sergio masci wrote:
> 
> Do you keep sending the same message until it is acknowledged (ACK/NAK) or 
> do you at some point decide "this message isn't getting through" and 
> discard it?

I first interpreted this as somehow referring to PIClist 
politics/protocol... heh...

> What happens if the slaves go off line for a while? Will you have a queue 
> of messages builing up clogging your network (continually being re-sent). 
> Will the messages have any meaning if they are delayed for too long.

I find these questions are generally best resolved by looking at an 
individual device and value.  E.g., for a pager event (a button is 
pressed in room A, intending to trigger a tune played in room B), I 
repeat the message up to five times or until I get an ACK, and play a 
confirmation/error sound in room A as feedback.  For a temperature 
sensor that's reporting frequently, maybe a simple broadcast with no ACK 
is fine.

So I think in general, a good protocol layer provides for these 
alternatives, and standardizes them, but the application layer needs to 
decide which is appropriate.
-- 
Timothy J. Weber
http://timothyweber.org
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