[tor-talk] About bandwidth weights selection

[saurav dahal]

Hello,

The following is the default Tor network in shadow simulator:

Total BW of Guard flagged nodes=258.15 MB/S
Total BW of Middle nodes=23.69 MB/S
Total BW of Exit flagged nodes=13.23 MB/S
Total BW of Guard+Exit flagged nodes=213.4 MB/S

Now, I inserted 40 guard nodes and 40 exit nodes, each of 5 MB/S in above
Tor network and performed the simulation.

Following are the bandwidth weights derived from the consensus document
when Guard and Exit nodes of 5MB/S are added separately:


Wbd=1454 Wbe=0 Wbg=4882 Wbm=10000 Wdb=10000 Web=10000 Wed=7091 Wee=10000
Weg=7091 Wem=10000 Wgb=10000 Wgd=1454 Wgg=5118 Wgm=5118 Wmb=10000 Wmd=1454
Wme=0 Wmg=4882 Wmm=10000


Then again, I added 80 Guard-Exit (EE) nodes, each 5MB/S and perform the
simulation.


Following are the bandwidth weights derived from the consensus document
when EE nodes of 5MB/S are added:


Wbd=4722 Wbe=0 Wbg=0 Wbm=10000 Wdb=10000 Web=10000 Wed=4826 Wee=10000
Weg=4826 Wem=10000 Wgb=10000 Wgd=452 Wgg=10000 Wgm=10000 Wmb=10000 Wmd=4722
Wme=0 Wmg=0 Wmm=10000


I calculated catch probability in both cases and found that the 2nd case
yields more probability.


By examining the above weights, how it is possible that the catch
probability for EE nodes are much higher than those of guard and exit node
separately? OR is there any other reason for this?


On Tue, Aug 12, 2014 at 7:10 PM, George Kadianakis <desnacked at riseup.net>
wrote:

> saurav dahal <dahal.saurav at gmail.com> writes:
>
> > Under which condition, the client will choose Guard flagged node and
> > Guard+Exit flagged node for guard position?
> >
>
> Tor will consider any node with the Guard flag during guard selection
> (this also includes Guard+Exit nodes). As you noticed, it will apply
> different weights to nodes with the Guard flag and to nodes with the
> Guard+Exit flag.
>
> Please read the "Guard nodes" section of path-spec.txt:
> https://gitweb.torproject.org/torspec.git/blob/HEAD:/path-spec.txt
>
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-- 

Saurav Dahal,
Wireless communication and Networking lab,
Dept. of Computer Engineering,
Chosun University,
309 Pilmun-daero, Dong-gu
Gwangju, 501-759 S.KOREA