On Jan 10, 2016, at 11:28 AM, G3YYD wrote:
> If the checksum character is in error?
Send "AGN?" of course :-).
You can even automate the "AGN?", but with poor propagation, the back and forth
could end up sounding like Packet Radio :-).
Sending the serial number twice is a form error detection, that is why we use
it today, but it is rather inefficient. And the response to an error is
similarly, either "I don't need that mult," or sending "AGN?"
Sending the exchange 3 times allow a single error to be corrected, but, like
repeating something twice, is also inefficient. Even the rudimentary Hamming
code is better for correcting single errors.
The "3 copies" methodology has even been used in hardware in spacecrafts.
Avizienis at JPL called it "Triple Modular Redundancy." Nowadays, in the same
vein as error correction codes like the Hamming code (the grand pappy of them
all), Arithmetic Codes are much more efficient hardware implementation than
triple modular redundancy.
Happy New Year 2016, David!
Chen, W7AY
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