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2 How it works 3 Protocol features and extensions 4 Clients 5 See also |
The first client was developed by Justin Frankel and Tom Pepper of Nullsoft, a division of AOL, in early 2000. On March 14, the program was made available for download on Nullsoft's servers. The event was prematurely announced on Slashdot, and thousands downloaded the program that day. The source code was to be released later, supposedly under the GNU General Public License (GPL).
The next day, AOL stopped the availability of the program over legal concerns and restrained the Nullsoft division from doing any further work on the project. This did not stop Gnutella; after a few days the protocol had been reverse engineered and compatible open source clones started showing up. This parallel development of different clients by different groups remains the modus operandi of Gnutella development today.
The Gnutella network would be a fully distributed alternative to semi-centralized systems like Napster. Initial popularity of the network was spurred on by Napster's threatened legal demise in early 2001. This growing surge in popularity revealed the limits of the initial protocol's scalabilty. In early 2001, variations of the protocol (implemented first in closed source clients) allowed scalabilty to improve somewhat. Instead of treating every user as client and server, some users were now treated as "ultrapeers", routing search requests and responses for users connected to them.
This allowed the network to grow in popularity. In late 2001, the Gnutella client LimeWire, which had driven much of the protocol's development, was released as open source. Morpheus a commercial file sharing group, on 28th Feb 2002 abandoned their FastTrack based peer-to-peer software and released a new client based on the open source Gnutella client Gnucleus.
Sometimes the word 'Gnutella' refers not to a particular project or particular piece of software, but to the open protocol used by various clients. Since new clients are under development all over, and since a new protocol is apparently on the way too, it is hard to say what the word 'Gnutella' will mostly stand for in the future.
The name is a word play on GNU and Nutella. Supposedly, Frankel and Pepper ate a lot of nutella working on the original project, and they were going to use the GNU GPL license on the finished program. Gnutella is not associated with the GNU project; see GNUnet for the GNU project's equivalent.
To envision how Gnutella works, imagine a large circle of users (called nodes), who each have Gnutella client software. The client software ships with a list of nodes, and when a particular user (call him/her A) starts their Gnutella software for the first time, the software tries to connect to each node in its list, discarding the ones that don't work. This list is long, so chances are that at least one (call it B) will work. Once it has connected, node B will send node A its own list of working nodes. Node A will try to connect to the nodes it was shipped with, as well as nodes it receives from other nodes, until it reaches a certain quota, usually user-specifiable. It will only connect to that many nodes, but it keeps the nodes it has not yet tried (it discards ones that it tries, but that don't work).
Now, when user A wants to do a search, it sends the request to each node it is actively connected to. It is possible that some of them will no longer work, in which case user A tries to connect to the nodes it has saved as backups. The number of actively connected nodes for user A is usually quite small (around 5), so each node then forwards the request to all the nodes it is connected to, and they in turn forward the request, and so on. In theory, the request will eventually find its way to every user on the Gnutella network.
If a search request turns up a result, the node that had the result contacts the searcher (whose IP address was included with the search request) directly. They negotiate the file transfer and the transfer proceeds. If more than one copy of the same file is found, the searcher can perform a "swarm" download - download pieces of the file from different nodes. This results in increased download rates.
Finally, when user A disconnects, the client software saves the list of nodes that it was actively connected to, and that it was keeping as a backup, for use next time it connects.
In practice, searching on the Gnutella network is often slow and unreliable. Each node is a regular computer user; as such, they are constantly connecting and disconnecting, so the network is never completely stable. Since individual users' connections are likely to be slow, it can take a very long time for a search request to traverse the entire network (which averages around 92,000-99,000 nodes at any time).
The real benefit of having Gnutella so de-centralized is to make it very difficult to shut the network down. Unlike Napster, where the entire network relied on the central server, Gnutella cannot be shut down by shutting down any one node. As long as there are at least two users, Gnutella will continue to exist.
The outdated Gnutella version 0.4 network protocol employs five different packet types, namely
The development of Gnutella is lead nowadays by the GDF (Gnutella Developer Forum). Many protocol extensions have been and are being developed, by the software vendors and free gnutella developers of the GDF. They include intelligent query routing, SHA checksums, parallel downloading in slices (swarming), etc.
There are efforts to finalize these protocol extensions in the Gnutella 0.6 specification at the Gnutella protocol development website [1]. The Gnutella 0.4 standard although being still the latest protocol specification since all extensions only exist as proposals so far is outdated. In fact, it is hard to impossible connecting with the 0.4 handshake.
In January 2003 Shareaza announced the Gnutella2 protocol which uses UDP rather then TCP/IP network protocol for searches, an extensible binary xml-like packet format and includes many of the above mentioned extensions. The
draft specification was released by them on March 26, 2003. For details see the Gnutella2 home page (http://www.gnutella2.com/)
Some popular Gnutella clients are:
History
How it works
Protocol features and extensions
These are mainly concerned with searching the Gnutella network. File transfers are handled using established HTTP protocols.Clients
See also