Link capacity upgrade threshold

Holmes,David A dholmes at
Tue Sep 1 22:00:56 UTC 2009

Another approach to collecting buffer utilization is to infer such
utilization from other variables. Active measurement of round trip times
(RTT), packet loss, and jitter on a link-by-link basis is a reliable way
of inferring interface queuing which leads to packet loss. A link that
runs with good values on all 3 measures (low RTT, little or no packet
loss, low jitter with small inter-packet arrival variation) can be
deemed not a candidate for bandwidth upgrades. The key to active
measurement is random measurement of the links so as to catch the
bursts. The BRIX active measurement product (now owned by EXFO) is a
good active measurement tool which randomizes probe data so as to, over
time, collect a randomized sample of link behavior.

-----Original Message-----
From: Aaron J. Grier [mailto:agrier at] 
Sent: Tuesday, September 01, 2009 12:19 PM
To: nanog at
Subject: Re: Link capacity upgrade threshold

On Tue, Sep 01, 2009 at 11:55:45AM +0100, Paul Jakma wrote:
> On Sun, 30 Aug 2009, Nick Hilliard wrote:
> >In order to get a really good idea of what's going on at a microburst
> >level, you would need to poll as often as it takes to fill the buffer
> >of the port in question.  This is not feasible in the general case,
> >which is why we resort to hacks like QoS to make sure that when there
> >is congestion, it is handled semi-sensibly.
> Or some enterprising vendor could start recording utilisation stats?

do any router vendors provide something akin to hardware latches to keep
track of highest buffer fill levels?  poll as frequently/infrequently as
you like...

  Aaron J. Grier | "Not your ordinary poofy goof." |
agrier at

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