[Ecn-sane] bittorrent & ecn

[Dave Taht <dave.taht@gmail.com>]

I was kind of wondering if ecn would be used by bittorrent clients and
servers. (it's not supported by utp, I think, but when you use tcp, it
uses default tcp options) So I loaded up (FOR SCIENCE!) 100+ common
torrents with no limits on connections with an inbound fq_codel based
shaper in place and ecn enabled on the torrent client.

Yep. ecn gets used. How many torrent servers negotiate it? How many
clients? (I imagine the entire apple universe does now)

qdisc fq_codel 130: parent 1:13 limit 1001p flows 1024 quantum 300
target 5.0ms interval 100.0ms ecn
Sent 669116971742 bytes 525750376 pkt (dropped 750412, overlimits 0 requeues 0)
backlog 288139b 201p requeues 0
maxpacket 1514 drop_overlimit 1047 new_flow_count 65837164 ecn_mark 70963
new_flows_len 0 old_flows_len 73

sleep 60

qdisc fq_codel 130: parent 1:13 limit 1001p flows 1024 quantum 300
target 5.0ms interval 100.0ms ecn
Sent 671021262523 bytes 527225759 pkt (dropped 792750, overlimits 0 requeues 0)
backlog 46605b 39p requeues 0
maxpacket 1514 drop_overlimit 1047 new_flow_count 66286036 ecn_mark 74965
new_flows_len 0 old_flows_len 29

Remarkably my connection stayed pretty darn usable. In fact, I hardly
noticed. My streaming radio glitched once. Web was fine, but gmail
took a while longer to load all the resources. Taking a packet capture
now.

This is theoretically the most expensive bit of research I've ever
done for the bufferbloat project, in a matter of hours I'll have
violated copyright ~800 times, which is about 200m dollars at 250k
per.

Folk are encouraged to use vpns for torrents nowadays, but I can't see
how that would work with libutp and a max rtt of 100ms before it
starts to back off. I guess I'll look at that next.

Dear RIAA: I promise to delete the files when I'm done, and I'm only
capturing headers on the capture. I'd rather someone with the
protection of a major university followup on this line of research....


-- 
Make Music, Not War

Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-435-0729