[Bloat] Detecting bufferbloat from outside a node

[Neil Davies]

On 27 Apr 2015, at 11:45, Toke Høiland-Jørgensen <toke at toke.dk> wrote:

> Neil Davies <neil.davies at pnsol.com> writes:
> 
>> Take a look at http://www.pnsol.com/publications.html, you may find
>> http://www.pnsol.com/public/PP-PNS-2009-02.pdf as a good starting
>> point.
> 
> I've seen this referred on the list before (I assume by you ;)), but
> haven't really grok'ed it before. I like the delta-Q measure as a way of
> thinking about overall network performance; and there's definitely
> parallels to thinking about the end-to-end 'latency budget', which I
> also find quite instructive (I think I it picked up from Joe Touch at
> some point).

You'll find the way that ∆Q can be decomposed into basis set of
∆Q|G, ∆Q|S and ∆Q|V - helps work out which parts of the budget 
get eaten up by different elements of the network design/architecture.

> 
> How do you deal with the fact that loss and delay can be exchanged for
> each other (via retransmissions)?

Yes, the QTA/∆Q framework is recursive in that sense - you can relate (for 
example) the "TCP layer ∆Q" to the "IP packet level ∆Q".

> 
> Also, which publication would you recommend if I'm interested in
> specifically how you 'Mathematically model behaviour and delta-Q' as you
> mention in that slide set? :)
> 

Depends on your starting point: 
 - if it is "how does this relate to the end user" - look at "the properties and mathematics of data transport quality" 
-  if it is "how do I measure this stuff in a real network" - take a look at "advanced network performance measurement techniques" (you can get to it off the links tab)

> -Toke

Neil