[tor-dev] Statistics on fraction of connections used uni-/bidirectionally

Florian Tschorsch tschorsch at informatik.hu-berlin.de
Mon Dec 16 13:43:30 UTC 2013

Hi Karsten,

we still believe that the statistics are useful. However we also agree
with Rob that since more and more relays report data the scatter plot
becomes confusing. I think some kind of aggregation would be helpful.

In one of our previous papers we assessed the performance impact of
simultaneous TCP connections in overlay networks [1]. There we found
that the occurring performance degradation is hard(er) to solve when
connections are used bidirectionally -- which is the motivation for
these statistics. From the current results I would presume that this is
the case in Tor most of the time.

In Future developments the statistics could become helpful.


[1] D. Marks, F. Tschorsch, and B. Scheuermann, "Unleashing Tor,
BitTorrent Co.: How to relieve TCP deficiencies in overlays," in 35th
IEEE Conference on Local Computer Networks (LCN'10), 2010, pp. 320–323.

On 16/12/13 05:34, Rob Jansen wrote:
> Hey Karsten,
> I think the statistics could be useful, though I don't currently utilize them. I think the current presentation is somewhat confusing. Perhaps we can try to brainstorm some alternative ways to present the data if the decision is that we should keep it around.
> Best,
> Rob
> On Dec 9, 2013, at 12:43 PM, Karsten Loesing wrote:
>> Björn, Florian,
>> a few years back (in 2010, to be precise) we added statistics to
>> little-t-tor reporting what fraction of connections is used
>> uni-/bidirectionally.  Quoting dir-spec.txt:
>>    [At most once]
>>    Number of connections, split into 10-second intervals, that are
>>    used uni-directionally or bi-directionally as observed in the NSEC
>>    seconds (usually 86400 seconds) before YYYY-MM-DD HH:MM:SS.  Every
>>    10 seconds, we determine for every connection whether we read and
>>    wrote less than a threshold of 20 KiB (BELOW), read at least 10
>>    times more than we wrote (READ), wrote at least 10 times more than
>>    we read (WRITE), or read and wrote more than the threshold, but
>>    not 10 times more in either direction (BOTH).  After classifying a
>>    connection, read and write counters are reset for the next
>>    10-second interval.
>> These statistics are disabled by default, but when they are enabled,
>> relays publish them in their extra-info descriptors.  And quite a few
>> relays do that.  Here's a (bad) visualization (that used to be slightly
>> less bad when fewer relays published these statistics):
>> https://metrics.torproject.org/performance.html#connbidirect
>> Here's the question: Is there still value in having these statistics?  I
>> recall that they were useful in 2010, but will that still be the case in
>> 2013?
>> If the answer is "yes", never mind.
>> If the answer is "no", I'd create a ticket and submit a patch to remove
>> code parts from little-t-tor, and I'd remove the not-really-useful graph
>> from the metrics website.
>> Cc'ing Rob, Aaron, and Roger as the people who typically have an
>> interest in these kinds of statistics.  If other tor-dev@ people have an
>> opinion on this, please raise your voice!
>> All the best,
>> Karsten

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