HP-UX SNAplus2 R7 APPC Programmer's Guide

Concepts
What Is APPC?
1.1.2 Communication between TPs
Many hardware and software elements in the SNA environment are required for two TPs to communicate with each
other. Figure 1–1,
Elements for Writing TPs illustrates the elements that pertain directly to programmers writing
TPs.
Figure 1–1 Elements for Writing TPs
TP A TP B
LU 1 LU 2
Conversation
Session
1.1.3 Logical Unit 6.2
Each TP is associated with a logical unit (LU) on a particular SNAplus2 local node and accesses the network
through that LU. Several TPs can be associated with the same LU. Each LU type uses a specific protocol. APPC
is supported by LU 6.2.
1.1.4 Sessions
Before two TPs can communicate, their LUs must be connected through an LU-to-LU session. An LU-to-LU session
is a logical connection between the two LUs. The session’s mode (set of networking characteristics) determines
how data moves between the two LUs.
1.1.5 Conversations
The communication between the two TPs occurs as a conversation within the LU-to-LU session. A TP can be
involved in several conversations simultaneously.
1.1.6 APPC Verbs
A TP accesses APPC through APPC verbs. The TPs use these verbs to instruct APPC to start a conversation,
send or receive data, and end a conversation. Each verb supplies parameters to APPC, which performs the desired
function and returns parameters to the TP. Some verbs complete quickly, after some local processing (for example
sending a small amount of data); other verbs may take some time to complete, depending on the partner TP and
the communications path (for instance, waiting for data or confirmation from the partner TP).
The TP issuing the verb is referred to as the local TP; the other TP is referred to as the partner TP.
Similarly, the LU serving the local TP is the local LU and the LU serving the partner TP is the partner LU.
TPs and LUs residing on other network nodes are also called remote TPs and remote LUs.
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