On Mon, Feb 24, 2014 at 1:10 PM, George Kadianakis desnacked@riseup.net wrote:
For example, I'm not sure if I'm using the correct bandwidth values. I'm currently using the value in 'w' lines of the consensus ('w Bandwidth=479'). I used to think that this is a unitless number, but looking at dir-spec.txt it seems to be "kilobytes per second". Is this the value I should be using to figure out which guards I should cut-off?
I was also under the impression that these weights are unitless, but they do seem to have some correlation to advertised average bandwidth. For example, if I sort the valid-after 2100UTC consensus by weights, and look at the 20 routers starting at weights of 1000,2000, 4000,8000,16000,32000, the median average bandwidth advertised by these nodes are:
weight - median advertised bandwidth 1000 - 795KBps 2000 - 1049KBps 4000 - 5181KBps 8000 - 6474KBps 16000 -12059KBps 32000 - 31457KBps
(For very low weights and very high weights the correlation breaks down pretty badly, though)
Any how, we would want to use the weights for cutoffs anyways, since otherwise "just lie to get above the guard threshold" becomes an interesting attack.
Another thought: we also should investigate how various thresholds affect the relationship between the cumulative guard weight total and the total exit weight.