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Concept
Terminal node controller
Summary
A terminal node controller (TNC) is a device used by amateur radio operators to participate in AX.25 packet radio networks. It is similar in function to the Packet Assembler/Disassemblers used on X.25 networks, with the addition of a modem to convert baseband digital signals to audio tones.
The first TNC, the VADCG board, was originally developed by Doug Lockhart, VE7APU, of Vancouver, British Columbia.
Amateur Radio TNCs were first developed in 1978 in Canada by the Montreal Amateur Radio Club and the Vancouver Area Digital Communications group. These never gained much popularity because only a bare printed circuit board was made available and builders had to gather up a large number of components.
In 1983, the Tucson Amateur Packet Radio (TAPR) association produced complete kits for their TNC-1 design. This was later available as the Heathkit HD-4040. A few years later, the improved TNC-2 became available, and it was licensed to commercial manufacturers such as MFJ.
In 1986, the improved "TNC+" was designed to run programs and protocols developed for the original TNC board.
TNC+ also included an assembler and a version of Forth (STOIC), which runs on the TNC+ itself, to support developing new programs and protocols.
A typical model consists of a microprocessor, a modem, and software (in EPROM) that implements the AX.25 protocol and provides a command line interface to the user. (Commonly, this software provides other functionality as well, such as a basic bulletin board system to receive messages while the operator is away.) Because the TNC contains all the intelligence needed to communicate over an AX.25 network, no external computer is required. All of the network's resources can be accessed using a dumb terminal.
The TNC connects to the terminal and a radio transceiver. Data from the terminal is formatted into AX.25 packets and modulated into audio signals (in traditional applications) for transmission by the radio. Received signals are demodulated, the data unformatted, and the output sent to the terminal for display.
Official source
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