Digital;s Networks: An Architecture With A Future

This document, "Digital's Networks: An Architecture With A Future," serves as a handbook introducing Digital Equipment Corporation's (DEC) networking products, primarily DECnet, and its foundational framework, the Digital Network Architecture (DNA).

Purpose and Audience: The handbook aims to describe the common DNA network concepts and the major network functions provided by DECnet. It is intended for readers familiar with communications technology, including personnel involved in new DECnet installations, system managers, and designers considering expanding their Digital systems or implementing computer networks.

Key Concepts and Architecture (DNA):

• Distributed Data Processing: DECnet enables computing power and resources to be brought directly to user locations, fostering a decentralized, peer-to-peer network environment. Any system (node) can initiate and accept communications without a central controlling system.
• Digital Network Architecture (DNA): This is the layered framework of specifications for all Digital communication products, conceptually similar to the International Standards Organization (ISO) Open Systems Interconnection (OSI) model. DNA defines interfaces (within a node) and protocols (between nodes in the same layer). Key layers include User, Network Management, Network Application, Session Control, End-to-End Communication (using Network Services Protocol - NSP), Routing, Data Link, and Physical Link.
• DECnet Phases: Digital has evolved DECnet through several phases, with Phase IV being the most current and backward-compatible with Phase III. Phase IV offers significant enhancements like increased node support (over 64,000 nodes, organized into areas), data link independence (supporting X.25, DDCMP, and Ethernet protocols), dedicated communication servers, and enhanced network management.

Core Capabilities and Functions of DECnet:

• Scalability & Flexibility: DECnet networks can range from two nodes to over 64,000, spanning local (LANs, e.g., Ethernet) and wide-area networks (WANs, using leased or switched lines). It supports a wide variety of Digital operating systems and hardware.
• Interoperability: DECnet provides gateways (e.g., DECnet/SNA Gateway for IBM SNA, DECnet Router/X.25 Gateway for packet-switched data networks - PSDNs) to allow communication with foreign vendor systems, offloading communication functions from general-purpose nodes.

• High-Level Network Functions:

  • Task-to-Task Communication: Enables programs on different nodes and operating systems to exchange data via "logical links."
  • Remote File and Record Access: Allows users and programs to access, manipulate, transfer, and submit files on remote nodes.
  • Network Terminal Facilities: Supports interactive terminal-to-terminal communication (e.g., Phone, TLK utilities) and "Network Virtual Terminal" (NVT) for direct access to remote node operating systems, even across different OS types in Phase IV.

• Underlying Mechanisms:

  • Nodes, Lines, and Circuits: Defines network entities, physical connections (lines), and logical connections (circuits) over them.
  • Data Link Protocols: Details DDCMP (byte-oriented, error-free, pipelining, piggybacking, point-to-point/multipoint), Ethernet (high-speed LAN, CSMA/CD, framing, addressing, error detection), and X.25 (packet-switched data networks, virtual circuits, flow control).
  • Routing: Determines the least-cost path for data packets between source and destination nodes, adapting to topology changes and managing network congestion. Phase IV introduces Level 1 (intra-area) and Level 2 (inter-area) routing for large networks.
  • Logical Links: Abstract communication paths between programs, managed by the End-to-End Communication and Session Control layers, handling data segmentation, reassembly, error, and flow control.

• Network System Management: Covers tools and procedures for configuring, operating, monitoring, and testing DECnet networks. This includes node generation, parameter definition (e.g., routing costs, passwords), line/circuit control, monitoring node activity (with counters and event logging), and testing (loopback, upline dumping for crash analysis). Digital's "Observer" software is highlighted as a tool for comprehensive network performance monitoring.

In essence, the document details how DECnet, built upon DNA, provides a robust, scalable, and flexible networking solution that enables seamless communication, resource sharing, and application interaction across diverse computing environments, both within Digital's ecosystem and with external systems.