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Cable TV giant and Internet service provider Comcast Corp. has been accused of blocking -- or at least throttling -- traffic from subscribers trying to share files through the popular BitTorrent peer-to-peer network.

What's BitTorrent? BitTorrent is a networking protocol that lets users who download client software share (transmit and receive) files from other users. These shared files can be any type of file, but BitTorrent is well known for sharing MP3 music files, software applications, movies and other videos. Many of these files are copyrighted. BitTorrent is somewhat similar to the old Napster network that was used by millions of users to share MP3 files, but it doesn't use central servers. Instead, users download metadata files (torrents) related to the file they wish to get. Then the client software sends out a request to "trackers," which are computers that coordinate the transfer of the file -- typically in many different parts from among many peers.

So, if many of these files are being shared illegally, what's the big deal about blocking -- or throttling -- the traffic? BitTorrent Inc., founded by the creator of the protocol, emphasizes that BitTorrent can be used for legally sharing files that aren't copyrighted and even offers the protocol/software as a legitimate service for businesses. Many others in the Internet community also use the technology for legitimate purposes. For example, Blizzard uses the BitTorrent protocol to distribute updates and patches to its popular World of Warcraft game.

Then why is Comcast (reportedly) hindering this traffic? There are no exact numbers available, but some have claimed BitTorrent traffic comprises a significant portion of total Internet traffic. Comcast has limited bandwidth available for its millions of customers and has reportedly cut off service for some users who used more than their share of bandwidth. The company has admitted it restricts users who consume too much bandwidth (not specifically BitTorrent traffic) to ensure all of its customers receive adequate service, although it won't officially say what the limit is.

What is Comcast's reply? The company says it doesn't block peer-to-peer traffic, but it does practice "reasonable network management" to ensure quality service for all it subscribers.

What does the other side say? Claims of Comcast interference with BitTorrent traffic have been circulating for many months, at least, but the issue came to the forefront recently when the Associated Press published results of its own investigation into the issue. The AP concluded that Comcast was hindering BitTorrent traffic.

I don't use BitTorrent, so why should I care? The dispute points to a larger issue called Net neutrality. This is a contentious dispute about the kinds of controls that Internet service providers can put on their networks. Those advocating for the principle of Net neutrality generally want to keep providers from regulating what kind of traffic or level of traffic is allowed. They also don't want providers to be able to charge different rates for different levels of service -- so consumers or companies would have to pay more to be guaranteed certain minimum levels of download/upload speed, for example. Those opposing Net neutrality generally maintain that some kind of control is necessary to promote improvements in equipment and services and guarantee minimum levels of performance. Others believe providers have the right to manage traffic on their network, but argue that -- especially in the Comcast case -- they should be more upfront about what they're doing.

What else is going on? Besides BitTorrent traffic, Comcast has been accused of blocking or throttling Lotus Notes traffic. Also, complaints about Comcast interfering with BitTorrent traffic have been filed with the FCC by online video distributor Vuze and the group Public Knowledge and other members of the Open Internet Coalition.

Where are things going from here? Comcast was recently sued by a California man for interfering in file sharing. At the time of this writing, Comcast hadn't officially commented on the suit. If the litigation proceeds, it could reveal details about exactly what Comcast is doing and eventually result in legislation or an FCC ruling to settle the legality of the practice.