Wired has an interesting article on Bram Cohen and BitTorrent, the filesharing software that has tens of millions of users and generates about a third of all internet traffic. Excerpts with edits and my comments added:
Bram Cohen is the creator of BitTorrent, one of the most successful peer-to-peer programs ever. BitTorrent lets users quickly upload and download enormous amounts of data, files that are hundreds or thousands of times bigger than a single MP3. Analysts at CacheLogic, an Internet-traffic analysis firm report that BitTorrent traffic accounts for more than one-third of all data sent across the Internet. Cohen showed his code to the world at a hacker conference in 2002, as a free, open source project aimed at geeks who need a cheap way to swap Linux software online. But the real audience turns out to be TV and movie fanatics. It takes hours to download a ripped episode of Alias or Monk off Kazaa, but BitTorrent can do it in minutes. As a result, more than 20 million people have downloaded the BitTorrent application. If any one of them misses their favorite TV show, no worries. Surely someone has posted it as a "torrent." As for movies, if you can find it at Blockbuster, you can probably find it online somewhere - and use BitTorrent to suck it down.
Cohen’s idea : Breaking a big file into tiny pieces might be a terrific way to swap it online. The problem with P2P file-sharing networks like Kazaa, he reasoned, is that uploading and downloading do not happen at equal speeds. Broadband providers allow their users to download at superfast rates, but let them upload only very slowly, creating a bottleneck: If two peers try to swap a compressed copy of Meet the Fokkers - say, 700 megs - the recipient will receive at a speedy 1.5 megs a second, but the sender will be uploading at maybe one-tenth of that rate. Thus, one-to-one swapping online is inherently inefficient. It's fine for MP3s but doesn't work for huge files.Cohen realized that chopping up a file and handing out the pieces to several uploaders would really speed things up. He sketched out a protocol: To download that copy of Meet the Fokkers, a user's computer sniffs around for others online who have pieces of the movie. Then it downloads a chunk from several of them simultaneously. Many hands make light work, so the file arrives dozens of times faster than normal. Paradoxically, BitTorrent's architecture means that the more popular the file is the faster it downloads - because more people are pitching in. Better yet, it's a virtuous cycle. Users download and share at the same time; as soon as someone receives even a single piece of Fokkers, his computer immediately begins offering it to others. The more files you're willing to share, the faster any individual torrent downloads to your computer. This prevents people from leeching, a classic P2P problem in which too many people download files and refuse to upload, creating a drain on the system. "Give and ye shall receive" became Cohen's motto, which he printed on T-shirts and sold to supporters.
Bram Cohen's approach is faster and more efficient than traditional P2P networking:
1. A single source file within a group of BitTorrent users, called a swarm, spreads around pieces of a film or videogame or TV show so that everyone has a chunk to share.
2. After the initial downloading, those pieces are then uploaded to other needy users in the swarm. The rules require every downloader to also do some uploading. Thus the more people trying to download, the faster everything is uploaded.
3. Before long, the swarm has shared all the pieces, and everyone has their own complete source.
Traditional Peer-to-Peer sites are slow because they suffer from supply bottlenecks. Even if many users on the network have the same file, swapping is restricted to one uploader and downloader at a time. And since uploading goes much slower than downloading, even highly compressed media can take many hours to transfer. BitTorrent is something deeper and more subtle. It's a technology that is changing the landscape of broadcast media. "All hell's about to break loose," says Brad Burnham, a venture capitalist with Union Square Ventures ... BitTorrent does not require the wires or airwaves that the cable and network giants have spent billions constructing and buying ... BitTorrent transforms the Internet into the world's largest TiVo. If enough people start getting their TV online, it will drastically change the nature of the medium ... The whole concept of must-see TV changes from being something you stop and watch every Thursday to something you gotta check out right now, dude. Just click here.What exactly would a next-generation broadcaster look like? The VCs at Union Square Ventures ... suspect the network of the future will resemble Yahoo! or Amazon.com - an aggregator that finds shows, distributes them in P2P video torrents, and sells ads or subscriptions to its portal. The real value of the so-called BitTorrent broadcaster would be in highlighting the good stuff, much as the collaborative filtering of Amazon and TiVo helps people pick good material. Man... this is amazing.. True convergence at work.