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| author | Nick Mathewson <nickm@torproject.org> | 2007-04-20 17:17:13 +0000 |
|---|---|---|
| committer | Nick Mathewson <nickm@torproject.org> | 2007-04-20 17:17:13 +0000 |
| commit | 671b990f5168771051b251162698354ebbf39a6c (patch) | |
| tree | fb23b727599773cfdcccf70d7e2e8eaf058961f8 | |
| parent | 6ee5bef092f6abed7019a3e730e9f8f42264eea4 (diff) | |
| download | tor-671b990f5168771051b251162698354ebbf39a6c.tar.gz tor-671b990f5168771051b251162698354ebbf39a6c.zip | |
r12760@Kushana: nickm | 2007-04-20 11:23:21 -0400
Describe a simpler implementation for proposal 108, and note some limitations in the proposal.
svn:r9993
| -rw-r--r-- | doc/spec/proposals/108-mtbf-based-stability.txt | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/doc/spec/proposals/108-mtbf-based-stability.txt b/doc/spec/proposals/108-mtbf-based-stability.txt index 0023df0778..0424b1e46d 100644 --- a/doc/spec/proposals/108-mtbf-based-stability.txt +++ b/doc/spec/proposals/108-mtbf-based-stability.txt @@ -23,17 +23,17 @@ Spec changes: Replace the current rule for setting the Stable flag with: - "Stable" -- A router is 'Stable' if it is active and its observed MTBF - for the past month is at or above the median MTBF for active routers. + "Stable" -- A router is 'Stable' if it is active and its observed Stability + for the past month is at or above the median Stability for active routers. Routers are never called stable if they are running a version of Tor known to drop circuits stupidly. (0.1.1.10-alpha through 0.1.1.16-rc are stupid this way.) - MTBF shall be defined as the mean length of the runs observed by a + Stability shall be defined as the mean length of the runs observed by a given directory authority. A run begins when an authority decides that the server is Running, and ends when the authority decides that the server is not Running. In-progress runs are counted when - measuring MTBF. + measuring Stability. Issues: @@ -44,3 +44,18 @@ Issues: Surely somebody has done this kinds of thing before. +Alternative: + + "A router's Stability shall be defined as the sum of $alpha ^ d$ for every + $d$ such that the router was not observed to be unavailable $d$ days ago." + + This allows a simpler implementation: every day, we multiply yesterday's + Stability by alpha, and if the router was running for all of today, we add + 1. + +Limitations: + + Authorities can have false positives and false negatives when trying to + tell whether a router is up or down. So long as these aren't terribly + wrong, and so long as they aren't significantly biased, we should be able + to use them to estimate stability pretty well. |