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:
"conn-bi-direct" YYYY-MM-DD HH:MM:SS (NSEC s) BELOW,READ,WRITE,BOTH NL [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