Cryptography Reference
In-Depth Information
Bob Downloads Music Using Gnutella
Background : Let us see how Gnutella works so we may achieve some un-
derstanding of how it compares and contrasts with the old Napster. There is
no central server, which was essentially the legal problem with the old Napster.
Each user, such as Bob, has Gnutella client software, which will have built-in
preexisting lists of other users IP addresses, and which may use IRC to find
suitable addresses from the list when requested. Typically, once the software
is installed on a given machine and connected to the Internet, it will try to
connect to the IP addresses with which it was shipped until it reaches some
preprogrammed quota, and stops, but keeps the addresses not tried.
1. Bob types in the name of the musiche is seeking, a song or a CD. The
Gnutella software seeks out appropriate machines with that music.
2. The Gnutella software on Bob's computer sends the names of the music
Bob wants to the other machines to see if it is located on their local disks.
Each one that does have it sends back the file name and IP address of the
machine on which it sits.
3. Simultaneously, each of the machines sends out Bob's request to all the
machines to which they are connected, and each of these machines repeats
the process in turn.
4. There is a limit placed on each request, called a TTH ( Time To Hop ),
meaning that the request must go out to say, seven levels deep before it
stops its own propagation.
5. Bob selects from the returned files via their IP addresses and his software
contacts the sender and negotiates the transfer.
6. Once Bob disconnects, his Gnutella software updates by saving the IP
addresses of those users who contacted him.
This is a clever mechanism for employing the peer-to-peer idea without vio-
lating any copyright laws since there is no central indexing server, just “friends”
sharing files via their computers. However, without that central server, the pro-
cess can take time. It could be a few minutes for a multilayer deep request
to be processed. Furthermore, Bob is giving up time on his own computer to
process requests coming in from other users, so he sacrifices bandwidth. More-
over, there is no guarantee he will find what he is looking for even with all
the machines involved. Yet the Gnutella idea works every time Bob connects
since, as long as there is one user to whom he can connect in the Gnutella
network, he is able to query all the interconnected machines. Yet no court
is likely to shut this scheme down since there is no central server for which a
court could issue the cease-and-desist order. Currently several hundred million
copies of the Gnutella software have been downloaded. For more information
see http://draketo.de/inhalt/krude-ideen/gnufu en.html .
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