BitTorrent today announced a new feature for its BitTorrent and uTorrent clients: Altruistic Mode. In short, the new experiment (available in BitTorrent 7.9.9 and above as well as uTorrent 3.4.9 and above) is for users who want to make sure that they upload more than they download, and who are okay with downloads never completing.
BitTorrent commonly refers to the infamous peer-to-peer (P2P) file-sharing protocol associated with piracy. But there is also a company by the name of BitTorrent, which owns the two most popular clients for the protocol: BitTorrent and uTorrent. Adding features like Altruistic Mode to these two clients means the feature could one day be adopted by other clients.
Altruistic Mode guarantees that your upload to download ratio is never much less than 2 to 1. Put another way, Altruistic Mode downloads if there are two peers who are interested, because for each new downloaded piece, it can upload to two peers. If there is only one interested peer, Altruistic Mode stops downloading, because it can’t uphold the ratio. Because BitTorrent peers upload as much as they can under normal conditions, the only way to improve the ratio is by downloading less. Thus, Altruistic Mode downloads will often never complete.
Why would you want to do this? BitTorrent explains the purpose of this mode and how it chose the ratio:
The intended use of Altruistic Mode is to help out a swarm. This can help other peers download faster or ensure a peer has a good sharing ratio. This is especially helpful in conditions where there are already plenty of seeds, which often happens after a torrent has been available for a while.
We selected a 2:1 ratio because it’s impossible to have a number of interested peers between 1 and 2, and 1 is too small, so that left 2 as a logical choice. Shooting for a higher ratio would result in very little uploading even in some conditions where it makes sense to do so, which was extremely confusing to users in testing and is a waste of resources. Going for a higher number could also cause swarms to no longer have a complete copy of the file if too many peers are in Altruistic Mode, which would harm not just the one peer in Altruistic Mode but other peers as well. Because of this, we feel that a 2:1 ratio is a sweet spot and aren’t offering any user configuration options for it.
Because Altruistic Mode isn’t how most users expect BitTorrent clients to function, the company has made sure it needs to be unlocked first (Preferences => BitTorrent => Enable Altruistic Mode). Only then can you turn it on from the download dialog or in the properties of a given torrent.
If this experiment goes well, BitTorrent is considering rolling out another feature in which a peer starts out in Altruistic Mode and later turns it off (returning to regular Download Mode). This would let peers who want to get a complete file eventually, but aren’t in a rush, help speed up the process for other peers who care about getting it sooner.