HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic SNA Concepts
An independent LU can act as a primary or as a secondary LU when establishing a session.
Multiple and Parallel Sessions
An independent LU can participate in sessions with more than one remote LU at the same time (multiple sessions).
An independent LU can also participate in parallel sessions, or multiple concurrent sessions with the same remote
LU.
Dependent LUs (including dependent LU 6.2) cannot have multiple sessions.
LUs with multiple and parallel sessions are shown in Figure 1–2,
Multiple and Parallel Sessions. LUA and LUB
have parallel sessions. LUA also has multiple sessions: two with LUB and one with LUD. LUD has multiple
sessions with LUA and LUC.
Figure 1–2 Multiple and Parallel Sessions
TP
TP
TP
TP
TP
Parallel Sessions
Multiple Sessions
TP
LUB
LUA
LUC LUD
1.2.8 Conversations
This section applies to LU 6.2 only.
Once a session is established between two LUs, the LU-LU session supports the exchange of information between
two TPs, which have the exclusive use of the session to execute a transaction. This exchange of information is
called a conversation. Only one conversation can use a particular session at a time, but sessions are serially reusable
(many conversations can use the same session, one after another).
To initiate a conversation, a source TP sends a request to its LU, asking it to allocate a conversation with a remote
TP. The invoking TP (or source TP) initiates the conversation, like the calling party in a telephone conversation.
The invokable TP or target TP (the remote TP) is the partner in the conversation, like the party who receives a
telephone call.
As shown in Figure 1–3, Communication between Transaction Programs and Logical Units, information is exchanged
between TPs and LUs to enable one node to communicate with another. Although the TPs appear to be
communicating directly, the LUs on each node are the intermediaries in every exchange.
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