Glossary - M
DS-1/DS-3 multiplexer (network)
Device which multiplexes 28 DS-1 signals into a single
DS-3 signal and vice versa. See
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,
- MAC Address
The hardware address of a device connected to a shared media. See also
Media Access Control, Ethernet,
- 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.
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.
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.
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)
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
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
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.
Maximum Cell Delay Variation (ATM)
Maximum CDV over a given
Maximum Cell Loss Ratio (ATM)
Maximum CTD over a given
QoS class, defined for
CBR and VBR traffic and
for cells with CLP = 0.
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.
Maximum Cell Transfer Delay
The maximum CTD over a given
- 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.
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.
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,
- Media Interface Connector (cable)
- 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
- 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.
Musical Instrument Digital interface
Exchange data format used between a computer and musical instruments.
Management Information Format (network, management, web)
Source of management information data for CIM
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.
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.
Million instructions per second (unit)
A measure of a computer's speed or power.
- 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.
- 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.
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.
- MultiMode Fiber Optic Cable (physical layer)
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.
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
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).
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:
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.
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.
Mean Rate (ATM)
Same as Average Cell Rate.
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.
- Maintenance Service Provider (network)
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.
Message Transfer System (messaging)
The collection of Message transfer Agents providing the Message
Transfer service Elements.
Maximum Transmission Unit
Maximum allowable size of a PDU. For instance, MTU size for
Ethernet is 1500 octets.
Mail User Agent (messaging)
User program to read and write mails.
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,
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
- 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
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.
- 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.