Kantronics KPC-9612 Plus, Руководство пользователя

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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 others’ packets. If you wanted to be absolutely sure that everyone got every-
thing 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 algo-
rithm 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.
Modes of Operation Packet Mode of Operation
User’s Guide 114 KPC-9612 Plus v 8.2