Re: [Bloat] Detecting bufferbloat from outside a node

[Paolo Valente <paolo.valente@unimore.it>]

Il giorno 27/apr/2015, alle ore 12:23, Toke Høiland-Jørgensen <toke@toke.dk> ha scritto:

> Paolo Valente <paolo.valente@unimore.it> writes:
> 
>> I am sorry, but I realized that what I said was incomplete. The main
>> cause of my concern is that, from outside the node, we do not know
>> whether a VoIP packet departs ad a given time because the application
>> wants it to be sent at that time or because it has waited in the
>> buffer for a lot of time. Similarly, we do not know how long the VoIP
>> application will wait before getting its incoming packets delivered.
> 
> No, not unless the application tells you (by, for instance,
> timestamping; depending on where in the network stack the timestamp is
> applied, you can measure different instances of bloat).

That’s exactly what I was thinking about. Actually it seems the only solution to me.

What apparently makes things more difficult is that I am not allowed either to choose the applications to run or to interfere in any way with the flows (e.g., by injecting some extra packet).

Any pointer to previous/current work on this topic?

> Or if you know
> that an application is supposed to answer you immediately (as is the
> case with a regular 'ping'), you can measure if it does so even when
> otherwise loaded.
> 

A ping was one of the first simple actions I suggested, but the answer was, as above: no you cannot ‘touch' the network!

> Of course, you also might not measure anything, if the bottleneck is
> elsewhere. But if you can control the conditions well enough, you can
> probably avoid this; just be aware of it. In Linux, combating
> bufferbloat has been quite the game of whack-a-mole over the last
> several years :)
> 

Then I guess that now I am trying to build a good mallet according to the rules of the game for this company :)

In any case, the target networks should be observable at such a level that, yes, all relevant conditions should be under control (if one does not make mistakes). My problem is, as I wrote above, to find out what information I can and have to look at.

Thanks,
Paolo


> -Toke


--
Paolo Valente                                                 
Algogroup
Dipartimento di Fisica, Informatica e Matematica		
Via Campi, 213/B
41125 Modena - Italy        				  
homepage:  http://algogroup.unimore.it/people/paolo/