OSI/FTAM Programming Reference Manual

Glossary
HP NonStop OSI/FTAM Programming Reference Manual—528611-001
Glossary-19
PDU
PDU. The encoded message transferred across the OSI network between peer entities—for
example, between an FTAM initiator and responder. Data, such as a block of
information being transferred or a protocol primitive, is encoded into a PDU for transfer
across the network. The PDU is decoded when it arrives at its destination. Types of
PDUs include the following:
•
APDU (application PDU): information exchanged between Application Layer
entities—this includes ACSE and presentation PDUs created to support the FTAM
protocol (FTAM PDUs, or FPDUs)
•
PPDU (presentation PDU): information exchanged between Presentation Layer
entities
•
SPDU (session PDU): information exchanged between Session Layer entities
•
TPDU (transport PDU): information exchanged between Transport Layer entities
permanent error. An ISO-defined type of diagnostic error that occurs every time the
sequence of events that caused the error is repeated, and implies the failure of at least
the present operation being performed. See also error type., informative message.,
and transient error.
permitted-actions attribute. A file attribute that can be returned in an F-READ-ATTRIB
indication or confirm or set in an F-CREATE request. It specifies the actions that can
be performed on the file or the mode of access to FADUs in the file. During the
F-CREATE service, the initiator proposes a set of values. The responder can either
accept the proposed values or change them to any set of values it can handle: for
example, a default set of permitted actions that is always used for a specific document
type regardless of what is proposed. The responder implements the set of permitted
actions in some way that maps them onto the underlying real system.
Physical Layer. Layer 1 in the OSI Reference Model. This layer establishes the actual
physical connection between the network and the computer equipment. Protocols at
the Physical Layer include rules for the transmission of bits across the physical
medium and rules for connectors and wiring.
PID (process identifier). The combination of the central processing unit (CPU) number and
the process identification number (PIN) for a process running on the NonStop
operating system.
port address. For X25AM lines, the logical port number used with the X.25 network; for
TLAM, the address used to communicate with a LAN controller.
PPDU (presentation PDU). See PDU.
presentation address. An unambiguous name used to identify a set of presentation service
access points (PSAPs) that are all located at a boundary between a Presentation
Layer implementation and an Application Layer implementation in the same open
system.