HP-UX SNAplus2 CPI-C Programmer's Guide (June 2003)

Concepts
What Is CPI-C?
Chapter 136
Conversations
The communication between the two programs occurs as a conversation
within the LU-to-LU session. A program can be involved in several
conversations simultaneously.
Contention
When both LUs attempt to allocate a conversation on the same session at
the same time, one must win (the contention winner) and one must lose
(the contention loser). The mode used by the two LUs specifies the
number of contention winner and contention loser sessions for each LU;
the contention winner LU and the contention loser LU are determined
when the session is established.
In a session, the contention loser LU must ask permission from the
contention winner LU before allocating a conversation. The contention
winner may or may not grant permission. The contention winner LU, on
the other hand, simply allocates a conversation when desired.
Characteristics
A conversation has a set of internal values that control the overall
operation of the conversation and the behavior of individual calls. These
values are called characteristics.
CPI-C Calls
A program accesses CPI-C through CPI-C calls. Each call performs a
particular action such as starting or ending a conversation, sending or
receiving data, setting an option that determines how subsequent CPI-C
calls will operate, or obtaining information about the options currently in
use. On each call, the program supplies parameters to CPI-C, which
performs the requested function and returns new parameters to the
program.
The program issuing the call is referred to as the local program; the
other program is referred to as the partner program. Similarly, the LU
serving the local program is the local LU; the LU serving the partner
program is the partner LU.
Programs and LUs residing on other nodes in the network are also called
remote programs and remote LUs.