There have been lots of debates in the Bittorrent community about the subject of sharing ratios. Some Bittorrent websites are tracking their members' sharing behavior across multiple torrents to force people to contribute. Users with a low upload to download ratio might get punished by having their accounts revoked or being barred access to new content.

Bittorrent inventor Bram Cohen came out strongly against sharing ratios a few weeks ago. Cohen claims that the Bittorrent protocol can deal with people contributing less than the amount of data they download. He blaimed sites with enforced sharing ratios for people trying to cheat those ratios in an interview with Zeropaid.com:

"Sites which do this are being extremely destructive, and the way they grandstand about how they're fostering sharing really ticks me off."

Matei Ripeanu, Miranda Mowbray, Nazareno Andrade and Aliandro Lima seem to disagree. The four scientists just published an extensive paper about Bittorrent at First Monday. They analyzed the sharing behaviour within six Bittorrent communities - and came to the conclusion that sharing rations and other social norms can be beneficial to a community:

"Easytree’s sharing ratio enforcement mechanism has, in some cases, the side effect of creating a motivation to upload original content, a type of contribution that requires more effort than simply uploading existing content. A member whose sharing ratio is below the low sharing threshold cannot join new torrents. In this situation, one way for the member to raise its sharing ratio is to contribute new content. In this case there is a substantial reward for the extra effort: regaining the ability to join new torrents."


However, sharing rations are not the only way to ecourage users to contribute. Some other methods are more technical and less obvious:

"For example, a user may subscribe to an RSS feed of a site that publishes past episodes of television series, and state interest in any new episode from a particular series. Whenever the RSS feed announces matching content, the user’s client will download it automatically. In the time between finishing a download and the user checking to see whether new files have arrived, the client remains connected as a seeder. Thus, as a side effect, broadcatching results in increased seeding and sharing because users maintain their clients running for longer time."

Some of the data used for the study seems to be a little older - they analyzed Btefnet, a site that is offline since it got sued in May 2005 by the MPAA - but it's still a fascinating read for anybody interested in the inner workings of Bittorrent and P2P sharing / gifting economies.