TCP/IP Configuration and Management Manual

Glossary
TCP/IP Configuration and Management Manual—427132-004
Glossary-16
subnetwork
addressing, routing continues as usual by dividing the destination address into an
Internet portion and local portion. Gateways and hosts inside a site using subnet
addressing interpret the local portion of the address by dividing it into a physical
network portion and host portion.
subnetwork. One or more intermediate systems that provide relaying and through which
end open systems may establish network connections.
Subnetwork Access Protocol (SNAP). In order to run the TCP/IP protocol suite over
IEEE networks, the Subnetwork Access Protocol (SNAP) defines the interface between
the IP layer and the LLC layer. The interface is accomplished through the use of an
extension of the LLC header that contains a predefined Service Access Point (SAP) for
use in the Source SAP (SSAP) and the Destination SAP (DSAP) fields of the LLC
header.
subsystem. (1) The software and/or hardware facilities that provide users with access to a
set of communications service. (2) For DSM, a program or set of processes that
manages a cohesive set of objects. Each subsystem has a process through which
applications can request services by issuing commands defined by that subsystem; in
some cases, this process is the entire subsystem. Many subsystems also have
interactive interfaces.
Subsystem Control Facility (SCF). A part of DSM, used to provide a common, interactive
management interface for configuring, controlling, and collecting information from
NonStop data communications products.
Subsystem Control Point (SCP). .n DSM, the management process for all data
communications subsystems on NonStop systems. There can be several instances of
this process. Applications using SPI send all commands for data communications
subsystems to an instance of this process, which in turn sends the commands on to
the manager processes of the target subsystems. SCP also processes a few
commands itself. It provides security features, version compatibility, support for tracing,
and support for applications implemented as NonStop process pairs. See also
management process
or manager process.
Subsystem ID (SSID). In DSM programmatic interfaces, a data structure that uniquely
identifies a subsystem to SPI. It consists of the name of the owner of the subsystem, a
subsystem number that identifies that particular subsystem, and a subsystem version
number. The subsystem ID is an argument to most of the SPI procedures.
Subsystem Programmatic Interface (SPI). In DSM, a set of procedures and associated
definition files used to define common message-based programmatic interfaces for
communication between requesters and servers—for instance, in a management
application. SPI includes procedures to build and decode specially formatted
messages; definition files in Pascal, TAL, C, COBOL85, and TACL for inclusion in
programs, macros, and routines using the SPI procedures; and definition files in DDL
for programmers writing their own subsystems.