Hello tor-dev,

I just added a tech report called "An Analysis of Tor Relay Stability" that might be interesting to people here to the metrics website:

https://metrics.torproject.org/papers/relay-stability-2011-06-30.pdf

From the introduction:

"The Tor network consists of around 2,000 relays and 500 bridges run by volunteers, some of which are on dedicated servers and some on laptops or mobile devices. Obviously, we can expect the relays run on dedicated servers to be more "stable" than those on mobile phones. But it is difficult to draw a line between stable and unstable relays. In most cases it depends on the context which relays count as stable:

[...]

In this analysis, we use a simulator to resemble how the directory authorities assign the Stable and Guard relay flags. This simulator uses archived directory data to decide when a relay was running and when it failed or was restarted. We further use this simulator to calculate future stability metrics that help us evaluate the quality of a given relay flag assignment. We modify the input parameters to Tor's stability metrics to see whether we can improve how the directory authorities should assign relay flags. The analysis data and simulator used in this report are available on the Tor metrics website at https://metrics.torproject.org/."

I also made the simulator code and input data available here:

https://metrics.torproject.org/papers.html

As always, feedback is highly appreciated!

Best, Karsten