[tor-scaling] Exploratory Analysis of Latency Tor data

Dennis Jackson djackson at mozilla.com
Tue Jul 9 04:38:15 UTC 2019

Hi all,

I've spent a week or so digging into some latency measurements of the Tor
network.  I've put together some graphs and my observations in a PDF here
which is created from a Google Slides Presentation (comments enabled) here
My cleaned up data sets and the source code for the graphs are also linked
at the end of the PDF in case anyone wants to play with it.

The takeaways:

   - Lots of graphs.
   - The Jan 2015 inflection point in the metrics data is due to 'siv'
   changing ISPs. Tor still has a bad phase followed by a good phase, but the
   change is more gradual and begins earlier.
   - There are still significant deviations between measurement servers in
   recent torperf data which are greater than can be explained by random
   - There are some exit nodes running behind a VPN which doubles or
   triples round trip time and worsens UX. However, current client/consensus
   code does not (directly) punish this.
   - *A non-negligible fraction of relays, get into a 'broken' state where
   round trip time is either normal for the relay, or delayed for 6 seconds. I
   can't find any explanation for this behavior. It seems to be consistent
   across Tor versions, host OS's and exit weighting. *
   - This is just an exploratory analysis. The dataset and analysis should
   be carefully examined before using it in any decision making.

If anyone can shed any light on the '6 second mystery', I'd be quite
interested! It also impacts nearly 1% of the requests in one dataset,
suggesting it might be having a real impact on UX.

Comments / Questions / Suggestions welcome, hope you all have a great time
in Stockholm!

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