Kantronics KPC–3 Plus User Manual
Also see for KPC-3 Plus: User guideUser guideManual
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Contents
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64Modes of OperationThis chapter covers the major ways in which you may use your Kantronics TNC. Fordetails on particular commands, see the ―Command Reference‖ chapter.Packet Mode of OperationThis section adds to the information presented earlier (in the Getting Started and othersections) on how packet radio uses digital information for communication. Byfamiliarizing yourself with the concepts presented here, you‘ll be aware of and, if youwish, able to change the default value(s) of the command parameters in your TNC tooptimize your packet activities.IntroductionInformation is Organized into “Packets”A packet is a group of characters with a flag and header at the beginning and achecksum and flag at the end. A flag is a specific character used to signify thebeginning and ending of a packet. The header is information indicating who the packetis from, who it is to, any relay stations needed to get to the destination and some controlinformation. A checksum is a complicated mathematical formula that produces anumber based on the combination of characters that are in the packet. This number isrecalculated by every station that receives the packet, and if it does not match thenumber that is in the packet, the packet is thrown away, thus near error-freecommunications. A packet is also called a frame.Your Packet Unit is a Terminal Node Controller (TNC)Packet radio modems, or packet modems, are generally referred to as TNCs. This―label‖ or ―moniker‖ was adopted when the Tucson Area Packet Radio Group (TAPR)developed their first ―TNC-1" packet radio modem kit in the early 1980s. The TNC is theworkhorse of packet radio. As a listening device it hears an audio signal from the radio,changes the data to digital form, determines if the data is a good packet and sends it towhatever device is attached, usually a computer. As a relay device it also checks thepackets it receives and determines if the packets need to be resent, then does so ifappropriate. As a sending device it receives digital data from the computer, packetizes itand changes it into audio tones, which are sent out to the radio. The rule the TNC usesto do all of this is called a protocol.Protocol for Amateur Packet Radio: AX.25The most commonly used protocol in amateur packet radio is AX.25. The details of theinner workings can be found in a book titled ―AX.25 Amateur Packet-Radio Link-LayerProtocol‖, which is available from the ARRL. Most TNC users will not need to or care togo into the details. The TNC takes care of the nitty gritty work for you, although thereare parameters you can set that determine how efficiently some of that work is done. |
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