Packet Modes of Operation
This chapter covers the major ways in which you may use your Kantronics
KAM’98 for packet operations. For details on particular commands, see the
“Command Reference” chapter.
Overview of Packet Communication
This section adds to the information presented in the introductory chapter on how
packet radio uses digital information for communication. By familiarizing your
-
self with the concepts presented here, you’ll be aware of and, if you wish, able to
change the default value(s) of the command parameters in your TNC to optimize
your packet activities.
Introduction
Information is Organized into “Packets”
A packet is a group of characters with a flag and header at the beginning and a
checksum and flag at the end. A flag is a specific character used to signify the be-
ginning and ending of a packet. The header is information indicating who the
packet is from, who it is to, any relay stations needed to get to the destination and
some control information. A checksum is a complicated mathematical formula
that produces a number based on the combination of characters that are in the
packet. This number is recalculated by every station that receives the packet and
if it does not match the number that is in the packet, the packet is thrown away,
thus near error-free communications. 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 the workhorse 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 to whatever device is attached, usually a com
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puter. As a relay device it also checks the packets it receives and determines if
the packets need to be resent, then does so if appropriate. As a sending device it
KAM’98 v 8.3 143 User’s Guide
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