SNAX/APC Configuration and Management Manual

SNAX/APC Configuration and Management Manual—138787
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Introduction
SNAX/APC allows programs in a Tandem system to communicate with programs in an
SNA network that support the logical unit session type 6.2 protocol (LU 6.2).
SNAX/APC provides a connection between local transaction programs (TPs) and remote
TPs—transaction programs running on other nodes in the network. SNAX/APC shields
the TP programmer from lower-level SNA protocols, while making the benefits of these
protocols available to programs in the Tandem Expand network through a high-level
interface.
For example, a TP running on a Tandem system can use SNAX/APC to request access to
a TP running on an IBM system. SNAX/APC schedules the allocation of an available
logical unit (LU) on the Tandem system, establishes the connection with the remote LU
type 6.2, and performs all the SNA communication functions throughout the transaction,
including error-handling and termination functions.
SNAX/APC offers support for the LU 6.2 basic and mapped conversation verbs, and
support for single, multiple, and parallel LU-LU sessions.
LU 6.2 and SNAX/APC Concepts
Over the years IBM has developed numerous specific program-to-program
communications methods such as Job Entry Subsystem (JES) and Customer Information
Control System (CICS)—but LU 6.2, in a departure from traditional SNA constructs,
allows a generalized mechanism for program-to-program communication. Typically
used for interactive database access, these transaction programs (TPs) communicate
through the use of Advanced Program-to-Program Communication (APPC) verbs that
form a protocol boundary between the TP and the LU.
LU 6.2 specifically uses the top four layers of the SNA model—transaction services,
presentation services, data flow control, and transmission control. (See Figure 1-1
.)