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Re: Solving the need for ISA or USB slots and Serial Ports



Don Woodward KD4APP wrote:

>UDP is not guaranteed for delivery whereas IP is - do you really want your
>rotator to be commanded to be moved without ever receiving a "stop"
>command? Of course the limit switches would kick in but it could
>potentially over-use some of these rotators which are not designed for
>constant use.
>
>Or even worse a TX command to key your radio without a unkey?

Protocol names (TCP vs UDP vs IP) notwithstanding,
this is an application where UDP might be the way to go.

The disadvantage of using TCP is that it will mindlessly
pound on the packets until it gets the response it's looking
for, *whether that response is still relevant or not*. Using UDP
with the retry mechanism in a higher-layer protocol makes
it possible to be a bit more intelligent about these things.

Example: send a transmitter key command. ACK gets lost.
TCP will pound on the key command until it gets the
ACK. A smarter protocol could try a couple of times for an
ACK, then send a shutdown command to try to put the
system in a safe state.

I've been doing a lot of work in my Real Job (tm) with
SCTP lately. It could be very handy too, but isn't something
you find on tiny single-board computers...

Laura Halliday VE7LDH     "Que les nuages soient notre
Grid: CN89mg                       pied a terre..."
ICBM: 49 16.05 N 122 56.92 W     - Hospital/Shafte

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