[Bloat] Detecting bufferbloat from outside a node

[Neil Davies]

On 27 Apr 2015, at 22:37, Toke Høiland-Jørgensen <toke at toke.dk> wrote:

> Neil Davies <neil.davies at pnsol.com> writes:
> 
> .......
>> One of my adages is that "network quality" doesn' t exist - just like
>> you can't buy a box of "dark" and make a room dark by opening the box,
>> you can't buy a box of "network quality" - delivering quality in
>> networks is managing (through bounding) the "quality attenuation"
> 
> That much seems obvious. But do you have any analytical models that can
> actual predict the magnitude of the quality attenuation for a given
> network, say? And if so, are they available somewhere?

Yes, we have models for various network elements (see Lucian's
thesis for the stuff at CERN for example - see website) and the rest we can ascertain
by measurement.

The problem with a generic model is that is configuration dependent, you can 
estimate the overall ∆Q|V (as a starting point) using existing queueing theory. 
The issue is then how such V is distributed on various timescales (see below).

We measure and model this stuff commercially, and customers tend to be very
sensitive about such metrics!  We do have a technical report that provides
a lot more background for a specific deployment (funded by a public body)
that has been accepted for publication and should be published soon.

> 
> Also, some of the documents linked to from your web site seems to allude
> to a scheduling algorithm of some sort. Is that available in paper form
> (or better, code!) anywhere?

Toke, once you accept that ∆Q exists and is conserved then the only role of 
queueing and scheduling is to "share out the disappointment" (i.e assign ∆Q|V
to the set of competing streams/flows/aggregates).

Yes there is better code (and better approaches, see the patents) but we've found
that the key issue is creating the configurations. Given ∆Q|V's conservation and
that network elements are overbooked (and they are definitely more overbooked in 
the desire for low loss and and consistent low latency than they are for capacity) the
question becomes "what is the overall desired outcome as the network element
reaches saturation" - we can tailor that to any (feasible) collection of desires - now
get people to express, in any way that can be quantified, those desires!

The "code" consists of a collection "quality attenuators" - like cherish/urgency
multiplexers, stochastic shaper/policers arranged in an acyclic graph (all in the 
patent disclosures) - that make up the data path. Associated with that is 
the configuration system: given a set of QTAs - "quantities of quality required (bounds 
on ∆Q) and precedence for breach during saturation"  - it constructs a configuration 
(if one exists) that fulfils that set of requirements - also returning probabilistic measures
of the extent to which individual QTAs are likely not to be fulfilled.

> 
> 
> Thanks for your answers, will also take a look at the paper you linked
> in your other email. :)
> 
> -Toke

Neil