OSI/AS Configuration and Management Manual

Glossary
OSI/AS Configuration and Management Manual—424119-001
Glossary-7
Presentation Layer
Method (TLAM) lines (for D4x-series releases) or Port Access Method (PAM) lines (for
G06 and later releases), the address used by TLAM or PAM to specify the address of the
connection to a local area network (LAN) controller.
Presentation Layer. Layer 6 in the Open Systems Interconnection (OSI) Reference Model
.
This layer resolves the differences of varying data formats between systems of different
vendors. It transfers data in a system-independent manner, performing appropriate
conversions at each system as necessary.
presentation selector (PSEL). A logical address in the Presentation Layer
through which
presentation services are made available. A single PSEL can service one or more
connections simultaneously.
presentation service access point (PSAP). A network-unique, physical address in the
Presentation Layer
through which connections are established and maintained. Also
called presentation address.
protocol data unit (PDU). Information delivered as a unit between peer entities that contains
data and/or control and address information.
release token. One of the four types of Session Layer
tokens that are associated with
functional units.
SCF. See Subsystem Control Facility (SCF)
.
sensitive command. A Distributed Systems Management (DSM)
command that can be
issued only by a restricted set of users. For Compaq communications subsystems, the
sensitive commands are those that can change the state or configuration of objects, start
or stop tracing, or change the values of statistics counters. Compare nonsensitive
command.
service. A set of primitives (operations) that a layer provides to the layer above it. The
service defines what operations the layer can perform on behalf of its users, but not how
these operations are implemented. A service relates to an interface between two layers,
with the lower layer being the service provider and the upper layer being the service
user.
service access point (SAP). The access means by which a pair of communicating entities in
adjacent layers use or provide services.
service data unit (SDU). Information passed across the network to a peer entity and then up
to the next layer.
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)
.
session. (1) In the context of Open Systems Interconnection (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.