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| author | Nick Mathewson <nickm@torproject.org> | 2006-10-01 21:59:09 +0000 |
|---|---|---|
| committer | Nick Mathewson <nickm@torproject.org> | 2006-10-01 21:59:09 +0000 |
| commit | 57ffca883d586c0b7e20eea2460587b409f9b302 (patch) | |
| tree | c308225bb41ec570809042c114a89b9982fef11c /doc/path-spec.txt | |
| parent | 219ad6395cea5403857c3adf1b938741dba79c4f (diff) | |
| download | tor-57ffca883d586c0b7e20eea2460587b409f9b302.tar.gz tor-57ffca883d586c0b7e20eea2460587b409f9b302.zip | |
r8826@totoro: nickm | 2006-10-01 17:58:45 -0400
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
Diffstat (limited to 'doc/path-spec.txt')
| -rw-r--r-- | doc/path-spec.txt | 27 |
1 files changed, 18 insertions, 9 deletions
diff --git a/doc/path-spec.txt b/doc/path-spec.txt index 77c0da2590..cfffd5289d 100644 --- a/doc/path-spec.txt +++ b/doc/path-spec.txt @@ -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. - - (XXXX We should do something to shift traffic away from exit nodes.) + For circuits that do not need to be not "fast", when choosing among + multiple candidates for a path element, we choose randomly. + + 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: |