>> Ethernet is not capable of performing in hard real-time. Check
>> some of the RFCs and other standards to see that ethernet involves
>> things like "random waits" in order to perform in many common
>> situations. The only way to avoid these situations is to have
>> exactly _one_ computer on the network.
That is not entirely true. While ethernet DOES involve potential collisions,
and random back-off periods in normal network operation, one can ensure
that collisions NEVER occur on a dedicated network where all the traffic
is under control of the real time system.
This is done by using a higher level message management scheme where no
two nodes can possibly transmit on the network at the same time, such
as in a host-polled or token passing scheme. While collisions may still
occur in error situations, such as multiple tokens or spontaneous regeneration
of lost tokens, or multiple remote stations with the same address, normal
realtime communications can be fairly predictable.
Rich Cloutier
SYSTEM SUPPORT SERVICES
