OSI/FTAM Programming Guide

ISO FTAM Concepts
HP NonStop OSI/FTAM Programming Guide—528612-001
2-12
Functional Units
Once the application program selects or creates a file, it establishes the file-selection
regime, and in so doing causes the association to move from the FTAM regime to the
file-selection regime. In the file-selection regime, the program can read or change
attributes of the selected file (F-READ-ATTRIB or F-CHANGE-ATTRIB) or open the file
(F-OPEN). It can also deselect the file (F-DESELECT) or delete the file (F-DELETE);
either action terminates the file-selection regime.
After the application program opens the file, the association moves from the
file-selection regime to the file-open regime. Within the file-open regime, the program
can locate or erase specific parts of a file (F-LOCATE, F-ERASE), or initiate reading or
writing of a part of a file (F-READ, F-WRITE). It can also close the file (F-CLOSE),
which terminates the file-open regime. (An individually addressable part of a file is
called a file-access data unit, or FADU; that concept and its implications are discussed
in some detail later in this section.)
Upon initiating the read (F-READ) or write (F-WRITE) of all or part of a file, the
program establishes the data-transfer regime, and the association moves from the
file-open regime to the data-transfer regime. In the data-transfer regime, the program
can send (F-DATA-IND) or receive (F-DATA) data, depending on whether it initiates the
regime with the read or write service, respectively. It can also request an end to data
transfer (F-TRANSFER-END) or cancel data transfer (F-CANCEL); either action
terminates the data-transfer regime.
Functional Units
ISO 8571 defines many FTAM services. However, a given implementation does not
necessarily support all defined services. To help identify services that both the initiator
and responder support, ISO 8571 groups the services into one required (kernel) and
nine optional functional units—that is, sets of FTAM services. Table 2-2 on page 2-13
shows the ISO FTAM functional units and the services they include. The primitives
corresponding to each service were listed in Table 2-1 on page 2-7.