[tor-bugs] #24674 [Core Tor/Torflow]: Bandwidth authorities should use geographically distributed bandwidth servers

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#24674: Bandwidth authorities should use geographically distributed bandwidth
servers
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 Reporter:  teor              |          Owner:  tom
     Type:  task              |         Status:  new
 Priority:  Medium            |      Milestone:
Component:  Core Tor/Torflow  |        Version:
 Severity:  Normal            |     Resolution:
 Keywords:  tor-bwauth        |  Actual Points:
Parent ID:  #24499            |         Points:  3
 Reviewer:                    |        Sponsor:
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Comment (by mikeperry):

 We discussed this on tor-internal two years ago. The conclusion we came to
 then was that the simplest (and best) plan is to make the list of URLs in
 https://gitweb.torproject.org/torflow.git/tree/NetworkScanners/BwAuthority/bwauthority_child.py#n51
 contain a handful of fast, geographically distributed mirrors.

 This way, all bw authorities will use the same file servers, and the
 results that they produce for each relay should be an approximate
 arithmetic mean of its performance with each bandwidth file server (this
 is approximate because we do some measurement filtering, and because the
 choice of url is random, not strictly round robin:
 https://gitweb.torproject.org/torflow.git/tree/NetworkScanners/BwAuthority/bwauthority_child.py#n131).

 Then, for more diversity, we can move individual bw auths to
 geographically diverse locations. The result of this is that the directory
 authorities will take the median of their votes for each relay.

 The key advantage between this plan and just having each bw auth pick its
 own file server location is that we avoid having degenerate pairing
 effects of fast location to fast location, and we also avoid the need to
 do the full pairing combinations of (bw auth, file server) to achieve
 similar diversity with fixed pairings.

 I believe that controlling things in this way is also superior to surprise
 emergent effects of using a CDN.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24674#comment:2>
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