[tor-dev] Per-transport bridge bandwidth and bridge counts

[Roger Dingledine]

On Sat, Jul 11, 2015 at 12:18:07PM -0700, David Fifield wrote:
> I made some graphs that show the count and total bandwidth of all
> bridges, broken down by transport.
> 	https://people.torproject.org/~dcf/graphs/pt-bandwidth-2015-07-11/pt-bandwidth.png
> 	https://people.torproject.org/~dcf/graphs/pt-bandwidth-2015-07-11/pt-count.png
> The top part of the graph is non-default bridges, and the bottom is
> default bridges (the ones that ship with Tor Browser).

Neat! Though alas you've done the thing that people do where they graph
twelve things at once, and all of them are basically variations on the
same color. So without some insight into the underlying data, I fear
these graphs are of limited use. (One fix is the one Karsten ended up
with on the metrics page, where you can choose which transports to graph,
providing an easy way to learn which line is which.)

> I have a question about getting bandwidth numbers. What I want is
> something like available bandwidth capacity; i.e., how much headroom
> transports have given their level of use.

Yeah, that isn't something that we explicitly provide. Nothing measures
it.

> I think that the bandwidth
> numbers I'm using are partially conflated with usage.

Correct.

> The bandwidth number I'm using is the "w Bandwidth=" line from a
> bridge-network-status document. It looks like this:
> 	w Bandwidth=2646
[snip]
> Another option for getting bandwidth is the "bandwidth" line in a
> bridge-server-descriptor document. It looks like this:
> 	bandwidth 1073741824 1073741824 2646895

The consensus weight for bridges is the min of these three bandwidth
values. Tonga does no bandwidth testing of its own currently.

> So it seems that bandwidth-observed is not what we want, because it's
> derived from current usage.

Well, ok. But it might be the best you've got. :)

> Yet another option is the speed of serving consensuses, the
> "dirreq-v3-tunneled-dl" line in a bridge-extra-info document:
> 	dirreq-v3-tunneled-dl complete=13624,timeout=1456,running=4,min=1938,d1=21008,d2=43181,q1=53397,d3=63519,d4=88911,md=117048,d6=146982,d7=180109,q3=199979,d8=223313,d9=298860,max=1558627
> You can take the "md=" field, for example, to get median B/s for serving
> consensuses.

Yes, this is an interesting option. It would be useful if all of the users
are distributed equally (with respect to user speed) over the bridges.
We originally put that feature in to measure *client* speeds, so it's
up for grabs whether it would work to turn it around and get something
useful about bridge speed.

--Roger