Re: [Bloat] Detecting bufferbloat from outside a node

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

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Paolo

You are asking about the epistemology! Good start. The only things you can “know” outside the node are the things you can observe. You can infer, from the characteristics of the observations, conformance to some avowed model of behaviour.

Welcome to the world operational, denotational and intentional semantics as it relates to network performance!

Neil

On 27 Apr 2015, at 11:19, Paolo Valente <paolo.valente@unimore.it> wrote:

> 
> 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/
> 
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