Re: [Bloat] Detecting bufferbloat from outside a node

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

Paolo

On 27 Apr 2015, at 12:54, Paolo Valente <paolo.valente@unimore.it> wrote:

> Thanks for the pointers. As for the epistemological implications of to my concerns, I must admit that I find them a little bit frightening :)
> 
> After browsing some of the presentations, the relevant component for my problem seems to be the variability V. However, it is not clear to me how I can measure or infer it in my situation, i.e., if I cannot:
> 1) have any feedback on the user experience;

You'll need to consider the ∆Q|G and the ∆Q|S as well - they contribute to the overall delay and that contributes to the delivered performance. Response time to get to a certain data flow rate (say for VoD) or recovery from a packet loss (for TCP) etc interact with all the factors.

We've created models (both analytic and experimental) which relate the delivered ∆Q (all of its factors) to QoE for various apps

> 2) measure the time that elapses between when a time-sensitive application puts a message in a socket and when that message is actually sent by the node in a packet;

This is why the capture model has to be one of "timed traces" of "observables" in the TCP model the socket is one location to measure (at the two ends), the network interfaces would be another

> 3) in the opposite direction, measure the time that elapses between when a packet arrives to the node and when the application receives the message contained in the packet.

Yes, you need to view this in both directions as you need to isloate the effect of the network transport from the processing (which also has an influence on the performance)

> 
> On which documents should I concentrate more to better understand this point?
> 
> Thanks,
> Paolo
> 
> Il giorno 27/apr/2015, alle ore 11:54, Neil Davies <neil.davies@pnsol.com> ha scritto:
> 
>> Paolo
>> 
>> Yes, it is - there is a whole methodology for detecting this and associated algebra for manipulation. It has been used at CERN, in various telcos and in various large scale, real time distributed systems to relate end user outcomes to the delay/loss characteristics of the network.
>> 
>> 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.
>> 
>> Neil
>> 
>> On 27 Apr 2015, at 10:48, Paolo Valente <paolo.valente@unimore.it> wrote:
>> 
>>> Hi,
>>> 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).
>>> 
>>> If such a general problem is to hard or impossible to solve, do you think it is still possible at least to understand, for some type of application, if the application is experiencing a high latency because of bloated buffers inside the node? (As above, by just observing packet flows from outside the node.)
>>> 
>>> Thanks,
>>> Paolo
>>> 
>>> _______________________________________________
>>> Bloat mailing list
>>> Bloat@lists.bufferbloat.net
>>> https://lists.bufferbloat.net/listinfo/bloat
>> 
> 
> 
> --
> Paolo Valente                                                 
> Algogroup
> Dipartimento di Fisica, Informatica e Matematica		
> Via Campi, 213/B
> 41125 Modena - Italy        				  
> homepage:  http://algogroup.unimore.it/people/paolo/
>