Introduction to Networking for NonStop S-Series Servers

Application Programming With Communications
Products
Introduction to Networking for HP NonStop S-Series Servers—520670-005
3-14
Types of Programming Interfaces
Types of Programming Interfaces
As explained in Section 2, Communications Product Concepts and Components, HP
offers communications programming interfaces on several levels of complexity. When
writing applications that use very high-level or high-level interfaces, programmers do
not have to worry about the details of communications protocol. (The most extreme
case of communications transparency is the Expand subsystem: the application needs
no special code to refer to a remote resource and is generally unaware of the Expand
subsystem, although in some cases special code is desirable for error-recovery in
unusual situations.)
When an application requires the use of a communications protocol not supported by a
high-level interface, programmers can use low-level interfaces, such as CP6100,
Envoy, EnvoyACP/XF, or SNAX SNALU; to use such products, the programmer needs
to have a good understanding of the protocol required by the target device or system.
Most HP communications subsystems provide programming interfaces based on file-
system procedure calls. A few significant subsystems, however, can be used even by
programmers who are not familiar with the NonStop Kernel operating system
environment. These subsystems provide application programming interfaces based on
computer industry standards.
The rest of this section describes these concepts in greater detail:
•
Using File-System Procedure Calls on this page
•
Using Standards-Based Interfaces on page 3-18
•
Language Support on page 3-19
Using File-System Procedure Calls
The programmatic interfaces of most communications products consist of file-system
procedures. To write an application program that uses a file-system interface, you must
have some understanding of the environment and services provided by the NonStop
Kernel operating system. This subsection gives a general description of file-system
procedure calls used with communications subsystems. Refer to the for a more
thorough description of programming on the NonStop Kernel operating system.
Files and Filenames
Not only disk files, but also processes and many other entities, are treated as files in
the NonStop Kernel operating system. (A file is a logical construct subject to certain
kinds of operations, like reading and writing.) Each file in a system has a unique
filename; the name of a communications line or point-to-point device corresponds to
that of the input/output process (IOP) controlling the line or device. Name extensions
are available for referring to multipoint devices and other entities subordinate to the
IOP—for communications products, subordinate entities are called subdevices—but
those extensions are not meaningful to the file system.