tor/doc/spec/proposals/167-params-in-consensus.txt

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Filename: 167-params-in-consensus.txt
Title: Vote on network parameters in consensus
Author: Roger Dingledine
Created: 18-Aug-2009
Status: Open
Target: 0.2.2
0. History
1. Overview
Several of our new performance plans involve guessing how to tune
clients and relays, yet we won't be able to learn whether we guessed
the right tuning parameters until many people have upgraded. Instead,
we should have directory authorities vote on the parameters, and teach
Tors to read the currently recommended values out of the consensus.
2. Design
V3 votes should include a new "params" line after the known-flags
line. It contains key=value pairs, where value is an integer.
Consensus documents that are generated with a sufficiently new consensus
method (7?) then include a params line that includes every key listed
in any vote, and the median value for that key (in case of ties,
we use the median closer to zero).
2.1. Planned keys.
The first planned parameter is "circwindow=101", which is the initial
circuit packaging window that clients and relays should use. Putting
it in the consensus will let us perform experiments with different
values once enough Tors have upgraded -- see proposal 168.
Later parameters might include a weighting for how much to favor quiet
circuits over loud circuits in our round-robin algorithm; a weighting
for how much to prioritize relays over clients if we use an incentive
scheme like the gold-star design; and what fraction of circuits we
should throw out from proposal 151.
2.2. What about non-integers?
I'm not sure how we would do median on non-integer values. Further,
I don't have any non-integer values in mind yet. So I say we cross
that bridge when we get to it.