OSI/AS Programming Manual

OSI Upper-Layer Concepts
APS Procedures Programming Concepts
056783 Tandem Computers Incorporated 2–5
An example of the sequence of primitives for an unconfirmed service is described
below, using as the starting point a data request issued by your application.
1. To send data to the remote application over an established connection, you call
APS_DATA_REQ_. OSI/AS generates a data request primitive, which contains
the data you are sending, and issues it to the service provider.
2. The remote application receives your request, including the data, as a data
indication primitive.
Figure 2-3 shows the service provider initiating an indication primitive—for example,
a P-P-ABORT indication primitive, indicating that an error was detected in this layer
or an underlying layer. Note that for ACSE connections, as for session and
presentation connections, OSI/AS sends an abort indication to both the local and the
remote application.
Figure 2-3. Primitives, Provider Indication
Your
Application
Service
Provider
Indication
Remote
Application
Indication
025
Tables 2-1 through 2-4 show which procedures to call:
To invoke request primitives (Table 2-1)
After you receive an indication primitive (Table 2-2) by calling
APS_EVENT_RECEIVE_ and APS_STATUS_
To invoke response primitives (Table 2-3)
After you receive a confirm primitive (Table 2-4) by calling
APS_EVENT_RECEIVE_ and APS_STATUS_
For Table 2-2, note that it is appropriate to call the APS_DATA_GETPARAM_
procedure after any indication primitive that can contain user data. For session
version 1, most indication primitives can contain user data; for session version 2, all
indication primitives except provider abort and provider exception report can contain
user data.