[mrtg] Re: Flat-lining W/O Rate Drop or Outage

[Alex van den Bogaerdt]

Jeff Hill wrote:

> Why would MRTG show a 64k ISDN connection flat-lining for short periods
> at rates of 2, 4 or 6kbps? There is no outage during these periods. 

There could be an outage in *monitoring* the link.  This will produce
the same result IIRC.

Perhaps the device is up but your monitoring process is not?  Or perhaps
it is unable to reach the target?

> Lastly, PSInet claims that bandwidth should be increased when average
> usage reaches 50%. I'm curious if anyone else has any experience in
> reasonable band usage.

This depends.  What do you promise the users of the link.  Personally,
I have to monitor peak usage, not average.  On some of the links I have
to monitor delay, not throughput.

This results in lines that may have an average, or even a peak rate of
20% being upgraded.  It is useless to monitor bandwith (alone) for these
links and other rules of the thumb apply.  For lines used only on
business hours for business purposes, peak usage will dictate when to
upgrade, averages will be low because it is bursty traffic.

I can imagine other links, for batch processing, such as email-only
links for instance, that can have an average usage of 80-90% before
being upgraded.  This also depends on expected growth of bandwidth
usage of course.  It would be silly to speed up mail delivery at the
costs involved with having 50% unused bandwidth.  A few seconds for
an email is nothing; a few seconds for interactive data processing
may be fatal.

regards,
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