>> and executed tha action, and ACK'ed, but the Transmitter does not see
>> the ACK? It will try again, and the receiver will execute again... and
>> if it is SET -> no problem, but if it is a Toggle -> troubles!
>
> This is a normal problem in any network where delivery is unreliable.  The
> usual solution is to associate a sequence number with each byte or command
> or packet.  If the same request is re-sent, then the same sequence number 
> is
> used.  The receiver can then detect and ignore multiple copies of the same
> request.
>
> Again, this has been a solved problem for a long time.  TCP associates a 
> 32
> bit sequence number with each byte, since it is a byte stream protocol.

Actually it has been solved a lot longer than that. Many of the earliest 
solutions used a 1-bit sequence number! Instead of a single ACK, there are 
two: types ACK-0 and ACK-1, which are alternated.

-- Bob Ammerman
RAm Systems

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