OSI/AS Configuration and Management Manual

OSI/AS Subsystem Description
OSI/AS Configuration and Management Manual—424119-001
7-4
Application Program Interface (API)
Application Program Interface (API)
The API is the interface between an application and the TAPS process. An application
accesses this interface by calling the APS (application, presentation, and session)
procedures. This interface becomes part of your application (as part of the system
library) when the APS procedures are bound into your program. For more information
on the APS procedures and the API, see the OSI/AS Programming Manual.
Downward Information Flow
The API receives requests from your application in APS procedure calls. The API
performs some verification and, if necessary, rejects APS procedures, with the
appropriate error. (TAPS also performs some verification it verifies parameter values
and sends an appropriate error if something is incorrect.)
Most of the APS procedures contain parameters that the API uses to invoke service
primitives. The API then sends the service primitives to the TAPS process.
The application distinguishes connections by connection endpoint identifiers (CEPIs).
Each CEPI is unique within your application. In APS procedure calls, the CEPI is used
in a way that is similar to how file numbers are used in file-system calls. The CEPI is
created by the API when your application initiates a connection using the
APS_ASSOC_CONNECTREQ_ procedure or waits for an incoming connection using
the APS_ASSOC_ATTACH_ procedure. The OSI manager process then selects
processes to create the layer subdevices necessary to manage the connections subdevices
are created only if no static or dynamic subdevices are available. At this stage, your
application receives the CEPI as output.
The application must specify this same CEPI in all subsequent procedure calls for the
connection. The CEPI exists until the application calls APS_DISCARD_.
Upward Information Flow
When API accepts an APS procedure call, it returns a STATUS indicator. Further details
about the status of the operation, errors detected, and TAPS subdevices can be obtained
by a call to APS_STATUS_. In waited cases, incoming service primitives are returned to
your application as completions to APS_EVENT_RECEIVE_ calls. In nowaited cases,
incoming service primitives are returned to your application as completions to
APS_EVENT_RECEIVE_ calls, followed by MFM_AWAITIOX_.
State Machine
There is no OSI-defined state machine in the API. Although there is an internal state
machine, a discussion of such is beyond the intent of this manual.
Note. The CEPI is not the same as the session connection identifier. Both identify the same
connection, but they are used in different contexts. The CEPI is the identifier known to the API.
The session connection identifier is known to the remote application.