M

MAC

Media Access Control: The lower sublayer in the Data Link layer, it is responsible for hardware addressing, media access, and error detection of frames. See also: Data Link layer and LLC.

MAC address

A Data Link layer address that every port or device needs in order to connect to a LAN. These addresses are used by various devices in the network for accurate location of ports, including the creation and revision of routing tables. MAC addresses are defined by the IEEE standard and their length is six characters. Variously called hardware address, physical address, or MAC-layer address.

MacIP

In AppleTalk, the Network layer protocol encapsulating IP packets in Datagram Delivery Protocol (DDP) packets. MacIP also supplies substitute ARP services.

MAN

Metropolitan-Area Network: Any network that encompasses a metropolitan area; that is, an area typically larger than a LAN but smaller than a WAN. See also: LAN and WAN.

manageability

Term used when discussing the benefits of a hierarchical network design. One of the benefits of a hierarchical network design is better management of the network.

Manchester encoding

A method for digital coding in which a mid-bit-time transition is employed for clocking, and a 1 (one) is denoted by a high voltage level during the first half of the bit time. This scheme is used by Ethernet and IEEE 802.3.

MAU

(Multi-station Access Unit) sometimes abbreviated MSAU. A multiport wiring hub for token-ring networks that can connect as many as eight lobes to a ring network. IBM refers to an MAU that can be managed remotely as a Controlled Access Unit.

maximum burst

Specified in bytes or cells, the largest burst of information exceeding the insured rate that will be permitted on an ATM permanent virtual connection for a short time and will not be dropped even if it goes over the specified maximum rate. Compare with: insured burst. See also: maximum rate.

maximum rate

The maximum permitted data throughput on a particular virtual circuit, equal to the total of insured and uninsured traffic from the traffic source. Should traffic congestion occur, uninsured information may be deleted from the path. Measured in bits or cells per second, the maximum rate represents the highest throughput of data the virtual circuit is ever able to deliver and cannot exceed the media rate. Compare with: excess rate. See also: maximum burst.

MBS

Maximum Burst Size: In an ATM signaling message, this metric, coded as a number of cells, is used to convey the burst tolerance.

MBONE

Multicast Backbone: The multicast backbone of the Internet, it is a virtual multicast network made up of multicast LANs, including point- to-point tunnels interconnecting them.

MCDV

Maximum Cell Delay Variation: The maximum two-point CDV objective across a link or node for the identified service category in an ATM network. The MCDV is one of four link metrics that are exchanged using PTSPs to verify the available resources of an ATM network. Only one MCDV value is assigned to each traffic class.

MCLR

Maximum Cell Loss Ratio: The maximum ratio of cells in an ATM network that fail to transit a link or node, compared with the total number of cells that arrive at the link or node. MCDV is one of four link metrics that are exchanged using PTSPs to verify the available resources of an ATM network. The MCLR applies to cells in VBR and CBR traffic classes whose CLP bit is set to zero. See also: CBR, CLP, and VBR.

MCR

Minimum Cell Rate: A parameter determined by the ATM Forum for traffic management of the ATM networks. MCR is specifically defined for ABR transmissions and specifies the minimum value for the allowed cell rate (ACR). See also: ACR and PCR.

MCTD

Maximum Cell Transfer Delay: In an ATM network, the total of the maximum cell delay variation and the fixed delay across the link or node. MCTD is one of four link metrics that are exchanged using PNNI topology state packets to verify the available resources of an ATM network. There is one MCTD value assigned to each traffic class. See also: MCDV.

MIB

Management Information Base: Used with SNMP management software to gather information from remote devices. The management station can poll the remote device for information, or the MIB running on the remote station can be programmed to send information on a regular basis.

media

The physical connecting wire or cable found in computer networks.

microsegmentation

The division of a network into smaller segments, usually with the aim of increasing bandwidth.

MIP

Multichannel Interface Processor: The resident interface processor on Cisco 7000 series routers, providing up to two channelized T1 or E1 connections by serial cables connected to a CSU. The two controllers are capable of providing 24 T1 or 30 E1 channel groups, with each group being introduced to the system as a serial interface that can be configured individually.

mips

Millions of Instructions Per Second: A measure of processor speed.

MLP

Multilink PPP: A technique used to split, recombine, and sequence datagrams across numerous logical data links.

MMP

Multichassis Multilink PPP: A protocol that supplies MLP support across multiple routers and access servers. MMP enables several routers and access servers to work as a single, large dial-up pool with one net- work address and ISDN access number. MMP successfully supports packet fragmenting and reassembly when the user connection is split between two physical access devices.

modem

Modulator-demodulator: A device that converts digital signals to analog and vice versa so that digital information can be transmitted over analog communication facilities, such as voice-grade telephone lines. This is achieved by converting digital signals at the source to analog for transmission, and reconverting the analog signals back into digital form at the destination. See also: modulation and demodulation.

modem eliminator

A mechanism that makes possible a connection between two DTE devices without modems.

modulation

The process of modifying some characteristic of an electrical signal, such as amplitude (AM) or frequency (FM), in order to represent digital or analog information. See also: AM.

MOSPF

Multicast OSPF: An extension of the OSPF unicast protocol that enables IP multicast routing within the domain. See also: OSPF.

MPOA

Multiprotocol over ATM: An effort by the ATM Forum to standardize how existing and future Network-layer protocols such as IP, Ipv6, AppleTalk, and IPX run over an ATM network with directly attached hosts, routers, and multilayer LAN switches.

MTBF

(Mean Time Between Failures) The statistically derived average length of time for which a system component operates before failing. MTBF is expressed in thousands or tens of thousands of hours, also called power- on hours, or POH.

MTU

Maximum Transmission Unit: The largest packet size, measured in bytes, that an interface can handle.

multicast

Broadly, any communication between a single sender and multiple receivers. Unlike broadcast messages, which are sent to all addresses on a network, multicast messages are sent to a defined subset of the network addresses; this subset has a group multicast address, which is specified in the packet’s destination address field. See also: broadcast.

multicast address

A single address that points to more than one device on the network. Identical to group address. See also: multicast.

multicast send VCC

A two-directional point-to-point virtual control connection (VCC) arranged by an LEC to a BUS, it is one of the three types of informational link specified by phase 1 LANE. See also: control distribute VCC and control direct VCC.

multilayer switch

A type of LAN switch, the device filters and forwards packets based on their Layer 2 MAC addresses and Layer 3 network addresses. It’s possible that even Layer 4 can be read. See also: LAN switch.

multiplexing

The process of converting several logical signals into a single physical signal for transmission across one physical channel. Contrast with: demultiplexing.