> On 7 Sep 2016, at 06:36, Philipp Winter <phw@xxxxxxxxx> wrote: > > On Tue, Sep 06, 2016 at 12:10:06PM -0400, Aaron Johnson wrote: >>> I suspect that one could approximate this number by accounting for the >>> probability of all exits being selected as guard, middle, and exit, but >>> I would prefer a simpler and more reliable approach. >> >> This doesn’t seem like a bad approximation to me, given that for as >> long as I have been aware, exits have had zero probability of being >> chosen in any position other than the exit position. > > Thanks, Aaron. You are right. Section 3.8.3 in dir-spec has the answer: > <https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt#n2611> > > I just proved this to myself with the small attached Python script. > Currently, exit bandwidth is the network's scarce resource, which is not > surprising since running an exit is riskier than running a guard or a > middle. Since exits are scarce, the bandwidth weights in case 3, > subcase A are currently in place: > <https://gitweb.torproject.org/torspec.git/tree/dir-spec.txt#n2726> > > In that case, the specification hard-codes the probability of an exit > taking on a non-exit role (Wgd, Wmd, and Wme) to 0. > <bandwidth-weights.py> It's also worth noting that Exits will serve directory documents and hidden service descriptors, and act as introduction and rendezvous points, so your estimates could be a few percentage points off. Tim Tim Wilson-Brown (teor) teor2345 at gmail dot com PGP C855 6CED 5D90 A0C5 29F6 4D43 450C BA7F 968F 094B ricochet:ekmygaiu4rzgsk6n xmpp: teor at torproject dot org
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