Re: [Bloat] Detecting bufferbloat from outside a node

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

Il giorno 27/apr/2015, alle ore 12:10, Paolo Valente <paolo.valente@unimore.it> ha scritto:

> 
> Il giorno 27/apr/2015, alle ore 11:57, Toke Høiland-Jørgensen <toke@toke.dk> ha scritto:
> 
>> Paolo Valente <paolo.valente@unimore.it> writes:
>> 
>>> a network-monitoring company got curious about bufferbloat issues and
>>> asked me to investigate a little bit the following issue (quite
>>> interesting in my opinion). Is it possible to detect, from outside a
>>> node, if the node is bufferbloated? In particular, the only action
>>> allowed would be to observe the packets entering and leaving the node
>>> (plus, of course, their timing).
>> 
>> Sure. Just measure the timing when the network is unloaded and compare
>> it to when it is loaded to capacity. We do that all the time.
>> 
>> The details of course depend on what you define by a 'node', what role
>> it plays in the network (does it forward or originate packets?), and
>> what control you have over the traffic flowing through it. :)
>> 
> 
> Let us consider, for example, a host with a VoIP call and a large-file transfer in progress. My concern is: from inside the host, we can measure the delays experienced by the VoIP application, but, form outside, how can we detect that the application is experiencing a high latency, or, indirectly, that there is bufferbloat and hence that the application is likely to be experiencing a high latency? (Of course, I am also about to read the documents suggested by Neil.)
> 

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.

Of course, if a bufferbloated state can be measured by other external measurements, then we can infer the problem indirectly.

Are there flaws in my above considerations?

Thanks,
Paolo

> 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/


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