<s>
JXTA	B-Language
(	O
Juxtapose	O
)	O
was	O
an	O
open-source	B-Application
peer-to-peer	O
protocol	O
specification	O
begun	O
by	O
Sun	O
Microsystems	O
in	O
2001	O
.	O
</s>
<s>
The	O
JXTA	B-Language
protocols	O
were	O
defined	O
as	O
a	O
set	O
of	O
XML	B-Protocol
messages	O
which	O
allow	O
any	O
device	O
connected	O
to	O
a	O
network	O
to	O
exchange	O
messages	O
and	O
collaborate	O
independently	O
of	O
the	O
underlying	O
network	B-Architecture
topology	I-Architecture
.	O
</s>
<s>
As	O
JXTA	B-Language
was	O
based	O
upon	O
a	O
set	O
of	O
open	O
XML	B-Protocol
protocols	O
,	O
it	O
could	O
be	O
implemented	O
in	O
any	O
modern	O
computer	O
language	O
.	O
</s>
<s>
Implementations	O
were	O
developed	O
for	O
Java	B-Language
SE	I-Language
,	O
C/C	O
++	O
,	O
C#	B-Application
and	O
Java	B-Language
ME	I-Language
.	O
</s>
<s>
The	O
C#	B-Application
Version	O
used	O
the	O
C++	B-Language
/C	O
native	O
bindings	O
and	O
was	O
not	O
a	O
complete	O
re-implementation	O
in	O
its	O
own	O
right	O
.	O
</s>
<s>
JXTA	B-Language
peers	O
create	O
a	O
virtual	O
overlay	B-Architecture
network	I-Architecture
which	O
allows	O
a	O
peer	O
to	O
interact	O
with	O
other	O
peers	O
even	O
when	O
some	O
of	O
the	O
peers	O
and	O
resources	O
are	O
behind	O
firewalls	B-Application
and	O
NATs	O
or	O
use	O
different	O
network	O
transports	O
.	O
</s>
<s>
In	O
addition	O
,	O
each	O
resource	O
is	O
identified	O
by	O
a	O
unique	O
ID	O
,	O
a	O
160	O
bit	O
SHA-1	B-Algorithm
URN	B-Protocol
in	O
the	O
Java	O
binding	O
,	O
so	O
that	O
a	O
peer	O
can	O
change	O
its	O
localization	O
address	O
while	O
keeping	O
a	O
constant	O
identification	O
number	O
.	O
</s>
<s>
"	O
In	O
November	O
2010	O
,	O
Oracle	O
officially	O
announced	O
its	O
withdrawal	O
from	O
the	O
JXTA	B-Language
projects	O
"	O
.	O
</s>
<s>
As	O
of	O
August	O
2011	O
,	O
the	O
JXTA	B-Language
project	O
has	O
not	O
yet	O
been	O
continued	O
or	O
otherwise	O
announced	O
to	O
retain	O
operations	O
,	O
neither	O
a	O
decision	O
was	O
made	O
on	O
the	O
assembly	O
of	O
its	O
Board	O
nor	O
an	O
answer	O
by	O
Oracle	O
regarding	O
a	O
pending	O
request	O
to	O
move	O
the	O
source-code	O
to	O
Apache	B-Application
license	I-Application
version	O
2	O
.	O
</s>
<s>
JXTA	B-Language
defines	O
two	O
main	O
categories	O
of	O
peers	O
:	O
edge	O
peers	O
and	O
super-peers	O
.	O
</s>
<s>
Each	O
peer	O
has	O
a	O
well	O
defined	O
role	O
in	O
the	O
JXTA	B-Language
peer-to-peer	O
model	O
.	O
</s>
<s>
They	O
usually	O
reside	O
on	O
the	O
border	O
of	O
the	O
Internet	O
,	O
hidden	O
behind	O
corporate	O
firewalls	B-Application
or	O
accessing	O
the	O
network	O
through	O
non-dedicated	O
connections	O
.	O
</s>
<s>
A	O
Rendezvous	O
peer	O
is	O
a	O
special	O
purpose	O
peer	O
which	O
is	O
in	O
charge	O
of	O
coordinating	O
the	O
peers	O
in	O
the	O
JXTA	B-Language
network	O
and	O
provides	O
the	O
necessary	O
scope	O
to	O
message	O
propagation	O
.	O
</s>
<s>
A	O
Relay	O
peer	O
allows	O
the	O
peers	O
which	O
are	O
behind	O
firewalls	B-Application
or	O
NAT	B-Protocol
systems	O
to	O
take	O
part	O
in	O
the	O
JXTA	B-Language
network	O
.	O
</s>
<s>
This	O
is	O
performed	O
by	O
using	O
a	O
protocol	O
which	O
can	O
traverse	O
the	O
firewall	B-Application
,	O
like	O
HTTP	B-Protocol
,	O
for	O
example	O
.	O
</s>
<s>
Any	O
peer	O
in	O
a	O
JXTA	B-Language
network	O
can	O
be	O
a	O
rendezvous	O
or	O
relay	O
as	O
soon	O
as	O
they	O
have	O
the	O
necessary	O
credentials	O
or	O
network/storage/memory/CPU	O
requirements	O
.	O
</s>
<s>
An	O
Advertisement	O
is	O
an	O
XML	B-Protocol
document	I-Protocol
which	O
describes	O
any	O
resource	O
in	O
a	O
P2P	O
network	O
(	O
peers	O
,	O
groups	O
,	O
pipes	O
,	O
services	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
The	O
communication	O
in	O
JXTA	B-Language
can	O
be	O
thought	O
as	O
the	O
exchange	O
of	O
one	O
or	O
more	O
advertisements	O
through	O
the	O
network	O
.	O
</s>
<s>
Pipes	O
are	O
a	O
virtual	O
communication	O
channel	O
used	O
by	O
JXTA	B-Language
to	O
exchange	O
messages	O
and	O
data	O
.	O
</s>
<s>
In	O
JXTA	B-Language
,	O
every	O
peer	O
is	O
a	O
member	O
of	O
a	O
default	O
group	O
,	O
NetPeerGroup	O
,	O
but	O
a	O
given	O
peer	O
can	O
be	O
member	O
of	O
many	O
sub-groups	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
The	O
Rendezvous	O
peers	O
have	O
an	O
optimized	O
routing	B-Protocol
mechanism	O
which	O
allows	O
an	O
efficient	O
propagation	O
of	O
messages	O
pushed	O
by	O
edge	O
peers	O
connected	O
to	O
them	O
.	O
</s>
<s>
There	O
is	O
not	O
any	O
mechanism	O
to	O
enforce	O
the	O
consistency	O
of	O
all	O
RPVs	O
across	O
the	O
JXTA	B-Language
network	O
,	O
so	O
a	O
given	O
RPV	O
can	O
have	O
a	O
temporary	O
or	O
permanent	O
inconsistent	O
view	O
of	O
the	O
other	O
rendezvous	O
peers	O
.	O
</s>
<s>
After	O
that	O
,	O
the	O
rendezvous	O
applies	O
a	O
Distributed	B-Operating_System
Hash	I-Operating_System
Table	I-Operating_System
(	O
DHT	O
)	O
function	O
so	O
that	O
it	O
can	O
forward	O
the	O
index	O
to	O
another	O
peer	O
in	O
the	O
RPV	O
list	O
.	O
</s>
