Media Access Control

In a WLAN network card, the MAC is radio controller protocol. It corresponds to the ISO Network Model's level 2 Data Link layer. The IEEE 802.11 standard specifies the MAC protocol for medium sharing, packets formats and addressing, and error detection. (2) Lower of the two sublayers of the data link layer defined by the IEEE. The MAC sub-layer handles access to shared media, such as whether token passing or contention will be used.

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, MAC-layer address, and physical 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.

An attack whereby a system attempts to impersonate another system by using its MAC address.

Metropolitan Access Exchange

One of a number of Internet exchange points.

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.

Metropolitan Area Network

Typically, they support transmission speeds from 1.5 megabits per second to 45 mbps. They can carry greater volumes of information further distances than local area networks and can support voice, video and data transmissions because of their high bandwidths.

Mobile Application Part

Part of the SS7 protocol used in GSM. MAP standards address registration of roamers and intersystem hand-off procedures.

Manufacturing Automation Protocol/Technical and Office Protocol .

Multicast Address Resolution Server

Mechanism for supporting IP multicast. A MARS serves a group of nodes (known as a cluster); each node in the cluster is configured with the ATM address of the MARS. The MARS supports multicast through multicast messages of overlaid point-to-multipoint connections or through multicast servers.

Maximum 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 multi-station access unit and is usually abbreviated MSAU to avoid confusion.

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.

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.

Megabytes

Megabit

1,048,576 bits or 1,204 kilobits.

Multimedia Backbone

Multicast Bone

A virtual network layered on top of the Internet to support IP multicast routing across point-to-point links. Because multicasting is a fast and inexpensive way to communicate information to multiple hosts, the M-Bone is used for transmitting audio and video on the Internet in real time.

Megabits per second

Maximum Burst Size

In an ATM signalling message, burst tolerance is conveyed through the MBS, which is coded as a number of cells. The burst tolerance together with the SCR and the GCRA determine the MBS that can be transmitted at the peak rate and still be in conformance with the GCRA.

Micro Channel Architecture

IBM's PC-bus architecture featuring a 32-bit input/output bus. In competition with Extended Industry Standard Architecture.

Multimedia Communications Community Of Interest

Maximum Cell Delay Variation

In an ATM network, the maximum two-point CDV objective across a link or node for the specified service category. 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.

Maximum Cell Loss Ratio

In an ATM network, 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. 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.

Multimedia Cable Network System Partners Ltd

Consortium of cable companies providing service to the majority of homes in the United States and Canada. This consortium drives a standard with the goal of having interoperable cable modems.

Maximum Cell Transfer Delay

In an ATM network, the sum of the MCDV and the fixed delay component across the link or node. 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.

Multipoint Control Unit

Endpoint on the LAN that provides the capability for three or more terminals and gateways to participate in a multipoint conference.

Mobile Data Intermediate System

A system to handle authentication, directory services, packet switching, and gateway services to landline data networks.

Message Disposition Notification

Message returned to the originator of an e-mail message indicating that the e-mail message has been opened.

Managed Data Network Service

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.

Signalling for signalling channels, used to set up a connection

Media Gateway

Media Gateway Controller

Multi Host Routing Protocol

Megahertz

One million Hertz.

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, usually through a GUI network management system. MIB objects are organized in a tree structure that includes public (standard) and private (proprietary) branches.

Mobile Internetworking Control Protocol

Device that prevents data frequencies (intended for a data device such as a router) from travelling over the telephone line and interfering with telephone calls.

Message Identifier

In ATM, used to identify ATM cells that carry segments from the same higher-layer packet.

Makes up the second level of the Internet hierarchy. They are the transit networks that connect the stub networks to the backbone networks.

Multipurpose Internet Mail Extensions

The standard for attaching non-ASCII files to Internet mail messages. These files include graphics, spreadsheets, formatted word-processor documents, audio files, and other binary data.

Million Instructions Per Second

Multiservice Interchange

Multichannel Multipoint Distribution Services

Wireless cable technology using frequencies in the 2.5 - 2.7 GHz band. One antenna can serve line-of-site customers in a thirty-mile radius. Customers use a twelve-inch dish to receive the signal and require a set-top box to descramble it. MMDS is very popular in much of the developing world because of the relatively low cost of passing a large number of subscribers.

MultiMode Fibre

Multimedia Mail over IP

Multichassis Multilink PPP

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 ISDN access number. MMP correctly handles packet fragmenting and reassembly when a user connection is split between two physical access devices.

Multilink PPP

A proposed standard for inverse multiplexing, a method of combining individually dialled channels into a single, higher speed data stream. MP is an extension of PPP that supports the ordering of data packets across multiple channels.

MPEG Audio layer 3

A popular digital compression format for music files.

Motion Picture Experts Group

Standard for compressing video. MPEG1 is a bit stream standard for compressed video and audio optimized to fit into a bandwidth of 1.5 Mbps. MPEG2 is intended for higher quality video-on-demand applications and runs at data rates between 4 and 9 Mbps. MPEG4 is a low-bit-rate compression algorithm intended for 64-kbps connections.

Audio codec 5—12/11-24 kbps

MultiProtocol Label Switching

A specification for layer 3 switching from the IETF. Similar to Cisco's tag switching, MPLS uses labels, or tags, that contain forwarding information, which are attached to IP packets by a router that sits at the edge of the network known as a label edge router (LER). The routers in the core of the network, known as label switch routers (LSRs), examine the label more quickly than if they had to look up destination addresses in a routing table. When fully implemented on the Internet, MPLS is expected to deliver the quality of service (QoS) required to adequately support real-time voice and video as well as service level agreements (SLAs) that guarantee bandwidth. Following in the tradition of the "dumb network," MPLS enables more decisions to be made at the periphery of the network.

Multichannel Point-to Point Protocol

A protocol that extends the capabilities of MP to support inverse multiplexing, session management, and bandwidth management. MPP allows you to combine up to 30 individual channels into a single high-speed connection.

Microprocessor Unit

Mobile Switching Centre

This contains all the control and switching elements for a cellular system, housed by the Mobile Telephone Switching Office.

Multi-Services Distant Terminal

Device that terminates broadband services, including video, at the end user's location.

Mobile Subscriber International Subscriber iDentity Number

Number that callers use to reach a mobile services subscriber.

Multiple Service Operator

Cable service provider that also provides other services such as data and/or voice telephony.

MultiService Platform

Multiservice Platform

Mobile Satellite Services

Message Transfer Agent

OSI application process used to store and forward messages in the X.400 Message Handling System. Equivalent to Internet mail agent.

Mail Transfer Agent

Software that implements SMTP and provides storage for mail messages to be forwarded or delivered to a local user. MTAs implement SMTP (RFC 821).

Mean-Time-Between-Failure

An average of the time from the point when a problem occurs to the time when the last problem occurred with a specific piece of equipment or an entire system.

Multicast Transport Protocol

Mean-Time-To-Restore

An average of the outage time from the point when a problem occurs to the point when service is restored.

Multi-tenant unit Office

Office blocks occupied by many companies, usually small- or medium-sized enterprises (SMEs)

Maximum Transmission Unit

Maximum packet size, in bytes, that a particular interface can handle.

A form of broadcast in which a packet is delivered to a pre-defined subset of all possible destinations. A specific multicast destination address is used.

A network in which a router sends packets to all addresses on a subscriber list. This type of network is different from both a unicast network (in which the router sends packets to one user at a time) and a broadcast network (in which the router sends packets to all users, whether they appear on a subscription list or not). The M-Bone is an example of a multicast network.

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.

Addressing scheme in IS-IS routing that supports assignment of multiple area addresses.

In general, a multiplexer optimises the use of communications facilities by configuring and bringing together many channels for efficient transmission on a network.

Circuit that has points served by three or more switches. Single communications channel (typically a leased telephone circuit) 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.

User access in which more than one terminal equipment is supported by a single network termination.

The ability to route multiple network protocols, including IP, IPX, and Appletalk.

Multiple customers sharing a common CTR.

Multiplexed Network for Distributive and Interactive services .

Mobile Virtual Network Operators

Mobile Virtual Network Operators

Multiple Virtual Storage

An IBM operating system that runs on IBM System/370-based mainframes.

Mail Exchange Record

DNS resource record type indicating which host can handle e-mail for a particular domain