OSI/AS Configuration and Management Manual

Introduction
OSI/AS Configuration and Management Manual—424119-001
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Access to ACSE, Presentation Layer, and Session
Layer
Access to ACSE, Presentation Layer, and Session Layer
Application programs can directly request and receive ACSE services through the API,
via APS procedure calls. The API procedures provide application programmers with a
procedural interface to the subsystems ACSE, Presentation Layer, and Session Layer
services.
Transport Layer Access
Compaq OSI/TS provides a programmatic interface that allows application programs to
use Transport Layer services directly. This interface uses standard Guardian file-system
procedures such as CLOSE, CONTROL, OPEN, SETMODE, SETPARAM, and
WRITEREAD to manage transport connections and transfer data; for a detailed
description, see the OSI/TS Configuration and Management Manual.
Network Layer Access
X25AM and TLAM (for D-series releases) or PAM (for G06 and above releases) also
provide programmatic interfaces that allow applications to bypass the upper layers and
the Transport Layer and use Network Layer or Data Link Layer services directly. For
descriptions of these interfaces, see the X.25 Access Method (X25AM) Manual, the
Multilan/TLAM Programming Manual, or the PAM Configuration and Management
Manual.
Selecting Processes
When a user application requests an ACSE, presentation, or session connection, or if it
is waiting for an incoming connection request, the OSI manager process:
1. Selects an NSP process to provide Network Layer services
2. Selects a TSP process to provide Transport Layer services
3. Selects a TAPS process to provide Session Layer services, Presentation Layer
services, and/or ACSE services
The three processes selected then serve all requests for that user until the user releases
that connection. Any combination of an NSP process, a TSP process, and a TAPS
process within a single subsystem can be bound together in this way to service a
connection. The OSI manager uses LDIB information in the MIB, along with other
address configuration information, to select the protocol processes that service a given
user during a connection.