OSI/AS Programming Manual

1 Introduction
056783 Tandem Computers Incorporated 1–1
This section presents an overview of the Tandem OSI/AS (Open Systems
Interconnection/Application Services) product. It begins by introducing the APS
(application, presentation, and session) procedures, the API (application
programmatic interface), and other significant software components of an OSI/AS
subsystem. It then summarizes the support provided by OSI/AS for the Session,
Presentation, and Application Layers of the OSI Reference Model.
For an explanation of the main concepts underlying the APS procedures, refer to
Section 2. For additional information about the OSI/AS subsystem, refer to the
Tandem OSI/AS Configuration and Management Manual.
What Are the APS
Procedures?
The APS procedures are a set of procedures, provided as part of OSI/AS, that can be
called from your C or TAL application programs. These procedures enable
applications to communicate over session, presentation, and ACSE connections with
one or more remote applications in an OSI environment.
Note The ACSE standards use the word “association” for an ACSE connection, which maps directly onto a
presentation connection. Because of the need to make general statements about connections that apply
to both ACSE and the layers below it, the Tandem OSI manuals use the word “connection” for all layers.
Specifically, the APS procedures allow you to:
Establish, monitor, and release OSI session, presentation, and ACSE connections
Send and receive data over the connections
Use tokens to determine who can initiate operations
Organize work on the connections by means of activities and synchronization
points
Send user exception reports and handle incoming exception reports
The OSI/AS application programmatic interface (API) interprets the requests and
responses specified in APS procedure calls and passes these requests and responses
to various OSI/AS subsystem processes. The API and the OSI/AS subsystem are
described on the following pages.
The APS procedure calls provide a procedural interface to OSI/AS, just as the
Guardian 90 file-system procedures provide a procedural interface to the file system.
As with the file-system procedures, you can call the APS procedures in either wait or
nowait mode, as described under “Wait and Nowait Mode” in Section 2. Note also
that API itself uses the file system by calling the file-system procedures internally.