Do incentives build robustness in BitTorrent? Michael Piatek, Tomas Isdal, Thomas Anderson, Arvind Krishnamurthy, Arun Venkataramani Offense by Patrick Wong, Xian Yi Teng Do incentives build robustness in BitTorrent?

Contribution? The paper seeks to show ‘incentives don’t build robustness in BitTorrent’ I have verified this years ago by setting my upload rate to 0 and still getting the whole file, then disconnecting immediately

Contribution? The paper seeks to show ‘a strategic peer can raise download speeds while still contributing the same’ Already proven by BitThief (‘Free Riding in BiTorrent is Cheap’, Locher et al., HotNets, 2006) – high download rates without uploading any data

Contribution? BitTyrant as example to show that incentives don’t build robustness Not a threat – if trackers don’t like it, they ban it

Strategic? Benefit of optimistic unchoking: Might discover faster peers at all points in time BitTyrant abolishes optimistic unchoking => does it catch peers that start out slow but become fast later? What is BitTyrant’s performance, long-term?

Strategic? BitTyrant designed not to upload too much if you cannot download so much in return Instead, look for people with higher upload rates instead so you can do a better deal Benefits people with higher upload capacities How many people have such connections? How much does it benefit low upload connections?

Suspicions so far Long-term performance? Low upload capacity performance? Does evaluation answer these questions?

Evaluation? Real-world swarms ‘evaluation’ What is their peer’s upload rate? (UW machines, fast network, capped at 128 KB/s upload) How about slower uploads? (question 2) Perhaps BitTyrant only benefits fast uploaders? Also, torrents with files larger than 1 GB ignored – why?

Evaluation PlanetLab ‘evaluation’ Ooh! Varying upload speed performance?! Wait! File size is 5 MB? Long-term performance? (question 1) Perhaps with this behavior, in long term, original client would catch up and outperform BitTyrant?

Suspicions so far Paper tries to do the obvious Questionable if BitTyrant really offers much performance benefit

Conclusion Everyone knows incentives don’t build robustness – How many people seed till 1.0 ratio? But this is not a threat to BitTorrent So we can raise download speeds while contributing the same? Other incentive-unrelated (upload-unrelated) ways of increasing download speeds exist (better network positioning – Ono)