Terminal node controller
Encyclopedia
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
operators to participate in AX.25
AX.25
AX.25 is a data link layer protocol derived from the X.25 protocol suite and designed for use by amateur radio operators. It is used extensively on amateur packet radio networks....
packet radio
Packet radio
Packet radio is a form of packet switching technology used to transmit digital data via radio or wireless communications links. It uses the same concepts of data transmission via Datagram that are fundamental to communications via the Internet, as opposed to the older techniques used by dedicated...
network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
s. It is similar in function to the Packet Assembler/Disassembler
Packet Assembler/Disassembler
A packet assembler/disassembler, abbreviated PAD is a communications device which provides multiple asynchronous terminal connectivity to an X.25 network or host computer. It collects data from a group of terminals and places the data into X.25 packets...
s used on X.25
X.25
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...
networks, with the addition of a modem to convert baseband digital signals to audio tones.
The TNC was originally developed by Doug Lockhart, VE7APU, of Vancouver
Vancouver
Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...
, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, and popularized by the Tucson Amateur Packet Radio
Tucson Amateur Packet Radio
TAPR is an international amateur radio organization. It was founded in Tucson, Arizona, in 1981 by a group of amateurs interested in developing a terminal node controller for amateur use. Thus, the group was named Tucson Amateur Packet Radio, Inc. After developing one of the first widely...
association with the TNC-1 and TNC-2.
Description
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
, a modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, and software (in EPROM
EPROM
An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...
) 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
Bulletin board system
A Bulletin Board System, or BBS, is a computer system running software that allows users to connect and log in to the system using a terminal program. Once logged in, a user can perform functions such as uploading and downloading software and data, reading news and bulletins, and exchanging...
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
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
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
Transceiver
A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...
. Data from the terminal is formatted into AX.25 packets and modulated
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
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. In addition to these functions, the TNC manages the radio channel according to guidelines in the AX.25 specification.
Current status
TNCs were uniquely necessary when home computerHome computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a single nontechnical user...
s lacked the sophistication needed to simultaneously manage a network connection and communicate with the user. They are still used today throughout a very popular position reporting network known as APRS
Automatic Position Reporting System
Automatic Packet Reporting System is an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet system and distributed globally for ubiquitous and immediate access...
on 144.390 MHz (in Europe 144.800 MHz)
Powerful desktop computers are commonplace in amateur radio stations. Software modems using the computer's soundcard have lowered hardware requirements even further. However, with their lower cost comes additional tweaking in order to make them work properly, and they often don't provide the decoding capabilities at low Signal/Noise ratios. Some handheld and mobile VHF radios currently on the market incorporate TNC abilities within the radio itself in support of the APRS
Automatic Position Reporting System
Automatic Packet Reporting System is an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet system and distributed globally for ubiquitous and immediate access...
protocol.
Many TNCs are still in use, especially in unattended stations where reliability is important. The importance of location to the APRS
Automatic Position Reporting System
Automatic Packet Reporting System is an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet system and distributed globally for ubiquitous and immediate access...
system has fueled development of a new generation of small low-power TNCs often integrated with a GPS module for use in mobile tracking stations.
APRS
Automatic Position Reporting System
Automatic Packet Reporting System is an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet system and distributed globally for ubiquitous and immediate access...
digipeating
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
protocols require specific naming conventions, and older TNCs may not have the required support to be used as a digipeater. However, almost any TNC can be pressed into service for Home or Tracker use. TNCs that were clones of the popular TAPR
TAPR
TAPR can mean:*Tucson Amateur Packet Radio*TAPR Open Hardware License...
TNC-2 may be upgradeable via the UIDIGI firmware project.
TNC/Radio data ports
Although typically described as data ports, the interface between a radio and a TNC is almost entirely analog audio (plus lines for PTT and squelchSquelch
In telecommunications, squelch is a circuit function that acts to suppress the audio output of a receiver in the absence of a sufficiently strong desired input signal.-Carrier squelch:...
). The connectors used for this purpose varies widely across TNC manufacturers, but modern radios that offer data ports have widely adopted the Mini-DIN 6-pin connector. This may actually be defined in an ISO-9002 standard.
Also used are full-size DIN connectors, modular telephone (RJ) connectors, and combinations of mini- and micro-headphone connectors (typically on handheld radios).
- 6-pin Mini-DIN
