[tor-bugs] #7509 [Tor]: Publish and use circuit success rates in extrainfo descriptors

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#7509: Publish and use circuit success rates in extrainfo descriptors
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 Reporter:  mikeperry                  |          Owner:                    
     Type:  enhancement                |         Status:  new               
 Priority:  normal                     |      Milestone:  Tor: 0.2.4.x-final
Component:  Tor                        |        Version:                    
 Keywords:  mumble-feature, tor-relay  |         Parent:  #5456             
   Points:                             |   Actualpoints:                    
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Comment(by aagbsn):

 Replying to [ticket:7509 mikeperry]:
 > arma suggests we publish create cell success rates in the extrainfo
 descriptors. We want to use these values to measure the actual rate of
 client circuit success network wide given our current path selection
 weights.

 I guess you mean that each relay publishes the average circuit success
 rate within a time window for all circuits, and not each edge (the success
 rate per relay).
 >
 > In this simple case, a graph traversal computation would do the trick,
 but ideally we want to do it in a way that is liar-resistant. Does this
 mean we should publish information on our observed peers' rates of CREATE
 success instead?
 Could you elaborate a bit here? What graph is being traversed?
 >
 > Perhaps this can be modeled as an eigenvalue problem, a-la eigenspeed
 (#5464). Since we're computing only a single scalar value for the whole
 network at the end as opposed to a vector of weights, there might be a
 simplification we could deploy that reduces the amount of stuff we need to
 shove into extrainfo.

 Perhaps you don't need each relay to report success rates for every relay
 it sees, but instead a (randomly selected?) subset?

 >
 > Either way, an extrainfo-based approach may end up being simpler to
 implement than a centralized scanner for reliably measuring circuit
 failure (see #7281).

 Perhaps it's worth doing both?
 >
 > I'm not sure I trust a fully self-reported scheme more without some kind
 of liar resistance, but it might end up that doing the graph traversal
 already bakes in as much liar resistance as you'd get from having each
 node report on its peers. It might be possible to prove this even, but
 something tells me empirical simulation is as close as we're going to get.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7509#comment:1>
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