NetWare SNA Glossary ACCESS CODE In Novell LAN-based 3270 and 5250 communications products, a name with up to 15 characters used to select a host session or group of host sessions through a specified gateway server. On the server, a host session, a group of up to 5 host sessions, or a pool or such sessions or session groups is defined under the access code. ACF/NCP Advanced Communications Function/Network Control Program. Software resident in an IBM 37x5 communications controller that manages communication between the host system attached to the controller and other devices on the network (usually, but not necessarily an SNA network). ACF/TCAM Advanced Communications Function for the Telecommunications Access Method. Host communications access method which provides similar functions to those provided by ACF/VTAM, plus some data queuing functions not provided by either ACF/VTAM or ACF/VTAME. ACF/VTAM Advanced Communications Function for the Virtual Telecommunications Access Method. System program which runs on an IBM host computers and controls communication between host application or service programs and terminals. The prefix ACF distinguishes contemporary VTAM releases from earlier ones which provided much less comprehensive support. ADAPTER See LAN adapter. ADDRESS An identifier for a physical or logical device on a network. In SNA networks, each physical unit, logical unit and system service control point has an address. In local area networks, each node on the network has an address. ADVANCED PROGRAM-TO-PROGRAM COMMUNICATION See APPC API Application Programming Interface. The module of network software that communicates with a user's application. In networks built on the ISO OSI model, APIs usually work on the seventh layer. APPC Advanced Program-to-Program Communications. An IBM protocol for developing peer-to-peer communications that allows programs to communicate with equal control. APPC is implemented through LU 6.2. APPLICATION LAYER The seventh layer of the ISO OSI model. This layer passes requests and responses between the network and applications. ASCII American standard Code for Information Interchange. A code for representing characters to a processor; each character is represented by 7 bits with an optional eighth bit for parity checking. ASCII is used on microcomputers; EBCDIC is used on IBM host computers. AS/400 IBM mainframe computer that can act as a host for a Token-Ring gateway connection. BROADCAST To send a message to all users on a network. CLUSTER CONTROLLER Also known as a control unit (IBM model numbers 3174, 3172, 3274). A machine that supervises terminals and other peripherals. When personal computers are connected to a host computer through a gateway, the gateway server functions as a cluster controller. COAXIAL CABLE Frequently called coax cable, a cable consisting of one conductor within another conductor, covered by an outer insulating shield. Coaxial cable is sometimes used to connect the gateway server to the host. COMMUNICATIONS CONTROLLER Also known as a front-end processor (IBM model numbers 3725, 3745, 3705, 3720). In remote environments, a machine directly attached to a host computer, that processes communication requests. CONNECTIONLESS SYSTEM A network type that treats each packet as an individual system communication (IPX, for example). Each packet contains a destination address, allowing it to be delivered independent of any other packet. CONNECTION ORIENTED SYSTEM A network in which two nodes establish a session before they communicate. During the session, the two nodes communicate only with each other. When the transmission is complete, the session is ended. CONTROL UNIT See cluster controller. CUT Control-Unit Terminal. An IBM 3270 terminal attached to a cluster controller that processes its keystrokes and managers its buffers. A control-unit terminal can support one host communications session at a tine. DATA FLOW CONTROL LAYER The fifth layer of the SNA model. The data flow control layer manages sessions and provides error recovery. DATA LINK CONTROL LAYER The second layer of the SNA model. The data link control layer constructs frames from a bit stream. DATA LINK LAYER The second layer of the ISO OSI model. The data link layer handles the translation between the electrical signals transmitted by the physical layer and the bit patterns required by the higher layers. DATA LINK TRACE In the SNA Gateway, a diagnostic test in which the gateway simulates the host to check for proper LAN functioning. DATA STREAM Data that is flowing between points on a network. A data stream is usually a succession of messages. DFT Distributed Function Terminal. A coaxially-connected device that does not require cluster-controller interaction to respond to keystrokes. distributed processing A data processing type in which more than one processor shares the execution of an application. In SNA networks, distributed processing is implemented through APPC. DOS Disk Operating System. The initial operating system used for System/360 mainframes; also, a loose term for a personal computer operating system, short for PC-DOS or MS-DOS. EBCDIC Extended Binary Coded Decimal Interchange Code. EBCDIC is for mainframes what ASCII is for microcomputers to represent different characters. EGA Enhanced Graphics Adapter. A display adapter for personal computers that provides monochrome or color monitors with 350-line resolution and graphics capabilities. END USER LAYER The seventh layer of the SNA model. The end user layer is the interface between the SNA network and user applications. FRAME A message sent over a network. A frame usually contains data plus address, control, and error-check information. On a LAN, this structure is frequently called a packet. FREE TOKEN A unique sequence of bits transmitted on a token ring network. Each node must wait for the token before it transmits. FRONT-END PROCESSOR (FEP) See communications controller. GATEWAY A network node that operates as an interface between different network types. Also a gateway server. GATEWAY SERVER A personal computer that runs NetWare SNA Gateway or NetWare SNA Gateway ELS software, and has a LAN adapter, and a host interface adapter that enables data transmission between gateway workstations and a host computer. GATEWAY WORKSTATION A personal computer in a LAN that is connected to the gateway server and runs NetWare 3270 LAN Workstation software. HALF-DUPLEX A two-way data transmission mode where data between two points is sent one direction at a time. HOST The controlling computer on a network, similar to a file server on a LAN. In SNA Gateway environments, the host is usually a mainframe or minicomputer. HOST INTERFACE ADAPTER An add-in board for personal computers that can provide direct or remote connections to a host computer. HOST SESSION A temporary logical connection established between two network addressable units; for example, a gateway workstation and a host computer. IBM 3174 A 3270 series cluster controller, introduced in 1987, that can support Category A coaxially-connected devices (in CUT mode or DFT mode, single and multiplexed) and/or Token-Ring devices. IBM 3270 IBM terminals that include models 3278, 3279, 3178 and the 3287 host-addressable printer. IBM 3274 A 3270 series cluster controller, that can support Category A coaxially-connected devices (in CUT mode or DFT mode, single and multiplexed). IBM 37XX FRONT END PROCESSOR A 3270 series IBM front-end processor that includes the 3705, 3720, 3725 and 3745 models. With its associated software, ACF/NCP, the 37XX controls the operation of a number of attached communication lines, which may be operating in a variety of modes and under a variety of protocols. The 3705 is no longer manufactured, but is often used as a non-specific reference for compatible communications. IBM TOKEN RING LAN A local area network access mechanism and topology in which a supervisory frame or token is passed from station to station in sequential order. To gain access to the network, stations must wait for the token to arrive before transmitting data. In a token ring, the next logical station receiving the token is the next physical station on the ring. INTERNETWORK An interconnected group of networks. IPL Initial Program Load. A command used to restart a host computer or a host virtual machine. Similar to reboot on a personal computer. IPX/SPX The Internetwork Packet Exchange/Sequenced Packet Exchange protocol. The Novell communications protocol for transmitting data packets on a LAN installed with NetWare. ISO International Standards Organization. The group that developed the OSI Reference Model. KBPS Kilobits per second. A unit of measure for high-speed data transmission. LAN See local area network. LAYER Part of a network architecture that performs services and passes data to another part. Many network architectures are designed with seven layers, with each layer providing isolated functions. LEASED LINE A dedicated or private line leased for exclusive use. LOCAL AREA NETWORK Also called a LAN. Personal computers and peripherals within a small area (such as a building or part of a building) that are linked so that they share data and resources. LOGICAL LINK The top sublayer of the data link layer. This sublayer control passes data to higher layers; the protocol differs (LLC) according to the network. LOGICAL UNIT A software component of an SNA network that allows a person or application to access the network; also called an LU. To the network, each user (whether a person or an application) is an LU. LU See logical unit. LU6.2 Logical unit type 6.2. In SNA networks, the logical unit that implements distributed processing and peer-to-peer communications. MULTICAST To send a message to more than one user on a network simultaneously. MULTIPLEXER A device that accepts many data lines and combines them into a single, high-speed, composite data stream. NAU Network Addressable Unit. A location in an SNA network that supports one or more ports for communication through the network. NAU SERVICES LAYER The sixth layer of the SNA model. The NAU services layer provides presentation services and session services to user processes. NCP See network control program. NetBIOS Network Basic Input/Output System. A network protocol used on many LANs. The Novell IPX/SPX protocol is a similar protocol. NETWORK ADDRESSABLE UNIT In an SNA network, a logical unit, physical unit or system service control point. NETWORK CONTROL PROGRAM (NCP) Firmware in a communications controller that processes control interrupts for the host. NETWORK LAYER The third layer of the ISO OSI model. The network layer performs switching and routing, especially important in large internetworks. NODE In a network, a physical point where components connect to each other. Loosely, a component of the network. For example, a workstation is a node on a LAN. Cluster controllers or host computers are nodes in SNA networks. Nodes on a LAN are similar to logical units and physical units in SNA networks. OFF-LINE TEST In the NetWare SNA Gateway, a diagnostic test used to check for problems in the connection between the gateway and the host. OSI MODEL Open Systems Interconnection Reference Model. The architecture developed by the ISO to standardize networking and data communications. The OSI model has seven layers: the physical, data link, network, transport, session, presentation, and application layers. The OSI model is frequently used for microcomputer networks, and the SNA model, for IBM host computer networks. PACKET A unit of information sent over a network. A packet contains data and control and address information. Packet is commonly used with microcomputer networks, and frame, with mainframe networks; the terms are synonymous. PATH CONTROL LAYER The third layer of the SNA model. The path control layer handles routing and traffic control. For example, it might group unrelated packets to send to the same address. PATH CONTROL NETWORK The part of an SNA network that links the network units and handles physical transmission. The path control network is similar to the physical and data link layers of the ISO OSI model. PEER PROCESS In a network model, processes operating on the same levels of different computers; for example, on layer 7 of computer A and layer 7 of computer B. PEER-TO-PEER NETWORK A network whose nodes can each act with equal authority, without having a master-slave relationship. PHYSICAL COMMUNICATION The actual transmission of data from one computer to another; this occurs on the physical layer of the OSI or SNA model. PHYSICAL LAYER The hardware connection (for example, cabling) between two computers used for transmitting data. PHYSICAL UNIT (PU) An SNA software component that manages a physical device and represents it to the network. Each PU supports one or more logical units (LUs). The closest microcomputer term is node, although it does not distinguish between physical and logical types. POOLING A method of assigning codes that control host session allocation on LAN workstations. Host sessions can be pooled in one of the three following ways: 1) All workstations use the same access code. 2) All workstations use a unique access code. 3) Some workstations use the same access code. PRESENTATION LAYER The sixth layer of the ISO OSI model. It performs layer frequently used routines, such as translating data between EBCDIC and ASCII. PRESENTATION TRACE A diagnostic trace used in the gateway to check the data flow between the gateway and the workstation. PRIMARY STATION In an SNA network, the station that controls the link and determines when other stations may transmit. Compare secondary station. PROTOCOL A set of rules, including data format and error handling, which governs communication between computers. PU See physical unit. REBOOT To restart a microcomputer. In host systems, this is frequently called an IPL or an IML. RS-232-C An Electronics Industries Association (EIA) standard for a common connection used to attach microcomputers to peripherals. SESSION LAYER The fifth layer of the ISO OSI Model, providing administrative jobs for the network, such as security. SDLC Synchronous Data Link Control. A protocol used to transfer data in SNA environments. SECONDARY STATION In an SDLC configuration, a station that is governed by a primary station. When using the SNA Gateway, the workstations are secondary stations. SESSION A logical connection between two nodes in a network that allows them to exchange messages. SNA See Systems Network Architecture. SNA model The seven-layer model for network operations that is part of the Systems Network Architecture. Compare OSI model. SPX Sequenced Packet Exchange. A protocol that allows two workstations or applications to communicate across the network. SPX uses the Internetwork Packet Exchange (IPX) protocol to deliver the messages. STATUS WORK One of the frame types sent from the gateway server to the host in response to a poll command, indicating the status of the gateway server. SWITCHED LINE Within a network, a line that is switched to establish a continuous pathway between the sender and the receiver. SYNCHRONOUS A data transmission mode that synchronizes entire blocks of data. SYSTEMS NETWORK ARCHITECTURE A set of protocols, message formats, and other specifications developed by IBM that unites several generations of computers, operating systems, peripheral devices, and telecommunications systems. SNA specifies how computer equipment connects and communicates. SYSTEM SERVICE CONTROL POINT An SNA software component that manages the network or a portion of it. TERMINAL A device with a keyboard and a monitor that sends and receives information on a network. A terminal usually cannot function as an independent system. TIC See token ring interface coupler. TOKEN FRAME A structure that contains data on a token ring network. When a node has data to transmit, it replaces a free token with a token frame. TOKEN RING INTERFACE COUPLER (TIC) Device on IBM 3725 or 3745, allowing the use of Token Ring topology for communication with local terminal emulation devices. The IBM 3174 cluster controller provides the same capability by way of its optional token-ring adapter. In many cases, the IBM 3174 will communicate with both the host and the terminal emulation devices via the Token Ring. TRANSMISSION CONTROL LAYER The fourth layer of the SNA network. This layer creates, manages and ends sessions. TRANSPORT LAYER The fourth layer of the ISO OSI model. This layer handles layer the sequencing and guaranteed delivery of packets. VIRTUAL COMMUNICATION Communication between corresponding layers of two computers in a network. For example, between layer 7 of one computer and layer 7 of another. Data is not transmitted directly between the corresponding layers. VIRTUAL TELECOMMUNICATION ACCESS METHOD (VTAM) See ACF/VTAM. WORKSTATION A network device that contains a central processing unit, a keyboard and a monitor. The closest mainframe equivalent is a terminal; however, terminals do not contain CPUs.