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Researchers Create Selfish BitTorrent Client
An anonymous reader writes "Researchers from the computer science department at the University of Washington have released BitTyrant, a new BitTorrent client that is designed to improve download performance via strategic selection of peers and upload rates. Their results call into question the effectiveness of BitTorrent's tit-for-tat reciprocation strategy which was designed to discourage selfish users. Clients are available for Windows, OS X, and Linux."
Selfish selection of peers can lead to cliques of clients on the same network. Tit-for-tat has been proven as a highly effective strategy in games resembling the iterated prisoner's dilemna, but it can be defeated when a large enough group of of agents cooperate. This link has more.
Some folks at ETH Zurich took it one step further, and wrote a client - BitThief - that doesn't upload and yet still can download as fast as a regular client. This is especially valuable in countries that define copyright violation to be the uploading of content.
"But it prioritizes users with high upload/download speeds. It's better the way it's now - everybody gets their files."
I disagree to an extent. What is high upload/download speed to one node is not neccessarily high upload/download speed to another node. It just depends on the network topography. It's possible for a DSL-connected node to have a faster upload/download connection to a node on a dial-up line than a T3 if the dial-up connection is significantly closer from a network standpoint. If done properly, prioritizing based on uploads could lead to more regionalized torrent relationships. Such a setup still has its downsides but I'm not convinced it's worse or even unfair.
Not rare, it's extremely common on private sites with specialized material. I've had trouble raising my ratio above 0.85 on DIME, in spite of having 250KB/s upload. It's annoying, but there's not much you can do about it.
LOAD "SIG",8,1
Ditto that. I only torrent stuff that is completely unavailable commercially: so-called "out-of-print" material. (What the hell: it's a bunch of zeros and ones, just like all the other zeros and ones. How can it be out of print?) If you're trying to get soundtracks from obscure 1980's movies or ripped '50's jazz LP's, it's pretty frequent that the number of seeders vastly outnumbers the number of people who are still trying to find it.
Nostalgia's not what it used to be.
Indeed, it's true that BitTyrant will not always improve performance, even when directly compared to other clients on the same torrent at the same time! There are several reasons for this:
- Data availability: Suppose seeders are sending out data at 20 k/sec, and a complete copy does not yet exist in the swarm. Then, even if you start downloading quickly, eventually you will catch up to the data production point and download at no faster than 20 k/sec.
- Luck of the draw: sometimes, you'll get a lucky peer (or seed) from the tracker. Because most trackers only return a subset of the peers available, BitTyrant can't make its peering selections with global information. If one client happens to get several high capacity peers that BitTyrant never sees, relative performance may be worse.
- Seed dominated performance: if there are a lot of seeds for a file, their altruistic contribution might dominate performance. BitTyrant is designed to improve download performance when tit-for-tat controls download speeds. This is typically the case when there are few seeds for a file, but many leechers.
These provide just a glimpse at the many factors that drive BitTorrent download performance. For a more thorough treatment, check out the paper:http://www.cs.washington.edu/homes/piatek/papers/
This is why we conducted an evaluation on not just one torrent, but more than 100, drawn from popular aggregation sites like mininova and piratebay. Aggregate statistics are necessary to have an idea of performance in general, as opposed to special cases that can arise.
Emule has a system like this, and it basically slows everything down in the name of fair sharing. It takes absolutely forever to start downloads, since you're stuck in a vicious "chicken and egg" circle of "I can't upload anything to download" and "I can't download anything to upload".
As it stands, Bittorrent is how the Edonkey protocol used to be before ratio systems were added to the clients; Fast. After Edonkey started adding anti-leech systems to the clients, the speed went into the toilet, and the queues started skyrocketing.
I suspect that if this catches on, you can kiss 300kb's downloads goodbye.
In Soviet Russia, Trojan exploits YOU!