z/OS Communications Server
Version 2 Release 1
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.
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.
AAL See ATM adaptation layer.
AARP See AppleTalk Address Resolution Protocol.
abend See abnormal end of task.
A dump that is produced when a program ends abnormally.
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.
A system failure or operator action that causes a job to end unsuccessfully.
ABR See area border router.
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
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
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.
In VTAM, a macroinstruction whose parameters are specified by the user
in an access method control block.
See ACB-based macroinstruction.
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.
In a user interface, a key or combination of keys that invokes an
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.
In data communication, a condition in which a data terminal equipment
(DTE) cannot call the DTE identified by the selection signals.
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.
A technique for moving data between main storage and input/output
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
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.
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.
See Advanced Communications Function for the Network Control
See Advanced Communications Function for the System Support Programs.
See Advanced Communications Function/Trace Analysis Program.
See Advanced Communications Function for the Telecommunications
See Advanced Communications Function for Virtual Telecommunications
ACK See acknowledgment.
The transmission of acknowledgment characters as a positive response to a
ACL See access control list.
ACO See automated console operation.
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
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.
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
To make a resource ready to perform its function. See also deactivate.
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.
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
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
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.
The application subsystem that is currently in an extended recovery facility
(XRF) session with a terminal user. See also alternate application.
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.
A link that is currently available for transmission of data.
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.
In TCP/IP, the state of a connection that is actively providing a service. See
also passive open.
Any program that is loaded and ready to be executed.
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.
See activate logical unit.
See activate physical unit.
ACU See automatic calling unit.
A mechanism for connecting two unlike parts or machines, or for
electrically or physically connecting a device to a computer or to another
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.
Data row compression that encompasses classic row compression and the
compression that is provided by automatically maintained page-level