801215 IBM SNA

This document is an internal Digital Equipment Corporation (DEC) Competitive Update from December 15, 1980, providing an analysis of IBM's System Network Architecture (SNA), with a focus on how DEC's Digital Network Architecture (DNA), including DECnet, compares and competes.

Key takeaways:

• Core Distinction: The document highlights that SNA and DNA (DECnet) are fundamentally designed to solve different problems. SNA is optimized for providing terminal and intelligent cluster controller access to large, centralized IBM hosts, thus increasing customer dependence on IBM. DNA, in contrast, aims for broad distribution of processing across small to large systems, reducing reliance on large mainframes.

• SNA Architecture:

  • It is a layered, hierarchical architecture with distinct node types: Hosts (containing System Services Control Point - SSCP), Communication Controllers (3705), Cluster Controllers (8100, 3274, 3790), and Terminals.
  • SNA's intelligence and functionality are primarily concentrated in the host, leading to significant software (VTAM, TCAM, NCP) and hardware (e.g., 3705 Communication Controller) overhead.
  • It predominantly uses half-duplex communication, a legacy from earlier IBM terminal designs, unlike DNA's full-duplex.
  • Network generation for SNA is described as complex, requiring explicit definition of all nodes and applications, taking weeks or months.
  • Session initiation in SNA requires more messages than DECnet.

• Competitive Landscape (as of 1980):

  • IBM's 4300 series (introduced in 1979) made IBM more competitive with DEC's VAX systems in a networking environment, prompting this analysis.
  • DECnet Advantages: The document positions DECnet as superior in distributed data processing due to its flexible network topology (not host-dependent), easier task-to-task communication (supporting high-level languages vs. SNA's Assembler requirement), more transparent file transfer/access, and quicker network generation.
  • Marketing Strategies Against SNA:
    • Terminals-Only Network: While SNA excels here, DEC argues it offers cost-effective solutions for its terminals, though it may lack support for some specialized terminals (e.g., Point of Sale).
    • Intelligent Network: DEC views its offerings (e.g., PDP-11s vs. 8100, VAX vs. 4300s) as superior for cluster controllers, especially with Digital's SNA Partitioned Emulation (PE) program.
    • Distributed Processing Network: DECnet is presented as the ideal solution for resource and data sharing, as SNA lacks support for slave node-to-node communication. DEC suggests alternative solutions utilizing CICS/IMS-based systems with Digital's 3271 PE to avoid SNA's high overhead.

In essence, the document serves as a guide for DEC's sales force to understand IBM's SNA, identify its limitations compared to DECnet, and formulate strategies to position DEC's distributed data processing solutions as a more suitable alternative for customers requiring peer-to-peer communication and less host-centric networking.