Introduction to Networking for NonStop S-Series Servers

Communications Product Concepts and
Components
Introduction to Networking for HP NonStop S-Series Servers—520670-005
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Processes
Processes
The part of an HP communications subsystem that runs in the NonStop S-series server
is implemented as one or more processes.
A process is an execution of a program under control of the HP NonStop Kernel
operating system. The same program file can execute concurrently multiple times;
each execution is a separate process. Processes communicate with each other
through file-system or message-system procedure calls. (Your application processes
use the file system.)
There are system processes and user processes. In general, system processes are
a permanent part of the operating system; they are automatically executed when a
processor is loaded, and they continue to exist as long as the host processor remains
available. User processes have only a temporary existence and are subject to creation,
execution, and termination. Your applications are user processes. A communications
subsystem can consist of system and user processes provided by HP.
Input/Output Processes (IOPs)
In the context of communications products, the system processes of major concern are
IOPs, an important feature of the NonStop Kernel operating system. IOPs manage
communications lines.
When an IOP works with other components to support a connection, the IOP is the
lowest-level component that runs on the NonStop S-series server. Some IOPs rely, for
the lowest-level protocol functions, on protocol modules that run in a ServerNet
adapter or SWAN concentrator.
An I/O process pair typically controls one or more communications lines, which are
physically connected to the system through a ServerNet adapter or SWAN
concentrator. IOPs may be configured in pairs so that in the case of a failure affecting
one of the processes, the other process can take control of the lines with minimal
disruption to applications. (Application users usually are not even aware that a failure
has occurred.)
To use any communications line, other processes must send requests to the process
that controls the line. The IOP, in turn, calls other procedures to handle the protocols of
the lines it controls and to achieve the physical transfer of data through the ServerNet
adapter or SWAN concentrator. The application process and the IOP can be located in
different nodes; the application interfaces are the same for local and remote
communications.