OSI/AS Management Programming Manual

Glossary
056785 Tandem Computers Incorporated Glossary-19
Service primitive. An abstract, implementation-independent interaction between a
service user and a service provider. Service primitives describe the sequences of
events between adjacent layers that occur through the service access point (SAP).
There are four types of service primitives; see confirm primitive, indication primitive,
request primitive, or response primitive. See also SAP.
Session. (1) In the context of OSI data transmission, the period during which two
entities can exchange data.
(2) In the context of a management application, the period during which an
application can issue commands to a subsystem.
Session Layer. Layer 5 in the OSI Reference Model. It allows the setup and termination
of and controls communication sessions between nodes on the network.
Session selector. See SSEL.
Simple token. In DSM programmatic interfaces, a token consisting of a token code and a
value that is either a single elementary field, such as an integer or a character string, or
a fixed (nonextensible) structure. Compare extensible structured token.
SNDCF (subnetwork dependent convergence function). A function in the Network Layer
that allows the OSI internet protocol (which usually operates over LANs) to operate
over other protocols, such as X.25.
SNPA (subnetwork point of attachment). A real, physical address, identifying the point of
attachment to a subnetwork. An OSI end system can be connected to one subnetwork
or to a number of different subnetworks:
one NSAP to one SNPA
many NSAPs to one SNPA
many NSAPs to many SNPAs
SPDU (session protocol data unit). See PDU.
SPI (Subsystem Programmatic Interface). 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.
SPI buffer. The buffer that contains an SPI message. See also SPI message.
SPI message. In DSM programmatic interfaces, a message specially formatted by the
SPI procedures for communication between a management application and a
subsystem or between one subsystem and another. An SPI message consists of a
collection of tokens. Note that an SPI message is a single block of information sent at
one time, as one interprocess message. There are two types of SPI messages,
distinguished by different sets of tokens in the header: command and response
messages, and event messages.