Step 6. The TNC receives the message, “HELLO”, and takes
charge of the situation, 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 orga
-
nized are fully defined by agreed-upon standards, so any
machine that knows the “rules” can make use of the in
-
formation. 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 pro-
tocol (e.g., TCP/IP) “on top” of AX.25, in which case the
packet is referred to by the name of the highest-level pro-
tocol.
Step 7. After the TNC assembles the “HELLO” message into a
packet of digital 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 ca
-
ble to the microphone connector on station WØXI’s
transceiver, and to the transmitter.
Step 9. The packet is transmitted by WØXI’s transceiver as a
burst of radio-frequency signals.
Introduction Packet Communication
User’s Guide 26 KAM’98 v 8.3
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