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Re: Cisco PPP DS-3 limitations - 42.9Mbpbs?

  • From: Stephen Sprunk
  • Date: Wed Feb 20 13:58:12 2002

Thus spake "Randy Bush" <randy@psg.com>
> if you're using five min (or three min) samples, and you're seeing 70%,
> peaks are likely much higher and some users' packets are being dropped.
> by 80%, enough packets are being dropped that users are likely to see
> the effects of exponential backoff.  things do not improve above 80%.

One should note that any utilization up to 59.8% is, on average,
indistinguishable from an empty line.  70% = 1.6x delay, 80% = 3.2x, 90% =
8.1x, and 95% = 18.05x.  Of course, once you figure in finite buffering,
anything past 59.8% is likely to be dropping packets.

ObMath: Plot r^2/(1-r).  Where the derivative exceeds one (r~0.598), delay
increases faster than traffic rate.  Assumes random arrival times.

S





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