HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic SNA Concepts
Physical Units
Each SNA node contains a physical unit (PU). The PU manages resources (such as link resources) and supports
communication with a host.
Note
On type 2.1 nodes (which can be APPN nodes), the control point provides PU services
in addition to providing other services (see Section 1.2.6, Network Accessible Units). Two
type 2.1 nodes (such as SNAplus2 nodes) can communicate directly, without requiring the
services of a host to establish communications.
Logical Units
Each SNA node contains one or more logical units (LUs). An LU provides a set of functions that are used by TPs
and end users to provide access to the network. LUs communicate directly with local TPs and devices.
SNA defines several types of LUs, each optimized for a specific class of applications. LUs of different types cannot
communicate with each other, but LUs of the same type can communicate even though they reside on different
kinds of systems.
For example, a TP running on a HP-UX system can communicate with a TP on an AS/400 computer as easily as
it can with a TP on another HP-UX system, as long as both TPs use the same LU type.
SNAplus2 supports the following LU types:
LU 6.2 (for APPC, 5250, APPC Application Suite, and CPI-C)
LU 6.2 supports program-to-program communication in a distributed data processing environment. The LU
6.2 data stream is either an SNA general data stream (GDS), which is a structured-field data stream, or a
user-defined data stream. LU 6.2 can be used for communication between two type 5 nodes, a type 5 node
and a type 2.0 or 2.1 node, or two type 2.1 nodes. (Type 2.1 nodes can serve as APPN nodes.)
This LU type provides more functions and greater flexibility than any other LU type. Unless you are
constrained by existing hardware or software, LU 6.2 is the logical choice when developing new applications.
Note
Only LU 6.2 can provide independent LU functions.
LU 3 (for 3270 printing)
LU 3 supports application programs and printers using the SNA 3270 data stream.
For example, LU 3 can support an application program running under Customer Information Control System
(CICS) and sending data to an IBM 3262 printer attached to an IBM 3174 Establishment Controller.
LU 2 (for 3270 displays)
LU 2 supports application programs and display workstations communicating in an interactive environment
using the SNA 3270 data stream. Type 2 LUs also use the SNA 3270 data stream for file transfer.
For example, the LU 2 protocol can support 3270 emulation programs, which enable workstations to perform
the functions of IBM 3270-family terminals. In addition, LU 2 is used by other programs to communicate
with host applications that normally provide output to 3270 display devices. Such TPs enable the workstation
to achieve a form of cooperative processing with the host.
LU 1 (for SCS printing and RJE)
LU 1 supports application programs and single- or multiple-device data processing workstations communicat-
ing in an interactive, batch-data transfer, or distributed data processing environment. The data streams used
by LU type 1 conform to the SNA character string or Document Content Architecture (DCA).
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