Overview
ISO 8571-1:1988/Amd 2:1993 is an amendment to the ISO FTAM (File Transfer, Access and Management) Part 1 general introduction. It extends the externally visible service definition of FTAM to incorporate overlapped access - a mechanism that allows a single initiator to perform many read and update operations more efficiently against structured files. The amendment describes how overlapped access operates within the OSI model’s file service, its constraints (presentation contexts, open regime), and its effects on the virtual filestore.
Key topics and technical requirements
- Overlapped access modes
- Consecutive access: permits queuing multiple read/write requests while a previous bulk-data transfer regime is in progress. Protocol Control Information (PCI) for one access can overlap with user data for another. The service remains serializable - the effect on the virtual filestore equals issuing the same requests in series.
- Concurrent access: allows read transfers to overlap with write transfers. This introduces non-determinism; reads may return data inconsistent with the current file state in some uses.
- Virtual filestore model: overlapped access operates within the same virtual filestore semantics as FTAM Part 1; effects of consecutive access are serializable.
- Protocol and session considerations
- Overlapped transfers occur within the set of presentation contexts established at file open.
- FADU locking (File Access Data Unit locking) and concurrency control are required to manage conflicts when overlapped access is used.
- Checkpointing is direction-specific during overlapped access; recovery mechanisms require session symmetric synchronization services (pending specification).
- Constraints
- File selection per association rules and presentation contexts remain in force.
- Recovery and session synchronization tools are necessary for robust overlapped-access recovery but may be unavailable without session symmetric services.
Practical applications
- Remote database access: using FTAM to submit many queries efficiently by queuing read requests (consecutive access) instead of strict serial exchanges.
- LAN fileserver optimization: diskless workstations can overlap multiple F-READ/F-WRITE operations to improve throughput.
- Bulk editing workflows: editors can read ahead while performing local edits on previous FADUs using concurrent access to reduce latency.
Who should use this standard
- Network protocol designers and implementers of FTAM and OSI file services
- Vendors of file servers, distributed file systems, and enterprise storage solutions integrating OSI-based file transfer
- System architects and software engineers designing high-performance remote file/database access over OSI networks
Related standards
- ISO 8571 Parts 2–5 (Virtual Filestore Definition, File Service Definition, File Protocol Specification, Protocol Implementation Conformance Statement)
- ISO/IEC JTC 1 publications and other OSI layer standards relevant to session and presentation services
Keywords: ISO 8571-1:1988/Amd 2:1993, FTAM, overlapped access, consecutive access, concurrent access, virtual filestore, file transfer access and management, OSI file services.