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Azureus Introduces DHT Layer
May 3, 2005
Thomas Mennecke
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Azureus, a leading java based BitTorrent client, has introduced DHT (Distributed Hash Table) to its client. DHT is a networking protocol that enhances the scalability and efficiency of decentralized networks by creating a virtual index rather than broadcasting search queries. Decentralized networks that utilized DHT technology are able to search and locate files significantly faster than networks that do not use this technology.

You may think to yourself, "So what, Azureus has incorporated DHT, many decentralized networks employ this technology."

The significance of adding this layer to Azureus is that it significantly increases the efficiency of file distribution. With the new version of Azureus, any client can choose to become a tracker or not. This is where DHT comes into play.

With DHT, each node is responsible for indexing a certain percentage of hash files on the network. For example, say there are 50 Azureus users all participating on the DHT portion of the network. If 8 decide to become nodes, each one will work together to become a virtual index (so-called "tracker-less.")

This allows a client to continue downloading a file even if the web-based tracker goes down. In addition, even if a tracker happens to go down, the swarms will continue to be maintained - even finding alternative file sources. Olivier from Azureus explains this new DHT implementation has a familiar origin.

"The technology behind the DHT (Distributed Hash Table = Distributed
Database) is Kademlia, (the "Kad" network in eMule is another Kademlia distributed hash table, Kad is heavily modified from the original specifications for performance reasons). Azureus implementation follows quite a lot the original Kademlia specifications so far."

Keep in mind this is not a "decentralized BitTorrent" network. The BitTorrent network and DHT network operate independently. DHT is a layer added on top of the BitTorrent network to assist in Azureus’ performance. BitTorrent is a distinct networking protocol, of which is specified by creator Bram Cohen. Anything existing outside of those specifications is not BitTorrent. Some articles have attempted to label the new Azureus as a “decentralized BitTorrent”, possibly confusing some with a dubious client named “eXeem.” Olivier makes it quite clear these two clients are not even in the same Universe.

“It has nothing to do with eXeem, and in terms of performance, searching the DHT is a matter of ms (milliseconds) when the content is available (ie, when it has results), and of seconds when it' s not. I don't know for sure how eXeem works, but from the test I did, it's not using a DHT.”

This story is filed in these Slyck News categories
BitTorrent :: BitTorrent Clients

You can read more from Azureus' website here

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