DECnet™ DIGITAL Network Architecture (Phase V) General Description

This document, "DECnet DIGITAL Network Architecture (Phase V) General Description," outlines the design and functions of Digital Equipment Corporation's network architecture, serving as a model for Phase V DECnet implementations. Published in September 1987, it focuses on two main advancements: deep integration with international Open Systems Interconnection (OSI) standards and enhanced support for large-scale networks.

Key aspects of DNA Phase V include:

• Layered Architecture: It is structured in a layered model, aligning closely with the OSI 7-layer model. For lower layers (Physical, Data Link, Network, Transport), DNA Phase V adopts relevant OSI standards (e.g., ISO 8802-3 for LANs, ISO 8473 for Network Layer, ISO 8073 for Transport Layer), while also retaining proprietary protocols (like DDCMP and NSP) to ensure backward compatibility with Phase IV DECnet systems during migration. OSI upper-layer protocols (Session, Presentation, Application) are supported as they become standardized.
• Naming Service: A significant new component, the Naming Service, provides a network-wide, distributed, and replicated database for unique names of systems, applications, and resources. This service enables location-independent addressing and simplifies the management of large networks by automating the distribution of crucial shared information like network addresses and protocol capabilities.
• Scalability: The Network Layer introduces hierarchical routing (Level 1 within "areas" and Level 2 between areas) and a dynamic adaptive routing algorithm designed to support very large networks, potentially comprising hundreds of thousands of systems.
• Network Management: Enhanced, distributed network management facilities are provided, utilizing new protocols like the Common Management Information Protocol (CMIP) and a new command language (Network Control Language - NCL) for remote configuration, monitoring, and diagnostics.
• Application Support: DNA Phase V supports a broad range of applications, including heterogeneous file access (Data Access Protocol - DAP), network virtual terminals, electronic mail (Mail-II, Message Router with X.400), and SNA interconnect applications, all designed to interoperate seamlessly with existing Phase IV applications.

The document serves as an introduction to DNA's functional specifications, aimed at readers with a background in communications technology, detailing its design goals and operational concepts.