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occurs. Turning this command ON will make the stream designators show on every
connected packet received. Turning STREAMCA ON will also add the callsign of the
―from‖ station beside the stream designator.
Round Table Discussions
Several people talking together present a difficult situation for packet radio since the
protocol requires two stations to connect in order to make sure they receive each
other‘s packets. If you wanted to be absolutely sure that everyone got everything you
said, you would have to connect to each person and retype everything to each person.
That could get a bit cumbersome, so most people use the Unproto Mode and are aware
that a collision may occur once in a while. You can usually tell by the conversation if
something was missed; if you don‘t get an answer to a question it‘s probably not that he
is ignoring you, but either the question or the answer was corrupted by a collision.
Selective Monitoring
With MONITOR ON, the BUDLIST command can help in setting up your monitoring so
you will see only those packets you want to see. You can list up to 10 calls in BUDLIST.
Timing
Dwait vs. Persistence and Slottime
When the TNC acts as a digipeater, packets received that need to be relayed are
retransmitted as soon as the frequency is clear. Other TNCs on frequency (should) hold
off or wait their turn, using a PERSISTENCE/SLOTTIME algorithm or DWAIT method to
determine when to transmit. This practice has been adopted to reduce collisions with
packets being digipeated, since these packets must (by the AX.25 protocol) be
acknowledged end-to-end. Kantronics‘ current TNCs (e.g. KPC-3, KPC-3 Plus,
KPC-9612, KPC-9612 Plus, among others), use the PERSIST/SLOTTIME algorithm to
gain channel access. The default value for DWAIT is set to zero. If the DWAIT method
is used, the TNC sending non-digipeat packets will wait for DWAIT (times 10
milliseconds) time of clear channel before beginning to key-up the radio to transmit.
The algorithm used with the PERSIST and SLOTTIME parameters helps avoid
collisions by randomizing the wait time before transmitting. The more random the timing
the less chance of two TNCs transmitting at the same time and colliding.
Once the TNC detects a clear frequency it will wait SLOTTIME (times 10 milliseconds).
Then, if the channel is still clear, it will generate a random number. If this number is
smaller than the setting of PERSIST the TNC will transmit. If it is larger it will wait
another SLOTTIME and then generate another random number and again decide
whether to transmit or not. When using PERSIST and SLOTTIME you should set
DWAIT to 0, since both will be used if specified.
As an example, let‘s assume that PERSIST is set to 63, and SLOTTIME is set to 10.
This value of SLOTTIME results in a random number being generated every 100
milliseconds. When the TNC sees that the channel is clear, it waits 100 ms, then
generates a random number between 0 and 255 (inclusive). If, in our example, the
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