DAP

This document is the Functional Specification for the Data Access Protocol (DAP) Version 4.1, published by Digital Equipment Corporation in March 1978.

DAP is a user-level protocol within DEC's Digital Network Architecture (DNA), specifically residing in the Application Layer. Its primary purpose is to enable remote file access and data transfer (to/from I/O devices and mass storage files) in a network environment, independently of the accessed operating system's I/O structure.

The specification details:

• Functional Capabilities: Including retrieving, storing, deleting, and renaming files; listing directories; executing command files; providing ASCII file transportability; supporting multiple data streams; and offering error recovery and random access.
• Message Formats: Standardized structures for various DAP messages (e.g., Configuration, Attributes, Access, Control, Data, Status, Acknowledge, Access Complete).
• File Organization: How different file types and record formats are handled for network transfer.
• Operational Procedures: Steps for setting up logical links, transferring data over the link, and terminating connections, including error handling.

The document is intended to assist developers and implementers in understanding DAP's features, message formats, and operational aspects within DECnet, clarifying how a user process interacts with a remote file system.