On Thu, Oct 23, 2014 at 10:32:41AM -0700, David Fifield wrote: > In the past few months of bridge user graphs, there is an apparent > negative correlation between obfs3 users and vanilla users: when one > goes up, the other goes down. If you draw a horizontal line at about > 5500, they are almost mirror images of each other. I don't see it with > any other transport pairs. Any idea why it might be? > > I can see what could cause a simultaneous decrease in vanilla and > increase in obfs3: Tor gets blocked somewhere and users switch to obfs3. > But I wouldn't expect blocking events to look so smooth or happen so > frequently, and it doesn't explain why the reverse change happens later > (obfs3 being blocked while Tor is unblocked is less plausible). I can > also understand the overall long-term trend of obfs3 increasing and > vanilla decreasing. But I don't see why they should mirror each other so > closely over short time periods. > > Some hypotheses: > 1. There are lots of users who have a mix of vanilla and obfs3 bridges > configured. Their tor (randomly?) chooses one of them, which usually > works. The number of such users is constant over the short term; > i.e. the sum of obfs3+vanilla is constant, but the proportion of > obfs3 and vanilla fluctuates randomly. > 2. Maybe vanilla-down/obfs3-up is caused by blocking events, and > vanilla-up/obfs3-down is caused by natural new-user churn and/or > coincidence. > 3. There is something about the way BridgeDB hands out bridges, or the > way in which users use it, that causes it to give out obfs3 bridges > at the expense of vanilla and vice versa. > 4. Some kind of feedback loop: obfs3 bridges get used and get > congested, so users switch to vanilla, which then get used and > congested, etc.
I meant to include a link to the source graph (where you can also experiment with adding other transports). https://metrics.torproject.org/users.html?graph=userstats-bridge-transport&transport=%3COR%3E&transport=obfs3#userstats-bridge-transport David Fifield _______________________________________________ tor-dev mailing list [email protected] https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev
