[tor-dev] Retiring old user number estimates

Karsten Loesing karsten at torproject.org
Tue Sep 17 09:24:18 UTC 2013

On 9/16/13 10:55 PM, Matthew Finkel wrote:
> Awesome work with these metrics. I am curious, however, why the new
> metrics are more correct than the old ones. The graphs are definitely
> smoother and including the requests to the Dir Auths seems correct,
> but are there other specific reasons for this choice?

The direct user numbers in the new approach are quite similar to the
ones in the old approach.  Including directory authorities is different,
right.  But the main reason for switching is that the code is much
cleaner, because it's shared code with computing bridge user numbers.
Oh, another reason is that results are much faster available than in the
old approach.  But the numbers aren't that different.

However, this is very different for bridge user numbers.  The old
approach counted total unique IP addresses seen at bridges, where
uniqueness was limited to single bridges.  The new approach is quite
similar to how we estimate direct user numbers; therefore the shared code.

I'm not sure how much detail to give here.  Maybe the tech report [0]
abstract explains this in some more detail:

As part of the Tor Metrics Project, we want to learn how many people use
the Tor network on a daily basis. Counting users in an anonymity network
is, obviously, a difficult task for which we cannot collect too
sensitive usage data. We came up with a privacy-preserving approach for
estimating directly connecting user numbers by counting requests to the
directory mirrors and deriving approximate user numbers from there. In
this report we describe a modified approach for estimating the number of
users connecting via bridges by evaluating directory requests made to
bridges. We compare this new approach to our current approach that
estimates bridge user numbers from total unique IP addresses seen at
bridges. We think that results from the new approach are closer to
reality, even though that means there are significantly fewer daily
bridge users than originally expected.

Let me know if there's something I should explain in more detail.

All the best,


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