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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
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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) below)
- XXXX Choosing the length - XXXX Choosing the length
For circuits that are not "fast", when choosing among multiple For circuits that do not need to be not "fast", when choosing among
candidates for a path element, we choose randomly. For "fast" circuits, multiple candidates for a path element, we choose randomly.
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.
(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 Additionally, we may be building circuits with one or more requests in
mind. Each kind of request puts certain constraints on paths: mind. Each kind of request puts certain constraints on paths: