HP-UX SNAplus2 R7 LUA Programmer's Guide

Concepts

LUs and Sessions

An LUA application uses an LU of type 0–3 that communicates with the host system by means of the SNAplus2

node. There are three sessions between the SNAplus2 node and the host node, as follows:

• The physical unit-system services control point (PU-SSCP) session, between the PU 2.1 and the host’s system

services control point (SSCP); this is used for controlling the PU.

• The SSCP session, between the SNAplus2 LU and the SSCP; this is used for controlling the LU.

• The LU session, between the SNAplus2 LU and the host LU; this is used for data transfer between the LU and

the host application.

The LUA application programming interface enables applications to send and receive data on the SSCP session

and on the LU session. It does not provide access to the PU-SSCP session. An LUA application can send data on

this session using the Management Services (MS) verb TRANSFER_MS_DATA; for more information, refer to the

HP-UX SNAplus2 MS Programmer’s Guide.

WINDOWS

For Windows operating systems, TRANSFER_MS_DATA is provided as part of the Common Service Verb (CSV)

API; for more information, refer to the HP-UX SNAplus2 CSV Programmer’s Guide.

UNIX

Figure 1–2, SNA Components Used for RUI Primary Communications, shows the SNA components used for LUA

communications using RUI primary to a downstream LU.

Figure 1–2 SNA Components Used for RUI Primary Communications

Primary RUI

application

LUA LU

Node

LUA

application

Downstream

LU Session

SSCP Session

PU-SSCP Session

An RUI Primary application uses an LU of type 0–3 that communicates with the downstream LU by means of the

SNAplus2 node. From the point of the downstream LU, the SNAplus2 LU acts as the host LU, and the SNAplus2

node acts as the host SSCP. The three sessions between these components, and the restrictions on access to these

sessions, are equivalent to those for an LUA application communicating with a host.

Each of the LU sessions provides two priorities of messages: normal and expedited. Expedited ﬂow messages take

precedence over other messages waiting to be transmitted on the same session. There are four different ﬂows on

which a message can be sent or received:

• SSCP session, expedited ﬂow

• LU session, expedited ﬂow

• SSCP session, normal ﬂow