> > Can anyone tell me where I can find `rule-of-thumb'
> > numbers on acceptiable network errors and collision
> > rates? I have a network that is having performance
> > problems and I don't hove a baseline to compare it
> > to. Any help would be appreciated. Thanks.
> Network *errors* (i.e. CRC errors) should be virtually non-existent on any
> Ethernet. I have rarely seen more than one per DAY that was not the cause of a
> malfunctioning device or improper cable configuration.
> Collision rates are a worthless metric. Unless they are exceeding 100%, they
> tell you very little about the condition of the network.
While this may be true for 10Mb/s Ethernet, I wouldn't set this
100Mb/s systems. Even though the BER is lower for 100BASE-TX, you are
bits in less time and will therefore perceive a 'compression' of errors.
when observed over an hour instead of a day you may actually be seeing
are well within the BER specification of the physical layer. In
perceived increase in errors is not a problem. Moving toward Gigabit
one would need to scale the BER requirement along with the data rate in
to maintain the same expectation. This would not be a good thing for the
since BER is directly related to cost. One of the reasons for this is
BER of the PHY would need to be so high to make the implied guarantees
would take years to actually simulate and test each part to meet the
specifications without making extrapolations.
I would advise against creating these 'rules of thumb' since they lead
dangerous myths and preconceptions. Still, if you must, an acceptable
would be to calculate the BER based on the CRC error count and compare
the standard requirement. This comparison is somewhat unfair to the
since this number will be different than the BER rate of the physical
itself because CRC errors are a measure of total system BER. Don't be
a few orders of magnitude difference.
Since a single bit error is enough to cause a CRC error, I would count
CRC error as a single bit error. This may not strictly be the case for
caused by bursty noise, but some approximation needs to be made in a
Much like the touted 30% collision myth, CRC errors do not spell
disaster until the
BER is very close to 1...your definition of 'very' may vary :-)
BTW, I agree 100% on collision rates.
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The opinions above are mine, all mine. (And I'm a happy miser.)