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
•APDU (application PDU): information exchanged between Application Layer
•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
