Glossary of Selected Terms (M-P)
 
Section M
MAC (medium access control) A layer 1 protocol used in conjunction with a given LAN or MAN physical medium to provide a standard interface to the layer 2 protocol.
MAC address The `hardware address' usually `burned into' ethernet or other LAN network interface cards (NICs) at the time of their manufacture. The address provides for the correct delivery of data frames across the LAN, and are coded in the form defined as the 48-bit IEEE unique identifier.
male connector A plug connector or socket which comprises the `pins' of the connector rather than the `holes' which appear in the corresponding female connector.
MAN (metropolitan area network) A type of data communications network suitable for interconnecting computer devices across a metropolitan area. Such networks typically have a bus or ring topology of up to about 100 km in total length.
managed object A conceptual `object' which may be monitored or controlled by means of a standard management protocol such as SNMP or CMIP. Managed objects are defined devices or functions, with a discrete number of possible states (e.g. on, off, transmit, receive, etc.).
management plane A conceptual communications connection between data switching devices for communicating network management information (e.g. for configuring the network, setting up permanent connections or monitoring performance).
manager Alternatively: a network management system or control software.
  Or: a human network manager or administrator.
Manchester code The line code used in ethernet LANs.
mark A binary digit of value `1'.
media Plural of medium.
medium A means by which information can be perceived, expressed, stored or transmitted.
message handling system (MHS) A conceptual model specified by ITU-T recommendation X400, describing an electronic mail system in which message devices (e.g. facsimile and telex machines, computers, word processors, etc.) intercommunicate.
message switching A means of data communication in which complete messages are conveyed together across the transport medium.
messaging service An interactive service based upon store-and-forward and mailbox transfer.
MIB (management information base) A collection of defined managed objects relating to given type of telecommunications device or interface (e.g. radio link, telephone exchange, subscriber ISDN line, etc.) and allowing for remote monitoring and configuration.
modem A term derived from a shortening of Modulator/DEModulator. A modem provides for the carriage of digital data information over analogue transmission lines.
modulation Modulation is a means of encoding information on to a carrier signal in order that it may be transmitted over a transmission line or radio link.
monomode fibre An optical fibre with a narrow central core of a different refractive index from the cladding which surrounds it. The narrowness of the core allows only very few ray paths to exist---so that dispersion is minimised---a single mode of transmission prevails. Such fibres allow for reliable long distance communication.
MPEG (motion pictures experts group) An industry grouping which has developed a number of coding standards for transmission of video signals (e.g. MPEG1, MPEG2, etc.).
MPLS (multiprotocol label switching) A network layer protocol designed for fast forwarding of flow-oriented data streams. MPLS is likely to be deployed at the core of high performance IP backbone networks and also used widely as the basis of VPN (virtual private network) services.
multimedia service A service in which interchanged information is a mixture of text, sound, graphics, video.
multimode fibre An optical fibre with a relatively wide central core. The relative large dimension of the core allows many differnet ray paths to exist---so that dispersion may be a problem. Typically multimode fibres are limited in range compared with monomode fibres.
multiplexing Multiplexing is a technique for combining a number of full duplex channels together to share the same transmission line or radio medium.
multipoint A communication or network configuration involving more than two end points.
multiprotocol A multiprotocol network is typically a LAN or layer 3 (e.g. IP)-based network capable of carrying multiple different types of transport, session and application protocols simultaneously.
Section N
network-node interface (NNI) A standardised interface used between switches or subnetworks within a given (data) network. Also called `network-network interface'
network layer The network layer is layer 3 of the open systems interconnection (OSI) model. This layer sets up an end-to-end connection across a real network, determining which permutation of individual links to be used.
network performance (NP) A specific term applied to performance measurement parameters which are designed to monitor only the end-to-end network connection part of a given communication (e.g. telephone call or computer application running via a data network).
NMS (network management system) A combination of workstation hardware and application software designed specifically for the purpose of aiding human network administrators in the management of a telecommunications network. noise Stray, unwanted and random signals interfering with the desired signal. Common forms of noise manifest as a low level crackling noise.
noise Stray, unwanted and random signals interfering with the desired signal. Common forms of noise manifest as a low level crackling noise.
Section O
optical fibre A glass fibre of only a hair's breadth dimension, capable of carrying very high digital bit rates with very little signal attenuation.
OSI (open systems interconnection) A conceptual model specified by the ITU-T X.200 series. The model describes the 7-layer process of communication between `cooperating' computers. The model is the standard for open communication between computers made by different manufacturers.
OSI model The seven layer conceptual model defining the process of communication between computer systems.
OSPF (open shortest path first) A standardised protocol used widely in the Internet and IP networks for conveying routing information between routers.
0x The prefix used to denote a hexadecimal number value.
Section P
packet An information or data block carried by a network layer (layer 3) protocol and identified by a protocol header (such as that of IP or X.25).
packet assembler/disassembler (PAD) A device enabling a character (i.e. asynchronous) terminal to be connected to a packet network.
packet-switching A type of exchange or network which conveys a string of information from origin to destination by cutting it up into a number of packets and carrying each independently.
packet transfer mode A telecommunication transfer technique in which information is carried in packets.
parallel data transmission Data transmission between computer devices using multiple lead wires or ribbon cables. Whole bytes of information (8 bits) are sent simultaneously by using a separate wire for each of the individual bits of the byte.
PCM (pulse code modulation) The method of conversion used to enable speech or some other analogue audio signal to be carried over a digital transmission path.
peer partner Protocols used for data communications are designed in a modular and layered fashion. Each layered protocol of the protocol stack is communicated between the two peer partner devices at either end of the link, connection or other communications path.
peering Peering is the term used to describe interconnections made between IP networks managed and operated by different organisations.
performance management One of the five main network management functions defined by the ISO management model. The others are accounting, security, configuration and fault management.
phase shift keying (PSK) When a binary data signal is phase modulated onto a carrier the effect is to create a transmitted carrier signal of one of a number of fixed phases. Jumping between these phases according to the incoming bit stream is known as keying.
physical layer Layer 1 of the open systems interconnection (OSI) model. The physical layer protocol is the hardware and software in the line terminating device which converts the databits needed by the datalink layer into the electrical pulses, tones or other form.
plesiochronous digital hierarchy (PDH) Digital transmission hierarchy in which individual line systems within a network do not run in exact synchronisation with one another. Instead free running or plesiochronous systems sometimes have to be corrected for slip and justification errors.
POP Alternative: post office protocol---a protocol used to retrieve Internet electronic mail into a client PC from a mail server.
  Or: point-of-presence---a connection point of a network---e.g. the site of the nearest NAS (network access server) of an Internet service provider's network.
port Alternative: a hardware connection on a networking device used to connect a line to another device.
  Or: an address (port number) used by a transport protocol (e.g. TCP or UDP) to indicate the protocol being used to code the user data field.
post office A term sometimes used to describe an electronic mail service or message depository.
PPP (point-to-point protocol) A protocol used particularly on dial-up access lines to the Internet to establish a datalink protocol and data frame carrying layer once the physical connection has been set up.
presentation layer Layer 6 of the open systems interconnection (OSI) model. The presentation layer defines the manner in which the data is encoded, eg binary, ASCII, IA5, IA2, EBCDIC, facsimile, etc.
presentation medium The means or device used to reproduce information to the user (multimedia).
PRI (primary rate interface) The $23\hbox{B}+\hbox{D}$ or $30\hbox{B}+\hbox{D}$ ISDN interface typically used to connect digital company telephone systems to the public ISDN, but also used for back-up lines.
primary multiplex (PMUX) A device performing the first stage of time division multiplexing. In the UK and Europe, a primary multiplexor converts 32 analogue signals to 2.048 Mbit/s time division multiplexed signal. In the US equivalent, instead 24 are multiplexed to 1.544 Mbit/s.
protocol A protocol is a procedure, set of commands or rules by which computer devices intercommunicate. Thus a protocol is the equivalent of a human language, with punctuation and grammatical rules.
protocol stack Individual protocols are generally designed to carry out a single control or data transfer function, as two peer devices communicate with one another. A number of different protocols are combined in a modular and layered fashion to undertake all the required communications functions. The combination of protocols is termed the protocol stack.
proxy A device (either client or server) which undertakes a given function on behalf of another device which is either incapable of the action itself or maybe for security reasons has delegated the task.