Marvin Sirbu (firstname.lastname@example.org)
Thu, 9 Apr 87 10:05:00 edt
The answer to your question is that the MAP people do not fully understand
all the sources of probabilistic delay that you catalog. Some are beginning
to get the idea, however; Allen Bradley, a major factory automation company,
has just contracted with Bridge to OEM Ethernet equipment.
In their defense however, they have always been concerned about the situation
which might arise when a failure in a manufacturing process causes 500
sensors to all start sending emergency warning messages at the same instant.
This can lead to lockup on an Ethernet in a way which should not occur on a
token bus. I have heard stories to the effect that one process control
company experienced such a lockup on a 128 kbps CSMA/CD network and became an
adament supporter of token buses as a result. (Whether that experience could
be recreated on a 10 Mbps network is questionable, of course.)
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