Compaq OSI/FTAM D43 manual SPDU session PDU information exchanged between Session Layer entities

Glossary

OSI Reference Model. A communications architecture, adopted by the ISO in 1984, that includes seven layers that define the functions involved in communications between two systems, the services required to perform these functions, and the protocols associated with these services. See also layer.

OSI subsystems. The Compaq subsystems that support the various layers and application service elements of the OSI Reference Model, including the FTAM subsystem, APLMGR, OSI/AS, OSI/TS, and TLAM or X25AM.

OSI/TS (Transport Services). The Compaq subsystem that manages the communication of messages from the Transport Layer on a local Compaq system to the Transport Layer on a remote system in an OSI network.

owner ID. The identity (Guardian user ID) of the owner of a process on a Compaq NonStop system.

parallel associations. Multiple associations running concurrently within a Compaq FTAM process.

parameter structures. DDL structures that define some of the reference parameters for the FTM, APS, and MFM procedures.

partially supported file attribute. A virtual filestore (VFS) file attribute, in a supported storage or security attribute group, for which any reference by the FTAM responder yields the result that no value is available, and any attempt to change the attribute fails. In summary, the VFS recognizes the attribute name but provides no value for it. Contrast with supported file attribute.

PDU (protocol data unit). 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

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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

OSI/FTAM Responder Manual—425199-001

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