Re: [Cake] Recomended HW to run cake and fq_codel?

[Jonathan Morton <chromatix99@gmail.com>]

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An important factor when designing the test is the difference between
intra-flow and inter-flow induced latencies, as well as the baseline
latency.

In general, AQM by itself controls intra-flow induced latency, while flow
isolation (commonly FQ) controls inter-flow induced latency.  I consider
the latter to be more important to measure.

Baseline latency is a factor of the underlying network topology, and is the
type of latency most often measured.  It should be measured in the no-load
condition, but the choice of remote endpoint is critical.  Large ISPs could
gain an unfair advantage if they can provide a qualifying endpoint within
their network, closer to the last mile links than most realistic Internet
services.  Conversely, ISPs are unlikely to endorse a measurement scheme
which places the endpoints too far away from them.

One reasonable possibility is to use DNS lookups to randomly-selected gTLDs
as the benchmark.  There are gTLD DNS servers well-placed in essentially
all regions of interest, and effective DNS caching is a legitimate means
for an ISP to improve their customers' internet performance.  Random
lookups (especially of domains which are known to not exist) should defeat
the effects of such caching.

Induced latency can then be measured by applying a load and comparing the
new latency measurement to the baseline.  This load can simultaneously be
used to measure available throughput.  The tests on dslreports offer a
decent example of how to do this, but it would be necessary to standardise
the load.

- Jonathan Morton

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