This glossary consists of two parts: SNA-related terms and SNA acronyms and abbreviations. Glossary definitions derive from the following IBM documents:
Systems Network Architecture Technical Overview (GC30-3073-2)
Systems Network Architecture Transaction Programmer's Reference Manual for
LU Type 6.2 (GC30-3084-2)
Synchronous Data Link Control Concepts (GA27-3093-3)
Introduction to Advanced Program-to-Program Communication (GG24-1584-01)
A link station that is directly connected to a given node by a link connection over which network traffic can be carried. A station that is connected permits dial-out; a station that is enabled permits dial-in.
A series of interprogram communication services that support distributed transaction processing, as provided by LU 6.2.
A set of tools and routines that permit programmers to write APPC programs using the SNA resources.
A program written for or by a user to process the user's application; in an SNA-network environment, the user is an end user. Contrast with service transaction program.
The verb issued by transaction programs using IRIS SNA SERVER or LU 6.2 to establish a connection with the underlying server.
The unit of control information and data that is transmitted between half-sessions. It consists of a request/response header (RH), followed by a request/response unit (RU).
The unit of control information and data that is passed over a link by data link control.
The unit of control information and data that is transmitted between path control components. A BTU may consist of one or more path information units (PIUs).
The LU-LU half-session defined at session activation as having to request and receive permission from the other LU-LU half-session in order to begin data exchange.
A text file that stores parameters for the configuration-definition verbs in a manner that can be interpreted by the s2_init configuration process.
(1) A system services control point (SSCP), which provides hierarchical control of a group of nodes within a network. (2) A control point local to a specific node that provides control of that node, either in the absence of SSCP control (for type 2.1 nodes engaged in peer-to-peer communications, such as a peripheral node control point, or PNCP) or to supplement SSCP control (such as a physical unit control point, or PUCP).
The logical connection between a pair of transaction programs that permits them to share an LU-LU session serially from transaction to transaction. While a conversation is active, it has exclusive use of an LU-LU session. Once completed, the same session can be used by successive conversations.
In SNA, the combination of the link connection and the link stations joining two adjacent network nodes.
The layer within a half-session that provides specific functions to control the flow of data.
An SNA layer that consists of the link stations that schedule data transfer over a link between two nodes and that perform error control for the link. SDLC is a type of data link control.
Protocols within the transaction services layer by which distributed office-application processes interchange data.
In data communication, pertaining to a simultaneous two-way transmission in both directions. Synonymous with full-duplex as opposed to half-duplex.
The network addressing system that extends the network address from 16 bits to 23 bits. The subarea portion of the address uses 8 bits to address subarea nodes. The element portion uses 15 bits to address resources within each subarea.
The LU-LU half-session defined at session activation as able to begin a transaction without requesting permission from the other LU-LU half-session to do so. Contrast with bidder.
A send-and-receive mode protocol that specifies LUs are able to send and receive requests simultaneously.
The optional control information present in the leading request units (RUs) of an RU chain that allows one half-session in an LU-LU session to perform such functions as: (1) carry a request that a conversation be established between two transaction programs; (2) carry information that relates to an error on the session or conversation; (3) carry LU-LU password verification data; (4) select a destination as the session partner and control the way the end-user data it sends is handled at the destination; (5) change the destination or the characteristics of the data during the session; and (6) transmit status or user information about the destination (for example, whether it is a program or a device) between session partners.
The combination of a gateway node and one or more gateway SSCPs that provides the name translation, network address translation, and SSCP rerouting functions between connected networks.
A send-and-receive mode protocol that specifies session partners must take turns sending and receiving. Half-duplex contention enables LUs to send requests to each other, but not at the same time. Half-duplex flip-flop allows LUs to alternate sending requests to one another. Parameters in the BIND identify one of the LUs as “first speaker.” The first speaker begins in the send state. The other LU becomes the sender when the first speaker sets the change direction indicator (CDI) in the request header of the last RU sent. The two LUs continue to switch between send and receive states until the session is deactivated. Conversations between type 6.2 logical units always use half-duplex flip-flop protocols.
A logical unit located in a host processor; for example, an ACF/TCAM LU consisting of a device message handler, an LU services component, and message control program code.
In an SNA network, the processing unit that contains a system services control point (SSCP).
A data processing system used to prepare programs and operating environments for use on another computer or controller.
Information (I) frames that transfer data. Besides indicating the format, the control field contains send and receive counts. SDLC procedures use the send count to ensure that these frames are received in their proper order; they use the receive count to confirm that received information frames are accepted.
A transmission coding method in which the DTE (data terminal equipment) changes the signal to the opposite state to send a binary 0 and leaves it in the same state to send a binary 1. Invert transmission coding method is also known as NRZI, non-return to zero inverted.
The main background process of the IRIS SNA SERVER that provides full connectivity for such SNA products as IRIS SNA LU 6.2 and IRIS SNA 3770. Synonymous with s2_schd.
The combination of the link connection and the link stations that joins adjacent nodes in a network; for example, a serial-by-bit connection under the control of synchronous data link control (SDLC). Synonymous with data link. A link connection is the physical medium of transmission; for example, a telephone wire or a microwave beam. A link includes the physical medium of transmission, the protocol, and associated communication devices and programming; it is both logical and physical.
The physical equipment that provides two-way communication between link stations; for example, a communication line and data circuit terminating equipment.
A term that distinguishes LUs of a pair with respect to location. Local means residing at the LU from whose perspective an activity is described. See also remote.
An address used in a peripheral node in place of a network address and paired with a network address by the boundary function in a subarea node. See also network address.
A port through which an end user accesses the SNA network in order to communicate with another end user and through which the end user accesses the functions provided by system services control points (SSCPs). An LU can support at least two sessions—one with an SSCP and one with another logical unit—and may be capable of supporting many sessions with other logical units.
Discrete, synchronized operation sequences that make up a distributed transaction. LUWs are used by transaction programs as part of the sync point function. Because these units are indivisible, any failure in an LUW invalidates the entire LUW (that is, all LUW processing by all transaction programs for the transaction). See also sync point function.
A group of logical units with similar characteristics that have been combined for easier allocation.
A level of security used at session activation to verify the identity of the remote LU.
A session between two logical units (LUs) that supports communication between two end users.
The process that begins with a session-initiation request from the logical unit (LU) to a control point and culminates in the activation of an LU-LU session. See also session activation.
The process that begins with a session-termination request from the logical unit (LU) to a control point and culminates in the deactivation of an LU-LU session.
A type of LU that supports sessions between two applications in a distributed data-processing environment using the SNA general data stream, which is a structured-field data stream, or a user-defined data stream.
A set of characteristics that may be associated with a session. Each mode characterizes a group of sessions with a particular partner LU. Multiple modes may exist for the same partner LU. Modes associated with different partner LUs, however, are considered distinct, even if they represent similar sets of characteristics.
An identifier of a set of session parameters for an LU-LU session; the mode name is used as an index into a mode table.
An address, consisting of subarea and element fields that identifies a link, a link station, or a network addressable unit. Subarea nodes use network addresses; peripheral nodes use local addresses. The boundary function in the subarea node to which a peripheral node is attached pairs local addresses with network addresses and vice versa. See also extended network addressing, local address, network name.
A logical unit, a physical unit, or a system services control point. It is the origin or the destination of information transmitted by the path control network. See also network name, network address. Each NAU has a network address that represents it to the path control network. (LUs may have multiple addresses for parallel LU-LU sessions.) The path control network and the NAUs together constitute the SNA network.
The symbolic identifier by which end users refer to a network addressable unit (NAU), a link station, or a link. See also network address.
An endpoint of a link, or a junction common to two or more links in a network. Nodes can be processors, controllers, or workstations. Nodes vary in routing and other functional capabilities. See also node type.
A designation of a node according to the protocols it supports and the network addressable units (NAUs) that it can contain. Five types are defined: 1, 2.0, 2.1, 4, and 5. Type 1, type 2.0, and type 2.1 nodes are peripheral nodes; type 4 and type 5 nodes are subarea nodes. Node types are also referred to by the type of physical unit they contain.
A connection between two nodes that does not have to be established by dialing. Contrast with switched link.
A protocol requested in the form-of-response-requested field of the request header (RH) that directs the receiver of the request not to return any response, regardless of whether or not the request is received and processed successfully.
A technique by which a receiving component controls the rate of transmission by a sending component to prevent overrun or congestion.
Two or more concurrently active sessions between the same two logical units (LUs) using different pairs of network addresses. Each session can have independent session parameters.
The component that manages and monitors the resources (such as attached links and adjacent link stations) of a node, as requested by an SSCP via an SSCP-PU session. Each node of an SNA network contains a physical unit.
Systematic querying of devices to determine operational status, to avoid contention, or to determine readiness to send or receive data.
A response indicating that a request was successfully received and processed. Contrast with negative response.
The logical unit (LU) that sends the Bind Session (BIND) request for a particular LU-LU session. Contrast with secondary logical unit.
A means of passing environment setup information to a target transaction program.
A header, optionally followed by a response unit (RU), that indicates whether the response is positive or negative and that may contain a pacing response.
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), or if negative, contains sense data defining the exception condition.
A term that distinguishes LUs of a pair with respect to location. A remote LU refers to a local LUs actual or potential session partner. See also local.
Submission of a job through an input unit that has access to a computer through a data link.
(1) A message unit that acknowledges receipt of a request; a response consists of a response header (RH), a response unit (RU), or both. (2) In SDLC, the control information (in the C-field of the link header) sent from the secondary station to the primary station.
Programs that are defined by SNA for providing transaction services. See also transaction program. Contrast with application transaction program.
The logical unit (LU) that receives the Bind Session (BIND) request for a particular LU-LU session. Contrast with primary logical unit.
The privileged logical connection used to negotiate the session limits on the other modes.
A logical connection between two network addressable units (NAUs) that can be activated, customized to provide various protocols, and deactivated, as requested. The session-activation request and response can determine options relating to such things as the rate and concurrence of data exchange, the control of contention and error recovery, and the characteristics of the data stream. See also LU-LU session.
The process of exchanging a session-activation request and a positive response between network addressable units (NAUs). See also LU-LU session initiation. Contrast with session deactivation.
The process of exchanging a session deactivation request and response between network addressable units (NAUs). Contrast with session activation.
A flow-control technique that permits a receiving half-session to control the data transfer rate (the rate at which it receives request units). It is used to prevent overloading a receiver with unprocessed requests when the sender can generate requests faster than the receiver can process them. See also pacing.
The maximum number of concurrently active LU-LU sessions a particular logical unit (LU) can support.
The parameters in a session-activation request that specify or constrain the protocols for a session between two network addressable units (NAUs).
One of the types of network services in the system services control point (SSCP) and in a logical unit (LU). These services provide facilities for a logical unit (LU) or a network operator to request that the SSCP initiate or terminate sessions between logical units.
The part of a user-application network that conforms to the formats and protocols of Systems Network Architecture (SNA). It enables reliable transfer of data among end users and provides protocols for controlling the resources of various network configurations. The SNA network consists of network addressable units (NAUs), other optional logical components such as boundary-function components, and the path control network.
A term to distinguish the role of individual transaction programs and LUs of a pair with respect to a conversation. The source transaction program (or its LU) is the initiator of a conversation. See also target.
A link between two nodes that is established by dialing. Contrast with nonswitched link.
A function that allows all transaction programs processing a distributed transaction to coordinate error recovery and maintain consistency among distributed resources, such as data bases.
A discipline for managing synchronous, code-transparent, serial-by-bit, information transfer over a link connection. Transmission exchanges may be full-duplex or half-duplex over switched or nonswitched links. The configuration of the link connection may be point-to-point, multipoint, or loop. SDLC conforms to subsets of the Advanced Data Communication Control Procedures (ADDCP) of the American National Standards Institute (ANSI) and High-level Data Link Control (HDLC) of the International Standards Organization (ISO).
A control point within an SNA network for managing the configuration, coordinating network operator and problem determination requests, and providing directory services and other session services for end users of a network. Multiple SSCPs, cooperating as peers with one another, can divide the network into domains of control, with each SSCP having a hierarchical control relationship to the physical units and logical units within its own domain.
The description of the logical structure, formats, protocols, and operational sequences for transmitting information units through and controlling the configuration and operation of networks.
A term to distinguish the role of individual transaction programs and LUs of a pair with respect to a conversation. The target is the transaction program (or its LU) towards which the source TP or LU directs the conversation. See also source.
An exchange between (1) a workstation and a program, (2) two workstations, or (3) two programs that accomplish a particular action or result.
A program that processes transactions in an SNA network. There are two kinds of transaction programs: application transaction programs and service transaction programs. See also conversation.
The name of the target transaction program to be executed at the remote site. Some programs have been assigned numbers (for example, DIA=0x20F0F0) that are recognized at all sites. The remote site is responsible for converting the requested name into a name known at that site.
Table 1. SNA Acronyms and Abbreviations
Current number of active bidders
Current active sessions
Activate logical unit
Activate physical unit
Adjacent link station
Adjacent link station name
Application program interface
Advanced program-to-program communication
Currently available size of RU to be sent
American National Standard Code for Information Interchange
Length of returned BIND
Basic transmission unit
Buffer length for BIND image
Length of MC buffer
Point to MC buffer
Current maximum sessions
Current minimum number of bidders
Current minimum number of first speakers
Customer information control system
Customer information control system for virtual storage
Configuration network management
Change number of sessions
Correlation wrap count
Control point name
Central processing unit identifier
Destination address field
Length of data
Pointer to data
Data flow control
Document interchange architecture
Disconnect mode information frames
Extended binary coded decimal interchange code
Error recovery procedures
Format and protocol language
Function management data
FMD NS (MA)
Function management network services management services
Function management header
Defined maximum sessions
Defined minimum number of bidders
Defined minimum number of first speakers
General data stream
Initiate session requests
Last in chain
Logical record Length
Local LU name
Local message correlator
Type of record to receive
Local pacing indicator
Link-level message size
LU destination address
Logical unit identifier
Fully qualified LU name
Logical unit security
Logical unit session limits
Logical unit status
Logical unit of work
Logical unit of work conversation correlator
Logical unit of work ID
Logical unit of Work LU name
Logical unit of Work sequence
Maximum number of basic transmission units
Maximum number of I-frames
Maximum number of retries
Maximum number of sessions
Maximum number of transaction programs
Mapped conversation component
Mapper control block
Memory size of SNA server
Minimum number of first-speaker sessions
Minimum number of auto-initiated sessions
Maximum message length
Pointer indicating space for message to be copied.
Maximum RU lower bound
Maximum size of RU to be sent
Maximum RU upper bound
Network addressable unit
Network addressable unit identifier
NAU composite state
Network control program
Non-return on zero
Non-return on zero inverted
Password (also PSWRD)
Size of PI buffer
Program initialization parameters
Partner LU's local name
Fully qualified partner's name
Peripheral node control point
Pointer to the RU structure
Partner's security acceptance
Physical unit control point
Receive sync-point result
Receive sync-point number
Receive sync-point issuer
Request header settings
Remote LU name
Local name for the remote LU
Receiver not ready
Receive pacing count
Request definite response
Request exception response
Ready to receive
Response queue name
Length of RU
RU sequence number
Session control block ID
Synchronous data link control
Secondary logical unit
Systems network architecture
SNA distribution services
SNA service manager
Send sync-point result
Send sync-point number
Send sync-point issuer
Set normal response mode
Session outage notification
Send pacing count
Pointer to the space to be initialized
System services control point
Set and test sequence numbers
Service provider identifier
Transaction program ID
Transmission header settings
Transaction program number
Size of the verb message buffer
Virtual telecommunications access method
What received indicator
Resource service identifier