Skip to main content

IBM Systems  >   System z  >   z/VM  >  

Copyright © 1987-02


This glossary describes the most common terms associated with TCP/IP communication in an internet environment, as used in the VM environment. Some terms and definitions are also included from standards organizations and comittees such as the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). For more detailed information, see About This Glossary.

For abbreviations, the definition usually consists only of the words represented by the letters; for complete definitions, see the entries for the words.

Last updated 01/14/2002.

Select a term

You can choose a letter of the alphabet, or choose "Numerics" to locate a term that begins with a number.


The abnormal termination of a program or task.

abstract syntax
A description of a data structure that is independent of machine-oriented structures and encodings.

Abstract Syntax Notation One (ASN.1)
The OSI language for describing abstract syntax.

active gateway
A gateway that is treated like a network interface in that it is expected to exchange routing information, and if it does not do so for a period of time, the route associated with the gateway is deleted.

active open
The state of a connection that is actively seeking a service. Contrast with passive open.

A piece of hardware that connects a computer and an external device.
An auxiliary device or unit used to extend the operation of another system.

The unique code assigned to each device or workstation connected to a network. A standard internet address uses a two-part, 32-bit address field. The first part of the address field contains the network address; the second part contains the local address.

address mask
A bit mask used to select bits from an Internet address for subnet addressing. The mask is 32 bits long and selects the network portion of the Internet address and one or more bits of the local portion. It is sometimes called a subnet mask.

address resolution
A means for mapping network layer addresses onto media-specific addresses. See ARP.

Address Resolution Protocol (ARP)
A protocol used to dynamically bind an internet address to a hardware address. ARP is implemented on a single physical network and is limited to networks that support broadcast addressing.

address space
A collection of bytes that are allocated, and in many ways managed, as a single entity by CP. Each byte within an address space is identified by a unique address. An address space represents an extent of storage available to a program. Address spaces allocated by VM range in size from 64KB to 2GB.

Advanced Interactive Executive (AIX)
IBM's licensed version of the UNIX operating system.

Advanced Program-to-Program Communications (APPC)
The interprogram communication service within SNA LU 6.2 on which the APPC/VM interface is based

Advanced Research Projects Agency (ARPA)
Now called DARPA, its the U.S. Government agency that funded the ARPANET.

Advanced Research Projects Agency Network (ARPANET)
A packet switched network developed in the early 1970's that is the forerunner of today's Internet. It was decommissioned in June 1990.

As defined in the SNMP architecture, an agent, or an SNMP server is responsible for performing the network management functions requested by the network management stations.

Advanced Interactive Executive.

American National Standard Code for Information Interchange (ASCII)
The standard code, using a coded character set consisting of 7-bit coded characters (8 bits including parity check), used for information interchange among data processing systems, data communication systems, and associated equipment. The ASCII set consists of control characters and graphic characters.
The default file transfer type for FTP, used to transfer files that contain ASCII text characters.

American National Standards Institute (ANSI)
An organization consisting of producers, consumers, and general interest groups that establishes the procedures by which accredited organizations create and maintain voluntary industry standards in the United States. ANSI is sponsored by the Computer and Business Equipment Manufacturer Association and is responsible for establishing voluntary industry standards.

American National Standards Institute.

Application Program Interface.

Advanced Program-to-Program Communications.

The use to which an information processing system is put, for example, a payroll application, an airline reservation application, a network application.

application layer
The seventh layer of the OSI (Open Systems Interconnection) model for data communication. It defines protocols for user or application programs.

Application Program Interface (API)
The formally defined programming-language interface between an IBM system control program or licensed program and its user. APIs allow programmers to write application programs that use the TCP, UDP, and IP layers of the TCP/IP protocol suite.

A parameter passed between a calling program and a called program.

Address Resolution Protocol.

Advanced Research Projects Agency.

Advanced Research Projects Agency Network.

American National Standard Code for Information Interchange.
The default file transfer type for FTP, used to transfer files that contain ASCII text characters.

Abstract Syntax Notation One.


asynchronous (ASYNC)
Without regular time relationship; unexpected or unpredictable with respect to the execution of program instruction. See synchronous.

asynchronous communication
A method of communication supported by the operating system that allows an exchange of data with remote device, using either a start-stop line or an X.25 line. Asynchronous communications include the file transfer and the interactive terminal facility support.

Athena Widgets
The X Window widget set developed by MIT for Project Athena.

Attachment Unit Interface (AUI)
Connector used with thick Ethernet that often includes a drop cable.

Attachment Unit Interface.

attention key
A function key on terminals that, when pressed, causes an I/O interruption in the processing unit.

authentication server
The service that reads a Kerberos database to verify that a client making a request for access to an end-service is the client named in the request. The authentication server provides an authenticated client ticket as permission to access the ticket-granting server.

Information encrypted by a Kerberos authentication server that a client presents along with a ticket to an end-server as permission to access the service.

The right granted to a user to communicate with, or to make use of, a computer system or service.

top of page

In a local area network multiple-bridge ring configuration, a high-speed link to which rings are connected by means of bridges. A backbone can be configured as a bus or as a ring.
In a wide area network, a high-speed link to which nodes or data switching exchanges (DSES) are connected.

background task
A task with which the user is not currently interacting, but continues to run.

Characteristic of any network technology that uses a single carrier frequency and requires all stations attached to the network to participate in every transmission. See broadband.

Basic Encoding Rules (BER)
Standard rules for encoding data units described in ASN.1. Sometimes incorrectly grouped under the term ASN.1, which correctly refers only to the abstract description language, not the encoding technique.

Basic Input/Output System (BIOS)
A set of routines that permanently resides in read-only memory (ROM) in a PC. The BIOS performs the most basic tasks, such as sending a character to the printer, booting the computer, and reading the keyboard.

An accumulation of data to be processed.
A group of records or data processing jobs brought together for processing or transmission.
Pertaining to activity involving little or no user action. See interactive

Bayonet Neill-Concelman (BNC)
A standardized connector used with Thinnet and coaxial cable.

Because It's Time NETwork (BITNET)
A network of hosts that use the Network Job Entry (NJE) protocol to communicate. The network is primarily composed of universities, nonprofit organizations, and research centers. BITNET has recently merged with the Computer and Science Network (CSNET) to form the Corporation for Research and Educational Networking (CSNET). See CSNET.

Basic Encoding Rules.

Berkeley Software Distribution (BSD)
Term used when describing different versions of the Berkeley UNIX software, as in "4.3BSD UNIX".

Byte File System.

A format for storage or transmission of binary data in which the most significant bit (or byte) comes first. The reverse convention is little-endian.

Basic Input/Output System.

Because It's Time NETwork.

A denial-of-service attack in which the TCP/IP stack is flooded with SYN packets that have spoofed source IP addresses and port numbers that match the destination IP addresses and port numbers. The Blat attack also has the URG flag turned on in the TCP header and has the ability to incrementally spoof the source IP address. Blat is a version of the Land attack.

A string of data elements recorded, processed, or transmitted as a unit. The elements can be characters, words, or physical records.

blocking mode
If the execution of the program cannot continue until some event occurs, the operating system suspends the program until that event occurs.

Bayonet Neill-Concelman.

Bootstrap Protocol Daemon

Bootstrap Protocol Daemon
The Bootstrap Protocol (BOOTP) allows a diskless client machine to discover its own IP address, the address of a server host, and the name of a file to be loaded into memory and executed.

A router that connects two or more networks and forwards packets among them. The operations carried out by a bridge are done at the physical layer and are transparent to TCP/IP and TCP/IP routing.
A functional unit that connects two local area networks (LANs) that use the same logical link control (LLC) procedures but may use different medium access control (MAC) procedures.

Characteristic of any network that multiplexes multiple, independent network carriers onto a single cable. This is usually done using frequency division multiplexing. Broadband technology allows several networks to coexist on one single cable; traffic from one network does not interfere with traffic from another, because the "conversations" happen on different frequencies in the ether, similar to a commercial radio system.

The simultaneous transmission of data packets to all nodes on a network or subnetwork.

broadcast address
An address that is common to all nodes on a network.

Berkeley Software Distribution.

bus topology
A network configuration in which only one path is maintained between stations. Any data transmitted by a station is concurrently available to all other stations on the link.

The method of sorting bytes under specific machine architectures. Of the two common methods, little endian byte ordering places the least significant byte first. This method is used in Intel** microprocessors. In the second method, big endian byte ordering, the most significant byte is placed first. This method is used in Motorola** microprocessors.

top of page


Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
The access method used by local area networking technologies such as Ethernet.

A condition in which entries for an entry field must conform to a specific lowercase, uppercase, or mixed-case format to be valid.

Comite Consultatif International Telegraphique et Telephonique.

A path in a system that connects a processor and main storage with an I/O device.

pertaining to attachment of devices directly by data channels (I/O channels) to a computer.
Pertaining to devices attached to a controlling unit by cables, rather than by telecommunication lines.
Synonymous with local, locally attached.

The sum of a group of data associated with the group and used for checking purposes.

Customer Information Control System.

Class A network
An internet network in which the high-order bit of the address is 0. The host number occupies the three, low-order octets.

Class B network
An internet network in which the high-order bit of the address is 1, and the next high-order bit is 0. The host number occupies the two low-order octets.

Class C network
An internet network in which the two high-order bits of the address are 1 and the next high-order bit is 0. The host number occupies the low-order octet.

Common Link Access to Workstation.

A function that requests services from a server, and makes them available to the user.
In z/OS, an address space that is using TCP/IP services.

client-server model
A common way to describe network services and the model user processes (programs) of those services. Examples include the name server and resolver paradigm of the DNS and file server/file client relationships such as NFS and diskless hosts.

client-server relationship
Any device that provides resources or services to other devices on a network is a server. Any device that employs the resources provided by a server is a client. A machine can run client and server processes at the same time.

Command List.

Create Link Pack Area.

Conversational Monitor System.

Comite Consultatif International Telegraphicque et Telephonique (CCITT)
The International Telegraph and Telephone Consultative Committee. A unit of the International Telecommunications Union (ITU) of the United Nations. CCITT produces technical standards, known as"recommendations," for all internationally controlled aspects of analog and digital communication.

The name and any parameters associated with an action that can be performed by a program. The command is entered by the user; the computer performs the action requested by the command name.

Command List (CLIST)
A list of commands and statements designed to perform a specific function for the user.

command prompt
A displayed symbol, such as İC:\¨ that requests input from a user.

Common Link Access to Workstation (CLAW)
A continuously executing duplex channel program designed to minimize host interrupts while maximizing channel utilization.

communications adapter
A hardware feature that enables a computer or device to become a part of a data network.

community name
A password used by hosts running Simple Network Management Protocol (SNMP) agents to access remote network management stations.

To translate a program written in a high-level language into a machine language program.
The computer actions required to transform a source file into an executable object file.

A program that translates a source program into an executable program (an object program).

Computer and Science Network (CSNET)
A large computer network, mostly in the U.S. but with international connections. CSNET sites include universities, research labs, and some commercial companies. It is now merged with BITNET to form CREN. See BITNET.

An association established between functional units for conveying information.
The path between two protocol modules that provides reliable stream delivery service. In an internet, a connection extends from a TCP module on one machine to a TCP module on the other.

Control Program (CP)
The z/VM operating system that manages the real processor's resources and is responsible for simulating select operating systems for individual users.

conversational monitor system (CMS)
A virtual machine operating system that provides general interactive time sharing, problem solving, and program development capabilities, and operates only under control of the z/VM control program.

Corporation for Research and Educational Networking (CREN)
A large computer network formed from the merging of BITNET and CSNET. See BITNET and CSNET.

Control Program.

Create Link Pack Area (CLPA)
A parameter specified at startup, which says to create the link pack area.

Corporation for Research and Educational Networking.

Carrier Sense Multiple Access with Collision Detection.


Computer and Science Network.
Customer Information Control System (CICS)

An IBM-licensed program that enables transactions entered at remote terminals to be processed concurrently by user written application programs. It includes facilities for building, using, and maintaining databases.

top of page


A background process usually started at system initialization that runs continuously and performs a function required by other processes. Some daemons are triggered automatically to perform their task; others operate periodically.

Direct Access Storage Device.

Defense Advanced Research Projects Agency.

An IBM relational database management system for the OS/390 or z/OS operating system.

database administrator (DBA)
An individual or group responsible for the rules by which data is accessed and stored. The DBA is usually responsible for database integrity, security, performance and recovery.

A basic unit of information that is passed across the internet, it consists of one or more data packets.

data link layer
Layer 2 of the OSI (Open Systems Interconnection) model; it defines protocols governing data packetizing and transmission into and out of each node.

data set
The major unit of data storage and retrieval in z/OS, consisting of a collection of data in one of several prescribed arrangements and described by control information to which the system has access. Synonymous with file in VM and OS/2.


Database administrator.

Double Byte Character Set.

Defense Data Network.

The unscrambling of data using an algorithm that works under the control of a key. The key allows data to be protected even when the algorithm is unknown. Data is unscrambled after transmission.

A value, attribute, or option that is assumed when none is explicitly specified.

Defense Advanced Research Projects Agency (DARPA)
The U.S. government agency that funded the ARPANET.

Defense Data Network (DDN)
Comprises the MILNET and several other Department of Defense networks.

destination node
The node to which a request or data is sent.

Direct Access Storage Device (DASD)
A device in which access to data is independent of where data resides on the device.

A named grouping of files in a file system.

Disk Operating System (DOS)
An operating system for computer systems that use disks and diskettes for auxiliary storage of programs and data.

display terminal
An input/output unit by which a user communicates with a data-processing system or sub-system. Usually includes a keyboard and always provides a visual presentation of data; for example, an IBM 3179 display.

Distributed Program Interface (DPI)
A programming interface that provides an extension to the function provided by the SNMP agents.

Dynamic Link Library.

Domain Name System.

In an internet, a part of the naming hierarchy. Syntactically, a domain name consists of a sequence of names (labels) separated by periods (dots).

Domain Name System (DNS)
A system in which a resolver queries name servers for resource records about a host.

domain naming
A hierarchical system for naming network resources.

Denial of Service.

Disk Operating System.

dotted-decimal notation
The syntactic representation for a 32-bit integer that consists of four 8-bit numbers, written in base 10 and separated by periods (dots). Many internet application programs accept dotted decimal notations in place of destination machine names.

double-byte character set (DBCS)
A set of characters in which each character is represented by two bytes. Languages such as Japanese, Chinese, Korean, which contain more symbols than can be represented by 256 code points, require double-byte character sets. Because each character requires 2 bytes, the typing, display, and printing of DBCS characters requires hardware and programs that support DBCS.

A contiguous sequence of bits or characters that comprises two computer words and is capable of being addressed as a unit.

Distributed Program Interface.

Dynamic Host Configuration Protocol Daemon

Dynamic Host Configuration Protocol Daemon
The Dynamic Host Configuration Protocol (DHCP) provides a framework for passing configuation information to hosts on a TCP/IP network. DHCP is based on the Bootstrap Protocol (BOOTP), adding the capability of automatic allocation of reusable network addresses and additional configuration options.

dynamic resource allocation
An allocation technique in which the resources assigned for execution of computer programs are determined by criteria applied at the moment of need.

dynamic link library (DLL)
A module containing dynamic link routines that is linked at load or run time.

top of page


Extended binary-coded decimal interchange code.

Exterior Gateway Protocol.

A process used by layered protocols in which a lower-level protocol accepts a message from a higher-level protocol and places it in the data portion of the low-level frame. As an example, in Internet terminology, a packet would contain a header from the physical layer, followed by a header from the network layer (IP), followed by a header from the transport layer (TCP), followed by the application protocol data.

The scrambling or encoding of data using an algorithm that works under the control of a key. The key allows data to be protected even when the algorithm is unknown. Data is scrambled prior to transmission.

ES/9370 Integrated Adapters
An adapter you can use in TCP/IP for VM to connect into Token-Ring networks and Ethernet networks, as well as TCP/IP networks that support X.25 connections.

The name given to a local area packet-switched network technology invented in the early 1970s by Xerox**, Incorporated. Ethernet uses a Carrier Sense Multiple Access/Collision Detection (CSMA/CD) mechanism to send packets.

In a VM operating system, a user-written command file that contains CMS commands, other user-written commands, and execution control statements, such as branches.

extended binary-coded decimal interchange code (EBCDIC)
A coded character set consisting of 8-bit coded characters.

extended character
A character other than a 7-bit ASCII character. An extended character can be a 1-bit code point with the 8th bit set (ordinal 128-255) or a 2-bit code point (ordinal 256 and greater).

Exterior Gateway Protocol (EGP)
A reachability routing protocol used by gateways in a two-level internet.

eXternal Data Representation (XDR)
A standard developed by Sun Microsystems, Incorporated for representing data in machine-independent format.

top of page


File Allocation Table.

Fiber Distributed Data Interface. Also used to abbreviate Fiber Optic Distributed Data Interface.

Fiber Distributed Data Interface (FDDI)
The ANSI standard for high-speed transmission over fiber optic cable.

Fiber Optic Network
A network based on the technology and standards that define data transmission using cables of glass or plastic fibers carrying visible light. Fiber optic network advantages are: higher transmission speeds, greater carrying capacity, and lighter, more compact cable.

In z/VM, a named set of records stored or processed as a unit. Synonymous with data set in z/OS.

File Allocation Table (FAT)
A table used to allocate space on a disk for a file.

File Transfer Access and Management (FTAM)
An application service element that enables user application processes to manage and access a file system, which may be distributed.

File Transfer Protocol (FTP)
A TCP/IP protocol used for transferring files to and from foreign hosts. FTP also provides the capability to access directories. Password protection is provided as part of the protocol.

foreign host
Any machine on a network that can be interconnected.

foreign network
In an internet, any other network interconnected to the local network by one or more intermediate gateways or routers.

foreign node
See foreign host.

The portion of a tape on a line perpendicular to the reference edge, on which binary characters can be written or read simultaneously.

File Transfer Access and Management.

File Transfer Protocol.

A computer word. In System/370, 32 bits or 4 bytes.

top of page


A windowless graphical object that looks like its equivalent like-named widget but does not support the translations, actions, or pop-up widget children supplied by that widget.

A functional unit that interconnects a local data network with another network having different protocols.
A host that connects a TCP/IP network to a non-TCP/IP network at the application layer. See also router.

gather and scatter data
Two related operations. During the gather operation, data is taken from multiple buffers and transmitted. In the scatter operation, data is received and stored in multiple buffers.

Graphics Context.

See Graphics Context.

Group Control System.

Graphical Data Display Manager.

Graphical Data Display Manager interface for X Window System. A graphical interface that formats and displays alphanumeric, data, graphics, and images on workstation display devices that support the X Window System.

Graphics data file.

Graphical Display Data Manager (GDDM)
A group of routines that allows pictures to be defined and displayed procedurally through function routines that correspond to graphic primitives.

Graphics Context (GC)
The storage area for graphics output. Also known as GC and GContext. Used only with graphics that have the same root and depth as the graphics content.

Group Control System (GCS)
A component of z/VM, consisting of a shared segment that you can In itial Program Load (IPL) and run in a virtual machine. It provides simulated z/OS services and unique supervisor services to help support a native SNA network.

top of page


A temporary data representation that identifies a file.

A contiguous sequence of bits or characters that constitutes half a fullword and can be addressed as a unit.

Houston automatic spooling priority system.

High-level Data Link Control.

header file
A file that contains constant declarations, type declarations, and variable declarations and assignments. Header files are supplied with all programming interfaces.

High-level Data Link Control (HDLC)
An ISO protocol for X.25 international communication.

High Performance File System (HPFS)
An OS/2 file management system that supports high-speed buffer storage, long file names, and extended attributes.

hop count
The number of gateways or routers through which a packet passes on its way to its destination.

A computer connected to a network, which provides an access method to that network. A host provides end-user services and can be a client, a server, or a client and server simultaneously.

Houston automatic spooling priority system (HASP)
A computer program that provides supplementary job management, data management, and task management functions such as control of job flow, ordering of tasks, and spooling.

High Performance File System.

HYPERchannel Adapter
A network interface used to connect a TCP/IP for z/VM or z/OS host into an existing TCP/IP HYPERchannel network, or to connect TCP/IP hosts togethe to create a TCP/IP HYPERchannel network.

top of page


Internet Activities Board.

Internet Control Message Protocol.

Institute of Electrical and Electronic Engineers.

Internet Engineering Task Force.

Interior Gateway Protocol.

include file
A file that contains preprocessor text, which is called by a program, using a standard programming call. Synonymous with header file.

Internet Message Access Protocol.

Information Management System.

Information Management System (IMS)
A database/data communication (DB/DC) system that can manage complex databases and networks.

initial program load (IPL)
The initialization procedure that causes an operating system to commence operation.

Indicates a label that is used to distinguish among the variations of the principal name. An instance allows for the possibility that the same client or service can exist in several forms that require distinct authentication.

Institute of Electrical and Electronic Engineers (IEEE)
An electronics industry organization.

Integrated Services Digital Network (ISDN)
A digital, end-to-end telecommunication network that supports multiple services including, but not limited to, voice and data.

Pertaining to a program or a system that alternately accepts input and then responds. An interactive system is conversational; that is, a continuous dialog exists between user and system. See batch.

Interior Gateway Protocol (IGP)
The protocol used to exchange routing information between collaborating routers in the Internet. RIP is an example of an IGP.

The largest internet in the world consisting of large national backbone nets (such as MILNET, NSFNET, and CREN) and a myriad of regional and local campus networks all over the world. The Internet uses the Internet protocol suite. To be on the Internet, you must have IP connectivity (be able to TELNET to, or PING, other systems). Networks with only electronic mail connectivity are not actually classified as being on the Internet.

Internet Activities Board (IAB)
The technical body that oversees the development of the Internet suite of protocols (commonly referred to as TCP/IP). It has two task forces (the IRTF and the IETF) each charged with investigating a particular area.

Internet address
A 32-bit address assigned to hosts using TCP/IP. An internet address consists of a network number and a local address. Internet addresses are represented in a dotted-decimal notation and are used to route packets through the network.

Internet Engineering Task Force (IETF)
One of the task forces of the IAB. The IETF is responsible for solving short-term engineering needs of the Internet.

International Organization for Standardization (ISO)
An organization of national standards bodies from various countries established to promote development of standards to facilitate international exchange of goods and services, and develop cooperation in intellectual, scientific, technological, and economic activity.

internet or internetwork
A collection of packet switching networks interconnected by gateways, routers, bridges, and hosts to function as a single, coordinated, virtual network.

internet address
The unique 32-bit address identifying each node in an internet. See also address.

Internet Control Message Protocol (ICMP)
The part of the Internet Protocol layer that handles error messages and control messages.

Internet Protocol (IP)
The TCP/IP layer between the higher level host-to-host protocol and the local network protocols. IP uses local area network protocols to carry packets, in the form of datagrams, to the next gateway, router, or destination host.

The capability of different hardware and software by different vendors to effectively communicate together.

Inter-user communication vehicle (IUCV)
A VM facility for passing data between virtual machines and VM components.

intrinsics X-Toolkit
A set management mechanism that provides for constructing and interfacing between composite X Window widgets, their children, and other clients. Also, intrinsics provide the ability to organize a collection of widgets into an application.

Internet Protocol

IP datagram
The fundamental unit of information passed across the Internet. An IP datagram contains source and destination addresses along with data and a number of fields that define such things as the length of the datagram, the header checksum, and flags to say whether the datagram can be (or has been) fragmented.

Initial Program Load.

Integrated Services Digital Network.

International Organization for Standardization.

Inter-User Communication Vehicle.

top of page


Job Control Language.

Job Entry Subsystem.

Japanese Institute of Standards.

Job Control Language (JCL)
A problem-oriented language designed to express statements in a job that are used to identify the job or describe its requirements to an operating system.

Job Entry Subsystem (JES)
An IBM System/390 licensed program that receives jobs into the system and processes all output data produced by the jobs.

The Japanese Academic and Research Network that connects various UNIX operating systems.

top of page


A graphic character set consisting of symbols used in Japanese ideographic alphabets. Each character is represented by 2 bytes.

A character set of symbols used on one of the two common Japanese phonetic alphabets, which is used primarily to write foreign words phonetically. See also kanji.

A system that provides authentication service to users in a network environment.

Kerberos Authentication System
An authentication mechanism used to check authorization at the user level.

Kiss-of-Death (KOD)
An IGMP based denial-of-service attack that depletes the stack's large envelopes. See KOX.


An IGMP based denial-of-service attack that depletes the stack's large envelopes and also has source IP address spoofing. KOX is a version of the Kiss-of-Death (KOD) attack.

top of page


The client that communicates with the OS/2 Presentation Manager to manage mail on the network.

Local area network.

A denial-of-service attack in which the TCP/IP stack is flooded with SYN packets that have spoofed source IP addresses and port numbers that match the destination IP addresses and port numbers. See Blat.

Line Printer Client (LPR)
A client command that allows the local host to submit a file to be printed on a remote print server.

Line Printer Daemon (LPD)
The remote printer server that allows other hosts to print on a printer local to your host.

A format for storage or transmission of binary data in which the least significant bit (or byte) comes first. The reverse convention is big-endian.

Local Location Broker.

local area network (LAN)
A data network located on the user's premises in which serial transmission is used for direct data communication among data stations.

local host
In an internet, the computer to which a user's terminal is directly connected without using the internet.

Local Location Broker (LLB)
In Network Computing System (NCS) Location Broker, a server that maintains information about objects on the local host and provides the Location Broker forwarding facility.

local network
The portion of a network that is physically connected to the host without intermediate gateways or routers.

logical character delete symbol
A special editing symbol, usually the at (@) sign, which causes CP to delete it and the immediately preceding character from the input line. If many delete symbols are consecutively entered, the same number of preceding characters are deleted from the input line.

Logical Unit (LU)
An entity addressable within an SNA-defined network. LUs are categorized by the types of communication they support.

Line Printer Daemon.

Line Printer Client.

Logical Unit.

LU-LU session
In SNA, a session between two logical units (LUs). It provides communication between two end users, or between an end user and an LU services component.

LU type
In SNA, the classification of an LU-LU session in terms of the specific subset of SNA protocols and options supported by the logical units (LUs) for that session.

top of page


Media Access Control.

mail gateway
A machine that connects two or more electronic mail systems (often different mail systems on different networks) and transfers messages between them.

Management Information Base (MIB)
A standard used to define SNMP objects, such as packet counts and routing tables, that are in a TCP/IP environment.

The process of relating internet addresses to physical addresses in the network.

A pattern of characters used to control retention or elimination of portions of another pattern of characters.
To use a pattern of characters to control retention or elimination of another pattern of characters.
A pattern of characters that controls the keeping, deleting, or testing of portions of another pattern of characters.

Maximum Transmission Unit (MTU)
The largest possible unit of data that can be sent on a given physical medium.

media access control (MAC)
The method used by network adapters to determine which adapter has access to the physical network at a given time.

Message Handling System (MHS)
The system of message user agents, message transfer agents, message stores, and access units that together provide OSI electronic mail.

Message Handling System.

Management Information Base.

A code, representing the instructions of an instruction set, which is implemented in a part of storage that is not program-addressable.

Military Network.

Military Network (MILNET)
Originally part of the ARPANET, MILNET was partitioned in 1984 to make it possible for military installations to have reliable network service, while the ARPANET continued to be used for research. See DDN.

Logical divisions of a physical direct access storage device.

modem (modulator/demodulator)
A device that converts digital data from a computer to an analog signal that can be transmitted on a telecommunication line, and converts the analog signal received to data for the computer.

see OSF/Motif**.

Multiple Protocol Routing. Implements the OSPF protocol described in RFC 158 items.

Maximum Transmission Unit.

The simultaneous transmission of data packets to a group of selected nodes on a network or subnetwork.

multiconnection server
A server that is capable of accepting simultaneous, multiple connections.

Multiple Virtual Storage (MVS)
Implies the MVS/ESA product.

A mode of operation that provides for the concurrent performance execution of two or more tasks.

Multiple Virtual Storage.

top of page


Network Address Translation.

name server
The server that stores resource records about hosts.

National Science Foundation (NSF)
Sponsor of the NSFNET.

National Science Foundation Network (NSFNET)
A collection of local, regional, and mid-level networks in the U.S. tied together by a high-speed backbone. NSFNET provides scientists access to a number of supercomputers across the country.

Network Computing Kernel.

Network Control Program.

Network Computing System.

Network Database.

Network Driver Interface Specification.

This device keyword specifies that this device is a 3172 LAN Channel Station that supports IBM Enterprise-Specific SNMP Management Information Base (MIB) variables for 3172. TCP/IP for VM supports SNMP GET and SNMP GETNEXT operations to request and retrieve 3172 Enterprise-Specific MIB variables. These requests are answered only by those 3172 devices with the NETMAN option in the PROFILE TCPIP file.

A system 390-based, IBM-licensed program used to monitor, manage, and diagnose the problems of a network.

An arrangement of nodes and connecting branches. Connections are made between data stations. Physical network refers to the hardware that makes up a network. Logical network refers to the abstract organization overlaid on one or more physical networks. An internet is an example of a logical network.

network adapter
A physical device, and its associated software, that enables a processor or controller to be connected to a network.

network administrator
The person responsible for the installation, management, control, and configuration of a network.

Network Computing Kernel (NCK)
In the Network Computing System (NCS), the combination of the remote procedure call runtime library and the Location Broker.

Network Computing System (NCS)
A set of software components developed by Apollo, Incorporated, that conform to the Network Computing Architecture (NCA). NCS is made up of two parts: the nidl compiler and Network Computing Kernel (NCK). NCS is a programming tool kit that allows programmers to distribute processing power to other hosts.

Network Control Program (NCP)
An IBM-licensed program that provides communication controller support for single-domain, multiple-domain, and interconnected network capability.

network database (NDB)
An IBM-licensed program that provides communication controller support for single-domain, multiple-domain, and interconnected network capability. NDB allows interoperability among different database systems, and uses RPC protocol with a client/server type of relationship. NDB is used for data conversion, security, I/O buffer management, and transaction management.

Network Driver Interface Specification (NDIS)
An industry-standard specification used by applications as an interface with network adapter device drivers.

network elements
As defined in the SNMP architecture, network elements are gateways, routers, and hosts that contain management agents responsible for performing the network management functions requested by the network management stations.

network file system (NFS)
The NFS protocol, which was developed by Sun Microsystems, Incorporated, allows computers in a network to access each other's file systems. Once accessed, the file system appears to reside on the local host.

Network Information Center (NIC)
Originally there was only one, located at SRI International and tasked to serve the ARPANET (and later DDN) community. Today, there are many NICs operated by local, regional, and national networks all over the world. Such centers provide user assistance, document service, training, and more.

Network Interface Definition Language (NIDL)
A declarative language for the definition of interfaces that has two forms, a Pascal-like syntax and a C-like syntax. NIDL is a component of the Network Computing Architecture.

Network Job Entry (NJE)
In object distribution, an entry in the network job table that specifies the system action required for incoming network jobs sent by a particular user or group of users. Each entry is identified by the user ID of the originating user or group.

network layer
Layer 3 of the Open Systems Interconnection (OSI) model; it defines protocols governing data routing.

network management stations
As defined in the SNMP architecture, network management stations, or SNMP clients, execute management applications that monitor and control network elements.

Network file system.

Network Information Center.

Network Interface Definition Language.

Network Job Entry.

In a network, a point at which one or more functional units connect channels or data circuits.
In a network topology, the point at an end of a branch.

nonblocking mode
If the execution of the program cannot continue until some event occurs, the operating system does not suspend the program until that event occurs. Instead, the operating system returns an error message to the program.

X.25 NCP Packet Switching Interface.

National Science Foundation.

National Science Foundation Network.

top of page


A byte composed of eight binary elements.

OfficeVision (OV)
IBM's new proprietary, integrated office management system used for sending, receiving, and filing electronic mail, and a variety of other office tasks. OfficeVision replaces PROFS.

Offload host
Any device that is handling the TCP/IP processing for the z/OS host where TCP/IP for z/OS is installed. Currently, the only supported Offload host is the 3172-3.

Offload system
Represents both the z/OS host where TCP/IP for z/OS is installed and the Offload host that is handling the TCP/IP Offload processing.

open system
A system with specified standards and that therefore can be readily connected to other systems that comply with the same standards.

Open Systems Interconnection (OSI)
The interconnection of open systems in accordance with specific ISO standards.
The use of standardized procedures to enable the interconnection of data processing systems.

Operating System/2 (OS/2)
Pertaining to the IBM licensed program that can be used as the operating system for personal computers. The OS/2 licensed program can perform multiple tasks at the same time.

Operating System/2.

OSF/Motif is an X Window System toolkit defined by Open Software Foundation, Inc. (OSF), which enables the application programmer to include standard graphic elements that have a 3-D appearance. Performance of the graphic elements is increased with gadgets and windowless widgets.

Open Systems Interconnection.

Open Shortest Path First. An Interior Gateway Protocol that distributes routing information within a single Autonomous System.

out-of-band data
Data that is placed in a secondary channel for transmission. Primary and secondary communication channels are created physically by modulation on a different frequency, or logically by specifying a different logical channel. A primary channel can have a greater capacity than a secondary one.


top of page


A sequence of binary digits, including data and control signals, that is transmitted and switched as a composite whole.

Packet Switching Data Network (PSDN)
A network that uses packet switching as a means of transmitting data.

A variable that is given a constant value for a specified application.

To analyze the operands entered with a command.

passive open
The state of a connection that is prepared to provide a service on demand. Contrast with active open.

Partitioned data set (PDS)
A data set in direct access storage that is divided into partitions, called members, each of which can contain a program, part of a program, or data.

Personal computer.

Personal Channel Attach.

PC Network
A low-cost, broadband network that allows attached IBM personal computers, such as IBM 5150 Personal Computers, IBM Computer ATs, IBM PC/XTs, and IBM Portable Personal Computers to communicate and to share resources.

Partitioned data set.

Public Data Network.

Protocol data unit.

In network architecture, any functional unit that resides in the same layer as another entity.

Personal Channel Attach (PCA)
see Personal System Channel Attach.

Personal Computer (PC)
A microcomputer primarily intended for stand-alone use by an individual.
Personal System Channel Attach (PSCA)
An adapter card to connect a micro-channel based personal computer (or processor) to a System/370 parallel channel.

physical layer
Layer 1 of the Open Systems Interconnection (OSI) model; it details protocols governing transmission media and signals.

physical unit (PU)
In SNA, the component that manages and monitors the resources, such as attached links and adjacent link stations, associated with a node, as requested by an SSPC via an SSPC-PU session. An SSPC activates a session with the physical unit in order to indirectly manage, through the PU, resources of the node such as attached links.

The command that sends an ICMP Echo Request packet to a host, gateway, or router with the expectation of receiving a reply.

Presentation Manager.

In OS/2, the 3270 client terminal emulation program that is invoked by the PMANT command.

On a multipoint connection or a point-to-point connection, the process whereby data stations are invited one at a time to transmit.
Interrogation of devices for such purposes as to avoid contention, to determine operational status, or to determine readiness to send or receive data.

Post Office Protocol.

An endpoint for communication between devices, generally referring to a logical connection.
A 16-bit number identifying a particular Transmission Control Protocol or User Datagram Protocol resource within a given TCP/IP node.

Synonymous with Portmapper.

A program that maps client programs to the port numbers of server programs. Portmapper is used with Remote Procedure Call (RPC) programs.

Post Office Protocol (POP)
A protocol used for exchanging network mail.

presentation layer
Layer 6 of the Open Systems Interconnections (OSI) model; it defines protocols governing data formats and conversions.

Presentation Manager (PM)
A component of OS/2 that provides a complete graphics-based user interface, with pull-down windows, action bars, and layered menus.

principal name
Specifies the unique name of a user (client) or service.

A standard that defines how text and graphics are presented on printers and display devices.

A unique, finite course of events defined by its purpose or by its effect, achieved under defined conditions.
Any operation or combination of operations on data.
A function being performed or waiting to be performed.
A program in operation; for example, a daemon is a system process that is always running on the system.

Professional Office Systems (PROFS)
IBM's proprietary, integrated office management system used for sending, receiving, and filing electronic mail, and a variety of other office tasks. PROFS has been replaced by OfficeVision. See OfficeVision.

Professional Office Systems.

A set of semantic and syntactic rules that determines the behavior of functional units in achieving communication. Protocols can determine low-level details of machine-to-machine interfaces, such as the order in which bits from a byte are sent; they can also determine high-level exchanges between application programs, such as file transfer.

Protocol data unit (PDU)
A set of commands used by the SNMP agent to request management station data.

protocol suite
A set of protocols that cooperate to handle the transmission tasks for a data communication system.

Personal System Channel Attach.

Packet Switching Data Network.

Physical unit.

Public Data Network (PDN)
A network established and operated by a telecommunication administration or by a Recognized Private Operating Agency (RPOA) for the specific purpose of providing circuit-switched, packet-switched, and leased-circuit services to the public.

top of page


A line or list formed by items in a system waiting for service; for example, tasks to be performed or messages to be transmitted. To arrange in, or form, a queue.

top of page


A denial-of-service attack in which TCP packets are sent to the stack with no header flags set. R4P3D is an augmented version of the Stream attack.

Resource access control facility.

Reverse Address Resolution Protocol.

read-only access
An access mode associated with a virtual disk directory that lets a user read, but not write or update, any file on the disk directory.

read/write access
An access mode associated with a virtual disk directory that lets a user read and write any file on the disk directory (if write authorized).

One of the three parts of a Kerberos name. The realm specifies the network address of the principal name or instance. This address must be expressed as a fully qualified domain name, not as a "dot numeric" internet address.

A process involving numerous steps, in which the output of each step is used for the successive step.

reduced instruction-set computer (RISC)
A computer that uses a small, simplified set of frequently used instructions for rapid execution.

Routing Daemon.

The attribute of a program or routine that allows the same copy of a program or routine to be used concurrently by two or more tasks.

Remote Execution Protocol (REXEC)
A protocol that allows the execution of a command or program on a foreign host. The local host receives the results of the command execution. This protocol uses the REXEC command.

remote host
A machine on a network that requires a physical link to interconnect with the network

remote logon
The process by which a terminal user establishes a terminal session with a remote host.

Remote Procedure Call (RPC)
A facility that a client uses to request the execution of a procedure call from a server. This facility includes a library of procedures and an eXternal data representation.

Remote Spooling Communications Subsystem (RSCS)
An IBM-licensed program that transfers spool files, commands, and messages between VM users, remote stations, and remote and local batch systems, through HASP-compatible telecommunication facilities.

Request For Comments (RFC)
A series of documents that covers a broad range of topics affecting internetwork communication. Some RFCs are established as internet standards.

A program or subroutine that obtains information from a name server or local table for use by the calling program.

resource access control facility (RACF)
An IBM-licensed program that provides for access control by identifying and by verifying the users to the system, authorizing access to protected resources, logging the detected unauthorized attempts to enter the system, and logging the detected accesses to protected resources.

resource records
Individual records of data used by the Domain Name System. Examples of resource records include the following: a host's Internet Protocol addresses, preferred mail addresses, and aliases.

response unit (RU)
In SNA, a message unit that acknowledges a request unit. It may contain prefix information received in a request unit. If positive, the response unit may contain additional information such as session parameters in response to BIND SESSION. If negative, it contains sense data defining the exception condition.

Restructured Extended Executor (REXX) language
A general purpose programming language, particularly suitable for EXEC procedures, XEDIT macros, or programs for personal computing. Procedures, XEDIT macros, and programs written in this language can be interpreted by the Procedures Language VM/REXX interpreter.

return code
A code used to influence the execution of succeeding instructions.
A value returned to a program to indicate the results of an operation requested by that program.

Reverse Address Resolution Protocol (RARP)
A protocol that maintains a database of mappings between physical hardware addresses and IP addresses.

Remote Execution Protocol.

Restructured Extended Executor language.

Request For Comments.

Routing Information Protocol.

Reduced instruction-set computer.

A device that connects networks at the ISO Network Layer. A router is protocol-dependent and connects only networks operating the same protocol. Routers do more than transmit data; they also select the best transmission paths and optimum sizes for packets. In TCP/IP, routers operate at the Internetwork layer. See also gateway.

Routing Information Protocol (RIP)
The protocol that maintains routing table entries for gateways, routers, and hosts.

routing table
A list of network numbers and the information needed to route packets to each.

Remote Procedure Call.

Remote Spooling Communications Subsystem.

Response unit.

top of page


Systems Application Architecture.

Single Byte Character Set.

Synchronous data link control.

The OS/2 mail server that uses Simple Mail Transfer Protocol to route mail from one host to another host on the network.

serial line
A network media that is a de facto standard, not an international standard, commonly used for point-to-point TCP/IP connections. Generally, a serial line consists of an RS-232 connection into a modem and over a telephone line.

The relationships of characters or groups of characters to their meanings, independent of the manner of their interpretation and use.
The relationships between symbols and their meanings.

A function that provides services for users. A machine can run client and server processes at the same time.

Shared File System.

Simple Mail Transfer Protocol (SMTP)
A TCP/IP application protocol used to transfer mail between users on different systems. SMTP specifies how mail systems interact and the format of control messages they use to transfer mail.

Simple Network Management Protocol (SNMP)
A protocol that allows network management by elements, such as gateways, routers, and hosts. This protocol provides a means of communication between network elements regarding network resources.

simultaneous peripheral operations online (SPOOL)
(Noun) An area of auxiliary storage defined to temporarily hold data during its transfer between peripheral equipment and the processor.
(Verb) To use auxiliary storage as a buffer storage to reduce processing delays when transferring data between peripheral equipment and the processing storage of a computer.

single-byte character set (SBCS)
A character set in which each character is represented by a one-byte code. Contrast with double-byte character set.

Structure for Management Information.

Simple Mail Transfer Protocol.

A denial-of-service attack in which an ICMP Echo Request is sent to a broadcast or multicast address. There are three variants of the Smurf attack. See Smurf-IC, Smurf-OB, and Smurf-RP.

A denial-of-service attack in which an ICMP Echo Request is sent to a broadcast or multicast address. "IC" denotes that incoming packets are using the TCP/IP stack to launch an attack. See Smurf-OB and Smurf-RP.

A denial-of-service attack in which an ICMP Echo Request is sent to a broadcast or multicast address. "OB" denotes that an outbound ICMP Echo Request matched the description of a Smurf attack. See Smurf-IC and Smurf-RP.

A denial-of-service attack in which an ICMP Echo Request is sent to a broadcast or multicast address. "RP" denotes that the ICMP Echo Reply packets being received by the stack do not match any Echo Requests that were sent. See Smurf-IC and Smurf-OB.

Systems Network Architecture.

SNA Network Link.

SNA Network Link
An SNA network link function of TCP/IP for z/VM and z/OS hosts running TCP/IP to communicate through an existing SNA backbone.

Simple Network Management Protocol.

Start of authority record.

An endpoint for communication between processes or applications.
A pair consisting of TCP port and IP address, or UDP port and IP address.

socket address
An address that results when the port identification number is combined with an internet address.

socket interface
An application interface that allows users to write their own applications to supplement those supplied by TCP/IP.

Simultaneous peripheral operations online.

The processing of files created by or intended for virtual readers, punches, and printers. The spool files can be sent from one virtual device to another, from one virtual machine to another, and to read devices.

Structured Query Language.

Structured Query Language/Data System.

start of authority record (SOA)
In the Domain Name System, the resource record that defines a zone.

A continuous sequence of data elements being transmitted, or intended for transmission, in character or binary-digit form, using a defined format.

A denial-of-service attack in which TCP packets are sent to the stack with no header flags set. See R4P3D.

Structured Query Language (SQL)
Fourth generation English-like programming language used to perform queries on relational databases.

Structured Query Language/Data System (SQL/DS)
An IBM relational database management system for the VM and VSE operating systems.

Structure for Management Information (SMI)
The rules used to define the objects that can be accessed through a network management protocol. See also MIB.

In the SNMP architecture, a subagent provides an extension to the utility provided by the SNMP agent.

A directory contained within another directory in a file system hierarchy.

A networking scheme that divides a single logical network into smaller physical networks to simplify routing.

subnet address
The portion of the host address that identifies a subnetwork.

subnet mask
A mask used in the IP protocol layer to separate the subnet address from the host portion of the address.

Synonymous with subnet.

A secondary or subordinate system, usually capable of operating independent of, or asynchronously with, a controlling system.


synchronous (SYNC)
Pertaining to two or more processes that depend on the occurrences of a specific event such as common timing signal.
Occurring with a regular or predictable time relationship. See asynchronous.

synchronous data link control (SDLC)
A data link over which communication is conducted using the synchronous data protocol.

A denial-of-service attack in which the initiator floods the TCP/IP stack with SYN packets that have spoofed source IP addresses, resulting in the server never receiving the final ACKs needed to complete the three-way handshake in the connection process.

Systems Application Architecture (SAA)
A formal set of rules that enables applications to be run without modification in different computer environments.

Systems Network Architecture (SNA)
The description of the logical structure, formats, protocols, and operational sequences for transmitting information units through, and controlling the configuration and operation of, networks.

top of page


An interactive messaging system that sends messages between the local host and a foreign host.

Transmission Control Protocol.

Transmission Control Protocol/Internet Protocol.

The Terminal Emulation Protocol, a TCP/IP application protocol for remote connection service. Telnet allows a user at one site to gain access to a foreign host as if the user's terminal were connected directly to that foreign host.

terminal emulator
A program that imitates the function of a particular kind of terminal.

Terminate and Stay Resident (TSR) program
A TSR is a program that installs part of itself as an extension of DOS when it is executed.

Trivial File Transfer Protocol.

Trivial File Transfer Protocol Daemon

Trivial File Transfer Protocol Daemon
The TFTP daemon (TFTPD server) transfers files between the Byte File System (BFS) and TFTP clients. TFTPD supports access to files maintained in a BFS directory structure that is mounted.

Encrypted information obtained from a Kerberos authentication server or a ticket-granting server. A ticket authenticates a user and, in conjunction with an authenticator, serves as permission to access a service when presented by the authenticated user.

ticket-granting server
Grants Kerberos tickets to authenticated users as permission to access an end-service.

Time Sharing Option (TSO)
An operating system option; for System/390 system, the option provides interactive time sharing from remote terminals

time stamp
To apply the current system time.
The value on an object that is an indication of the system time at some critical point in the history of the object.
In query, the identification of the day and time when a query report was created that query automatically provides on each report.

An informally defined protocol for transmitting 3270 data streams over Telnet.

In a local network, the symbol of authority passed among data stations to indicate the station temporarily in control of the transmission medium.

See bus topology.

token ring
As defined in IEEE 802.5, a communication method that uses a token to control access to the LAN. The difference between a token bus and a token ring is that a token-ring LAN does not use a master controller to control the token. Instead, each computer knows the address of the computer that should receive the token next. When a computer with the token has nothing to transmit, it passes the token to the next computer in line.

token-ring network
A ring network that allows unidirectional data transmission between data stations by a token-passing procedure over one transmission medium, so that the transmitted data returns to the transmitting station.

Transmission Control Protocol (TCP)
The TCP/IP layer that provides reliable, process-to-process data stream delivery between nodes in interconnected computer networks. TCP assumes that IP (Internet Protocol) is the underlying protocol.

Transmission Control Protocol/Internet Protocol (TCP/IP)
A suite of protocols designed to allow communication between networks regardless of the technologies implemented in each network.

transport layer
Layer 4 of the Open Systems Interconnection (OSI) model; it defines protocols governing message structure and some error checking.

An unsolicited message that is sent by an SNMP agent to an SNMP network management station.

Trivial File Transfer Protocol (TFTP)
A TCP/IP application primarily used to transfer files among personal computers. TFTP allows files to be sent and received, but does not provide any password protection or directory capability.

Time Sharing Option.

Terminate and stay resident. TSR usually refers to a terminate-and-stay-resident program.

top of page


User Datagram Protocol.

A function that uses the services provided by a server. A host can be a user and a server at the same time. See client

User Datagram Protocol (UDP)
A datagram level protocol built directly on the IP layer. UDP is used for application-to-application programs between TCP/IP hosts.

user exit
A point in an IBM-supplied program at which a user routine may be given control.

user profile
A description of a user, including user ID, user name, defaults, password, access authorization, and attributes.

top of page


virtual address
The address of a location in virtual storage. A virtual address must be translated into a real address to process the data in processor storage.

Virtual Machine (VM)
A licensed software operating system that manages the resources of a real processor to provide virtual machines to end users. As a time-sharing system control program (CP), the conversational monitor system (CMS), the group control system (GCS), and the Dump Viewing facility (DVF).

Virtual Machine Communication Facility (VMCF)
A connectionless mechanism for communication between address spaces.

Virtual Machine/ESA (VM/ESA)
An IBM-licensed program that manages the resources of a single computer so that multiple computing systems appear to exist. Each virtual machine is the functional equivalent of a real machine.

virtual storage
Storage space that can be regarded as addressable main storage by the user of a computer system in which virtual addresses are mapped into real addresses. The size of virtual storage is limited by the addressing scheme of the computing system and by the amount of auxiliary storage available, not by the actual number of main storage locations.

Virtual Telecommunications Access Method (VTAM)
An IBM-licensed program that controls communication and the flow of data in an SNA network. It provides single-domain, multiple-domain, and interconnected network capability.

Virtual Machine

Virtual Machine Communication Facility.

Virtual Machine/Enterprise System Architecture

Virtual Machine Serviceability Enhancements Staged/Extended.

Virtual Telecommunications Access Method.

top of page


Wide area network.

well-known port
A port number that has been preassigned for specific use by a specific protocol or application. Clients and servers using the same protocol communicate over the same well-known port.

wide area network (WAN)
A network that provides communication services to a geographic area larger than that served by a local area network.

The basic data type of the X Window System Toolkit. Every widget belongs to a widget class that contains the allowed operations for that corresponding class.

An area of the screen with visible boundaries through which a panel or portion of a panel is displayed.

working directory
The directory in which an application program is found. The working directory becomes the current directory when the application is started.

top of page


X Client
An application program which uses the X protocol to communicate windowing and graphics requests to an X Server.

eXternal Data Representation.

The CMS facility, containing the XEDIT command and XEDIT subcommands and macros, that lets a user create, change, and manipulate CMS files.

X Server
A program which interprets the X protocol and controls one or more screens, a pointing device, a keyboard, and various resources associated with the X Window System, such as Graphics Contexts, Pixmaps, and color tables.

X Window System
The X Window System is a protocol designed to support network transparent windowing and graphics. TCP/IP for z/VM and Z/OS provides client support for the X Window System application program interface.

X Window System API
An application program interface designed as a distributed, network-transparent, device-independent, windowing and graphics system.

X Window System Toolkit
Functions for developing application environments.

A CCITT communication protocol that defines the interface between data terminal equipment and packet switching networks.

X.25 NCP Packet Switching Interface (X.25 NPSI)
An IBM-licensed program that allows users to communicate over packet switched data networks that have interfaces complying with Recommendation X.25 (Geneva** 1980) of the CCITT. It allows SNA programs to communicate with SNA equipment or with non-SNA equipment over such networks.

top of page


To modify or dump an individual text file/data set using the ZAP command or the ZAPTEXT EXEC.

ZAP disk
The virtual disk in the VM operating system that contains the user-written modifications to VTAM code.

In the Domain Name System, a zone is a logical grouping of domain names that is assigned to a particular organization. Once an organization controls its own zone, it can change the data in the zone, add new tree sections connected to the zone, delete existing nodes, or delegate new subzones under its zone.

top of page


IBM Interconnect Controller.


IBM Establishment Controller.

Refers to a series of IBM display devices; for example, the IBM 3275, 3276 Controller Display station, 3277,3278, and 3279 Display Stations, the 3290 Information Panel, and the 3287 and 3286 printers. A specific devicetype is used only when a distinction is required between device types. Information about display terminal usage alsorefers to the IBM 3138, 3148, and 3158 Display Consoles when used in display mode, unless otherwise noted.

37xx Communication Controller
A network interface used to connect a TCP/IP for z/VM or z/OS network that supports X.25 connections. NCP with X.25 NPSI must be running in the controller, and VTAM must be running on the host.

IBM Network Processor.

IBM LAN Station.

Refers to a series of processors, namely the IBM 9373 Model 20, the IBM 9375 Models 40 and 60, and the IBM 9377 Model 90 and other models.

top of page