Thursday, September 23, 2010

BitTorrent clients

Studies of torrent P2P networks are always interesting. I recently read two papers (TopBT: A Topology-Aware and Infrastructure-Independent BitTorrent Client and Taming the Torrent: A Practical Approach to Reducing Cross-ISP Traffic in Peer-to-Peer Systems) about improving the efficiency of torrent P2P networks. One of the biggest problems with torrent systems is that, generally, the only metric used to select peers is download speed. To a P2P user this seems good because it ensures that you are getting your content in the fastest possible manner. However, for ISP's this can be bad because traffic that travels onto other ISP networks costs money. Companies like Comcast have throttled torrent traffic to minimize its effects on their network. P2P systems are a wonderful way of sharing information (legal information, Wink) and these studies are geared towards finding a way in which P2P systems, like BitTorrent, can be used minimizing the cost on ISP's.

Taming the Torrent proposes a system called Ono that uses content distribution networks (CDN) to calculate proximity values for peers in a network. The idea is that if two peers resolve to the same CDN node, then they must be close to each other and possibly within the same ISP autonomous system (AS). This system relies heavily on the fact that CDN's would be willing to provide such a service for free, but I think such as assumption is okay considering companies like Google provide all kinds of cloud services for free around the world. By using CDN's as a reference point, Ono is able to reduce cross-ISP traffic and select peers within the same AS about a third of the time. On average, it is also able to increase download rates by 207%. Pretty impressive!

TopBT's results aren't quite as impressive, but it doesn't rely on a third party service either, which is good. TopBT uses various tools to measure the network between potential peers. Along with measuring download rate, it also uses ping and traceroute to measure the link as well as gain important information about the autonomous systems respective peers are in. The challenge this solution has is that many routers are configured to block ping and traceroute. It thus becomes difficult to figure out the proximity of a peer. Despite these road blocks, TopBT is able to reduce inter ISP traffic by 25% and increase download time by about 15%.

One of the interesting things both of these papers did was release their software for the world to use in order to acquire data. I mean who wouldn't want a torrent client that increases download time by 207% percent. It just rubs me a little funny that the data they got was probably a result of thousands of people obtaining media illegally. Just an interesting thought in conclusion.

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