Ethernet, Aloha and CSMACD 2397

Ethernet is used in hard RT vital safety-critical systems all the time. It's a matter of system design to make sure that collisions or a network failure doesn't result in unsafe conditions. Of course, if a Token advocate designed a CSMA-CD system you would end up with a disaster, because they would take the simplicity of working collision detection-backoff algorithms that work and layer on all sorts of crap to guarantee timeslots etc and end up with a system that doesn't work.

In fact I would be very critical of a safety-critical system where a network failure (here I'm lumping "excessive collisions" in with "network failure" which isn't too far off for Ethernet but of course the Token advocates will jump all over me for this) results in unsafe conditions.

Of course, I work in an industry where we take pride in our vital relays and vital processors having to meet more stringent failsafe standards than the detonation systems in thermonuclear weapons :-). But unlike say aerospace or road vehicle systems, my industry has the advantage that setting all signals to stop, dropping speed commands, and applying full-service brakes is the failsafe condition. It's hard to claim that shutting down an airplane's engines or applying full braking on a road vehicle is a failsafe condition...!

Tim.