A - D E - H I - L M - P Q R S T U - Z Glossary of Selected Terms (Q-T)   Section Q QAM (quadrature amplitude modulation) A complex method of modulation used in modern modems to allow very high data rates to be carried reliably and relatively error-free. QAM is a combination of phase and amplitude modulation. quality of service (QOS) Expressed as one of a number of different parameters (e.g. latency) which are designed to measure the performance of communications applications which operate by means of telecommunications networks. Section R real-time application An application requiring the real-time transfer of live data or other signals (e.g. an audio channel or a live video link). regenerator A device inserted at an intermediate stage of a digital transmission line to counteract the effects of signal deterioration which occur on long lines. As far as possible the device regenerates the original bit stream. repeater A device inserted at an intermediate stage of an analogue transmission line to counteract the effects of signal deterioration (particularly attenuation) which occur on long lines. RFC (request for comments) A document issued by the Internet engineering task force (IETF) and defining technical standards, protocols or procedures suggested to be used in IP-data networks and the Internet. RIP (routing information protocol) A simple routing protocol used widely in small-scale router and IP networks. RJ-11 connector A small, usually clear plastic telephone connector or socket, approximately 10 mm wide and 7 mm high (with 6 contacts), typically used to connector telephones or modems to the analogue telephone network. RJ-45 connector A small, usually clear plastic data and general-purpose telecommunications connector or socket approximately 12 mm wide and 7 mm high (with 8 contacts), typically used to connect computers and other DTE to LAN switches. Also used widely to make ISDN connections. RMON (remote monitoring) A MIB (management information base) intended to be used by networking monitoring devices (probes) for observing the network performance of an IP-based network. router A switching device (i.e. node) used in the Internet or Intranet for determining the appropriate routing of a given data message through a data network to the desired destination and for forwarding the message. routing protocol A protocol used to share network topology and routing information between routers, in order that they may calculate the best routes to all reachable destinations and therefore generate their routing tables. routing table A table held in a router which relates the network address (e.g. IP-address) to the appropriate outgoing route (i.e. next hop) to be used for forwarding the associated data. Section S SDH (synchronous digital hierarchy) Modern digital transmission hierarchy in which individual line systems within a network are designed to run exactly synchronously with one another. This gives major management and topology administration benefits. SDLC (synchronous datalink control) Synchronous data link control. IBM's equivalent of HDLC, forming the layer 2 of IBM's systems network architecture (SNA). security management One of the five main network management functions defined by the ISO management model. The others are accounting, configuration, performance and fault management. segment An information or data block carried by a transport layer (layer 4) protocol and identified by a protocol header (such as that of TCP or UDP). serial data transmission Data transmission between computer devices using only a single circuit path. Whole bytes of information (8 bits) are sent in a sequential pattern. Serial transmission is used across long-distance telecommunications networks (cf. parallel transmission). server Term applied to a computer device or software program running an application serving clients. session A relationship (if you like, a `connection') between two communicating computer applications in different locations for the purpose of data transfer. session layer Layer 5 of the open systems interconnection (OSI) model. When established for a session of communication, the two devices at each end of the overall connection must conduct their `conversation' in an orderly manner. simplex A mode of telecommunications transmission in which only one direction of communication is possible. SNA (systems network architecture) A standard framework of communications methods used in particular in networks of IBM computer devices. SNMP (simple network management protocol) A network management protocol widely used for managing corporate data networks and the Internet. socket A combination of an IP address and a TCP or UDP port number---the socket provides all the address details necessary to facilitate setting up communication. SONET (synchronous optical network) The North American technology which preceded SDH (synchronous digital hierarchy) and is based upon similar principles. statistical multiplexing A method of data lineplant economy in which different data communication `conversations' share the same line by making use of each other's idle periods. STD (standard) A document issued by the Internet engineering task force (IETF) now declared to be a standard, and probably previously published as an RFC (request for comments) document. storage medium The physical means to store information or data (multimedia). STP (shielded twisted pair) Term applied particularly to indoor cabling of a type in which twisted copper pairs are `wrapped' immediately inside the plastic sheathing with a foil shield. The shielding serves to reduce electromagnetic disturbances from or to the cable. switch A device or node used in a network to make connections. synchronisation The method by which the bit patterns appearing on digital line systems may be properly clocked and interpreted---allowing the beginning of particular patterns and frame formats to be correctly identified. synchronous data transfer Data transfer employing a strictly regular pattern, rather than (as in asynchronous operation) using start and stop bits to distinguish character patterns from idle line operation. Section T TCP (transmission control protocol) The most commonly used transport protocol of the IP-suite. TCP provides for a reliable and connection-oriented transport service. TCP/IP The combination of transport and network protocols most commonly used for data communication across IP networks or the Internet. telecommunications management network (TMN) The technical architecture conceived by ITU to provide for overall coordinated management of telecommunications networks. time division multiplex (TDM) A technique allowing a number of different digital signals to share the same high bit rate digital transmission line by dividing it into a number of smaller component bit rates, each interleaved in time with the others. token ring LAN A popular type of physical infrastructure used for local area network interconnection of PCs and other computer devices within an office environment. Used particularly in networks of IBM mainframes and personal computers. transaction A single communications activity undertaken between two intercommunicating devices. transport layer Layer 4 of the open systems interconnection (OSI) model. The transport layer provides for end-to-end data relaying service across any type of data network (e.g. packet network or circuit switched network). trunk A circuit interconnecting network nodes. Particularly a long distance circuit. tunneling The encapsulation of data packets encoded in one protocol for carriage by a network using a different protocol. Often used to provide for secure remote connections to a private network (e.g. intranet) across the public Internet. twisted pairs Metallic conductor wires, twisted in pairs corresponding to the legs of a 2-wire circuit.