OSI/TS Management Programming Manual

Glossary
056786 Tandem Computers Incorporated Glossary-15
PDU (protocol data unit). Information delivered as a unit between peer entities that
contains data and/or control and address information. There are five types of PDUs
used by OSI/AS and OSI/TS:
PDU Function
APDU (application PDU) Information exchanged between Application Layer entities
IPPDU (internet protocol PDU) Information exchanged between Network Layer entities
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
PDV (presentation data value) list. The form in which the Presentation Layer transmits
data. It consists of a sequence of encoded data values.
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.
PIN. See process identification number.
Port address. For X25AM lines, the logical port number used to specify the address of
the connection to the X.25 network. For TLAM lines, the address used by TLAM to
specify the address of the connection to a LAN controller.
Predefined value. A commonly used value—for instance, a value for a token or a field in
a token—that is given a name in a set of definition files.
Preferred binary encoding method. A binary encoding method defined in ISO 8348,
Addendum 2, and used by Network Layer protocols to encode NSAP addresses in
preparation for the inclusion of the NSAP addresses in NPDUs.
Presentation context. The combination of an abstract syntax (such as ASN.1) and
assignment of a transfer syntax to each on a Presentation Layer connection. For
OSI/AS, the local application provides a list of up to 16 presentation context
definitions, each consisting of a presentation context identifier, an abstract syntax
name, and up to three transfer syntax names. (Users of ACSE can provide up to 15
presentation context definitions; the presentation context for ACSE is supplied by
OSI/AS.) The remote application decides which of the named transfer syntaxes is to
be used for each presentation context and specifies that transfer syntax in the
presentation context definition result list.
Presentation context definition list. For Tandem OSI/AS, a list containing up to sixteen
presentation context definitions. Each presentation context definition contains a
presentation context identifier (PCID), an abstract syntax name, and up to three
transfer syntax names.
Presentation context definition result list. For Tandem OSI/AS, a list containing up to
sixteen elements, each indicating the called application’s acceptance or rejection of one
of the presentation context definitions proposed in the presentation context definition
list.