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IP: Gnutella and Freenet Represent True Technological Innovation
From: Dave Farber <farber () cis upenn edu>
Date: Mon, 15 May 2000 06:32:55 -0400



Date: Sun, 14 May 2000 09:12:39 -0700
From: "Tim O'Reilly" <tim () oreilly com>
To: farber () central cis upenn edu


A must-read for people who've heard about these technologies and want a
clear exposition of how they work, not just fearmongering about them.
Whether you love or fear Napster and its even more revolutionary cousins
gnutella and freenet, this is an article you ought to read.

http://www.oreillynet.com/pub/a/network/2000/05/12/magazine/gnutella.html

"The computer technologies that have incurred the most condemnation
recently --
Napster, Gnutella, and Freenet -- are also the most interesting from a
technological
standpoint. I'm not saying this to be perverse. I have examined these
systems'
architecture and protocols, and I find them to be fascinating. Freenet
emerged from
a bona fide, academically solid research project, and all three sites
are worth serious
attention from anyone interested in the future of the Internet."

--
Tim O'Reilly @ O'Reilly & Associates, Inc.
101 Morris Street, Sebastopol, CA 95472
+1 707-829-0515, FAX +1 707-829-0104
tim () oreilly com, http://www.oreilly.com<x-html>



<http://www.oreillynet.com>








by Andy Oram
05/12/2000

Related Articles:

Napster and MP3: La Revolucion or La Larceny?

Music Industry Turns Heat on Net Music Pirates

Why the RIAA is Fighting a Losing Battle

Napster: Popular Program Raises Devilish Issues

<http://dave.oreillynet.com/stories/storyReader$13>Why the RIAA Still 
Stands a Chance

The computer technologies that have incurred the most condemnation 
recently -- <http://www.napster.com/>Napster, 
<http://gnutella.wego.com/>Gnutella, and 
<http://freenet.sourceforge.net/>Freenet -- are also the most interesting 
from a technological standpoint. I'm not saying this to be perverse. I 
have examined these systems' architecture and protocols, and I find them 
to be fascinating. Freenet emerged from a bona fide, academically solid 
research project, and all three sites are worth serious attention from 
anyone interested in the future of the Internet.

In writing this essay, I want to take the hype and hysteria out of current 
reports about Gnutella and Freenet so the Internet community can evaluate 
them on their merits. This is a largely technical article; I address the 
policy debates directly in a companion article, 
<http://www.webreview.com/pub/2000/05/12/platformindependent/index.html>The 
Value of Gnutella and Freenet. I will not cover Napster here because its 
operation has received more press. It's covered in "Napster: Popular 
Program Raises Devilish Issues" by Erik Nilsson, and frankly, it is less 
interesting and far-reaching technically than the other two systems.

In essence, Gnutella and Freenet represent a new step in distributed 
information systems. Each is a system for searching for information; each 
returns information without telling you where it came from. They are 
innovative in the areas of distributed information storage, information 
retrieval, and network architecture. But they differ significantly in both 
goals and implementation, so I'll examine them separately from this point on.


Gnutella basics



Each piece of Gnutella software is both a server and a client in one, 
because it supports bidirectional information transfer. The Gnutella 
developers call the software a "servent," but since that term looks odd 
I'll stick to "client." You can be a fully functional Gnutella site by 
installing any of several available clients; lots of different operating 
systems are supported. Next you have to find a few sites that are willing 
to communicate with you: some may be friends, while others may be 
advertised Gnutella sites. People with large computers and high bandwidth 
will encourage many others to connect to them.

Evil or Just Controversial?:

Open Source software such as Gnutella and Freeware are spreading as 
quickly as a virus. But are they really so unhealthy? Andy Oram points out 
the advantages--and disadvantages--of controversial technologies in this 
week's edition of 
<http://www.webreview.com/pub/2000/05/12/platform/index.html>Platform 
Independent on Web Review.

You will communicate directly only with the handful of sites you've agreed 
to contact. Any material of interest to other sites will pass along from 
one site to another in store-and-forward fashion. Does this sound 
familiar, all you grizzled, old UUCP and Fidonet users out there? The 
architecture is essentially the same as those unruly, interconnected 
systems that succeeded in passing Net News and e-mail around the world for 
decades before the Internet became popular.

But there are some important differences. Because Gnutella runs over the 
Internet, you can connect directly with someone who's geographically far 
away just as easily as with your neighbor. This introduces robustness and 
makes the system virtually failsafe, as we'll see in a minute.

Second, the protocol for obtaining information over Gnutella is a kind of 
call-and-response that's more complex than simply pushing news or e-mail. 
Figure 1 shows the operation of the protocol. Suppose site A asks site B 
for data matching "MP3." After passing back anything that might be of 
interest, site B passes the request on to its colleague at site C -- but 
unlike mail or news, site B keeps a record that site A has made the 
request. If site C has something matching the request, it gives the 
information to site B, which remembers that it is meant for site A and 
passes it through to that site.

Figure 1. How Gnutella retrieves information

I am tempted to rush on and describe the great significance of this simple 
system, but I'll pause to answer a few questions for those who are curious.
   * How are requests kept separate? Each request has a unique number, 
generated from random numbers or semi-randomly from something unique to 
the originating site like an Ethernet MAC address. If a request goes 
through site C on to site D and then to site B, site B can recognize from 
the identifier that it's been seen already and quietly drop the repeat 
request. On the other hand, different sites can request the same material 
and have their requests satisfied because each has a unique identifier. 
Each site lets requests time out, simply by placing them on a queue of a 
predetermined size and letting old requests drop off the bottom as new 
ones are added.
   * What form does the returned data take? It could be an entire file of 
music or other requested material, but Gnutella is not limited to 
shipping around files. The return could just as well be a URL, or 
anything else that could be of value. Thus, people are likely to use 
Gnutella for sophisticated searches, ending up with a URL just as they 
would with a traditional search engine. (More on this exciting 
possibility later.)
   * What protocol is used? Gnutella runs over HTTP (a sign of Gnutella's 
simplicity). A major advantage of using HTTP is that two sites can 
communicate even if one is behind a typical organization's firewall, 
assuming that this firewall allows traffic out to standard Web servers on 
port 80. There is a slight difficulty if a client behind a firewall is 
asked to serve up a file, but it can get by the firewall by issuing an 
output command called GIV to port 80 on its correspondent. The only 
show-stopper comes when a firewall screens out all Web traffic, or when 
both correspondents are behind typical firewalls.
   * How does the system stop searching? Like IP packets, each Gnutella 
request has a time-to-live, which is normally decremented by each site 
until it reaches zero. A site can also drastically reduce a time-to-live 
that it decides is ridiculously high. As we will see in a moment, the 
time-to-live limits the reach of each site, but that can be a benefit as 
well as a limitation.
   * How is a search string like "MP3" interpreted? That is the $64,000 
question, and leads us to Gnutella's greatest contribution.
Pages: 1, 2, 3, 4

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