DTJ505PF

This document describes the redesign and implementation of the DECnet Network Process (DNP) transport component for Digital's PATHWORKS client software, specifically for versions 4.1 (DOS) and 2.0 (OS/2). PATHWORKS integrates Intel-based personal computers into Digital's network environment, providing services like file sharing, printing, terminal emulation, and application access using the DECnet protocol.

The primary challenges with previous DNP versions were high memory consumption, suboptimal performance for small data transfers, and increased maintenance costs due to separate codebases for DOS and OS/2.

To address these issues, the development team aimed to double performance for small data transfers, reduce memory usage by 50%, and significantly lower maintenance costs by unifying the codebase. The chosen solution was a complete rewrite of the DNP component in assembly language to achieve optimal efficiency.

Key design improvements included:

• Consolidating source code for both DOS and OS/2 versions.
• Optimizing internal data structures, such as reducing the size of Request (REQ) data structures from 48 to 22 bytes.
• Enhancing flow control mechanisms (e.g., using XON/XOFF for NetBIOS links).
• Streamlining the architecture by allowing the NetBIOS module to directly call the Network Services Protocol (NSP) module.
• Improving efficiency by storing pointers to user requests rather than copying data.
• Addressing NetBIOS compatibility issues identified in previous versions.

The project successfully met its goals:

• Memory Usage: The resident size of the DNP component was reduced from 53KB to 33KB, allowing it to handle over 200 concurrent network links (up from 64).
• Performance: Performance for small data transfers nearly doubled, a crucial improvement for typical PC network applications.
• Maintenance Costs: The total lines of source code for combined DOS/OS/2 versions were reduced from 73,000 (DOS only in v4.0) to 53,000. Debugging was simplified due to the common codebase and improved NetBIOS compatibility.

In conclusion, the redesign of the DNP component for PATHWORKS version 4.1 was a significant success, achieving substantial gains in performance, memory efficiency, and maintainability.