DECnet/OSI A Technical Overview

This document, "DECnet/OSI: A Technical Overview" by Digital Equipment Corporation, outlines Digital's networking architecture (DECnet) in the context of Open Systems Interconnection (OSI) standards.

Key areas covered include:

1. The Value of Standards: Emphasizes that standards are crucial for multi-vendor environments, enabling common architectures, information sharing, and cost reduction. Digital's extensive participation and leadership in various international standards organizations (like ISO, ANSI, IEEE, CCITT) since 1979 are highlighted.

2. The Seven-Layer OSI Model: Explains the ISO-defined, seven-layer peer-to-peer network architecture, detailing the function of each layer (Application, Presentation, Session, Transport, Network, Data Link, Physical). It also introduces core OSI terminology and concepts like Protocol Data Units (PDUs) and the principles of layered communication. Specific ISO standards associated with each layer, such as FTAM (File Transfer, Access, and Management) and X.400 MHS (Message Handling System) at the Application Layer, are mentioned. The document also details various IEEE 802 LAN standards (802.3 Ethernet, 802.4 Token Bus, 802.5 Token Ring) and FDDI (Fiber Distributed Data Interface), providing their characteristics and differences.

3. DECnet/OSI Implementation: This section elaborates on DECnet's integration with OSI. It covers DECnet/OSI's data link layer protocols (DDCMP, HDLC, X.25, CSMA/CD, FDDI) and its network layer functions, including adaptive link-state routing, which is designed for scalability and rapid convergence. It details DECnet and OSI addressing structures (Initial Domain Part, Domain Specific Part, Area, Node ID) and the support for multiple routing domains to manage network complexity. Other features like autoconfiguration and multi-link/multi-homing end systems are also presented.

4. Network Management and Naming Service: Digital's commitment to open systems is demonstrated through its Enterprise Management Architecture (EMA), a standards-based framework for managing entire enterprise networks (both DNA and non-DNA). Key management protocols like CMIP/CMIS and MOP are noted. The DNA Naming Service is introduced as a critical component for providing global names for network objects, emphasizing its design goals for scalability, robustness, and decentralized management.

5. OSI Products and Applications: The document showcases Digital's OSI-compliant products available at the time, including the Message Router X.400 Gateway (MR/X) for messaging, File Transfer and Access Management (FTAM) for file operations, and the VAX OSI Application Kernel (OSAK) for developing OSI-based applications. These products leverage the VAX OSI Transport Service and are designed to operate over common network types like X.25 WANs and ISO 8802-3 LANs.

6. DECnet/OSI Phase V Migration: Finally, the document discusses the migration path to DECnet/OSI Phase V, highlighting new features such as significantly expanded addressing capabilities (larger Node ID and Area fields) and enhanced network management. It emphasizes Phase V's backward compatibility with Phase IV nodes, allowing for interconnected operations and continued use of existing applications, with specific rules for interoperability in mixed environments.

In essence, the document serves as a comprehensive technical overview illustrating Digital's strategic move to align its proprietary DECnet architecture with open, international OSI standards to meet the demands of growing and increasingly diverse network environments.