>>>>> "Dresner," == Dresner, Norman A <[EMAIL PROTECTED]> writes:
>> -----Original Message----- From: Paul Koning
>> >>>>> "Kulwinder" == Kulwinder Atwal <[EMAIL PROTECTED]> writes:
>>
Kulwinder> What can be done is that real time networking protocols
Kulwinder> can be added. ... Where deterministic behavior has to be
Kulwinder> guaranteed and there is no room for error.
>> Those are dangerous words, because they are often associated with
>> a nasty but common misconception.
>>
>> ALL networks have non-zero error rates.
Dresner,> [BIG SNIP]
Dresner,> [Norm Says:] Well,,, Not quite.
Dresner,> There are a large class of networks that are designed to
Dresner,> have "errors", networks like Ethernet that work by
Dresner,> collision-detection.
Dresner,> But there are a larger class of networks that have "no
Dresner,> errors" during normal operation, for example networks that
Dresner,> work on master-slave protocols and token-ring networks.
Dresner,> {Also MIL-1553x MUXBUS networks which I'm heavily involved
Dresner,> with}
See, that's just what I mean. You missed my point by saying "during
normal operation".
ALL networks have bit errors. Consequently, ALL networks have packet
loss. If you think otherwise, you're making a mistake. Yes, those
rates are low, but they must always be non-zero. that's basic physics.
(If they are low enough, you can often get away with mistaking the
rate for zero -- for a while anyway.)
Token passing networks are a particularly nasty example. They are
often held up as "deterministic". Baloney. The most vulnerable clump
of bits in such networks is the token (because it spends so much time
on the wire) and loss of the token causes a LARGE glitch in
operation.
By the way, Ethernet collisions are not errors, and it's misleading to
call them that even in quotes. But that wasn't my point, really.
paul
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