z/OS Communications Server Glossary Version2Release1 Glossary This glossary provides terms and definitions for the z/OS Communications Server software and products. For other terms and definitions, see the IBM Terminology website. Numerics 31-bit storage addressing An addressing structure introduced with the MVS/XA operating system that supports addressing up to 2 GB of real and virtual memory, in addition to the prior support for 24-bit addressing. The architecture has since been extended with 64-bit addressing. 3270 data stream The commands, control codes, orders, attributes, and data or structured fields for 3270 devices, that are transmitted inbound to an application program or outbound to a terminal. A AAL See ATM adaptation layer. AARP See AppleTalk Address Resolution Protocol. abend See abnormal end of task. abend dump A dump that is produced when a program ends abnormally. ABM 1. See activity based management. 2. See asynchronous balanced mode. abnormal end of task (abend) The termination of a task, job, or subsystem because of an error condition that recovery facilities cannot resolve during execution. abnormal termination A system failure or operator action that causes a job to end unsuccessfully. ABR See area border router. abstract syntax A data specification that includes all distinctions that are needed in data transmissions, but that omits (abstracts) other details such as those that depend on specific computer architectures. See also Abstract Syntax Notation One, Basic Encoding Rules. Abstract Syntax Notation One (ASN.1) 1. The international standard for defining the syntax of information data. It defines a number of simple data types and specifies a notation for referencing these types and for specifying values of these types. The ASN.1 notations can be applied whenever it is necessary to define the © Copyright IBM Corporation 2013 © IBM Corporation 2000, 2013 1 abstract syntax of information without constraining in any way how the information is encoded for transmission. See also Basic Encoding Rules. 2. In open systems interconnection (OSI), a notation for defining data structures and data types. The notation is defined in international standards ISO 8824/ITU X.208 and ISO 8825/ITU X.209. See also abstract syntax. ACB 1. See application control block. 2. See adapter control block. 3. See access method control block. ACB address space In VTAM, the address space in which the access method control block (ACB) is opened. See also associated address space, session address space. ACB-based macroinstruction In VTAM, a macroinstruction whose parameters are specified by the user in an access method control block. ACB macroinstruction See ACB-based macroinstruction. ACB name A name that is specified either on the VTAM APPL definition statement or on the VTAM application program's access method control block (ACB) macroinstruction. See also network name. accelerator In a user interface, a key or combination of keys that invokes an application-defined function. accept An action in which a listener receives a connection request. access The ability to read, update, or otherwise use a resource. Access to protected resources is usually controlled by system software. access barred In data communication, a condition in which a data terminal equipment (DTE) cannot call the DTE identified by the selection signals. access control In computer security, the process of ensuring that users can access only those resources of a computer system for which they are authorized. access control list (ACL) In computer security, a list associated with an object that identifies all the subjects that can access the object and their access rights. access method A technique for moving data between main storage and input/output devices. access method control block (ACB) A control block that links an application program to Virtual Storage Access Method (VSAM) or Virtual Telecommunications Access Method (VTAM). access method services (AMS) A multifunction utility named IDCAMS that is used to manage catalogs, devices, and both VSAM and non-VSAM data sets. 2 z/OS Communications Server Glossary access procedure The protocol used to gain access to a shared resource; for example, in a local area network, the shared resource is the transmission medium. The medium access protocol specified by the IEEE 802 standard are CSMA/CD token bus and token ring. access register (AR) A register through which one address space accesses the data in another address space or data space. access register mode (AR mode) The address space control mode in which the system uses general-purpose registers and the corresponding access register (AR) to resolve an address in an address space or a data space. See also address space control mode. access unit A unit that allows attaching devices to access a local area network (LAN) at a central point, such as a wiring closet or an open work area. ACDI See Asynchronous Communications Device Interface. ACF See Advanced Communications Function. ACF/NCP See Advanced Communications Function for the Network Control Program. ACF/SSP See Advanced Communications Function for the System Support Programs. ACF/TAP See Advanced Communications Function/Trace Analysis Program. ACF/TCAM See Advanced Communications Function for the Telecommunications Access Method. ACF/VTAM See Advanced Communications Function for Virtual Telecommunications Access Method. ACK See acknowledgment. acknowledgment (ACK) The transmission of acknowledgment characters as a positive response to a data transmission. ACL See access control list. ACO See automated console operation. acquire 1. In VTAM, to take over resources that were formerly controlled by an access method in another domain or to resume control of resources that were controlled by that domain but released. See also release, resource takeover. 2. In a VTAM application program, to initiate and establish a session with another logical unit (LU). The acquire process begins when the application program issues a macroinstruction. See also accept. action A defined task that an application performs on an object as a result of an event. See also rule. Glossary 3 ActionMedia II (IBM PS/2 ActionMedia II) An IBM MultiMedia solution that uses Digital Video Interactive (DVI) technology. Capture and playback adapters provide digital video and audio. activate To make a resource ready to perform its function. See also deactivate. activate link In SNA, a command used to initiate link activation. activate logical unit (ACTLU) In SNA, a command used to activate a logical unit. activate physical unit (ACTPU) In SNA, a command used to activate a physical unit. active 1. In VTAM, pertaining to a major or minor node that has been activated by VTAM. Most resources are activated as part of VTAM start processing or as the result of a VARY ACT command. See also pending active session. 2. Pertaining to a node or device that is connected or is available for connection to another node or device. 3. Pertaining to a resource that is currently operational. See also inoperative. 4. Pertaining to a file, page, or program that is in main storage or memory, as opposed to a file, page, or program that must be retrieved from auxiliary storage. active application The application subsystem that is currently in an extended recovery facility (XRF) session with a terminal user. See also alternate application. active gateway A gateway that is treated like a network interface in that it is expected to exchange routing information. If it does not do so for a period of time, the route associated with the gateway is deleted. active link A link that is currently available for transmission of data. active monitor In a token-ring network, a function performed at any one time by one ring station that initiates the transmission of tokens and provides token error recovery facilities. Any active adapter on the ring has the ability to provide the active monitor function if the current active monitor fails. active open In TCP/IP, the state of a connection that is actively providing a service. See also passive open. active program Any program that is loaded and ready to be executed. active window The window with which a user is currently interacting. This is the window that receives keyboard input. It is distinguishable by the unique color of its title bar and border. 4 z/OS Communications Server Glossary activity based management (ABM) A method for managing activities to increase both their value to customers and company profit. ACTLU See activate logical unit. ACTPU See activate physical unit. ACU See automatic calling unit. adapter A mechanism for connecting two unlike parts or machines, or for electrically or physically connecting a device to a computer or to another device. adapter control block (ACB) In NCP, a control block that contains line control information and the states of I/O operations for BSC lines, SS lines, or SDLC links. adaptive compression Data row compression that encompasses classic row compression and the compression that is provided by automatically maintained page-level dictionaries. adaptive pacing See adaptive session-level pacing. adaptive rate-based congestion control (ARB congestion control) An exchange of information between connection endpoints that is used to estimate congestion as part of the ARB algorithm. adaptive session-level pacing A form of session-level pacing in which session components exchange pacing windows that may vary in size during the course of a session. This allows transmission within a network to adapt dynamically to variations in availability and demand of buffers on a session-by-session basis. Session-level pacing occurs within independent stages along the session path according to local congestion at the intermediate and endpoint nodes. See also fixed session-level pacing, session-level pacing. adaptive session pacing See adaptive session-level pacing. address A unique code or identifier for a register, device, workstation, system, or storage location. address aliasing See network address translation. address class In Internet communications, the categorization by the part of an IP address that distinguishes the network address from the host address.