managed FRAD) means that the Frame Relay Access Device (FRAD) is located at the customer premise but the FRADs are provided, installed and managed by service providers.

Managed Object
In network management, Managed Object refers to a network device or process that can be managed by a network management system.

Manchester Encoding
Manchester Encoding, also known as Phase Encoding (PE), is a synchronous clock encoding technique used by the physical layer to encode the clock and data of a synchronous bit stream. Manchester Encoding is used in the Ethernet media systems. Manchester coding provides a simple way to encode arbitrary binary sequences without ever having long periods without level transitions, thus preventing the loss of clock synchronisation, or bit errors from low-frequency drift on poorly-equalized analog links. In this technique, the actual binary data to be transmitted over the cable are not sent as a sequence of logic 1's and 0's (known technically as Non Return to Zero (NRZ)). Instead, the bits are translated into a slightly different format that has a number of advantages over using straight binary encoding (i.e. NRZ).

Martian Packet
Martian Packets, sometimes simply called Martian or packets from Mars, are the packets with source addresses not routable by some computer on a network segment on the grounds that they are of no evident "terrestrial" (i.e. normal) source. Martian packets can arise from network equipment malfunction, misconfiguration of a host, or simple coexistence of two logical networks on a single physical layer. For instance, if the IP networks of 192.168.34.0/24 and 10.2.3.0/24 operate on the same Ethernet segment, packets from 10.2.3.4 are Martians to the computer at 192.168.34.9, and vice versa.

Martian: Packets from Mars
Martian, also known as Martian Packet or packets from Mars, is a humorous term applied to packets that turn up unexpectedly on the wrong network because of bogus routing entries. It is also used as a name for a packet that has an altogether bogus (nonregistered or ill-formed) Internet address.

Master Control Port
Master Control Port is a physical interface on an MPLS Label Switch Controller (LSC) that is connected to one end of a slave control link.

MATV: Master Antenna TV
Master Antenna TV (MATV) is a mini cable system relaying the broadcast channels usually to a block of flats or a small housing estate.

MAU: Medium Attachment Unit
Medium Attachment Unit (MAU), also referred to as a transceiver, provides the physical and electrical interface between an Ethernet device and the medium system to which it is connected. On original Thicknet Ethernet, the MAU was typically clamped to the Ethernet cable. In most modern switched or hubbed Ethernet systems, neither the MAU nor the AUI interfaces exist, and the CAT5 cable connects directly into an Ethernet socket on the host or router.

MAU: Multistation Access Unit (or MSAU)
Multistation Access Unit (MSAU or MAU) is a 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 a router.

MaxAge Timer
MaxAge Timer is a Spanning-Tree Protocol (STP) timer that defines how long a bridge or switch should wait after the last received hello message before believing that the network topology has changed, and it can no longer hear the hello messages sent by the root bridge or switch. The MaxAge timer specifies the lifetime of a stored BPDU received on a designated port. After the timer expires, other ports can become designated ports.

Maximum Burst
Maximum Burst, with a unit in bytes or cells, 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.

Maximum Rate
Maximum Rate, in an ATM or Frame Relay network, is the 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.

Mb: Megabit
Megabit (Mb), approximately 1,000,000 bits, is a unit of measure of information and data storage.

MB: Megabyte
Megabyte (MB), approximately 1,000,000 bytes and 8,000,000 bits, is a unit of measure of information and data storage.

MBBS
MBBS was a popular BBS system in the Nordic countries during the mid-1990s. It was created by a team of Oslo-based enthusiasts, led by Mike Robertson. As many BBS system of that era, it was only available for the DOS platform. Since one process could only handle one node, multitaskers such as DESQview or Microsoft Windows were necessary in order to run multi-node BBSes. MBBS had to use the only viable means of interprocess communication under DOS, namely to read and write to a set of files in a common subdirectory. Since these files were accessed very often, many sysops moved them to a RAM disk.

MBONE: Multicast Backbone
Multicast Backbone (MBONE), also known as Multicast backbone of the Internet, is a virtual multicast network composed of multicast LANs and the point-to-point tunnels that interconnect them.

Mbps: Megabits Per Second
Megabits Per Second (Mbps), is a bit rate expressed in millions of binary bits per second. Megabytes Per Second (MBps) is eight times more than the Megabits Per Second (Mbps).

MBps: Megabytes Per Second
Megabytes Per Second (MBps) is a bit rate expressed in millions of binary bytes per second. Megabytes Per Second (MBps) is eight times more than the Megabits Per Second (Mbps).

MBS: Maximum Burst Size
Maximum Burst Size (MBS), coded as a number of cells, is a term used in ATM (Asynchronous Transfer Mode) to specify the maximum number of cells which can be transmitted at the contracted Peak Cell Rate(PCR). In an ATM signaling message, burst tolerance is conveyed through the MBS. The burst tolerance together with the SCR and the Generic Cell Rate Algorithm (GCRA) determine the MBS that can be transmitted at the peak rate and still be in conformance with the GCRA.

MCA: Micro Channel Architecture
Micro Channel Architecture (MCA) is proprietary 16 or 32-bit parallel computer bus interface commonly used in some IBM PCs and some UNIX workstations and servers. MCA has been replaced by PCI. MCA is no longer used in new computer designs.

MCDV: Maximum Cell Delay Variation
Maximum Cell Delay Variation (MCDV), a term in the ATM networking, is the maximum two-point CDV objective across a link or a node for the specified service category. MCDV is one of four link metrics exchanged using PTSPs to determine the available resources of an ATM network. There is one MCDV value for each traffic class.

MCLR: Maximum Cell Loss Ratio
Maximum Cell Loss Ratio (MCLR), a term in the ATM networking, is the maximum ratio of cells that do not successfully transit a link or node compared with the total number of cells that arrive at the link or node. MCLR is one of four link metrics exchanged using PTSPs to determine the available resources of an ATM network. The MCLR applies to cells in the CBR and VBR traffic classes whose CLP bit is set to zero.

MCNS: Multimedia Cable Network System Partners Ltd
Multimedia Cable Network System Partners Ltd. (MCNS) is a consortium of cable companies to drive a standard with the goal of having interoperable cable modems. The standard Data Over Cable Service Interface Specification (DOCSIS) is a result of MCNS.

MCR: Minimum Cell Rate
Minimum Cell Rate (MCR) is an ATM ABR service traffic descriptor, in cells/sec, that is the minimum rate at which the source is always allowed to be sent. MCR may be set to zero. The bandwidth available from the network may vary, but shall not become less than MCR.

MCTD: Maximum Cell Transfer Delay
Maximum Cell Transfer Delay(MCTD), a term in an ATM network, is the sum of theMaximum Cell Delay Variation (MCDV) and the fixed delay component across the link or node. MCTD is one of four link metrics exchanged using PTSPs to determine the available resources of an ATM network. There is one MCTD value for each traffic class.

MD: Mediation Device
Mediation Device (MD) provides protocol translation and concentration of telemetry information originating from multiple network elements and transport to an Operations Support System (OSS).

MDI Uplink
MDI Uplink refers to a Medium Dependent Interface port (MDI port) that is used as an uplink port (i.e., connector) on a network hub or on a network switch to connect to other hubs or switches via a conventional straight-through cable, i.e., without requiring a crossover cable.

MDI: Medium-dependant Interface
Medium Dependent Interface (MDI) is an Ethernet port connection that allows network hubs or switches to connect to other hubs or switches without a null-modem, or crossover, cable. In the case of thick coaxial Ethernet, the most commonly used MDI is a type of clamp that is installed directly onto the coaxial cable. For twisted-pair Ethernet, the MDI is an eight-pin connector, which is also referred to as a RJ-45 telephone-style jack. The eight-pin jack provides a connection to the four twisted-pair wires used to carry network signals in the 10-Mbps twisted-pair media system.

MDIX: Medium Dependent Interface Crossover
Medium Dependent Interface Crossover (MDIX or MDI-X), a version of the Medium Dependent Interface (MDI), enables connections between like devices (e.g., two hubs) by crossing the transmit-receive circuits. The straight-through cable connecting an MDI port on one hub or switch is inserted into an MDIX port on the other hub or switch. Both MDI-to-MDI and MDIX-to-MDIX connections use crossover cables. For example, an Ethernet port connection that allows networked end stations (i.e., PCs or workstations) to connect to each other using a null-modem, or crossover cable is an MDIX.

MDN: Message Disposition Notification
Message Disposition Notification (MDN) is a message returned to the originator of an e-mail message indicating that the e-mail message has been opened.

Media
Media, also known as physical media in networking, refers to 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).

Media Rate
Media Rate is the maximum traffic throughput for a particular physical media type.

Media Stream
Media Stream is a single media instance, for example, an audio stream. A media stream can be on demand or live. On-demand streams are stored on a server for a long period of time, and are available to be transmitted at a user's request. Live streams are only available at one particular time, as in a video stream of a live sporting event.

Mesh
Mesh is a network topology in which devices are organized in a manageable, segmented manner with many, often redundant, interconnections strategically placed between network nodes. Mesh network topology is one of the key network architectures in which devices are connected with many redundant interconnections between network nodes such as routers and switches. In a mesh topology if any cable or node fails, there are many other ways for two nodes to communicate. While ease of troubleshooting and increased reliability are definite pluses, mesh networks are expensive to install because they use a lot of cabling. Often, a mesh topology will be used in conjunction with other topologies (such as Star, Ring and Bus) to form a hybrid topology. Some WAN architecture, such as the Internet, employ mesh routing. There are two types of mesh topologies: full mesh and partial mesh:

Mesh Networking
Mesh networking refers to a topology to connect network devices. It allows for continuous connections and reconfiguration around blocked paths by "hopping" from node to node until a connection can be established. Mesh networks are self-healing and highly reliable: the network can still operate even when a node breaks down or a connection goes bad.

Message
Message in computer networking typically refers to the application layer (Layer 7) logical grouping of information/data. A message often composed of a number of lower-layer logical groupings such as packets or datagrams. The terms datagram, frame, packet, and segment are also used to describe logical information groupings at various layers of the OSI reference model.

Message Switching
Message Switching, also known as store-and-forward switching, refers to a 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.

Message Unit
Message Unit refers to a unit of data processed by any network layer as defined in the OSI 7 layers model.

Meta tags
Meta tags are optional elements defined in the header portion of an HTML or PHP file for web pages. Meta tags contain information about the web page document such as the author, language, keywords describing the document, a description of the document, etc.

Metasignaling
Metasignaling is a process running at the ATM layer that manages signaling types and virtual circuits.

Metric
Metric refers to a a unit of measure in many systems and algorithms. For example, routing protocol algorithms requires a defined metric to determine the best pathway for traffic to use to reach a particular destination.

MFA Forum
The MFA Forum is an international, industry-wide, non-profit association of telecommunications, networking, and other companies focused on advancing the deployment of multi-vendor, multi-service packet-based networks, associated applications, and interworking solutions. MFA focuses on three key technologies: MPLS, Frame Relay and ATM, and it was merged from a few organizations including Frame Relay Forum, ATM Forum, etc.

MGC Switchover
Media Gateway Controller (MGC) Switchover refers to the rerouting of signalling traffic by the signalling gateway as required (and requested by the MGCs) between related MGCs in the event of failure or unavailability of the currently used MGC. The traffic is rerouted from the primary MGC to the backup MGC.

MGC: Media Gateway Controller
A Media Gateway Controller (MGC), also known as call agent or softswitch, is a system used in the Voice over IP telephony architectures to control a number of dumb terminals and the Media Gateways. The MGC receives signalling information (like dialed digits) from the media gateway and can instruct it to alert the called party, to send and receive voice data etc. There are several protocols which can be used between MGC and media gateway: SGCP, IPDC, MGCP, H.323 and Megaco/H.248. MGC can interface with other signalling protocols, like SS7 and SIP.

MGW: Media Gateway
Media Gateway (MGW), a unit connecting different types of networks, performs translation between disparate networks such as PSTN; data network based on IP or ATM; 2G, 2.5G and 3G radio access networks or PBX. Media Gateways enable multimedia communications across Next Generation Networks over multiple transport protocols such as ATM, IP and TDM. One of MGW's main functions is to convert between the different transmission and coding techniques. Media streaming functions such as echo cancellation, DTMF, and tone sender are also located in the MGW. Media Gateways are controlled by a Media Gateway Controller (also known as a Call Agent or a Soft Switch) which provides the call control and signaling functionality. Communications between Media Gateways and Call Agents are achieved by means of protocols such as MGCP or Megaco or H.248.

MHP: Multimedia Home Platform
Multimedia Home Platform (MHP) is a set of common application programming interfaces (API) designed to create an operating system-independent, level playing field for broadcasters and consumer-electronics manufacturers. The goal is to provide all DVB-based terminals (set-tops, TVs, and multimedia PCs) full access to programs and services built on the DVB Java (DVB-J) platform.

MHS: Message Handling System
Message Handling System (MHS) provides message handling services for communications between distributed applications. Typically MHS is based on the ITU-T X.400 recommendations. NetWare MHS is a different (though similar) entity that also provides message-handling services.

MIB: Management Information Base
A Management Information Base (MIB) is a type of database used to manage the devices in a communications network. It comprises a collection of objects in a (virtual) database used to manage entities (such as routers and switches) in a network. Objects in the MIB are defined using a subset of Abstract Syntax Notation One (ASN.1) called "Structure of Management Information Version 2 (SMIv2). Simple Network Management Protocol (SNMP), MIBs are used as the information objects and the format of the MIBs are defined as part of the SNMP. MIB-I refers to the initial MIB definition; MIB-II refers to the later definition. SNMPv2 includes MIB-II and adds some new objects.

MIC: Media Interface Connector
Media Interface Connector (MIC) is the FDDI de facto standard connector. MIC is a pair of fiber optic connectors that link the fiber media to the FDDI or other cable. The MIC consists of both the plug terminated to a optical cable and the receptacle which is contained within the FDDI node.

Microcode
Microcode is the 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.

Microfilter
Microfilter is a device that prevents data noice from traveling over the telephone line and interfering with telephone calls. For example, a microfilter is a small device that plugs into the normal BT telephone socket and splits the line into both a standard BT telephone socket and a ADSL broadband socket. Failure to have a microfilter correctly installed on all BT socket you use may result in interference (buzzing noises etc.) on your telephone and / or reduced performance and possible loss of service on your broadband access. Also, in a burglar alarm that uses the telephone line, it is important to use a microfilter to reduce noice in the phone line.

Microsegmentation
Microsegmentation is a term used to describe the segmentation of a collision domain into as many segments as there are circuits, minus one (#segments = #circuits - 1). This microsegmentation performed by the switch cuts the collision domain down so that only two nodes coexist within each collision domain. In this way, collisions are decreased and only the two NICs which are directly connected via a point-to-point link are contending for the medium.

MID: Message Identifier
Message Identifier (MID), a term in ATM networking, is used to identify ATM cells that carry segments from the same higher-layer packet.

Mid-level Network
Mid-level Network, also known as regional network, is the second level of the Internet hierarchy. They are the transit networks that connect the stub networks to the backbone networks.

Midsplit
Midsplit is a special type of broadband cable system that divides the available frequencies into two groups: one for transmission and the other for reception.

Migration data host
A migration data host, a term in the IBM APPN networking, is a VTAM data host that communicates to APPN resources as an APPN EN and communicates to directly attached VTAMs and NCPs using subarea flows. Unlike an ICN, a migration data host does not translate between APPN and subarea protocols, and it cannot own NCPs or provide ISR. A migration data host is often implemented during migration from subarea SNA to APPN because the migration allows data hosts to be accessed from an APPN node or subarea node concurrently.

MII: Medium Independent Interface
Medium Independent Interface (MII) provides a 40-pin connection to outboard transceivers (also called PHY devices). It is used to attach 802.3 interfaces (MACs) to a variety of physical media systems.

MILNET: Military Network
Military Network (MILNET) is the unclassified portion of the Defense Data Network (DDN), a worldwide set of military networks running at different security levels. In the 1990s, MILNET became the Non-classified Internet Protocol Router Network (NIPRNET).

Mirror Site
Mirror sites are most commonly used to provide multiple sources of the same information, and are of particular value as a way of providing reliable access to large downloads. Mirroring is a one-way operation whereas file synchronization is two-way. On the Internet, a mirror site is an exact copy of another Internet site (a web site or database).

Mirroring
In computer industry, mirroring is a data duplicate technique used to provide higher availability of computer data. On the Internet, a mirror site is an exact copy of another Internet site (often a web site).

Mips: Millions of instructions per second
Millions of instructions per second (Mips) is number of instructions executed by a processor per second. Mips is a measure of the processing speed of a micro processor.

Mixing Segment
Mixing Segment is a bus segment capable of supporting two or more devices on the same bus. Coaxial cable segments are classified as mixing segments.

MLS: Multilayer Switch
A multilayer switch (MLS) is a computer networking device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers. A Multilayer Switch (MLS) can prioritize packets by the 6 bits in IP DSCP (differentiated services Code Point). Some MLSs are also able to route between VLAN and/or ports like a common router. The routing is normally as quick as switching (at wirespeed). Some switches can use up to OSI layer 7 packet information; they are called layer 4-7 switches, content-switches, web-switches or application-switches.

MMF: Multimode Fiber (MM Fiber)
Multimode Fiber (MM Fiber or MMF) is a fiber-optic medium in which light travels in multiple modes or allows the propagation of multiple frequencies of light.

MML: Man-Machine Language
Man-Machine Language (MML) is the industry standard command line language used to manage telecommunications network elements.

MMoIP: Multi-Media over IP
Multi-Media over IP (MMoIP), a concept introduced by telecommunication technology vendors, refers to providing multiple services such as voice, data and video using the packet technology over the IP network.

MMP: Multichassis Multilink PPP
Multichassis Multilink PPP (MMP) extends MLP support across multiple routers and access servers. MMP enables multiple routers and access servers to operate as a single, large dial-up pool, with a single network address and an ISDN access number. MMP correctly handles packet fragmenting and reassembly when a user connection is split between two physical access devices.

Mnet
Mnet, a free software and open source project run solely by hackers volunteering in the public interest, is a distributed, peer to peer, file store. Mnet is also an emergent network, in which the important features of the network result from the interactions of nodes operated by autonomous people or organizations who do not explicitly coordinate with one another.

Modem Eliminator
Modem Eliminator is a device allowing the connection of two DTE devices without modems.

Modem server
Modeml server is an equipment that allows a modem at the customer premise to connect to a network.

Mosaic
Mosaic is a World Wide Web browser and Gopher client developed at the National Center for Supercomputing Applications (NCSA) beginning in 1992, and officially ending on January 7, 1997. NCSA Mosaic was originally designed and programmed for Unix's X Window System. Marc Andreessen, the leader of the team that developed Mosaic, left NCSA and, with four other former students and staff of the University of Illinois, started Mosaic Communications Corporation. Mosaic Communications eventually became Netscape Communications Corporation, producing Netscape Navigator. Spyglass licensed the technology and trademarks from NCSA for producing their own web browser but never used any of the NCSA Mosaic source code. Spyglass Mosaic was later licensed by Microsoft, and it was modified and renamed Internet Explorer.

Mozilla Firefox
Mozilla Firefox, or simply known as Firefox, is a free, open source, cross-platform, graphical web browser developed by the Mozilla Corporation and hundreds of volunteers. Firefox includes an integrated pop-up blocker, tabbed browsing, live bookmarks, support for open standards, and an extension mechanism for adding functionality. Although other browsers have some of these features, Firefox became the first such browser to include them all and achieve wide adoption.

MQI: Message Queuing Interface
Message Queuing Interface (MQI) is an international standard API that provides functionality similar to that of the Remote Procedure Call (RPC) interface. MQI is implemented strictly at the application layer, while RPC is functioning at the session, presentation and application layers.

MRM: Multicast Routing Monitor
Multicast Routing Monitor (MRM) is a management diagnostic tool that provides network fault detection and isolation in a large multicast routing infrastructure. It is designed to notify a network administrator of multicast routing problems in near real time.

MRP: Multiservice Route Processor
Multiservice Route Processor (MRP) is a card that acts as a voice-and-data-capable router and that can carry voice traffic over an IP network and can link small-to-medium-size remote Ethernet LANs to central offices (COs) over WAN links. The MRP has two slots that support WAN interface cards (WICs), voice interface cards (VICs), or both in combination.

MRTG: Multi Router Traffic Grapher
The Multi Router Traffic Grapher (MRTG) is a tool to monitor the traffic load on network links. Normally, MRTG retrieves the statistics/raw data using the SNMP protocol, once the configuration on the values taken, periodically the scheduler will update the statistics and then the graphics for monitoring traffic/workload etc. MRTG generates HTML pages containing graphical images which provide a live visual representation of the traffic.

MSAU: Multistation Access Unit (or MAU)
Multistation Access Unit (MSAU or MAU) is a 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 a router.

MSB: Most Significant Bit
Most Significant Bit (MSB), sometimes referred to as the left-most bit, is the 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.

MSLT Adjustment: Minimum Scan Line Time Adjustment
Minimum Scan Line Time (MSLT) Adjustment is an alternative to Scan Line Fix Up meant to eliminate fax failures caused by an excessive number of received page errors because of data loss. MSLT adjustment sets a minimum MSLT value that an ingress gateway communicates to a sending fax machine. This value overrides an MSLT of lesser value that is supplied by a receiving fax machine.

MSLT: Minimum Scan Line Time
Minimum Scan Line Time (MSLT) is the time set by the receiving fax machine and sent to the sending machine during the initial handshaking. MSLT defines how much time the receiving machine requires to print a single scan line.

MSN SysOp
An MSN SysOp is a high ranking volunteer or a paid employee who monitors the actions and enforces policy on the MSN chat and the MSN Internet services.

MSO: Multiple Service Operator
Multiple Service Operator(MSO) refers to an cable service provider that also provides other services, such as data and/or voice telephony.

MSS: Maximum Segment Size
Maximum Segment Size (MSS) is the largest amount of data, specified in bytes, that a computer or communications device can handle in a single, unfragmented piece. For optimum communications, the number of bytes in the data segment and the header must add up to less than the number of bytes in the maximum transmission unit (MTU).

MTA: Message Transfer Agent
Message Transfer Agent(MTA) is the OSI application process used to store and forward messages in the X.400 Message Handling System. Equivalent to Internet mail agent, MTA implements SMTP and provides storage for mail messages to be forwarded or delivered to a local user.

MTBF: Mean Time Between Failure
Mean Time Between Failure (MTBF) is the "average" time between failures, the reciprocal of the failure rate in the special case when failure rate is constant. Calculations of MTBF assume that a system is "renewed", i.e. fixed, after each failure, and then returned to service immediately after failure.

MTTR: MeanTime to Repair
MeanTime to Repair(MTTR) is the average time needed to return a failed device or system to service.

MTU: Maximum Transmission Unit
Maximum Transmission Unit (MTU) is the largest physical packet size in bytes that can be passed by a layer of a communications protocol. A MTU parameter is usually associated with a communications interface (NIC, serial port, etc.). Each type of networks may have different size of MTU. The MTU for Ethernet is 1500 bytes. Higher-level network protocols like TCP/IP can be configured with a maximum packet size, but this setting is distinct from the physical MTU. Any messages larger than the MTU are divided into smaller packets before being sent. The MTU of a network has important implications on the performance of computer communications because that too large an MTU size may mean retransmissions if the packet encounters a router that can't handle that large a packet, and too small an MTU size means relatively more header overhead and more acknowledgements that have to be sent and handled.

MUD: Multi-user Dungeon
Multi-user Dungeon (MUD) refers to the adventure, role playing games, or simulations played on the Internet. Players interact in real time and can change the "world" in the game as they play it. Most MUDs are based on the Telnet protocol.

Multiaccess Network
Multiaccess network is a type of network that allows multiple devices to connect and communicate simultaneously.

Multicast
Multicast is the communication between a single sender and multiple receivers on a network. Multicast technologies are used to reduce network traffic when there are many receivers that want to listen to or view the same source simultaneously by delivering a single stream of information to hundreds of recipients. For an n-party video conference, a (n-1) times lower bandwidth is needed. "Multicast" is typically used to refer to IP Multicast using of a multicast address. IPv6 supports unicast, multicast, and anycast, but Broadcast in IPv6 has disappeared as a term, but is considered one form of multicast. But there are also other protocols implemented the multicast concept such as Asynchronous Transfer Mode (ATM) which has built-in mechanisms for "point-to-multipoint" or "multipoint-to-multipoint" connections.

Multicast Address
A multicast address is an identifier for a group of hosts that have joined a multicast group. In Ethernet, Multicast Address is an 48-bit identifier naming the group of stations that should receive a packet on the network. In IPv4, it is historically known as a class D address, a type of IP address, which ranges from 224.0.0.0 to 239.255.255.255, or, equivalently, 224.0.0.0/4. In IPv6, multicast addresses all have the prefix ff00::/8.

Multicast Forward VCC
Multicast Forward VCC (Virtual Channel Connection) is a type of VCC in the ATM network. It is set up by the BUS to the LEC (LAN Emulation Client) as a leaf in a point-to-multipoint connection.

Multicast Group
Multicast Group is a dynamically determined group of IP hosts identified by a single IP multicast address.

Multicast Router
Multicast Router is 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.

Multicast Send VCC
Multicast Send VCC (Virtual Channel Connection) is a type of VCC in an ATM network. It is a bi-directional point-to-point VCC set up by an LEC (LAN Emulation Client) to a BUS. One of three data connections is defined by Phase 1 LANE.

Multicast Server
Multicast Server is used to establish a one-to-many connection to each device in a virtual LAN (VLAN), or a broadcast domain for each VLAN segment. The multicast server forwards incoming broadcasts only to the multicast address that maps to the broadcast address.

Multidrop Line
Multidrop Line, sometimes called a multipoint line, is a communications line with multiple cable access points.

Multi-Homed
Multihomed(Multi-Homed) indicates a host (computer) connected to two or more networks or having two or more network addresses. For example, a network server may be connected to a serial line and a LAN or to multiple LANs. Multihoming is a technique often used to increase the reliability of the internet connection of an IP network, in which case a computer is connected to multiple ISPs.

Multihomed Host
Multihomed Host is attached to multiple physical network segments in an OSI Connectionless Network Service (CLNS) network.

Multihoming
Multihoming is an addressing scheme in IS-IS routing that supports the assignment of multiple area addresses.

Multi-instance Option
Multi-instance Option is a Cable Modem Termination System (CMTS) option under DOCSIS that can occur multiple times in an option set.

Multi-Layer Switching
Multi-Layer Switching is simply the combination of traditional Layer 2 switching with Layer 3 routing in a single product. Multilayer switching is new, and there is no industry standard yet on nomenclature. Vendors, analysts, and editors don't agree about the specific meaning of terms such as multilayer switch, Layer 2 router, Layer 3 switch, IP switch, routing switch, switching router, and wirespeed router. The term multilayer switch seems to be the best and most widely used description of this class of product that performs both Layer 3 routing and Layer 2 switching functions.

Multiple Domain Network
Multiple Domain Network is an IBM SNA network with multiple System Services Control Points (SSCPs).

Multiplexer
A multiplexer, also known as mux or muldex, is a device that encodes information from two or more data sources (usually a power of two) into a single channel. The multiplexer has a single output, which has the same value as the selected data input. They are used in situations where the cost of implementing separate channels for each data source is more expensive than the cost and inconvenience of providing the multiplexing/demultiplexing functions.

Multiplexing
Multiplexing is a technique of combining multiple channels over a transmission path and then recovering or de-multiplexing the separate channels at the receiving end. Using multiplexing, multiple logical signals can be transmitted simultaneously across a single physical channel. The multiplexing process may following one of the principles such as TDM, FDM, CDM, or WDM, etc. Multiplexing may take placing in software, where multiple threads of information streams are delivered to a device or process at the same time.

Multipoint
Multipoint refers to a communication configuration in which several terminals or stations are connected together. Multipoint is a single communications channel to which two or more stations or logical units are attached although only one can transmit at a time. Such arrangements usually require a polling mechanism under the control of a master station to ensure that only one device transmits at a time.

Multipoint Control Unit
Multipoint Control Unit is an endpoint on the LAN that provides the capability for three or more terminals and gateways to participate in a multipoint conference.

Multipoint-Unicast
Multipoint-Unicast is a process of transferring protocol data units (PDUs) where an endpoint sends more than one copy of a media stream to different endpoints. This might be necessary in networks that do not support multicast.

Multiport Repeater
Multiport Repeater is a layer 2 active device, having multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port.

MultiRate
MultiRate is a data service consisting of a single circuit whose bandwidth is a multiple of 64 kbps. This circuit consists of one or more B channels. For example, a user can dial a first call at 384 kbps (using 6 B channels), and then dial at second call at 512 kbps (using 8 B channels). This service is available over T1 PRI lines only. MultiRate is also known as Switched Nx64 data service.

MultiService Switch
MultiService Switch is a type of network switch that can provide switching to data as well as voice and video. It is a network device designed for the converged network of multiple services.

Multi-Unicast
Multi-Unicast is a transmission of duplicate data streams, one to each user. In multi-unicast, multiple users request the same data from the same server at the same time. Contrast with IP multicast, unicast.

Multivendor Network
Multivendor Network is a network using equipment from more than one technology vendor. Multivendor networks may have compatibility problems.

Multizone network
Multizone network is a local area network with multiple segments each may serve different functions or for different departments.

MUX: Multiplexer
A multiplexer, also known as mux or muldex, is a device that encodes information from two or more data sources (usually a power of two) into a single channel. The multiplexer has a single output, which has the same value as the selected data input. They are used in situations where the cost of implementing separate channels for each data source is more expensive than the cost and inconvenience of providing the multiplexing/demultiplexing functions.

MX Record: Mail exchange record
Mail exchange record (MX record) is a DNS resource record type indicating which host can handle e-mail for a particular domain.