HP-UX SNAplus2 R7 APPC Programmer's Guide

Concepts
What Is APPC?
1.1.7 The Conversation Process
A conversation begins when both of the following happen:
1. One TP (the invoking TP) instructs APPC to start another TP (the invoked TP) and allocate a conversation
between the two TPs.
2. The invoked TP notifies APPC that it is ready to communicate with the invoking TP.
During the conversation, the two TPs exchange status information and application data.
A conversation ends when a TP instructs APPC to deallocate the conversation.
1.1.8 Conversation Types
A conversation can be mapped or basic. At allocation time, the invoking TP specifies whether a conversation
is to be basic or mapped. Certain APPC verbs are used in mapped conversations only; others are used in basic
conversations. You cannot use a basic-conversation verb in a mapped conversation or vice versa.
In general, mapped conversations are used by application TPs. Application TPs are programs that accomplish tasks
for end users. Mapped conversations are less complex than basic conversations. In a mapped conversation, the
sending TP sends one record at a time: the receiving TP receives one record at a time.
Basic conversations are normally used by service TPs. Service TPs are programs that provide services to other
local programs. Basic conversations provide an experienced LU 6.2 programmer with a greater degree of control
over the transmission and handling of data. For more information, see Section 2.11,
Basic Conversations.
1.1.9 Multiple Conversations
A TP can be involved in several conversations simultaneously. Each conversation requires an LU-to-LU session.
A common use of multiple conversations is for an invoked TP to invoke another TP, which, in turn, invokes another
TP, and so on. Figure 1–2, Invoking TPs Using Multiple Conversations shows how TP A invokes TP B, and TP B
then invokes TP C. TPs A and C are not in conversation with each other, but only with TP B.
Figure 1–2 Invoking TPs Using Multiple Conversations
TP A TP B
LU 1 LU 2
Conversation
Session
TP C
LU 3
Conversation
Session
1.1.10 Half-Duplex and Full-Duplex Conversations
Depending on how the two TPs in a conversation need to interact, the conversation can operate in two ways.
Half-duplex
In a half-duplex conversation, control is passed between the two TPs so that one TP is always in control of
the conversation at any time. The controlling TP can send data, or can pass control to the other TP. The other
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