LAN GLOSSARY EDITED BY BONNY HINNERS 1 BASE5 An implementation of the StarLAN IEEE Standard on a baseband medium at 1 megabit per second. The maximum segment length is 500 meters. 10BASE2 An implementation of the Ethernet IEEE standard on thin coaxial cable, a baseband medium, at 10 megabits per second. The maximum segment length is just under 200 meters. 10BASE5 An implementation of the Ethernet IEEE standard on twinaxial cable, a baseband medium, at 10 megabits per second. The maximum segment length is 500 meters. 10BASE-T An implementation of the Ethernet IEEE standard on 24 gauge unshielded twisted-pair wiring, a baseband medium, at 10 megabits per second. 3+3COM Corporation's networking system implementing parts of Xerox's XNS (Xerox Network Systems) and microsoft/IBM PC LAN protocols. 802.3 Defined by the IEEE, these standards govern the use of CSMA/CD (Carrier Sense Multiple Access/Collision Detection) network access method used by Ethernet networks. 802.4 Defined by the IEEE, these standards govern the use of the token bus network access method. 802.5 Defined by the IEEE, these standards govern the use of the token ring network access method. AC (Access Control) On Token Ring networks, this byte contains the token indicator and frame priority. ACCESS METHOD set of rules by which networks arbitrate their use. ACCOUNTING MANAGEMENT reports costs for network resources requested by users and groups. It is also one of five categories of network management defined by the ISO. ACSE (Association Control Service Element) An application-level protocol. active/passive device A device such as a Token Ring MAU (Multistation Access Unit) that supplies current for the loop is considered active. One that does not supply current is considered passive. ADDRESS a unique identifier assigned to networks and stations so that each device can be separately designated to receive and reply to messages. AFP (Apple Talk Filing Protocol) In an AppleTalk network, this presentation-level protocol governs remote file access. ALAP (AppleTalk Link Access Protocol) In an AppleTalk network, this link access layer (or data link layer) protocol governs packet transmission on LocalTalk. ANALOG a transmission scheme that continually varies the waveform over an infinite range of voltage. ANOLOG RECORDING transfer method that converts data from digital to analog format. ANSI (American National Standards Institute) Principal group in the U.S. for defining standards. ANSI represents the U.S. in the ISO. API (Application Program Interface) A set of programming functions and routines that provides access between protocol layers, such as between an application an dnetwork services. APPC (Advanced Program-to-Program Communications) Primarily for personal computers in an SNA (System Network Architecture) network to communicate with a mainframe host, this implementation of LU (Logical Unit) 6.2 uses high-level program interaction. APPLESHARE apple computers network system implementing the AppleTalk protocols. APPLETALK PROTOCOL suite defined by Apple Computer for connecting computers and peripherals using shielded twisted-pair wiring and transfer rates of about 230.4 kilobytes per second. The network and transport-level protocols include Datagram Delivery Protocol (DDP), AppleTalk Transaction Protocol (ATP), AppleTalk Session Protocol (ASP), and the Name Binding Protocol (NBP). APPLICATION LAYER the seventh layer of the OSI (Open Systems Interconnection) model for data communications. It defines protocols for user or application programs, ARCnet A 2.5 megabit per second baseband, token-passing network designed by Datapoint Corporation that supports up to 255 nodes. ARP (Address Resolution Protocol) TCP/IP protocol for determining a DLC (data-link control) address from an IP (Internet Protocol) address. ARPA (Advanced Research Projects Agency) The group within the U.S. Department of Defense that developed ARPANET, the first major packet-switched network. ASCII (American Standard Code for Information Interchange) A seven-bit binary code standardized by ANSI for use by personal computers and some mainframes to represent alphanumeric and graphical characters. An additional bit is included to for an eight-bit character byte. ASYNCHRONOUS TRANSMISSION a data transmission technique controlled by start and stop bits at each end of a character and characterized by an undetermined time interval between characters. AUDIT TRAILS a record of events on the network including when users requested specific resources. AUI (Attachment Unit Interface) Connector used with thick Ethernet that often includes a drop cable. BACK-END Database server functions and procedures for manipulating data. BACKBONE CABLE on which two or more stations or networks may be attached. BACKUP OFF-LINE copies of data for protection against system failures. BALUN (balance, unbalance) Device for matching impedance between a balanced and an unbalanced line, usually twisted-pair wire and coaxial cable respectively. BANDWIDTH used to indicate transmission capacity in Hertz, this represents the difference between the highest and lowest frequencies available for signals. BASEBAND A network in which the entire bandwidth of the transmission medium is used by a single digital. Unlike broadband, no modulation techniques are used. BAUD MEASUREMENT of signaling speed indicating line changes per second, where line changes can represent one or more bits. Only for line changes representing a single bit, baud is equal to bits per second. BINDARY NETWARE database of user names, passwords, groups, and accounting information. BNC Standardized connector used with Thinnet and coaxial cable. BOOT PROM (Boot Programmable Read-Only Memory) A processor chip usually mounted on the network interface card that enables a personal computer to load the operating system from the network. BRIDGE A device operating at the data link layer to connect local or wide-area networks that use the same protocol. BROADBAND A network in which the bandwidth can be shared by multiple simulations signals that are encoded with radio- frequency modulation. BROADCAST The address for all nodes in a network or the message sent to all nodes. BROUTER A device that can route specific protocols and bridge others, thus combining the capabilities of bridges and routers. BUFFER A temporary storage location that provides uninterrupted data flow between devices as keyboards and processors or processors and printers until the data from one be accepted by the other. BUS TOPLPOGY A network topology in which nodes are connected to a single cable with terminators at each end. CACHE MEMORY location set aside to store frequently accessed data for improved system performance. CASCADED STARS Topology in which a centralized multiport repeater serves as the focal point for many other multiport repeaters. CCITT (Consultstive Committee for International Telegraphy and Telephony) Group within the international Telecommunications Union (ITU) that defines data communications standards. Cheapernet See Thinnet CLIENT A node that requests network services from a server. CLIENT-SERVER computing A technique with which processing can be distributed between nodes requesting information (clients) and those maintaining data servers. CMIP/CMIS (Common Management Information Protocol/Services) Standards described by the OSI (Open System Interconnection) for managing heterogeneous networks. COAXIAL CABLE data transmission medium with a single-wire conductor insulated from EMI/RFI (Electromagnetic Interference/Radio Frequency Interference). COMMON CARRIER a licensed, private utility company that supplies data and voice communications services. CONCURRENCY CONTROL rules that regulate data access to multiple users on a database server. CONTENTION NETWORK access method in which nodes compete for transmission by sending signals at will. CPU (Central Processing Unit) A personal computer's primary microprocessor chip. CRC (Cyclical Redundancy Check) Error checking technique in which bytes at the end of a packet are used by the receiving node to detect transmission problems. The bytes represent the result of a calculation performed on the data portion of the packet before transmission. If the results for the same calculation on the received packet are not equal to the transmitted results, the receiving node can request that the packet be resent. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) Network access method using contention similar to CSMA/CD used by LocalTalk networks. Unlike CSMA/CD, in this method the sending node requests permission to send from the intended receiving node. If the receiving node responds with a clear to send signal, transmission begins. CSMA/CD (Carrier Sense Multiple Access/Collision Detection) Network access method in which nodes contend for the right to send data. If two or more nodes attempt to transmit at the same time, they abort their transmission until a random time period of microseconds has transpired and then attempt to resend. DAT (Digital Audio Tape) Medium for storing digital rather than analog data. DATA INTEGRITY a measure of accuracy based on error detection. DATA LINK LAYER2, Layer2 of the OSI (Open Systems Interconnection) model; it defines protocols governing data packetizing and transmission into and out of each node. DATABASE SERVER a computer that stores data centrally for network users and managers and often uses client-server software to distribute the processing of that data between itself and nodes requesting information. DATAGRAM IN THE INTERNET PROTOCOLS (IP), this refers to a packet containing destination address and data. DB-9 a standardized connector with 9 pins for token ring and serial connections. DB-15 a standardized connector with 15 pins for Ethernet transceivers. DB-25 a standardized connector with 25 pins for parallel or serial connections. DCE (Data Communications Equipment) A device that establishes, maintains, and terminates a data communications session and provides encoding or conversion if necessary. DDD (Direct Distance Dialing) A telephone service with which a subscriber can call someone outside the area without requiring operator assistance. DECNET Digital Equipment Corporation's network system and protocols. DEDICATED SERVER a node on which applications are limited to maintaining network resources; no user applications are available. DES (Data Encryption Standard) U.S. government standard for data encryption. DID (Direct Inward Dialing) A telephone service with which subscribers can have calls within a system routed to a specified telephone without switchboard assistance. DISK DUPLEXING fault tolerance method in which two disk controllers are used in a single server. DLC (Data Link Control) Protocols governing packet information including destination address, source address, and control information. DMA CHANNEL (Direct Memory Access Channel) Memory access method independent of the CPU (Central Processing Unit). DNS (Domain Name Service) A TCP/IP protocol for discovering and maintaining network resource information distributed among different servers. DOS (Disk Operating System) The operating system developed by Microsoft and often ported by computer manufactures such as IBM to run specifically on their computers. DOWN TIME Period when the network is unavailable to users. DQDB (Distributed Queue Dual Bus A communication technique proposed for MANS (Metropolitan Networks). EBCDIC (Extended Binary Coded Decimal Intercharge Code) An eight- bit binary code standardized by IBM for use by its mainframes to represent alphanumeric and graphical characters. EEHLLAPI (Entry Emulator High Level Language Applications Programming Interface) An IBM API Subset of HLLAPI. EISA (Expanded Industry Standard Architecture) Compaq's improved bus architecture that is backwards compatible with ISA (Industry Standard Architecture). ELECTRONIC MAIL (e-mail) An application with which users can send information to other users with whom they share a data communication connection. EMI/RFI (Electromagnetic Interference/Radio Frequency Interference) A form of "noise" on data transmission mediums that can reduce data integrity and increase transmission errors. EMULATION The imitation of one device by another. ENTERPRISEWIDE NETWORK Internetwork connecting all sites of a single corporation worldwide. ESDI (Enhanced Small Device Interface) Interface type for computer adapter and controller boards. ETHERNET a 10 megabits per second baseband, CSMA/CD network originally designed by Xerox Corporation. ETHERNET TALK Apple Talk protocol governing Ethernet transmissions. Also the apple computer ethernet adapter and drivers. The first implementation, Phase 1, was replaced by Phase 2 in 1989. ETHERTYPE a two-byte code indicating protocol type in an Ethernet packet. FAULT MANAGEMENT DETECTS, isolates and corrects network faults. It is also one of five categories of network management defined by the ISO. FAULT TOLERANCE The ability of a system to perform fault management and continue operating in the event of system failures. FC (Frame Control) On token Ring networks, this data supplies the frame type. FCC (Federal Communications Commission) Government agency that supervises, licenses, and controls standard for all forms of radio and electromagnetic transmissions. FDDI (Fiber-Optic Data Distribution Interface) A 100 megabits per second data transfer interface for fiber optic cable. FIBER OPTIC CABLE glass or plastic fibers over e=which modulated light pulses from laser or LED (Light Emitting Diode) can transmit data. It is not subject to interference or electronic eavesdropping. FILE LOCKING Method of data management which reserves a file for the first user that requests it, thus locking out other users. FILE SERVER A computer that stores data centrally for network users and managers access to that data. File servers can be dedicated so that no processes other than network management can be executed while the network is available, or nondedicated so that standard user applications can run while the network is available. FLAGS signals passed between processes. FLOW CONTROL hardware or software mechanism such as a buffer that manages data transmissions when the receiving device cannot accept data. FRONT-END Client application for presenting, entering, and updating data. FTAM (File Transfer Access and Management) An application level protocol governing file access. FTP (File Transfer Protocol) A TCP/IP application protocol governing file transfer. GATEWAY a device connecting two or more networks that may use different protocols and media. Gateways can connect locally or over wide areas. GOSIP (Government OSI Profile) A version of the OSI (Open System Interconnection) Model designed specifically for the U.S. government. HDLC (High-level Data Link Control) An ISO protocol for X.25 international communications. HELICAL SCAN storage method that increases media capacity by laying data out in diagonal strips. HETEROGENEOUS NETWORKS, networks composed of hardware and software from multiple vendors usually implementing multiple protocols. HUB a concentrator or repeater in a star topology at which node connections meet. IEEE (Institute of Electrical and Electronics Engineers) a professional organization within the ISO that assists with the creation of networking standards. IMPEDANCE MEASUREMENT of resistance to current that a transmission medium offers. It is measured in ohms. INTERFACE AREA of connection through which information can be exchanged. INTERNET connected networks including those of the National Science Foundation and the advanced projects research agency. INTERNETWORK a collection of two or more connected networks that may be dissimilar. INTEROPERABILITY The ability to operate and exchange information in a heterogeneous network. I/O ADDRESS (Input/Output address) Starting address for data input and output. IP (Internet Protocol) TCP/IP protocol governing packet forwarding. IPC (Interprocess Communications) a protocol for data exchange between applications or threads. IPX (Internetwork Packet eXchange) NetWare protocol similar to IP (Internet Protocol). IRQ (Interrupt Request) The method by which hardware devices request processor attention. ISA (Industry Standard Architecture) The popular architecture for personal computer buses, such as the IBM PC, XT, and AT. ISDN (Integrated Services Digital Network) Protocol proposed for carrying voice, data, facsimile, and video signals across a network. ISO (International Standards Organization) An international organization that creates networking standards including the OSI (Open System Interconnections) model. JABBER NETWORK error caused by an interface card continually sending corrupted data onto the network. LAN (Local Area Network) A system of software and hardware connected by a common data transmission medium and limited to a geographical area less than about 10 kilometers. LAN-AWARE applications that have file and record locking for use on a network. LAN-IGNORANT applications written for single users only. These are not recommended for use on LAN's. LAN-INSTINSIC applications written for client-server networks. LAN MANAGER MICROSOFT'S network operating system based on OS/2. LAN SERVER IBM'S implementation of LAN manager. LAP (Link Access Protocol) Apple Talk protocols including ELAP for Ethernet and LLAP for LocalTalk. LAT (Local Area Transport) DECnet protocol governing communications between terminals and hosts. LEASED LINE a private telephone line reserved for the leasing customers use. LED LIGHT emitting diode. LLC (logical link control) A layer 2 protocol governing transmission, also known as the IEEE 802.2 standard. LOCAL TALK a 230 kilobits per second baseband network using the CSMA/CA access method. LOOPBACK a diagnostic test in which a signal is transmitted across a medium while the sending device waits for tits return. LOOSELY COUPLED A multiprocessor computer in which the CPUs (Central Processing Units) have separate memory and system buses. LU (Logical Unit) An IBM protocol suite primarily for SNA (System Network Architecture) network. LU 6.2 (Logical Unit 6.2) An IBM protocol suite governing peer- tp-peer communications in an SNA (System Network Architecture) network. MAC (Medium Access Control) A layer 2 protocol governing access to transmission media. MAN (Metropolitan Area Network) A network capable of high-speed data communications over distances up to about 80 kilometers. MANCHESTER ENCODING a digital encoding method that describes a bit value by transition between two signals and that is self- clocking. MAP (Manufacturing Automation Protocol) a version of the OSI (Open System Interconnection) model for manufacturing environments developed by General Motors. MAPPING REDIRECTING local resources to network resource. MAU (Multistation Access Unit) A concentrator or transceiver for attracting nodes to a transmission medium. MCA (Microchannel Architecture) IBM's proprietary bus architecture that offers improved performance over ISA (Industry Standard Architecture) and is used primarily in PS/2 computer system. MIB (Management Information Base) a database of network management information used by CMIP (Common Management Information Protocol) and SNMP (Simple Network Management Protocol).Mirroring a fault tolerance method in which a backup data storage device maintains data identical to that on the primary device and can replace the primary if it fails. MODEM (Modulator-demodulator) a device that converts digital and analog signals. MODULATION The alternation of a signal's frequency, phase, or amplitude. MOUNT The method in NFS and other networks by which nodes access network resources. MULTICAST An address for a selection of nodes in a network, or the message sent to a selection of nodes. MULTIPROCESSOR A computer with more than one Central Processing Unit (CPU) that can be accessed simultaneously by an operating system adapted to this architecture. MULTITASKING The process of swapping from one task to another without losing track of either. Usually accomplished by time slicing any shared resources. MULTI-USER SOFTWARE An application designed for simultaneous access by two or more network nodes. It typically employs file and/or record locking. NBP (Name Binding Protocol) AppleTalk protocol for translating device names to addresses. NDIS (Network Driver Interface Specification) Specification for a generic device driver for network interface cards that is independent of hardware and protocol. NETBIOS (Network Basic Input/Output System) A widely-used protocol governing data exchange and network access. NETWARE Novell's network operating system using IPX (Internetwork Packet Exchange) and SPX (Sequential Packet Exchange) protocols. NETWORK A system of software and hardware connected in a manner to support data transmission. NETWORK ARCHITECTURE A description of data formats and procedures used for communication between nodes. NETWORK LAYER, Layer 3 of the OSI (Open Systems Interconnection) model; it defines protocols governing data routing. NETWORK LOADABLE MODULE (NLM) An application or driver that resides on a netware server to provide additional resource management capabilities. NETWORK TOPOLOGY The arrangement of nodes usually forming a star, ring, tree, or bus pattern. NFS (Network File System) Sun microsystem's network operating system based on TCP/IP protocols. NIC (Network Interface Controller) Adapter board that provides the physical connection between a computer and the network medium. Also called network interface card. NODE any device including servers and workstations connected to a network; also the point where devices are connected. NONDEDICATED SERVER a node on which user applications are available while network resource maintenance applications execute in the background. NOS (Network Operating System) Controlling software for a network, which may run on top of DOS, that oversees resource sharing and often provides security and administrative tools. OS/2 Microsofts multi-threaded, multitasking, single-user operating system. OSI Model (Open System Interconnection) The seven-layer protocol model defined by the OSI for data communications. PACKET a collection of bits comprising data and control information formatted for transmission from one node to another. PACKET FILTER the ability to search a packet to determine its destination and to then route it accordingly. This ability helps to control network traffic. PACKET FORWARDING copying the packet to another node without looking at destination address. PACKET SWITCHING a data transmission method that routes packets along the most efficient path and allows a communications to be shared by multiple connections. PAD (Packet Assembler/Disassemble) a device for connecting a terminal or computer to an X.25 network. PAP (Printer Access Protocol) An appletalk protocol governing transmissions between workstations and printers or similar devices. PCF (Physical Control Fields) The AC (Access Control) and FC (Frame Control) bytes in a token Ring header. PEER-TO-PEER a system in which two or more nodes or processes can initiate communications with each other. Usually describes a network in which all nodes have the ability to share resources with other nodes so that a dedicated server can be implemented but is not required. PERFORMANCE MANAGEMENT measures and records resource utilization. It is one of the categories of network management defined by the ISO. PHASE MODULATION altering a characteristic of a sine wave, specifically its phase. PHYSICAL LAYER, layer 1 of the OSI (Open System Interconnection) model; it details protocols governing transmission media and signals. PINOUTS pin configurations for cabling. PIPE a device that acts as an interface or buffer between applications and devices. POINT-TO-POINT LINK a direct connection between only two nodes. POLLING an access method with which a hub asks each node in turn if it has data to transmit. PRESENTATION LAYER, layer 6 of the OSI (Open System Interconnection) model; it defines protocols governing data formats and conversions. PRINT SERVER a computer that manages printers and print requests from other nodes. PRINT SPOOLER an application that manages print requests or jobs so that one job can be processed while other jobs are placed in a queue until the printer has finished with preceding jobs. PROPAGATION DELAY the time required for data to travel from transmission point to destination. PROTECTED MODE CPU (Central Processing Unit) mode in which application must request memory allocations from the operating system, and these allocations are then protected from other applications requests. PROTOCOL a standardized set of rules that specify the format, timing, sequencing, and/or error checking for data transmission. PROTOCOL STACK A representation of the hierarchical nature of protocol suite. PROTOCOL SUITE a hierarchical set of related protocols. PUBLISHING making resources available to network users. QBE (Query By Example) a database front-end that requests the user to supply an example of the type of data to be retrieved. QUREY LANGUAGE a programming language that permits users to retrieve information from the database. QUEUE an ordered list of items waiting to be processed. RAM (Random Access Memory) Memory in which data is temporarily stored processing. RAM BASE ADDRESS (Random Access Memory Base Address) Starting address for memory dedicated to a specific task. RARP (Reverse Address Resolution Protocol) A TCP/IP protocol governing the translation of a DLC (Data Link Control) address to an IP (Internet Protocol) address. REAL MODE CPU (Central Processing Unit) mode in h=which applications have direct access to physical memory of the computer. RECORD LOCKING a method a managing shared data on a network by preventing more than one user from accessing the same segment of data at the same time. REDIRECTOR an application that intercepts request for resources local to a node on the network and redirects those request elsewhere on the network. REPEATER a device that regenerates and often amplifies signals to extend transmission distance. It is independent of protocol and media. RESPONSE TIME the time required between transmission of the last character of message and reception of the first reply character. RFC request for comment RG-58 Coaxial cable with 50-ohm impedance used by Thinnet. RG-62 Coaxial cable with 93-ohm impedance used by ARCnet. RING TOPOLOGY a network topology in which nodes are connected to a closed loop no terminators are required because there are no unconnected ends. RJ-11 Four-wire modular connectors for phone lines. RJ-45 Eight-wire modular connectors for Star Lan networks and some phone lines. ROUTE DISCOVERY process through which a router can learn LAN topology by passing information about its address and the LANs it connects and receiving the same information from others. ROUTER a device that connects networks and supports the required protocols for packet filtering. RPC (Remove Procedure Call) A protocol governing the method with which an application activates processes on other nodes and retrieves the results. SCSI (Small Computer System Interface) an interface type for computer adapters and controller boards. SDLC (Synchronous Data Link Control) A protocol for SNA (systems network architecture) networks similar to LLC (Logical Link Control). SECURITY MANAGEMENT protects a network from invalid accesses. It is one of the management categories defined by the ISO. SEF (Source Explicit Forwarding) Security feature that allows transmissions only from specified stations to be forwarded by bridges. SEMAPHORE a method with which multiple applications can coordinate related operations using messages. SERVER a computer that provides shared resources, such as files and printers, to the network. SESSION an active communications connection between nodes or applications. SESSION LAYER, layer 5 of the OSI (Open Systems Interconnection) model; it defines protocols governing communications between applications. SHARED MEMORY portion of memory accessible to multiple processes. SHEILDED WIRING protected from electromagnetic and radio frequency interference by metal-backed mylar foil and plastic ar PVC. SMTP (Simple Mail Transfer Protocol) governing electronics mail transmissions. SNA (Systems Network Architecture) IBM's protocols governing mainframe communications. SNMP (Simple Network Management Protocol) TCP/IP protocol governing network monitoring. SOCKETS IN API (Application Program Interface) for communications between Unix and TCP/IP. SPOOL (Simultaneous Peripheral Operation On-Line) See print spooler SPP (Sequenced Packet Protocol) XNS (Xerox Network Systems) protocol governing sequenced data. SPX (Sequential Packet Exchange) Novells implementation of SPP (Sequential Packet Protocol). SQL (Structured Query Language) a widely used programming language for manipulating database information. STA (Spanning Tree Algorithm) A technique for determining the most desirable path between segments of a multiloop, bridged network. STAR LAN AT&T's network operating system implementing CSMA/CD. STAR TOPOLOGY a network topology in which nodes are connected to a common device such as a hub or concentrator. STORE-AND-FORWARD a message switching technique in which messages are temporarily stored at intermediate points before being retransmitted to the next destination. STREETTALK VINES (Virtual Network Software) protocol for discovering and maintaining network resource information distributed among different servers. SYNCHRONOUS TRANSMISSION a data transmission scheme in which the interval between transmitted characters is fixed so that start and stop bits are not required. T1 A 1.544 megabits per second multichannel transmission system for voice or data provided by long distance carriers. T-CONNECTOR a T shaped device with two female and one male BNC connectors. TCP (Transmission Control Protocol) TCP/IP protocol governing sequenced data. TCP/IP (Transmission Control Protocol/Internet Protocol) A protocol suite developed by ARPA (Advanced Research Projects Agency). TELNET TCP/IP protocol governing character-oriented terminal data. THICKNET CABLING scheme using twinaxial cable. THINNET CABLING scheme using 50 ohm coaxial cable. THREADS Individual processes within a single application. TIE LINES (Terminal Interface Equipment Lines) long-distance leased lines reserved for the leasing company. TIGHTLY COUPLED a multiprocessor computer in which the CPU's (Central Processing Units) share memory and one system bus. TOKEN the character sequence passed among nodes in sequence to indicate which one has permission to transmit. TOKEN BUS a bus topology network using a token passing access method. TOKEN PASSING a network access method that requires nodes to wait for their turn before transmitting data. Turns are indicated by a character sequence that passes from one node to the next. TOKEN RING a 4 megabit per second or 16 megabit per second network using a ring topology and a token passing access method. TOP (Technical Office Protocol) a version of the OSI (Open System Interconnection) model for the office developed by Boeing. TRANSCEIVER An AUI (Attachment Unit Interface) device for receiving and transmitting data that often provides collision detection as well. TRANSPORT LAYER, layer 4 of the OSI (Open System Interconnection) model; it defines protocols governing message structure and some error checking. TREE TOPOLOGY a network topology in which nodes are connected by cables to a trunk cable with a central retransmission facility. TRIGGERS uncompiled code residing on an intelligent database server. TWISTED PAIR CABLE a wiring scheme with one or more pairs of 18 to 24 gauge copper strands. The strands are twisted to improve protection against electromagnetic and radio frequency interference. Cable may be either shielded or unshielded. TYPE 1 CABLE Shielded two-pair cable. TYPE 3 CABLE unshielded twisted pair cable UNINTERRUPTIBLE POWER supply battery backup system to provide power in the event of power failures or fluctuations. Particularly important for network servers, bridges, and gateways. UNITY GAIN refers to the balance between signal loss on a broadband network and signal gain through amplifiers. UNSHEILDED WIRING not protected from electromagnetic and radio frequency interference, but covered with plastic and/or PVC. VALUE ADDED PROCESS (VAP) An application designed to load and run automatically on a NETWARE server in order to help manage resources. VINES (Virtual Network Software) Banyan's network operating system based on Unix and its protocols. VIRTUAL CIRCUIT a communications link that appears to be dedicated circuit and passes sequential packets between devices usually in a packet switching network. VTAM (Virtual Telecommunications Access Method) On an SNA (Systems Network Architecture) network, this application provides access to shared information. WAN (Wide Area Network) a network capable of transmissions over large geographic areas that uses transmissions lines provided by a common carrier. WORKSTATION a networked computer typically reserved for end-user applications. WORM (Write Once Read Many) Optical disk to which data may be written once and not altered, but from which data can be retrieved as often as necessary. X.25 CCITT protocol governing packet-switched networks using virtual circuits. X.400 CCITT protocol governing international electronic mail transmissions. X.500 CCITT protocol governing the maintenance of files and directories on multiple systems. XNS (Xerox Network Systems) Xerox's data communications protocols. ZONE one or more connected AppleTalk networks grouped according to network usage.