Glossary Q-Z

Q

• Q.921/931 ITU-TS (formerly CCITT) Q Series Recommendations describing Lap- D, the Layer Two protocol for an ISDN D-channel.
• Qbit (Qualifier bit) In X.25 networks, bit 8 in an octet of packet header. It is used to indicate if a packet contains control information.
• QLLC (Qualified Logical Link Control) Routines to provide Synchronous Data Link Control.
• Quartet Signaling Part of the 100BaseVG-AnyLAN proposed standard involving transmission over all four wire pairs simultaneously in voice-grade UTP cable, expanding its capacity to 100Mbit/s.

  R

• RS standards Laid down by the EIA, RS232c approximates to V.24/28; RS422 to V.11; RS423 to V.10 and RS449 to V.36.
• RARP (Reverse Address Resolution Protocol) The TCP/IP protocol a diskless machine uses at startup to find its IP address.
• Redirect A packet switching function that routes a call to an alternative network address if the link to the original address is not working. It is carried out by end point switches.
• Redirector A LAN device driver that translates operating system requests into network events and transmits them to the right protocol stack.
• Regeneration A method of boosting a digital signal. Remote bridge LAN-to-LAN bridge that links geographically distant LANs across a wide area link.
• RFC (Request For Comment) Document series begun in 1969 describing the Internet suite of protocols and related experiments.
• RPC (Remote Procedure Call) A means of communication between two tasks running on separate machines linked by a LAN. One machine can request a service, typically computation, from the other, by executing a high level request known as a language procedure call. RPCs are an underlying architectural element of distributed processing and client/server computing.
• RPL (Remote Program Load) Starting a computer and loading the operating system into memory when the operating system software is provided by a server on the network.
• Reconfiguration The process of physically altering the location or functionality of network or system elements. Automatic configuration describes the way sophisticated networks can readjust themselves in the event of a link or device failing, enabling the network to continue operation.
• Red Book The 1984 compilation of the ITU-TS's standards for telecommunications, including some for ISDN.
• Redirect A packet switching function that routes a call to an alternative network address if the link to the original network is not available. It is carried out by the end point switches.
• Redundancy Otherwise known as fault-tolerance, in data transmission, this refers to characters and bits that can be removed from a transmission without affecting the message. In data processing and data communications, it means providing backup for components: should one of them fail, the system continues to run without operation. Total redundancy is usually impractical, but financial institutions and other organizations with mission-critical applications attempt to install a high level of redundancy on the basis that downtime loses money, lives, depending on the business.
• Repeater A device that extends the maximum length of cable that can be used in a single network. In fiber networks, it is an optoelectrical module that receives an optical signal and converts it into an electrical form.
• Ring topology A layout scheme in which the network takes the form of a closed loop with the devices attached into the ring. Every workstation is linked to two others, one on each side. All data is passed from node to node in one direction only, each PC acting as a repeater for the next one in the loop. Response time is determined by the number of stations on the ring - the more there are, the slower it works. If one PC fails, the loop is broken, though most rings have self-healing capacity to reconfigure and continue operation. IBM's Token passing ring ensures that the failed station is removed and its neighbors are then directly connected.
• Ring in and Ring out Token Ring connectors on the MSAU connecting the unit to trunk cabling. The Wrap feature is implemented at these interfaces.
• RMON (Remote Monitoring) SNMP specification for multivendor statistics-gathering by a standards-based (de facto SNMP) management station from de facto standard (RMON)-compliant devices.
• Roaming The ability of a mobile communications device to move freely from one part the whole of a network operator's system or another.
• RIP (Routing Information Protocol) The protocol used by Berkeley 4BSD Unix systems to exchange routing information among a small group of computers. Implemented by the Unix program "routed", RIP is derived from an earlier protocol of the sa me name developed at Xerox.
• RJ11 Popular name for the standard four-wire modular connector for phone connections.
• RJ45 Popular name for the eight-pin modular connector in the 10BaseT standard for UTP connections to workstations or smart wiring hubs. The actual connector is described in ISO standard 8877.
• Rlogin (Remote Login) The service offered by Berkeley 4BSD Unix systems that allows users of one machine to connect to other Unix systems across an internet and interact as if their terminals connected to the machines directly. Although Rlogin offers essentially the same service as Telnet, it is superior because the software passes information about the user's environment to the remote machine.
• Router Network interconnector device operating at OSI Network Layer (Level Three) that supports a particular Network Layer protocol and related stack, such as TCP/IP, DecNet, XNS, SNA, OSI IP, IPX. These days routers tend to support multiple protocols by a variety of methods, such as Protocol Independent Routing. A router can be used to link LANs together locally or remotely as part of a WAN. A network built using routers is often termed an internetwork.
• Routing Process of delivering a message across one or more networks via the most appropriate path.
• Routing table Information stored within a router that contains network path and status information. It is used to select the most appropriate route to forward information along.
• RS232-C An EIA standard which is the most common way of linking data devices together. An interface for linking DCEs and DTES, it defines the electrical characteristics of the signals from such devices. RS232 is suitable for both synchronous and asynchronous communications and specifies a 25-pin connector, traditionally the DB-25. 20 of the pins carry out routine system operation while the rest are reserved for modem testing or unallocated. For this reason it is never safe to assume that two RS232 devices will work together. Newer, more compact RS232 interfaces have nine pins only and an adapter card is needed. It is functionally similar to the ITU-TS's V.24 and V.28 standards.
• RS422 EIA recommended standard to extend the RS232 50ft limit. It is most commonly implemented on 25-pin connectors (DB-25s) and is electrically compatible with the ITU-TS V.11 standard.
• RS423 The EIA recommended standard for cable lengths that extend the RS232 50ft limit. It was introduced in tandem with RS422 but is not widely used. Electrically compatible with the ITU-TS's V.10 Recommendation.

  S

• SAA (Systems Application Architecture) IBM's common application development environment, enabling software to be developed to run on a broad range of IBM hardware, under a range of operating systems: MVS/ESA, VM/ESA, OS/400 and OS/2 EE. This is achieved through a set of standard interfaces for applications (programming), user and communications.
• SDH (Synchronous Digital Hierarchy) ITU-TS synchronous transmission standards aligned with Sonet above 155Mbit/s, aimed at network operators. Designed with ATM in mind, SDH has many advantages over existing transmission technologies including flexibility in managing the transmission, reconfiguration and control and switching at data rates to 622Mbit/s and beyond. SDH-based networks are being implemented by operators in various parts of Europe and developed by major players such as Alcatel and Northern Telecom.
• SDLC (Synchronous Data Link Control) An IBM protocol for use in SNA (System Network Architecture) environments. It controls an individual link while catering for other network needs and can operate over full or half duplex lines. SDLC is a bit oriented protocol, using a variety of patterns to flag the beginning and end of a frame or packet. Different bit patterns are used to convey address, control and header fields which accompany the transmission and guide the frame to its destination.
• Segment A bus LAN term meaning an electrically continuous piece of the bus. Segments can be joined together using repeaters or bridges.
• Serial interface Hardware for sending and receiving data one bit at a time.
• Server A node that permits other nodes on the LAN to access its resources. The server may be dedicated, in which case this is its sole function, or non-dedicated, where the node can be used in other ways, such as a workstation.
• Service point IBM network management term for a system that allows non-SNA equipment and network components to be incorporated into an SNA management structure.
• Services A general term for resources made available by a server to other nodes on the network. In Microsoft LAN Manager terminology, this concept is broadened to include all main components of the LAN Manager software.
• Session A logical connection between two nodes on a network for the exchange of data; alternatively, any live link between any two data devices, such as a minicomputer and a dumb terminal. A session is also used simply to describe connection time. Session Layer Level Five of the OSI data communications model, drawn up by the ISO, ensures the management of dialogue between applications by providing the protocols for assembling physical messages into logical messages to all dialogue between e nd systems.
• SGMP (Simple Gateway Monitoring Protocol) A predecessor of SNMP.
• Shielded Twisted Pair A twisted pair of cables surrounded by a wire gauze shield, commonly used by IBM.
• Simplex A communications system or link which can only carry a signal in one direction.
• SIR (Speaker Independent [Voice] Recognition) Technologies for the automated conversion of speech to accurate and meaningful textual information, typically ASCII. It typically accepts input from callers to voice processors where callers are using rotary dial instead of DTMF phones. SIR products have deliberately limited vocabularies, but are increasing due to the vast installed base of non-DTMF phones.
• Slotted Ring A LAN architecture that continually carries a constant number of fixed length packets or slots round the ring. The nodes then use, by replacement, empty slots as they pass through, to transmit data. All the nodes have the ability to recognize empty slots or addressed to them. This network architecture is also known as a Cambridge Ring.
• Smart wiring hub A network concentrator enabling multiple media to be supported and managed from a central location. When supporting structured wiring systems, smart hubs provide port management.
• SMB (Server Message Block) A Microsoft - originated distributed system which enables access to another computer's files and peripherals over the network as if they were local.
• SMDS (Switched Multimegabit Data Services) A public packet-switched high-speed data service that extends LAN-like performance to MANs and WANs with no distance limit. Although reflecting DQDB MAN standards, SMDS can also run over ATM. It offers variable data packet size, Virtual Private Network and Closed User Group features, transmission rates up to 34Mbit/s today and 150Mbit/s in the future.
• SMTP (Simple Mail Transfer Protocol) The TCP/IP standard protocol for transferring electronic mail messages from one machine to another. SMTP specifies how two mail systems interact and the format of control messages they exchange to transfer mail.
• SNA (Systems Network Architecture) IBM's layered communications protocol for sending data between IBM hardware and software. Shortly to celebrate its Pearl anniversary (it was first announced way back in September 1974), it is defined today in terms of a stack of seven layers. While there is some commonalty between the layers of OSI and SNA, it is difficult to make a direct mapping. SNA has traditionally been a hierarchical network architecture for homogeneous networking between IBM systems , but in the 'new' SNA IBM has added increasing support for peer to peer networking through the development of Advanced Peer to Peer Communications. SNA is managed through the NetView network management system.
• SNADS (SNA Distribution Services) A standardized asynchronous distribution service architecture for the transmission of files or jobs around an IBM SNA network. It is implemented as a transaction service of the SNA network.
• SNI (SNA Network Interconnect) (In IBM SNA) The way in which autonomous SNA networks can be connected, while still allowing them to be independently managed.
• SNMP (Simple Network Management Protocol) A transmission protocol defined by the IAB in RFC1157 for TCP/IP-based network management, widely accepted as a de facto standard for LAN network management. SNMP is used to monitor IP gateways and their networks. It defines a set of variables that the gateway must keep and specifies that all operations on the gateway are a side-effect of fetching or storing to the data variables. It consists of three parts: structure of management information (SMI) , Management Information Base (MIB) and the protocol itself. The SMI and MIB define and store the set of managed entities; SNMP itself conveys information to and from these entities. The public domain standard is based on the operational experience of TCP /IP internetworks within Darpa/NSFnet.
• SNMPv2 A combination of two proposed updates to SNMP: Secure SNMP and Simple Management Protocol. Its 12 documents and 400 pages define everything from SMI to a Manager-to-Manager MIB, plus much-needed security improvements.
• Sockets IBM term for software interfaces that allow two Unix application programs to talk via TCP/IP protocols.
• Sonet (Synchronous Optical NETwork) Transport network for synchronously multiplexed tributary signals. The standard defines a set of transmission rates, signals and interfaces for fiber optic transmission. Sonet is also an emerging standard proposed by Bellcore (Bell Communications Research, the standards organization of the US Bell Operating companies) for a synchronous optical transmission protocol. The broadband fiber network it supports is formed by a family of network elements conforming to the Sonet interface requirements. The basic electrical signal runs at 51.840Mbit/s - approximately 51 times the bandwidth of a standard US, T1 leased line (1.544Mbit/s). Sonet grows in multiples of the basic signal into the multi-Gigabit range. It is intended to be able to add and drop lower bit rate signals from the higher bit rate signal without needing electrical demultiplexing.
• Source Routing IEEE standard for 802.5 Token Ring environments from an IBM development. A workstation (source) determines the router through the LAN internetwork. It sends a "discovery" or explorer packet along all active paths in the network, eventually reaching the destination host. Once received, the packet is sent back to the originator. Along the way, each bridge traversed adds its designator to the discovery packet. When it arrives at the originator, it contains complete routing information and the originator can send its data with that information attached. SR-compliant bridges generally need less processing power since most of the work is done by the originating workstation. A liability of SR is that the number of discovery packets traversing the network increases dramatically as the number of Token Ring LAN segments and internetworking devices between the stations grows.
• Source Routing Transparent (SRT) An algorithm under consideration by IEEE combining Transparent Bridging for Ethernet networks and Source Routing of Token Ring networks for interconnectivity of the two LAN types. Upward migration to FDDI is guaranteed. The bridge applies either TB or SR logic to each frame according to frame type.
• Spanning Tree Algorithm Part of an IEEE standard. A mechanism for detecting and preventing loops from occurring in a multi-bridged environment. When three or more LAN segments are connected by bridges, a loop can occur. As a bridge forwards all packets which are not recognized as being local, some packets can circulate for long periods of time, eventually degrading system performance. This algorithm ensures only one path connects any pair of stations, selecting one bridge as the 'root' bridge, with the highest priority one as identifier, from which all paths should radiate.
• Speech Concatenation Voice processing term for economical digitized speech playback. It uses independently recorded files of phrases or file segments linked under application program control to produce a customized response in natural sounding language. Examples could be bank balances or bus schedules. It is done for speed and economy, lending itself to limited, structured vocabularies that are best stored in ram or readily accessible from disk.
• Spool (Simultaneous Peripheral Operation On Line) A program or device that controls the flow of data to an outputting device such as a printer. Spooling means that a user can send data to a device which is already occupied and can rest assured that the data will be passed onto the desired destination as soon as possible. Spooling of printer output is achieved on a LAN by means of a print server. It is also important in WANs for providing a buffer for time non-critical applications such as Electronic Mail and File Transfer.
• Spoofing A method of fooling network end stations into believing that keep-alive signals have come from and return to the host. Polls are received and returned locally at either end of the network and are transmitted only over the open network if there is a condition change. The result is a non-time critical network with a minimum of keep-alive traffic between deterministic end stations, while retaining the opportunity to send flags should an end station alter its state. The synchronous approach harks back to unreliable circuits and the need to check end station existence at regular intervals. Now networks are more reliable, spoofing by routers is an acceptable compromise.
• SQE(T) (Signal Quality Error (Test) Function of transceivers immediately acter its attached computer has transmitted on to the LAN. The transceiver sends a simple test signal over the AUI back to the computer, ensuring the computer knows it has a working connection. Because it acts as a confidence check and "pulses" down the line, it is also called a heartbeat.
• SQL (Structured Query Language) A standardized query language that can be used for querying databases across a network in client/server applications. It can be used to interrogate the database, and extension to the language allow the database to be updated through it as well.
• Standalone server In LAN Manager terminology, a server that maintains its own user accounts database and does not participate in logon security.
• Star Topology A network layout or design in which each node is connected to a central hub. The hub establishes, maintains and terminates all connections between the nodes. In a LAN, the hub is likely to be a workstation, whereas in larger multi-point networks the hub is more likely to a multiplexer.
• SDTM (Statistical Time Division Multiplexing) A technique whereby a multiplexer apportions time on a dynamic basis only to those channels which are active.
• Store and forward A buffering technique in which messages or packets are received in their entirety by an intermediary, ever if the ultimate recipient is not presently able to receive, This is used exclusively in the context of electronic mail across wide area networks, and occasionally for terminal I/O.
• StreetTalk Banyan Systems' directory system which provides a distributed database of names addresses accessible from Vines.
• Sub-Area Network The original hierarchical approach used in the construction of IBM SNA backbone networks. The structure of a Sub-Area Network is predefined. The relationship between the components of the network and the links is generated into the software in the host systems involved. The network can, however, be modified without having to re-build the definition of the entire network. A new node can de added by defining it in the adjacent nodes to which it is directly attached. Such a network is constructed around a backbone of communications controllers to which the host systems are attached.
• SVC (Switched Virtual Circuit) A temporary virtual circuit between two users.
• Switch Equipment used to connect and distribute communications between a trunk line or backbone and individual nodes.
• Switched attachment The IBM term for linking devices to host computers through a PBX capable of handling data switching.
• Synchronous transmission A method of communication in which data is sent in blocks, without the reed for start and stop bits between each byte. Synchronization is achieved by sending a clock signal along with the data, and by sending specia l bit patterns to denote the start of each block.
• SSCP (Systems Services Control Point) In an IBM SNA environment the SSCP resides in a host processor and is responsible for central control, directory services and operational functions in the network; either alone or in combination with SSCPs in other processors.

  T

• TA (Telecommunications Administration) A body, usually a company, that provides public telecommunications services.
• T1 A committee belonging to the ANSI whose role is to establish US standards for digital telephony, particularly ISDN. The committee is in no way responsible for or involved with the T1 (1.5Mbit/s) circuit standards.
• T1 A US and Japanese standard for high-speed data transmission at 1.544Mbit/s - 24 64Kbit/s channels plus 8Kbit/s' control information are provided. Also called a DS1.
• T3 A US standard for high-speed data transmission at 44.736Mbit/s, providing the equivalent bandwidth of 28 T1 circuits. Also called a DS3.
• T-Carrier The US standards for digital transmission lines. The line types are of the form Tn or TIC, and the corresponding line signal standards of the form DSn or DSIC.
• Tap The connecting device on cable-based LANs like Ethernet, linking to the main transmission medium.
• TCP (Transmission Control Protocol) The standard transport level protocol that provides the full duplex, stream service on which many application protocols depend. TCP allows a process or one machine to send a stream of data to a process on another. Software implementing TCP usually resides in the operating system and uses the IP to transmit information across the network.
• TCP/IP (Transmission Control Protocol/Internet Protocol) font The suite of protocols developed and used by DAR PA and the US DOD. They build up to Layer Four of the ISO OSI model, but there is no direct correspondence layer for layer. Three main protocols sit above TCP/IP: Telnet, FTP and SMTP.
• TDM (Time Division Multiplexer/Multiplexing) Multiplexer which apportions the time available on its Composite link between its channels, interleaving data from successive channels. The method divides up digital channels to make maximum use of their bandwidth, by taking input from each source in turn. TDMs use one of two methods to achieve this, bit interleaving for synchronous protocols and character interleaving for asynchronous protocols.
• TDMA (Time Division Multiple Access) In LAN technology, a high-speed, burst mode of operation that can interconnect LANs. First used as a multiplexing technique on shared communications satellites.
• Teletex ITU-TS standard for text and message communications intended to replace telex-operating at 2,400bps, it accommodates upper and lower case characters and has a well-defined format for transmission and text presentation.
• Teletext Method of transmitting pages of information using broadcast transmission techniques. Embraces both standard broadcast transmission systems and in-house/cable systems using this format.
• Terminal emulation Software that allows a PC to mimic the attributes of a dumb terminal normally attached to a mainframe or mini-computer, giving the user with access to function keys and control sequences which the host applications normally use when communicating with one of their own dumb terminals. The most commonly emulated terminals are Dec's VT100 terminal and IBM's 3270.
• TFTP (Trivial File Transfer Protocol) The TCP/IP standard protocol for file transfer with minimal capability and minimal overhead. TFTP depends on the connectionless datagram delivery service, UDP.
• Thin Ethernet An 802.3 LAN that uses smaller than normal diameter coaxial cable; often used to link PCs together. It runs at the same frequency as Ethernet but at smaller distances. Colloquially called Cheapernet.
• Timeout The expiration of a pre-defined interval which then triggers some action. For example, in a 30-second, no activity timeout, disconnection occurs after 30 seconds of no data activity. Simple eh? Alternatively, the length or existence of such an interval.
• Token Unique information in a packet header which acknowledges that control of the network is to be relinquished upon receipt of the packet. An empty packet containing a token is forwarded by the recipient to the next node. The token packet passes round the LAN continuously and, as it goes by, give each workstation the all-clear to transmit data.
• Token Bus A LAN with a bus topology that uses token passing as its access method. The sequence of nodes is not governed by physical architecture, but is controlled by software. Arcnet and Map are examples.
• Token passing A technique for restricting access to a network, to a single node at a time. A token is passed from node to node, granting permission to transmit data. The sender attaches its message to the token which conveys it across the LAN to its destination, The message is ignored by all other nodes, and is acted upon by the addressee, When the recipient has accepted the message, it releases the token so that the next node wishing to send can use it.
• Token Ring A 4/16Mbit/s LAN architecture which uses a token passing access method to allow nodes on the network to transmit data. Defined in IEEE 802.5 with a ring architecture, a special data packet, called a token, is passed continuously from node to node (see Token passing, above). The sequence of nodes is governed by the physical order in which the nodes appear on the ring. Every node on the ring sees the data, but only the addressed receiving node will accept it.
• Top (Technical and Office Protocols) A Functional Profile originated by Boeing to separate networking in a non-shop floor environment. TOP was designed from the outset to be compliant with the ISO OSI seven-layer model. Development has beer merged with MAP, and the two functional profiles share a common integration strategy, and have a single (Map/Top) user group.
• TP-4/IP A term given to the ISO protocol suite that closely resembles TCP/IP. Transceiver - A communications device and software capable of transmitting and receiving (see also MAU). Transmission block - A sequence of continuous data characters or bytes transmitted as a unit, over which a coding procedure is usually applied for synchronous or error control purposes.
• Transparent Bridging So named because the intelligence necessary to make relaying decisions exists in the bridge itself and is thus "transparent" to the communicating workstations. It involves frame forwarding, learning workstation addresses and ensuring no topology loops exist (in conjunction with the Spanning Tree algorithm).
• Transport driver A network device driver that implements a protocol for communicating between LAN Manager and one or more media access control drivers. The transport driver transfers LAN Manager events between computers on the local area ne twork.
• Transport Layer The Fourth Layer in the OSI model, drawn up by the ISO. The purpose of the transport layer is to act as an intermediary between the user and the network. All layers above the transport layer are network independent.
• Tree topology A graphic description of a network topology where there is only one route between any two nodes.
• Trellis coding An advanced method of modulation which combines coding of both amplitude and phase. This gives a greater throughput and lower error rate for speeds above 9.6Kbit/s.
• Trunk in token ring, a trunk is the cable running between MSAUs and can be either fiber or shielded twisted pair cable. STP uses two positive transmit wires in normal mode, with no crossover, while fiber has one transmit fiber and one receiver fiber. In normal mode, the second pair of wires is not used it acts as backup and implements the Wrap feature.
• Twisted Pair Two insulated copper wires twisted together with the twists or lays varied in length to reduce potential signal interference between the pairs. Where cables comprise more than 25 pairs, they are usually bundled and wrapped in a cable sheath. Twisted pair is the most common medium for connecting phones, computers and terminals to PABXS. With the IEEE ratification of 10BaseT for networking 10Mbit/s Ethernet over UTP telephony wiring, twisted pair has become ubiquitous. As well as performance at Ethernet rates, it offers cost benefits to the end user through flexibility - ease of relocation. New data-grade and even voice-grade UTP methods support l00Mbit/s transmission, with 155Mbit/s ATM a probability.
• Type A Intelligent Network term describing IN services evoked by, and affecting, a single user. Most of them can only be invoked during call setup or teardown.
• Type B Intelligent Network term describing IN services invoked at any point by, and affecting directly, several users.

  U

• UDP (User Datagram Protocol) The IP standard protocol that allows an application program on one machine to send a datagram to an application program on another machine. UDP uses the Internet IP to deliver datagrams.
• UPS (Uninterruptible Power Supply) A battery, attached to a piece of hardware, for example a server, that provides backup power for conducting an orderly shutdown if the server's normal power supply fails.
• UTP (Unshielded Twisted Pair) The standard cabling used for telephone lines. The standard IEEE 802.3, 10BaseT, defines use of Ethernet over UTP for rates up to l0Mbit/s. The general LAN medium of choice for the 1990s, UTP is marketed in brands such as AT&T's PDS (Systimax) and OSCA.

  V

• Van (Value Added Network)/Vans (Value Added Network Service) A data transmission network which guarantees data security and integrity through added computer control and communications, from the sender to the recipient often in the manner of a door-to-door courier or freight forwarder.
• Vaporware Products announced but not yet commercially available. Often used by suppliers to lock users in with the promise of great things to come.
• Videoconferencing Video and audio communication between two or more parties via a video-codec (coder/decoder) at either end linked by digital circuits. Formerly needing in excess of 300Mbit/s bandwidth, systems are now available offering acceptable quality for general use at 128Kbit/s and high-quality 71KHz audio. Factors influencing the growth of videoconferencing are improved compression technology, reduced cost through VLSI chip technology, low-cost switched digital networks - particularly ISDN - the emergence of standards and applications. Main players include BT, PictureTel and Compression Labs Inc.
• Videoconferencing standards ITU-TS H.261 was the standards watershed. Announced in November 1990, it relates to the decoding process used when decompressing videoconferencing pictures, providing a uniform process for codecs to read the incoming signals. Originally defined by Compression Labs Inc. Other important standards are H.221: communications framing; H.230 control and indication signals and H.242d: call set-up and disconnect. Encryption, still-frame graphics coding and data transmission standards have still to be developed.
• Videotex Term invented by the ITU to describe TV equipment used to display computer-based data, whether sent via a telephone (often called viewdata) or a broadcasting charnel (Teletext). ITU distinguishes between interactive or broadcast videotex.
• VIM (Vendor Independent Messaging) Standard for the application interface to e-mail from Lotus, WordPerfect and others. It will include MAPI compliance.
• Vines Banyan Systems' Virtual Networking operating system is based on Unix system V. This network operating system provides transparent communication across heterogeneous networks and is more expansive in concept, although attracting far fewer users, than Novell's NetWare.
• Virtual circuit A link that seems and behaves like a dedicated point to point line or a system that delivers packets in sequence, as happens on an actual point to point network. In reality, the data is delivered across a network via the most appropriate route. The sending and receiving devices do not have to be aware of the options and the route is chosen only when a message is sent. There is no prearrangement, so each virtual connection exists only for the duration of that one transmission .
• Virtual Container (VC) SDH defines a number of Containers, each corresponding to an existing plesiochronous rate. Information from a plesiochronous signal is mapped into the relevant container along with control information known as the "path overhead". The container plus path overhead form a VC.
• Virtual LAN A logical rather than a physical LAN comprising workgroups drawn together for business reasons or for a particular project irrespective of each member's actual location. Members are likely to belong to several such LANs as their job function dictates. Such LANs await the maturity of high-speed transmission technologies such as ATM before they can exist in any viable form.
• Virtual teams Ad hoc groups of users formed to solve particular problems without taking them away from their desks. A useful option made feasible with groupware.
• Virtual company Company built on the basis of teleworking with limited central office administration. Made possible by improved communications and groupware software, it is a phenomenon of the future.
• VPN (Virtual Private Network) The provision of private voice and data networking from the public switched network through advanced public switches. The network connection appears to the user as an end-to-end, nailed-up circuit without actually involving a permanent physical connection, as in the case of a leased line. VPNs retain the advantages of private networks but add benefits like capacity on demand.
• Virus Code that attaches itself to a program and makes copies of itself. It may or may not cause accidental or malicious damage, but is a serious nuisance particularly in a networked environment and where dependence on IT is heavy. Anti-virus applications such as Norton are available, but security should be augmented by procedures and regular backups.
• Voice-grade channel, Voice-grade line A channel or line offering the minimum bandwidth suitable for voice frequencies, usually 300bit/s to 3.4Kbit/s.
• Voice Mail A system that records, stores and retrieves voice messages; either a standalone device or those that integrate to some extent with a user's phone system. Standalone voice mail is similar to a collection of answering machines but able to instruct each machine (voice mailbox) to carry out a range of features such as call forwarding. Messages can be delivered at a pre-arranged time, tagged and edited. Integrated systems indicate messages waiting via a light on a user's phone and/or an alphanumeric display. If the phone rings for a specified number of rings, it can default to a mailbox which delivers its invitation to leave a message and records the results.
• VSAT (Very Small Aperture Terminal) One-meter diameter satellite dishes used by remote sites, as opposed to the 3m dishes used by head office, in a satellite-linked network. The central office is able to broadcast or multicast data to the remote sites. In Europe, regulatory restrictions are gradually being lifted to allow two-way transmission. The US does not labor under the same protectionism and so has a flourishing VSAT community that allows the remote site to reply using the same link.
• V.Fast Forerunner to the V.34 modem standard due for ratification by 1995. V.Fast modems send a 1Mbyte file typically in under 1.5 minutes.
• V Series A group of ITU-TS recommendations governing data transmission over telephone lines. Series includes:
  • V.21 300bit/s duplex modem for use over PSTN
  • V.22 1200bit/s duplex modem for use over PSTN and leased lines
  • V.22 bis 2.4Kbit/s duplex modem for use over PSTN and leased lines.
  • V.23 600/1200bit/s modem for use over PSTN.
  • V.24 Definitions of interchange circuits between DTE and DCE.
  • V.25 bis Automatic calling and answering equipment on the PSTN.
  • V.26 2.4Kbit/s modem for use over leased lines
  • V.26 bis 2400/1200bit/s half duplex modem for use over PSTN.
  • V.26 ter 2400/1200 bit/s full duplex modern for use over PSTN.
  • V.27 4.8Kbit/s modem for use over leased lines.
  • V.27 bis 4800/2400bit/s modem for use over leasedline.
  • V.27 ter 4800/2400bit/s modem for use over PSTN
  • V.29 9.6Kbit/s modem for use over leased lines.
  • V.32 Up to 9.6Kbit/s bps modern for use over PSTN or leased lines.
  • V.32 bis Up to 14.4Kbit/s modem for use over PSTN or leased lines.
  • V.42 Error control procedures.
  • V.42 bis Data compression technique for use with V.42
• VTAM (Virtual Telecommunications Access Method) An IBM software routine: the virtual access method for 3270 systems.

  W

• WAN (Wide Area Network) A network which covers a larger geographical area than a LAN and where telecommunications links are implemented, normally leased from the appropriate PTO(s). Examples of WANs include packet switched networks, public data networks and Value Added Networks.
• Wiring closet Location, usually a physical box in which the cabling on a particular floor is terminated, typically in a wiring frame.
• Wiring frame Frame used to organize and manage the termination and connection of multiple cables.
• Windowing Generic method of displaying data on screen, mimicking looking at several pieces of paper at once. Each window can be resized, moved and otherwise manipulated. It lies at the heart of making multiuser systems user-friendly and points the way for presetting tomorrow's applications.
• Windows The now ubiquitous Microsoft standalone operating system with integral graphical user interface, running on top of MS Dos. Version 4.0 is imminent.
• Windows for Workgroups (WFWG) A Microsoft operating system running on each PC that allows between two and 20 users to share information such as files and e-mail by clicking on icons. There is no server as such, but WFWG is compatible with NetWare and LAN Manager.
• Windows NT (New Technology) Microsoft's scalable 32-bit version of Windows aimed at high-end workstation "power" users. It is a standalone operating system that is also a "network ready" system capable of being a small application server for a workgroup of Windows based PCs.
• Windows NT Advanced Server (NTAS) An extension of Microsoft's Windows NT and incorporating all its features, NTAS is a server operating system offering centralized management and security, fault tolerance and multiple connectivity options. Geared to client/server computing on practically any network, not least NetWare and Vines as well as LAN Manager.
• WOSA (Windows Open Service Architecture) A framework of open-ended interfaces allowing Microsoft Windows and applications running under it to integrate with enterprise computing environments. It includes APIs for messaging (MAPI), standard access to databases (ODBC) and extensions to financial services.
• Workflow automation The flow of documents around an organization in a prescribed order (workflow) can be automated, delivering an hierarchical and controlled form of workgroup computing. Workgroup computing - Method of organizing a business around productive teams using computer support to enable cooperative working and to eliminate time/space restrictions. An extension of conventional LAN working.
• Workstation Term used freely to mean a PC, node, terminal or high-end desktop processor (for CAD/CAM and similar intensive applications) - in short, a device that has data input and output and operated by a user.
• Wrap Redundancy measure in IBM token ring LANs. Trunk cabling used in token ring TCUs contains two data paths: a main and back-up (normally unused). If the trunk cable is faulty, the physical disconnection of the connector at a TCU causes the signal from the main path to wrap onto the back-up and maintain the loop.

  X

• X Series Recommendations drawn up 51 by the ITU-TS to establish interfaces for Terminal Equipment (DTE) and Data Circuit Terminating Equipment (DCE) and public data networks (PDN). The series includes:
  • X.1 International user classes of service.
  • X.2 International data transmission services and optional facilities.
  • X.3 Packet Assembly/Disassembly (pad).
  • X.4 International Alphabet No.5 for character oriented data.
  • X.20 Asynchronous communications interface definitions for use over the PSTN.
  • X.20 bis V-series compatible modem, asynchronous communications interface definitions for use over the PSTN.
  • X.21 Synchronous communications interface definitions for use over the PSTN.
  • X.21bis V-series compatible modem, synchronous communications interface definitions for use over the PSTN.
  • X.25 Interface between DTE and DCE for terminals using packets over public data networks.
  • X.28 DTE/DCE interface for asynchronous DTE accessing a pad.
  • X.29 Definition of handshake protocol for use between pads and between the pad and DTE.
  • X.30 Support of X.20 bis, X.21 and X.21 bis DTEs by ISDN.
  • X.31 Support of packet mode DTEs by ISDN.
  • X.32 Interface between DTE and DCE for terminals operating in packet mode accessing public data networks via PSTN, ISDN or circuit switched PDN.
  • X.50 Fundamental parameters of multiplexing scheme for the international interface between synchronous data networks.
  • X.50bis Fundamental parameters of 48Kbit/s transmission for the international interface between synchronous data networks.
  • X.51 Fundamental parameters of multiplexing scheme for the international interface between synchronous data networks using 10-bit envelope structure.
  • X.51bis Fundamental parameters of a 481Kbit/s transmission scheme for the international interface between synchronous data networks using a 10-bit envelope structure.
  • X.58 Fundamental parameters of multiplexing scheme for the international interface between synchronous data networks using a 10-bit envelope structure.
  • X.60 Common channel signaling for circuit switched data applications.
  • X.61 Signaling system no.7 - data user part.
  • X.70 Terminal and transit control signaling for asynchronous services on international circuits between anisochronous data networks.
  • X.71 Decentralized terminal and transit control signaling on international circuits between synchronous data networks.
  • X.75 Packet switched signaling between public networks providing data transmission services.
  • X.80 Interworking of inter-exchange signals for circuit switched data services.
  • X.92 Hypothetical reference connections for synchronous PDNs.
  • X.96 Call progress signals in PDNs.
  • X.110 international routing principles and routing plan for PDNs.
  • X.121 International numbering plan for PDNs.
  • X.130 Call set-up and clear-down times for international connection to synchronous PDNs.
  • X.132 Grade of service over international connections to PDNs.
  • X.400 A message handling system standard that permits the electronic exchange of text as well as other electronic data like graphics and fax. The X.400 standard is an overview which is broken down under these numbers:
    • X.402 Overall Architecture.
    • X.403 Conformance Testing.
    • X.407 Abstract service definition conventions.
    • X.408 Encoded information type conversion rules.
    • X.411 Message transfer system.
    • X.413 Message store.
    • X.419 Protocol specifications.
    • X.420 Interpersonal messaging system.
  • X.500 A directory standard that lets applications like e-mail access information which can either be central or distributed. The benefit of a directory is the ability to minimize the impact on the user of changes to a network. The standard is broken down under subsequent numbers:
    • X.501 Models.
    • X.509 Authentication framework.
    • X.511 Abstract service definition.
    • X.518 Procedures for distributed operation.
    • X.519 Protocol specifications.
    • X.520 Selected attribute types.
    • X.521Selected object types.
• Xapia (X.400 Application Programming Interface Association) Body standardizing the interface to X.400 e-mail services. Other APIS, like VIM and MAPI, are likely to comply with Xapia when it is finalized.
• X/Open A body comprising of computer vendors, responsible for researching, defining and publicizing open systems.
• X.Windows A networked GUI based on a client/server architecture, it displays information from multiple networked hosts on a single workstation. Available on PCs as X.terminal emulation and emulation on LAN servers.

  Y

  Z