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- Filename: 108-mtbf-based-stability.txt
- Title: Base "Stable" Flag on Mean Time Between Failures
- Version: $Revision: 12105 $
- Last-Modified: $Date: 2007-01-30T07:50:01.643717Z $
- Author: Nick Mathewson
- Created:
- Status: Open
- Overview:
- This document proposes that we change how directory authorities set the
- stability flag from inspection of routers declared Uptime to the
- authorities' perceived mean time between failure for the router.
- Motivation:
- Clients prefer nodes that the authorities call Stable. This flags are (as
- of 0.2.0.0-alpha-dev) set entirely based on the nodes' declared values for
- uptime. This creates an opportunity for malicious nodes to declare
- falsely high uptimes in order to get more traffic.
- Spec changes:
- Instead of setting the current rule for setting the Stable flag:
- "An authority should call a server Stable if its observed MTBF for
- the past month is at or above the median MTBF for Valid servers.
- MTBF 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."
- Issues:
- How do you define a clipped MTBF? If the current month begins with one
- day at the end of a one-year uptime, and then has 29 days of uptime, do we
- average one day and 29 days? Or do we average one year and 29 days? Or
- take 29 days on its own and discard the year?
- Surely somebody has done this kinds of thing before.
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