Introduction to Networking for NonStop S-Series Servers

Communications Product Concepts and
Components
Introduction to Networking for HP NonStop S-Series Servers—520670-005
2-4
Communications Subsystems
Communications Subsystems
A software product that provides users with access to a set of communications
services is called a communications subsystem (CSS). For example, the Expand
subsystem allows you to use resources such as files and devices on other systems in
the Expand network. (The Expand subsystem is described in Section 5, Expand
Network.) Subsystems vary in the functions they provide and in the resources they
manage. Many subsystems allow applications to communicate with specialized
devices; a few subsystems exist to perform management services or to provide
management interfaces to other communications subsystems.
A subsystem typically includes one or more of the types of components shown in
Figure 2-1 on page 2-3; for example, one subsystem might include a higher-level
process and several input/output processes (IOPs), while another might include an IOP
and a protocol module. These types of components are described in Input/Output
Processes (IOPs) on page 2-6 and Levels of Protocol Support on page 2-8.
Figure 2-2 on page 2-5 provides an example of how subsystems interact to support the
work of applications. The Expand subsystem—which consists of multiple processes on
a node—can use the NonStop TCP/IP subsystem or the X.25 Access Method (X25AM)
subsystem to provide data transmission over local area networks (LANs) or wide area
networks (WANs), respectively. (The Expand subsystem also has other
communications interface options; NonStop TCP/IP and X25AM are merely examples.)
Management subsystems, such as the Subsystem Control Point (SCP), interact with
other communications subsystems to convey requests or collect management
information from those subsystems. SCP is a focal point for managing components at
all levels of a stack or even all the communications products within a system.