OSI/AS Management Programming Manual

2 Communicating With the
OSI/AS Processes
056785 Tandem Computers Incorporated 2–1
This section describes how a management application sends Subsystem Programmatic
Interface (SPI) messages to, receives SPI responses from, and retrieves event messages
generated by the processes in the OSI/AS subsystem.
Communicating
Through SCP
To manage the OSI/AS subsystem, your application sends commands to be performed
by the OSI manager, TAPS, TSP, and NSP processes. To communicate with these
processes, the application opens a process called the Subsystem Control Point (SCP)
and sends the OSI/AS commands to it. SCP acts as an intermediary between
applications and data communications subsystems such as OSI/AS. It forwards some
commands to the subsystem processes and performs a few commands itself.
The Communications Management Programming Manual describes how to run the SCP
process and describes, in detail, communication through SCP. In brief, this
communication consists of the following steps:
1. The application opens the SCP process.
2. The application sends an SPI-format request (an OSI/AS command) to SCP. A
token in the command indicates to SCP that the request is for the OSI/AS
subsystem; another token identifies which OSI/AS process should receive the
command.
3. SCP checks whether the OSI/AS process that is to receive the command is open. If
it is not, SCP opens it and, if this is the first command sent to this OSI/AS process,
it gets the version of the process.
4. For D-series systems, SCP compares the PINs of both the requesting and receiving
processes. When the OSI manager process or a TAPS process are running at a
high PIN they can only request communication with TAPS, TSP, or NSP servers
that are also running at a high PIN. If the OSI manager process or a TAPS process
request communication with low PIN processes, SCP returns the error ZCOM-
ERR-PIN-TOO-BIG.
5. SCP performs security validation on the request, and checks whether the version
of the OSI/AS subsystem’s DSM interface is compatible with the application.
6. If all is well, SCP forwards the request to the appropriate OSI/AS process.
7. The OSI/AS process then performs the requested action, formats a response, and
sends the response to SCP.
8. SCP forwards the response to the application.
9. Before terminating, the application closes the SCP process.
Usually the OSI/AS process remains open, once opened by SCP, even if SCP is closed.
The OSI/AS process will be closed if SCP is stopped or if any file-system error occurs.
It will be reopened when SCP issues the next request directed to the process.