OSI/AS Programming Manual

Overview of OSI/AS Support for ACSE
Introduction
056783 Tandem Computers Incorporated 1–9
Overview of OSI/AS
Support for ACSE
The procedures described in this manual also provide access to the functions of the
association control service element (ACSE) within the Application Layer (Layer 7) of
the OSI Reference Model. The formal definitions of the ACSE service and protocol are
given in the OSI standards ISO 8649 and ISO 8650. OSI/AS supports version 1 of the
ACSE service and protocol.
The information in the ACSE standards is not duplicated here, except where it is
needed to provide context. The remainder of this subsection briefly outlines the
functions of ACSE and the ACSE support provided by OSI/AS.
What Are the Functions of
ACSE?
The Application Layer provides all functions that imply communication between open
systems and that are not already performed by the lower layers. It includes several
separate groups of functions (application service elements) that fall into two
categories: common application service elements, which apply to a wide variety of
applications, and specific application service elements, which apply to some
particular style of communication. ACSE is one of the common application service
elements defined for the Application Layer.
ACSE provides a means for an OSI application entity to establish a connection
(association) with another application entity. The entities can identify themselves by
means of application entity titles and can specify an application context for the
connection. ACSE provides only a few primitives: those for establishing and releasing
connections. Other primitives are provided by the underlying Presentation Layer.
What ACSE Support Does
OSI/AS Provide?
OSI/AS provides the primitives defined by ACSE for establishing and releasing ACSE
connections.
The following restrictions apply to the use of application entity titles with OSI/AS:
OSI/AS supports only format-2 application entity titles; it does not support
format-1 titles.
OSI/AS does not negotiate the matching of application entity titles in requests and
responses; that task is left up to the application.