[45805] in North American Network Operators' Group
Re: Cisco PPP DS-3 limitations - 42.9Mbpbs?
daemon@ATHENA.MIT.EDU (Stephen Sprunk)
Wed Feb 20 13:56:11 2002
Message-ID: <021c01c1ba40$2ddce890$e1876540@ssprunkpc>
From: "Stephen Sprunk" <ssprunk@cisco.com>
To: "Randy Bush" <randy@psg.com>,
"Stephen J. Wilcox" <steve@opaltelecom.co.uk>
Cc: <nanog@merit.edu>
Date: Wed, 20 Feb 2002 12:29:07 -0600
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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
