[tor-relays] Improving Node Connection Testing

[starlight.2015q2 at binnacle.cx]

>Mostly, latency and packet loss in nodes
>will negatively impact Tor's usability. . .

Was reading this thread and thought
of potentially useful and perhaps
not overly difficult BWauth
enhancement--perhaps worth
considering as part of ongoing
efforts to rework the BWauth
scripts.

When measuring a node, a BWauth
could spawn a 'tcpdump -w' PCAP
capture of the specific test
connection traffic and SIGTERM
it when that's finished.

Then run some tool or another
to analyze the connection for
SACKs and/or other indications
of the quality of the relay and
path.

Here's one example:

https://github.com/lennart-schulte/tcpdump-analyzer

Alternately, such a mechanism could
rely on a continuous 'tcpdump' running
with a large circular buffer and a
script or program could follow the test
connections and spit out a statistical
summary for completed ones to a
text log that would then be consumed
by the BWauth scripts.

If the idea has potential, someone
could perform a casual passive
'tcpdump' of test traffic and
examine a few connections.