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David B. Tuttle, Principal Engineer  
Profile, Products, Projects, Publications


CTX Logo Cambridge Telecommunications Inc.
5 Old Concord Road, Burlington MA
purchased October 1979 by GTE Telenet Communications
Cambridge Telecommunications was a privately-held contract engineering company founded by Rubin Gruber and Greg Burch, exploiting their experience with IBM compatible terminal products at Sanders Associates in New Hampshire.

CTX changed focus in 1978 to develop microprocessor-based X.25 interface hardware, the CTX 9101 concentrator and the CTX 9301 management station.  The CTX 9101 was a rack-mountable chassis with optional hardware redundancy that provided expandable remote terminal connectivity based on Zilog Z80s. The CTX 9301 used the same chassis built into a desk unit with 4 floppy disk drives (5.25") for local storage, to provide a central management station for the CTX 9101 concentrators. The CTX 9301 ran with MP/M-80, the multiprogramming version of CP/M, on a Zilog Z80A processor.

In October 1979, Cambridge Telecommunications was purchased by Telenet Communications Corp. (TCC) of Tysons Corner, VA a scant few months after Telenet had been acquired by General Telephone & Electronics (GTE) Corp.

Specific projects & activities:

  • First-level manager for a group of 5 to 8 software engineers
  • Bell Canada SNAP protocols, precursor to X.25
  • Bolt Beranek and Newman (BB&N) custom networking at Citibank
  • IBM terminal networking for online processing
  • Promoted out of management to senior technical staff, 1980

Products delivered:

  • Data-Network Modified Emulation Program (DMEP) -- 1979
  • CTX 9101 Terminal Interface Adapter -- 1979
  • CTX 9301 Management Station -- (prototype) 1979
  • TP3010 Terminal Interface Adapter -- 1980
  • TP3030 Management Station -- 1980
  • TP3025 X.25 Concentrator -- 1982

Documents, presentations, papers:

  • DataNetwork Modified Emulator Program (DMEP) for the IBM 3704/3705
    Cambridge Telecommunications Inc. (CTX), product documentation, 1979.
  • 3270 Display System Protocol, 3270DSP
    Approved and issued August 1981 by GTE Telenet, Tymnet, and Datapac.
    Second edition updates issued July 1983.
  • HPAD, An HDLC Packet Assembler/Disassembler Protocol for X.25 Networks
    Issued jointly by GTE Telenet and IBM Corp., 1984.


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This page last updated on  24-Feb-2013.