Kantronics KPC–3 Plus User Manual page 22

Now that WØXI is in ―conversation‖ mode, the operator types in the message,
Step 4.
―HELLO‖, and presses the ENTER key on the computer to indicate the end of
the message and the beginning of the message's journey.
The computer sends the message, ―HELLO,‖ to the TNC for processing.
Step 5.
The TNC receives the message, ―HELLO‖, and takes charge of the situation,
Step 6.
performing a number of complex operations: it uses the ―connection‖
information about where the message is to go and the path it is to take and
combines this with the message itself to assemble a ―packet‖ of digital
information for transmission from the transceiver.
The details of what is in the packet and how it is organized are fully defined
by agreed-upon standards, so any machine that knows the ―rules‖ can make
use of the information.
The standard for amateur packet radio at this time is AX.25, so let's assume
the packet assembled in the TNC is an AX.25 packet.
Technical note: All amateur radio packets use the AX.25 standard, but it is
possible to use another standard or protocol (e.g., TCP/IP) "on top" of AX.25,
in which case the packet is referred to by the name of the highest-level
protocol.
After the TNC assembles the ―HELLO‖ message into a packet of digital
Step 7.
information in the TNC, it passes the packet on to a modem, which is also in
the TNC, which transforms the information into a series of audio signals for
serial transmission to station WØXI's transceiver.
Step 8. The TNC orders the transceiver to send a message (i.e., keys push-to-talk)
and then sends the audio version of the ―packet‖ through the radio port of the
TNC, up a cable to the microphone connector on station WØXI's transceiver,
and to the transmitter.
The packet is transmitted by WØXI's transceiver as a burst of radio-frequency
Step 9.
signals.
Step 10. The ―HELLO‖ packet, including address information (i.e., to, from, via) and
other control information, is now on the air, where it may be correctly
interpreted by all appropriately configured (i.e., AX.25 packet) stations that
receive the signal.
Step 11. KBØNYK is on the air and is running AX.25 packet, but it is too far away from
WØXI to pick up the signal, so does not get the message as it is sent from
WØXI.
Step 12. As we know from the ―connection,‖ already established, intermediate station
NØGRG, an AX.25 packet radio station, is on the air, and is close enough to
receive the radio burst sent by WØXI. It receives the burst of radio signals
from WØXI and passes the audio signals on to its TNC for processing. The
TNC (e.g., a KPC-3 Plus) transforms the signal from audio to digital, analyzes
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