[Tmrg] (limited) measurement of file size vs congestion level

[Sally Floyd]

Fabio -

Many thanks for the report.

- Sally
...
> 3. However, based on our experience (we have seen many severe  
> congestion events in this network), I can report the following  
> qualitative observations
>
>   A.  the user abandoning  process seems to be "with threshold" :  
> if you consider the frequency of TCP RST as a gross indicator of  
> user (or server) impatience, we saw that for mild congestion (right  
> before the peak hour, on a congested link) the RST stay at  
> physiological level (pretty low), while it sharply jumps to  
> abnormally high values when the congestion becomes severe (during  
> the peak hour)
>
>  B. if you look at the distribution of the number of packets  
> downloaded by each users in fixed timebins (e.g. 1 min), you see  
> that after a capacity upgrade that removes a congestion points,  
> such distribution changes, with more user downloading more packets  
> (as expected).
>
>
> 4. My expectation is that the users regulate the  duration of the  
> *session* and the total download rate (often across multiple  
> parallel TCP connection) based on the experienced response time,  
> there it is the *session* attributes (duration, rate), rather than  
> the *file* ones, that are dependent on the congestion level. At the  
> TCP level, this might means that it´s the connection arrival  
> process that is mostly impacted, rtaher than the size (the latter  
> is probably affected only in the tail of long files, which are  
> probably truncated upon congestion).
> Furthermore, after a certain threshold (severe congestion), users  
> or servers suddenly get crazy and start to reclick/reset the  
> downloads, and eventually give up the session.
...
> [1] "User patience and the Web: a hands-on investigation", by  
> Rossi, Casetti, Mellia, @ Globecom 2003.
> [2] F. Ricciato, F. Vacirca, P. Svoboda, Diagnosis of Capacity  
> Bottlenecks via Passive Monitoring in 3G Networks: an Empirical  
> Analysis, Computer Networks, vol. 51, n.4, pp. 1205-1231, March 2007
> [3]  http://userver.ftw.at/~ricciato/darwin/

- Sally
http://www.icir.org/floyd/