<s>
Gnutella	B-Protocol
is	O
a	O
peer-to-peer	O
network	O
protocol	O
.	O
</s>
<s>
In	O
June	O
2005	O
,	O
Gnutella	B-Protocol
's	O
population	O
was	O
1.81	O
million	O
computers	O
increasing	O
to	O
over	O
three	O
million	O
nodes	O
by	O
January	O
2006	O
.	O
</s>
<s>
The	O
first	O
client	B-Protocol
(	O
also	O
called	O
Gnutella	B-Protocol
)	O
from	O
which	O
the	O
network	O
got	O
its	O
name	O
was	O
developed	O
by	O
Justin	O
Frankel	O
and	O
Tom	O
Pepper	O
of	O
Nullsoft	O
in	O
early	O
2000	O
,	O
soon	O
after	O
the	O
company	O
's	O
acquisition	O
by	O
AOL	O
.	O
</s>
<s>
The	O
source	O
code	O
was	O
to	O
be	O
released	O
later	O
,	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
(	O
GPL	B-License
)	O
;	O
however	O
,	O
the	O
original	O
developers	O
never	O
got	O
the	O
chance	O
to	O
accomplish	O
this	O
purpose	O
.	O
</s>
<s>
This	O
did	O
not	O
stop	O
Gnutella	B-Protocol
;	O
after	O
a	O
few	O
days	O
,	O
the	O
protocol	O
had	O
been	O
reverse	O
engineered	O
,	O
and	O
compatible	O
free	B-Application
and	I-Application
open	I-Application
source	I-Application
clones	O
began	O
to	O
appear	O
.	O
</s>
<s>
This	O
parallel	O
development	O
of	O
different	O
clients	O
by	O
different	O
groups	O
remains	O
the	O
modus	O
operandi	O
of	O
Gnutella	B-Protocol
development	O
today	O
.	O
</s>
<s>
Among	O
the	O
first	O
independent	O
Gnutella	B-Protocol
pioneers	O
were	O
Gene	O
Kan	O
and	O
Spencer	O
Kimball	O
,	O
who	O
launched	O
the	O
first	O
portal	O
aimed	O
to	O
assemble	O
the	O
open-source	O
community	O
to	O
work	O
on	O
Gnutella	B-Protocol
and	O
also	O
developed	O
"	O
GNUbile	O
"	O
,	O
one	O
of	O
the	O
first	O
open-source	O
(	O
GNU-GPL	O
)	O
programs	O
to	O
implement	O
the	O
Gnutella	B-Protocol
protocol	O
.	O
</s>
<s>
The	O
Gnutella	B-Protocol
network	O
is	O
a	O
fully	O
distributed	O
alternative	O
to	O
such	O
semi-centralized	O
systems	O
as	O
FastTrack	B-Protocol
(	O
KaZaA	B-Protocol
)	O
and	O
the	O
original	O
Napster	B-Application
.	O
</s>
<s>
The	O
initial	O
popularity	O
of	O
the	O
network	O
was	O
spurred	O
on	O
by	O
Napster	B-Application
's	O
threatened	O
legal	O
demise	O
in	O
early	O
2001	O
.	O
</s>
<s>
This	O
growing	O
surge	O
in	O
popularity	O
revealed	O
the	O
limits	O
of	O
the	O
initial	O
protocol	O
's	O
scalability	B-Architecture
.	O
</s>
<s>
In	O
early	O
2001	O
,	O
variations	O
on	O
the	O
protocol	O
(	O
first	O
implemented	O
in	O
proprietary	B-Application
and	O
closed	B-Application
source	I-Application
clients	O
)	O
allowed	O
an	O
improvement	O
in	O
scalability	B-Architecture
.	O
</s>
<s>
Instead	O
of	O
treating	O
every	O
user	O
as	O
client	B-Protocol
and	O
server	O
,	O
some	O
users	O
were	O
now	O
treated	O
as	O
ultrapeers	B-Protocol
,	O
routing	O
search	O
requests	O
and	O
responses	O
for	O
users	O
connected	O
to	O
them	O
.	O
</s>
<s>
In	O
late	O
2001	O
,	O
the	O
Gnutella	B-Protocol
client	B-Protocol
LimeWire	B-Application
Basic	O
became	O
free	B-Application
and	I-Application
open	I-Application
source	I-Application
.	O
</s>
<s>
In	O
February	O
2002	O
,	O
Morpheus	B-Protocol
,	O
a	O
commercial	O
file	O
sharing	O
group	O
,	O
abandoned	O
its	O
FastTrack-based	O
peer-to-peer	O
software	O
and	O
released	O
a	O
new	O
client	B-Protocol
based	O
on	O
the	O
free	B-Application
and	I-Application
open	I-Application
source	I-Application
Gnutella	B-Protocol
client	B-Protocol
Gnucleus	O
.	O
</s>
<s>
The	O
word	O
Gnutella	B-Protocol
today	O
refers	O
not	O
to	O
any	O
one	O
project	O
or	O
piece	O
of	O
software	O
,	O
but	O
to	O
the	O
open	O
protocol	O
used	O
by	O
the	O
various	O
clients	O
.	O
</s>
<s>
The	O
name	O
is	O
a	O
portmanteau	O
of	O
GNU	B-Operating_System
and	O
Nutella	O
,	O
the	O
brand	O
name	O
of	O
an	O
Italian	O
hazelnut	O
flavored	O
spread	O
:	O
supposedly	O
,	O
Frankel	O
and	O
Pepper	O
ate	O
a	O
lot	O
of	O
Nutella	O
working	O
on	O
the	O
original	O
project	O
,	O
and	O
intended	O
to	O
license	O
their	O
finished	O
program	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
Gnutella	B-Protocol
is	O
not	O
associated	O
with	O
the	O
GNU	B-Operating_System
project	O
or	O
GNU	B-Operating_System
's	O
own	O
peer-to-peer	O
network	O
,	O
GNUnet	B-Language
.	O
</s>
<s>
On	O
October	O
26	O
,	O
2010	O
,	O
the	O
popular	O
Gnutella	B-Protocol
client	B-Protocol
LimeWire	B-Application
was	O
ordered	O
shut	O
down	O
by	O
Judge	O
Kimba	O
Wood	O
of	O
the	O
United	O
States	O
District	O
Court	O
for	O
the	O
Southern	O
District	O
of	O
New	O
York	O
when	O
she	O
signed	O
a	O
Consent	O
Decree	O
to	O
which	O
recording	O
industry	O
plaintiffs	O
and	O
LimeWire	B-Application
had	O
agreed	O
.	O
</s>
<s>
This	O
event	O
was	O
the	O
likely	O
cause	O
of	O
a	O
notable	O
drop	O
in	O
the	O
size	O
of	O
the	O
network	O
,	O
because	O
,	O
while	O
negotiating	O
the	O
injunction	O
,	O
LimeWire	B-Application
staff	O
had	O
inserted	O
remote-disabling	O
code	O
into	O
the	O
software	O
.	O
</s>
<s>
Since	O
LimeWire	B-Application
was	O
free	B-Application
software	I-Application
,	O
nothing	O
had	O
prevented	O
the	O
creation	O
of	O
forks	B-Application
that	O
omitted	O
the	O
disabling	O
code	O
,	O
as	O
long	O
as	O
LimeWire	B-Application
trademarks	O
were	O
not	O
used	O
.	O
</s>
<s>
The	O
shutdown	O
did	O
not	O
affect	O
,	O
for	O
example	O
,	O
FrostWire	B-Protocol
,	O
a	O
fork	B-Application
of	O
LimeWire	B-Application
created	O
in	O
2004	O
that	O
carries	O
neither	O
the	O
remote-disabling	O
code	O
nor	O
adware	O
.	O
</s>
<s>
On	O
November	O
9	O
,	O
2010	O
,	O
LimeWire	B-Application
was	O
resurrected	O
by	O
a	O
secret	O
team	O
of	O
developers	O
and	O
named	O
LimeWire	B-Language
Pirate	I-Language
Edition	I-Language
.	O
</s>
<s>
It	O
was	O
based	O
on	O
LimeWire	B-Application
5.6	O
BETA	O
.	O
</s>
<s>
To	O
envision	O
how	O
Gnutella	B-Protocol
originally	O
worked	O
,	O
imagine	O
a	O
large	O
circle	O
of	O
users	O
(	O
called	O
nodes	O
)	O
,	O
each	O
of	O
whom	O
has	O
Gnutella	B-Protocol
client	B-Protocol
software	I-Protocol
.	O
</s>
<s>
On	O
initial	O
startup	O
,	O
the	O
client	B-Protocol
software	I-Protocol
must	O
bootstrap	O
and	O
find	O
at	O
least	O
one	O
other	O
node	O
.	O
</s>
<s>
Various	O
methods	O
have	O
been	O
used	O
for	O
this	O
,	O
including	O
a	O
pre-existing	O
address	O
list	O
of	O
possibly	O
working	O
nodes	O
shipped	O
with	O
the	O
software	O
,	O
using	O
updated	O
web	O
caches	O
of	O
known	O
nodes	O
(	O
called	O
Gnutella	B-Protocol
Web	O
Caches	O
)	O
,	O
UDP	B-Protocol
host	O
caches	O
and	O
,	O
rarely	O
,	O
even	O
IRC	B-Protocol
.	O
</s>
<s>
Once	O
connected	O
,	O
the	O
client	B-Protocol
requests	O
a	O
list	O
of	O
working	O
addresses	O
.	O
</s>
<s>
The	O
client	B-Protocol
tries	O
to	O
connect	O
to	O
the	O
nodes	O
it	O
was	O
shipped	O
with	O
,	O
as	O
well	O
as	O
nodes	O
it	O
receives	O
from	O
other	O
clients	O
until	O
it	O
reaches	O
a	O
certain	O
quota	O
.	O
</s>
<s>
When	O
the	O
user	O
wants	O
to	O
do	O
a	O
search	O
,	O
the	O
client	B-Protocol
sends	O
the	O
request	O
to	O
each	O
actively	O
connected	O
node	O
.	O
</s>
<s>
In	O
version	O
0.4	O
of	O
the	O
protocol	O
,	O
the	O
number	O
of	O
actively	O
connected	O
nodes	O
for	O
a	O
client	B-Protocol
was	O
quite	O
small	O
(	O
around	O
5	O
)	O
.	O
</s>
<s>
Since	O
version	O
0.6	O
(	O
2002	O
)	O
,	O
Gnutella	B-Protocol
is	O
a	O
composite	O
network	O
made	O
of	O
leaf	O
nodes	O
and	O
ultra	O
nodes	O
(	O
also	O
called	O
ultrapeers	B-Protocol
)	O
.	O
</s>
<s>
The	O
leaf	O
nodes	O
are	O
connected	O
to	O
a	O
small	O
number	O
of	O
ultrapeers	B-Protocol
(	O
typically	O
3	O
)	O
while	O
each	O
ultrapeer	B-Protocol
is	O
connected	O
to	O
more	O
than	O
32	O
other	O
ultrapeers	B-Protocol
.	O
</s>
<s>
Leaves	O
and	O
ultrapeers	B-Protocol
use	O
the	O
Query	O
Routing	O
Protocol	O
to	O
exchange	O
a	O
Query	O
Routing	O
Table	O
(	O
QRT	O
)	O
,	O
a	O
table	O
of	O
64	O
Ki-slots	O
and	O
up	O
to	O
2	O
Mi-slots	O
consisting	O
of	O
hashed	O
keywords	O
.	O
</s>
<s>
A	O
leaf	O
node	O
sends	O
its	O
QRT	O
to	O
each	O
of	O
the	O
ultrapeers	B-Protocol
to	O
which	O
it	O
is	O
connected	O
,	O
and	O
ultrapeers	B-Protocol
merge	O
the	O
QRT	O
of	O
all	O
their	O
leaves	O
(	O
downsized	O
to	O
128	O
Ki-slots	O
)	O
plus	O
their	O
own	O
QRT	O
(	O
if	O
they	O
share	O
files	O
)	O
and	O
exchange	O
that	O
with	O
their	O
own	O
neighbors	O
.	O
</s>
<s>
Ultrapeers	B-Protocol
do	O
that	O
check	O
before	O
forwarding	O
a	O
query	O
to	O
a	O
leaf	O
node	O
,	O
and	O
also	O
before	O
forwarding	O
the	O
query	O
to	O
a	O
peer	O
ultra	O
node	O
provided	O
this	O
is	O
the	O
last	O
hop	O
the	O
query	O
can	O
travel	O
.	O
</s>
<s>
In	O
the	O
classic	O
Gnutella	B-Protocol
protocol	O
,	O
response	O
messages	O
were	O
sent	O
back	O
along	O
the	O
route	O
taken	O
by	O
the	O
query	O
,	O
as	O
the	O
query	O
itself	O
did	O
not	O
contain	O
identifying	O
information	O
for	O
the	O
node	O
.	O
</s>
<s>
This	O
scheme	O
was	O
later	O
revised	O
,	O
to	O
deliver	O
search	O
results	O
over	O
UDP	B-Protocol
,	O
directly	O
to	O
the	O
node	O
that	O
initiated	O
the	O
search	O
,	O
usually	O
an	O
ultrapeer	B-Protocol
of	O
the	O
node	O
.	O
</s>
<s>
Thus	O
,	O
in	O
the	O
current	O
protocol	O
,	O
the	O
queries	O
carry	O
the	O
IP	B-Protocol
address	I-Protocol
and	O
port	O
number	O
of	O
either	O
node	O
.	O
</s>
<s>
This	O
lowers	O
the	O
amount	O
of	O
traffic	O
routed	O
through	O
the	O
Gnutella	B-Protocol
network	O
,	O
making	O
it	O
significantly	O
more	O
scalable	B-Architecture
.	O
</s>
<s>
If	O
the	O
user	O
decides	O
to	O
download	O
the	O
file	O
,	O
they	O
negotiate	O
the	O
file	B-Protocol
transfer	I-Protocol
.	O
</s>
<s>
If	O
the	O
node	O
which	O
has	O
the	O
requested	O
file	O
is	O
not	O
firewalled	B-Application
,	O
the	O
querying	O
node	O
can	O
connect	O
to	O
it	O
directly	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
node	O
is	O
firewalled	B-Application
,	O
stopping	O
the	O
source	O
node	O
from	O
receiving	O
incoming	O
connections	O
,	O
the	O
client	B-Protocol
wanting	O
to	O
download	O
a	O
file	O
sends	O
it	O
a	O
so-called	O
push	O
request	O
to	O
the	O
server	O
for	O
the	O
remote	O
client	B-Protocol
to	O
initiate	O
the	O
connection	O
instead	O
(	O
to	O
push	O
the	O
file	O
)	O
.	O
</s>
<s>
These	O
are	O
usually	O
the	O
ultrapeers	B-Protocol
of	O
a	O
leaf	O
node	O
and	O
they	O
are	O
announced	O
in	O
search	O
results	O
.	O
</s>
<s>
The	O
client	B-Protocol
connects	O
to	O
one	O
of	O
these	O
push	O
proxies	O
using	O
an	O
HTTP	B-Protocol
request	O
and	O
the	O
proxy	O
sends	O
a	O
push	O
request	O
to	O
a	O
leaf	O
on	O
behalf	O
of	O
the	O
client	B-Protocol
.	O
</s>
<s>
Normally	O
,	O
it	O
is	O
also	O
possible	O
to	O
send	O
a	O
push	O
request	O
over	O
UDP	B-Protocol
to	O
the	O
push	O
proxy	O
,	O
which	O
is	O
more	O
efficient	O
than	O
using	O
TCP	B-Protocol
.	O
</s>
<s>
Push	O
proxies	O
have	O
two	O
advantages	O
:	O
First	O
,	O
ultrapeer-leaf	O
connections	O
are	O
more	O
stable	O
than	O
routes	O
.	O
</s>
<s>
Second	O
,	O
it	O
reduces	O
the	O
amount	O
of	O
traffic	O
routed	O
through	O
the	O
Gnutella	B-Protocol
network	O
.	O
</s>
<s>
Finally	O
,	O
when	O
a	O
user	O
disconnects	O
,	O
the	O
client	B-Protocol
software	I-Protocol
saves	O
a	O
list	O
of	O
known	O
nodes	O
.	O
</s>
<s>
This	O
contains	O
the	O
nodes	O
to	O
which	O
the	O
client	B-Protocol
was	O
connected	O
and	O
the	O
nodes	O
learned	O
from	O
pong	O
packets	O
.	O
</s>
<s>
The	O
client	B-Protocol
uses	O
that	O
as	O
its	O
seed	O
list	O
,	O
when	O
it	O
next	O
starts	O
,	O
thus	O
becoming	O
independent	O
of	O
bootstrap	O
services	O
.	O
</s>
<s>
In	O
practice	O
,	O
this	O
method	O
of	O
searching	O
on	O
the	O
Gnutella	B-Protocol
network	O
was	O
often	O
unreliable	O
.	O
</s>
<s>
Also	O
,	O
the	O
bandwidth	O
cost	O
of	O
searching	O
on	O
Gnutella	B-Protocol
grew	O
exponentially	O
to	O
the	O
number	O
of	O
connected	O
users	O
,	O
often	O
saturating	O
connections	O
and	O
rendering	O
slower	O
nodes	O
useless	O
.	O
</s>
<s>
This	O
observation	O
identified	O
the	O
Gnutella	B-Protocol
network	O
as	O
an	O
unscalable	B-Architecture
distributed	O
system	O
,	O
and	O
inspired	O
the	O
development	O
of	O
distributed	B-Operating_System
hash	I-Operating_System
tables	I-Operating_System
,	O
which	O
are	O
much	O
more	O
scalable	B-Architecture
but	O
support	O
only	O
exact-match	O
,	O
rather	O
than	O
keyword	O
,	O
search	O
.	O
</s>
<s>
To	O
address	O
the	O
problems	O
of	O
bottlenecks	O
,	O
Gnutella	B-Protocol
developers	O
implemented	O
a	O
tiered	O
system	O
of	O
ultrapeers	B-Protocol
and	O
leaves	O
.	O
</s>
<s>
Nodes	O
which	O
are	O
capable	O
of	O
routing	O
messages	O
are	O
promoted	O
to	O
ultrapeers	B-Protocol
.	O
</s>
<s>
Ultrapeers	B-Protocol
accept	O
leaf	O
connections	O
and	O
route	O
searches	O
and	O
network	O
maintenance	O
messages	O
.	O
</s>
<s>
This	O
greatly	O
improved	O
efficiency	O
and	O
scalability	B-Architecture
.	O
</s>
<s>
Additionally	O
,	O
gnutella	B-Protocol
adopted	O
a	O
number	O
of	O
other	O
techniques	O
to	O
reduce	O
traffic	O
overhead	O
and	O
make	O
searches	O
more	O
efficient	O
.	O
</s>
<s>
One	O
of	O
the	O
benefits	O
of	O
having	O
Gnutella	B-Protocol
so	O
decentralized	O
is	O
to	O
make	O
it	O
very	O
difficult	O
to	O
shut	O
the	O
network	O
down	O
and	O
to	O
make	O
it	O
a	O
network	O
in	O
which	O
the	O
users	O
are	O
the	O
only	O
ones	O
who	O
can	O
decide	O
which	O
content	O
will	O
be	O
available	O
.	O
</s>
<s>
Unlike	O
Napster	B-Application
,	O
where	O
the	O
entire	O
network	O
relied	O
on	O
the	O
central	O
server	O
,	O
Gnutella	B-Protocol
cannot	O
be	O
shut	O
down	O
by	O
shutting	O
down	O
any	O
one	O
node	O
.	O
</s>
<s>
Gnutella	B-Protocol
once	O
operated	O
on	O
a	O
purely	O
query	O
flooding-based	O
protocol	O
.	O
</s>
<s>
The	O
outdated	O
Gnutella	B-Protocol
version	O
0.4	O
network	O
protocol	O
employs	O
five	O
different	O
packet	O
types	O
,	O
namely	O
:	O
</s>
<s>
File	B-Protocol
transfers	I-Protocol
are	O
instead	O
handled	O
by	O
HTTP	B-Protocol
.	I-Protocol
</s>
<s>
The	O
development	O
of	O
the	O
Gnutella	B-Protocol
protocol	O
is	O
currently	O
led	O
by	O
the	O
Gnutella	B-Protocol
Developers	O
Forum	O
(	O
The	O
GDF	O
)	O
.	O
</s>
<s>
Many	O
protocol	O
extensions	O
have	O
been	O
and	O
are	O
being	O
developed	O
by	O
the	O
software	O
vendors	O
and	O
by	O
the	O
free	O
Gnutella	B-Protocol
developers	O
of	O
the	O
GDF	O
.	O
</s>
<s>
These	O
extensions	O
include	O
intelligent	O
query	O
routing	O
,	O
SHA-1	B-Algorithm
checksums	O
,	O
query	O
hit	O
transmission	O
via	O
UDP	B-Protocol
,	O
querying	O
via	O
UDP	B-Protocol
,	O
dynamic	O
queries	O
via	O
TCP	B-Protocol
,	O
file	B-Protocol
transfers	I-Protocol
via	O
UDP	B-Protocol
,	O
XML	B-Protocol
metadata	O
,	O
source	O
exchange	O
(	O
also	O
termed	O
the	O
download	O
mesh	O
)	O
and	O
parallel	O
downloading	O
in	O
slices	O
(	O
swarming	O
)	O
.	O
</s>
<s>
There	O
are	O
efforts	O
to	O
finalize	O
these	O
protocol	O
extensions	O
in	O
the	O
Gnutella	B-Protocol
0.6	O
specification	O
,	O
at	O
the	O
Gnutella	B-Protocol
protocol	O
development	O
website	O
.	O
</s>
<s>
The	O
Gnutella	B-Protocol
0.4	O
standard	O
is	O
outdated	O
but	O
it	O
remains	O
the	O
latest	O
protocol	O
specification	O
because	O
all	O
extensions	O
,	O
so	O
far	O
,	O
exist	O
as	O
proposals	O
.	O
</s>
<s>
The	O
Gnutella	B-Protocol
protocol	O
remains	O
under	O
development	O
.	O
</s>
<s>
Despite	O
attempts	O
to	O
make	O
a	O
clean	O
break	O
with	O
the	O
complexity	O
inherited	O
from	O
the	O
old	O
Gnutella	B-Protocol
0.4	O
and	O
to	O
design	O
a	O
clean	O
new	O
message	O
architecture	O
,	O
it	O
remains	O
one	O
of	O
the	O
most	O
successful	O
file-sharing	O
protocols	O
to	O
date	O
.	O
</s>
<s>
The	O
following	O
tables	O
compare	O
general	O
and	O
technical	O
information	O
for	O
a	O
number	O
of	O
applications	O
supporting	O
the	O
Gnutella	B-Protocol
network	O
.	O
</s>
<s>
The	O
tables	O
do	O
not	O
attempt	O
to	O
give	O
a	O
complete	O
list	B-Protocol
of	I-Protocol
Gnutella	I-Protocol
clients	I-Protocol
.	O
</s>
<s>
The	O
tables	O
are	O
limited	O
to	O
clients	O
that	O
can	O
participate	O
in	O
the	O
current	O
Gnutella	B-Protocol
network	O
.	O
</s>
