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r8826@totoro: nickm | 2006-10-01 17:58:45 -0400

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Disprefer exit nodes for entry, middle positions (fixes bug 200).  Also, switch to using a uint64_t to hold "total bandwidth for all nodes" under consideration; crypt_rand_int would have died at 2GB/s network capacity.


svn:r8571
This commit is contained in:
Nick Mathewson 2006-10-01 21:59:09 +00:00
parent 5353ddd05e
commit 992a3b271b
1 changed files with 17 additions and 8 deletions
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25
path-spec.txt
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@ -157,15 +157,24 @@ of their choices.
below)
- XXXX Choosing the length
For circuits that are not "fast", when choosing among multiple
candidates for a path element, we choose randomly. For "fast" circuits,
we choose
a given router with probability proportional to its advertised bandwidth
[the smaller of the 'rate' and 'observed' arguments to the "bandwidth"
element in its descriptor]. If a router's advertised bandwidth is greater
than MAX_BELIEVEABLE_BANDWIDTH (1.5 MB/sec), we clip to that value.
For circuits that do not need to be not "fast", when choosing among
multiple candidates for a path element, we choose randomly.
(XXXX We should do something to shift traffic away from exit nodes.)
For "fast" circuits, we a given router as an exit with probability
proportional to its advertised bandwidth [the smaller of the 'rate' and
'observed' arguments to the "bandwidth" element in its descriptor]. If a
router's advertised bandwidth is greater than MAX_BELIEVEABLE_BANDWIDTH
(1.5 MB/sec), we clip to that value.
For non-exit positions on "fast" circuits, we pick routers as above, but
we weight the clipped advertised bandwidth of Exit-flagged nodes depending
on the fraction of bandwidth available from non-Exit nodes. Call the
total clipped advertised bandwidth for Exit nodes under consideration E,
and the total clipped advertised bandwidth for non-Exit nodes under
consideration N. If E<N/2, we do not consider Exit-flagged nodes.
Otherwise, we weight their bandwidth with the factor (E-N/2)/(N+E-N/2) ==
(2E - N)/(2E + N). This ensures that bandwidth is evenly distributed over
nodes in 3-hop paths.
Additionally, we may be building circuits with one or more requests in
mind. Each kind of request puts certain constraints on paths: