OSI/AS Programming Manual

OSI Upper-Layer Concepts
APS Procedures Programming Concepts
2–16 056783 Tandem Computers Incorporated
The action you can take depends on the functional units and tokens available, but
must be one of the following actions:
Resynchronize the connection using APS_RESYNCREQ_.
Abort the connection using APS_ASSOC_ABORTREQ_.
Interrupt the activity using APS_ACTIVITY_INTERRUPTREQ_.
Discard the activity using APS_ACTIVITY_DISCARDREQ_.
Give the data token (and, optionally, other tokens) to the remote application using
APS_TOKEN_GIVE_. (Do not use this option to clear the exception if
resynchronization or activity management is available.)
Abruptly discard the API’s context information for the connection using
APS_DISCARD_.
Note that user exception reports must be cleared by the accepting user (that is, the user
receiving the exception report). However, provider exception reports can be cleared
by either user.
ACSE and Presentation
Concepts
This subsection provides a few basic definitions related to user data encoding on
presentation and ACSE connections.
Session users, and users of presentation and ACSE connections in X.410-1984 mode,
need not be concerned with user data encoding.
Note If the mode parameter for a presentation or ACSE connection is set to X.410-1984 mode, OSI/AS does
not encode or decode any user data, and all other APS procedure parameters specific to presentation
and ACSE connections are ignored.
Basic Definitions
An abstract syntax is a specification of Application Layer data or application protocol
control information by using notation rules that are independent of the encoding
technique used to represent the information. An abstract syntax can be viewed as
describing the abstract structure of the data. Abstract syntaxes are defined using
Abstract Syntax Notation-1 (ASN.1), described in ISO 8824.
ASN.1 enables simple and complex data types to be defined and enables values of
these types to be specified, without determining how an instance of a type is to be
represented during transmission. It defines a number of simple data types (such as
boolean, integer, bit string, and octet string) and the notation used to reference them;
mechanisms for constructing structured types (sequence, set, and choice) from the
more basic types; and a number of other useful types.
A transfer syntax determines the way in which data is represented as bit patterns
during data transmission. It describes exactly how bytes from the abstract syntax will
be sent to the remote peer, and how the remote peer will decode the bytes and put
them into the abstract syntax. Currently, only one transfer syntax is supported: Basic
Encoding Rules (BER), defined in ISO 8825. For considerations about OSI/AS support