On Sun, Oct 12, 2014 at 06:43:10AM +1100, teor wrote:
On 11 Oct 2014, at 23:00 , tor-dev-request@lists.torproject.org wrote:
Date: Fri, 10 Oct 2014 14:33:52 +0100 From: Steven Murdoch Steven.Murdoch@cl.cam.ac.uk
I?ve just published a new paper on selecting the node selection probabilities (consensus weights) in Tor. It takes a queuing-theory approach and shows that what Tor used to do (distributing traffic to nodes in proportion to their contribution to network capacity) is not the best approach.
[snip]
For more details, see the paper: http://www.cl.cam.ac.uk/~sjm217/papers/#pub-el14optimising
[snip]
This is fantastic, Steven - and although we've changed Tor's consensus weights algorithm, we still waste bandwidth telling clients about relays that wold slow the network down.
Your result further supports recent proposals to remove the slowest relays from the consensus entirely.
I find this theoretically very interesting and an important contribution, but I'm less sure what conclusions it supports for Tor as implemented and deployed. A first major question is that the results assume FIFO processing of cells at each relay, but Tor currently uses EWMA scheduling and is now moving even further from FIFO as KIST is being adopted. There are other questions, e.g., that the paper assumes it is safe to ignore circuits and streams (not just for FIFO vs. prioritized processing but for routing and distribution of cells across relays as well---or said differently, Tor's onion routing, but this isn't). But I'm thinking if I'm correct even about this one point, then it would be extremely premature to directly apply the conclusions of this work to practical proposals for improving Tor performance. Then of course there are those pesky security implications to worry about ;>) My comments are not meant at all to question the value of the paper, which I think contributes to our understanding of such networks. Rather I am cautioning against applying its results outside the scope of its assumptions.
Cf. the KIST paper, which itself cites the EWMA introduction paper and subsequent related work. http://www.nrl.navy.mil/itd/chacs/sites/edit-www.nrl.navy.mil.itd.chacs/file... or http://www.robgjansen.com/publications/kist-sec2014.pdf
aloha, Paul