Bottlenecks and link upgrades

Thu Aug 13 10:05:03 UTC 2020

>
> With tongue in cheek, one could say that measured instantaneously, the
> load on a link is always either zero or 100% link rate...
>

Actually, that's a first-class observation !

On Thu, Aug 13, 2020 at 12:00 PM Simon Leinen <simon.leinen at switch.ch>
wrote:

> m Taichi writes:
> > Just my curiosity. May I ask how we can measure the link capacity
> > loading? What does it mean by a 50%, 70%, or 90% capacity loading?
> > Load sampled and measured instantaneously, or averaging over a certain
> > period of time (granularity)?
>
> Very good question!
>
> With tongue in cheek, one could say that measured instantaneously, the
> load on a link is always either zero or 100% link rate...
>
> ISPs typically sample link load in 5-minute intervals and look at graphs
> that show load (at this 5-minute sampling resolution) over ~24 hours, or
> longer-term graphs where the resolution has been "downsampled", where
> downsampling usually smoothes out short-term peaks.
>
> From my own experience, upgrade decisions are made by looking at those
> graphs and checking whether peak traffic (possibly ignoring "spikes" :-)
> crosses the threshold repeatedly.
>
> At some places this might be codified in terms of percentiles, e.g. "the
> Nth percentile of the M-minute utilization samples exceeds X% of link
> capacity over a Y-day period".  I doubt that anyone uses such rules to
> automatically issue upgrade orders, but maybe to generate alerts like
> "please check this link, we might want to upgrade it".
>
> I'd be curious whether other operators have such alert rules, and what
> N/M/X/Y they use - might well be different values for different kinds of
> links.
> --
> Simon.
> PS. We use the "stare at graphs" method, but if we had automatic alerts,
>     I guess it would be something like "the 95th percentile of 5-minute
>     samples exceeds 50% over 30 days".
> PPS. My colleagues remind me that we do alert on output queue drops.
>
> > These are questions have bothered me for long. Don't know if I can ask
> > about these by the way. I take care of the radio access network
> > performance at work. Found many things unknown in transport network.
>
> > Thanks and best regards,
> > Taichi
>
> > On Wed, Aug 12, 2020 at 3:54 PM Mark Tinka <mark.tinka at seacom.com>
> wrote:
>
> >  On 12/Aug/20 09:31, Hank Nussbacher wrote:
>
> >  At what point do commercial ISPs upgrade links in their backbone as
> well as peering and transit links that are congested?  At 80%
> >  capacity?  90%?  95%?
>
> >  We start the process at 50% utilization, and work toward completing the
> upgrade by 70% utilization.
>
> >  The period between 50% - 70% is just internal paperwork.
>
> >  Mark.
>
>

-- 
Ing. Etienne-Victor Depasquale
Assistant Lecturer
Department of Communications & Computer Engineering
Faculty of Information & Communication Technology
University of Malta
Web. https://www.um.edu.mt/profile/etiennedepasquale
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