DFM Series

This document is the User Guide for the DFM Series Intelligent Communications Processor, published by Digital Equipment Corporation in January 1986. It serves as a comprehensive technical manual for installing, testing, programming, and operating the DFM unit.

The DFM is described as an intelligent communications multiplexer designed to optimize data flow and reduce costs by allowing multiple terminals to share a single high-speed communication link, modems, and telephone lines.

Key aspects covered in the guide include:

1. DFM Features:

   • Intelligent Multiplexing: Utilizes statistical time division with dynamic bandwidth allocation, supporting aggregate baud rates significantly higher than the concentrated link speed.
   • Channel Flexibility: Supports asynchronous, switched, synchronous (including DDCMP protocol), and unused channel types, with capabilities like speed conversion, flow control conversion, and autobaud.
   • Switching & Contention: Enables any channel to connect to any other, facilitating efficient computer port allocation, terminal contention for shared resources, and automatic disconnection for inactive channels.
   • Network Management & Control: Provides interactive commands via a supervisory channel for system programming, monitoring (error counts, utilization statistics, EIA signal status), and diagnostic testing. It also supports down-line loading of parameters for easy configuration.
   • Modular Design & Expandability: Features a modular design for quick maintenance and upgrades, expandable in 4-channel increments up to a maximum of 16 channels.
   • Maximized Throughput: Achieved through a multi-microprocessor design, internal Direct Memory Access (DMA), dedicated input/output buffers for each channel, and automatic error correction (Cyclic Redundancy Check - CRC) for asynchronous data.
   • Security: Offers password-secured access levels (User, System Manager, Channel Operator) and group access lists to restrict unauthorized channel connections.

2. Applications and Configurations: Illustrates various network setups, including channel switching and contention, single-unit switching, tail circuits, dial-up timesharing, satellite links, and multi-DFM configurations handling both asynchronous and synchronous traffic.

3. Pre-installation Planning: Guides users through site setup, equipment selection (DFM unit size, cables, integral or external modems), and environmental/power requirements. It includes a hardware selection guide and an inventory form.

4. Installation: Details the physical unpacking, visual inspection, checking of modules, and identification of controls and indicators (LEDs and pushbuttons) on the DFM unit and its modules. It outlines a comprehensive pre-installation bench test to verify system and link operation and familiarize operators with the unit.

5. Operation and Configuration: Explains how to use the DFM unit for unswitched and switched channel applications, providing step-by-step programming examples. It includes a detailed description of all DFM commands, their syntax, privilege levels, and examples for setting various system, link, and channel parameters.

6. Troubleshooting and Testing: Offers a systematic approach to identifying and resolving problems with DFM hardware, modems, and telephone facilities. It describes automatic self-tests, various diagnostic tests (e.g., Link Loopback, Echo, Pattern, Signals tests), and the interpretation of LED indicators.

Appendices provide further technical details, including DFM functional specifications, comprehensive information on compatible link modems (including their switchpack and jumper settings), detailed cable wiring diagrams, a blank configuration worksheet, signal characteristics, and a list of software level incompatibilities.