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OSI/FTAM Programming Guide

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ISO FTAM Concepts
HP NonStop OSI/FTAM Programming Guide—528612-001
2-14
Service Classes
Service Classes
In addition to functional units, ISO 8571 defines five service classes. Service classes
are subsets of FTAM services defined as combinations of functional units and
constraints on allowed protocol. ISO FTAM defines these five service classes:
•
File transfer
•
File access
•
File management
•
File transfer and management
•
Unconstrained class
NonStop FTAM supports all ISO-defined service classes except for the unconstrained
class.
The service classes are described in the following paragraphs. Note that service
classes are negotiated according to an order of preference described in greater detail
in Negotiation of Service Class and Functional Units on page 2-21.
The file-transfer service class consists of services that provide for moving files (or parts
of files) between nodes. The protocol for the file-transfer service class uses grouped
operations, in which multiple primitives are encoded in the same PDU. Grouped
operations minimize protocol overhead by reducing the number of PDUs exchanged
before and after data transfer.
The file-access service class allows the initiating entity to operate on remote files by
performing operations on file-access data units (FADUs) in those files.
The file-management service class includes services that permit a series of
independent confirmed service exchanges to control the virtual filestore. (The virtual
filestore is a system-independent model of a file storage system; this important concept
is explained later in this section.) The file-management class does not include
file-transfer mechanisms.
The file-transfer-and-management service class is a combination of the features of the
file-transfer and file-management service classes.
The unconstrained class includes the services available in the kernel functional unit
and, optionally, the services of any other functional units.
Table 2-3 on page 2-15 lists the mandatory and optional functional units that define
each service class.