OSI/AS Programming Manual

OSI Upper-Layer Concepts
APS Procedures Programming Concepts
2–18 056783 Tandem Computers Incorporated
If you are using the OSI/AS implementation of ACSE, you must not propose a
presentation context for ACSE itself in the connect request; OSI/AS will supply it in
the presentation context definition list. OSI/AS supplies the following presentation
context for ACSE:
Abstract syntax:
{ joint-iso-ccitt association-control (2) abstract-syntax (1)
apdus (0) version1 (1)
}
Transfer syntax (BER):
{ joint-iso-ccitt asn1 (1) basic-encoding (1) }
You can propose up to 15 other presentation contexts for an ACSE connection.
The called application decides which of the transfer syntax names is to be used for
each presentation context, and returns this information in the presentation context
definition result list. The presentation context definition result list indicates the
acceptance or rejection of each of the presentation context definitions proposed in the
presentation context definition list. The presentation context definition result list is set
in a presentation or ACSE connect response through a call to
APS_ASSOC_CONNECTRSP_. It can be retrieved in a presentation or ACSE connect
indication and confirm with a call to APS_ASSOC_GETPARAM_.
The presentation default context result in a connect response indicates your
acceptance or rejection of the presentation default context name, if one is specified.
How the Presentation Context Definition Result List Is Set
The following paragraphs explain how the fields in the presentation context definition
result list are set by OSI/AS in a connect indication, by your application in a connect
response, and by OSI/AS in a connect confirm.
In a Connect Indication. Because OSI/AS does not perform encoding on behalf of the
application, you must decide which of the proposed transfer syntax names is to be
used in each presentation context. This approach differs from the approach specified
in the OSI standards, which expects the Presentation Layer to make the decision.
In the connect indication, OSI/AS sets the number of elements in the presentation
context definition result list to the same number that appears in the presentation
context definition list. For each corresponding element in the presentation context
definition list, OSI/AS sets the following values in the presentation context definition
result list:
The result is set to indicate acceptance of the proposed presentation context.
The transfer syntax name is not set.
The reason is set to no value.