Re: [Bloat] Detecting bufferbloat from outside a node

[Neil Davies <neil.davies@pnsol.com>]

Toke


On 27 Apr 2015, at 13:03, Toke Høiland-Jørgensen <toke@toke.dk> wrote:

> Neil Davies <neil.davies@pnsol.com> writes:
> 
>> I don't think that the E2E principle can manage the emerging
>> performance hazards that are arising.
> 
> Well, probably not entirely (smart queueing certainly has a place). My
> worry is, however, that going too far in the other direction will turn
> into a Gordian knot of constraints, where anything that doesn't fit into
> the preconceived traffic classes is impossible to do something useful
> with.
> 
> Or, to put it another way, I'd like the network to have exactly as much
> intelligence as is needed, but no more. And I'm not sure I trust my ISP
> to make that tradeoff... :(

Ah - no such thing as intelligence here - you need to go for stochastics: 
there is no-way that E2E (or any other non-local control mechanism, cf SDN) 
can respond quickly enough - the system is more "ballistic" (hence the stochastic
dynamics as a better framing)

> 
>> We've seen this recently in practice: take a look at
>> http://www.martingeddes.com/how-far-can-the-internet-scale/ - it is
>> based on a real problem we'd encountered.
> 
> Well that, and the post linked to from it
> (http://www.martingeddes.com/think-tank/the-future-of-the-internet-the-end-to-end-argument/),
> is certainly quite the broadside against end-to-end principle. Colour me
> intrigued.

Yep - direct consequence of packet neutral behaviour !

> 
>> In someways this is just control theory 101 rearing its head... in
>> another it is a large technical challenge for internet provision.
> 
> It's been bugging me for a while that most control theory analysis (of
> AQMs in particular) seems to completely ignore transient behaviour and
> jump straight to the steady state.

Several years ago I calculated how long it would take a gigabit ethernet (with a 100 
buffer queue) to reach steady state (be within 1 part in 10^5)  when offered 100% 
offered load - it was six months! (usual mathematical caveats apply). Networks are
*NEVER* in steady state! We tend to try and make the "predictable" over 10 seconds -
at least beyond 10seconds control theory has a chance!

> 
> -Toke