Friday, May 12, 2006

BitTorrent goes legitimate

The inventor of BitTorrent has struck a deal with Warner Bros. to distribute movies online. I'm not sure why Warner Bros. feel they need to pay Bram to use his technology, but I'm sure he's happy enough about it.

Of course, Warner Bros. are getting into P2P technology not as a way share the videoware. The new system will be fully encumbered, and apparently no cheaper than buying a DVD in the shops. The main motivation for Warner Bros. seems to be getting free bandwidth for the huge download volumes involved.

It's worth asking where this free bandwidth is coming from. After all, someone must be providing it. Unfortunately it seems that BitTorrent just distributes the cost amongst all the ISPs involved. That wouldn't be so bad, but BitTorrent doesn't make particularly good use of the bandwidth. A file in a BitTorrent download swarm ends up crossing the expensive transcontinental links multiple times because BitTorrent users are downloading from each other.

I wonder whether this is why ADSL Internet providers always give such paltry upload speeds. Here in Europe, transatlantic traffic costs the ISP real money, and the more their users make use of file sharing, the more transatlantic traffic they cause.

It was considerations like this that motivated my patch to Azureus which was later turned into a rather popular plugin by some guys I never met. In its current incarnation it displays flags to show the locations of the peers you are currently downloading to or from. (In my version you just got the 2-letter country codes, which was probably more informative, but less colorful.) In fact I think what is really needed is for the peer selection heuristics to be modified to automatically take the distance to the peers into consideration. In a lot of countries there is a free exchange point that the ISPs can use to exchange data without a volume charge. If BitTorrent preferred 1) peers on the same ISP 2) peers on the same exchange 3) peers on the same continent, it would be much more ISP-friendly, which ultimately is good for everyone. It would probably be faster too.

The Julia system addresses some of these concerns. As far as I can work out they use heuristics to determine which peers are close to each other. In fact I think this data could easily be provided by the ISPs, and it would clearly be in their interest to do so. An obvious way to do it would be by storing configuration information in the Domain Name Service database, which is provided for you by your ISP. It's not the first time that the DNS has been abused to store information unrelated to its original purpose. (I seem to remember that someone even 'uploaded' the pgp source code to the DNS back when it was export controlled, thus causing Internet name servers to circumvent the export restrictions.)

It will be interesting to see whether the deal means that P2P technologies are becoming legitimate or whether the project will just confirm the adage that the only part of Video on Demand that is missing is the demand. Given the draconian DRM restrictions planned for the project that's not unlikely. Also, last I checked, the firewall changes needed to make BitTorrent work well were a little daunting for an individual. Finding a way to simplify this would be a big step forward for P2P protocols.

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