<s>
Peer-to-peer	O
caching	B-General_Concept
(	O
P2P	B-Protocol
caching	I-Protocol
)	O
is	O
a	O
computer	B-Architecture
network	I-Architecture
traffic	O
management	O
technology	O
used	O
by	O
Internet	O
Service	O
Providers	O
(	O
ISPs	O
)	O
to	O
accelerate	O
content	O
delivered	O
over	O
peer-to-peer	O
(	O
P2P	O
)	O
networks	O
while	O
reducing	O
related	O
bandwidth	O
costs	O
.	O
</s>
<s>
P2P	B-Protocol
caching	I-Protocol
is	O
similar	O
in	O
principle	O
to	O
the	O
content	O
caching	B-General_Concept
long	O
used	O
by	O
ISPs	O
to	O
accelerate	O
Web	O
(	O
HTTP	B-Protocol
)	O
content	O
.	O
</s>
<s>
P2P	B-Protocol
caching	I-Protocol
temporarily	O
stores	O
popular	O
content	O
that	O
is	O
flowing	O
into	O
an	O
ISP	O
's	O
network	O
.	O
</s>
<s>
If	O
the	O
content	O
requested	O
by	O
a	O
subscriber	O
is	O
available	O
from	O
a	O
cache	B-General_Concept
,	O
the	O
cache	B-General_Concept
satisfies	O
the	O
request	O
from	O
its	O
temporary	O
storage	O
,	O
eliminating	O
data	O
transfer	O
through	O
expensive	O
transit	O
links	O
and	O
reducing	O
network	B-Protocol
congestion	I-Protocol
.	O
</s>
<s>
P2P	O
content	O
responds	O
well	O
to	O
caching	B-General_Concept
because	O
it	O
has	O
high	O
reuse	O
patterns	O
reflecting	O
a	O
Zipf's-like	O
distribution	O
.	O
</s>
<s>
Some	O
P2P	B-Protocol
caching	I-Protocol
devices	O
can	O
also	O
accelerate	O
HTTP	B-Protocol
video	B-Application
streaming	I-Application
traffic	O
from	O
YouTube	B-General_Concept
,	O
Facebook	B-Application
,	O
RapidShare	O
,	O
MegaUpload	B-Application
,	O
Google	B-Application
,	O
AOL	O
Video	O
,	O
MySpace	B-Application
and	O
other	O
web	O
video-sharing	O
sites	O
.	O
</s>
<s>
P2P	B-Protocol
caching	I-Protocol
involves	O
creating	O
a	O
cache	B-General_Concept
or	O
temporary	O
storage	O
space	O
for	O
P2P	O
data	O
,	O
using	O
specialized	O
communications	O
hardware	O
,	O
disk	O
storage	O
and	O
associated	O
software	O
.	O
</s>
<s>
This	O
cache	B-General_Concept
is	O
placed	O
in	O
the	O
ISP	O
's	O
network	O
,	O
either	O
co-located	O
with	O
the	O
Internet	O
transit	O
links	O
or	O
placed	O
at	O
key	O
aggregation	O
points	O
or	O
at	O
each	O
cable	O
head-end	O
.	O
</s>
<s>
Once	O
a	O
P2P	O
cache	B-General_Concept
is	O
established	O
,	O
the	O
network	O
will	O
transparently	O
redirect	O
P2P	O
traffic	O
to	O
the	O
cache	B-General_Concept
,	O
which	O
either	O
serves	O
the	O
file	O
directly	O
or	O
passes	O
the	O
request	O
on	O
to	O
a	O
remote	O
P2P	O
user	O
and	O
simultaneously	O
caches	B-General_Concept
that	O
data	O
for	O
the	O
next	O
user	O
.	O
</s>
<s>
To	O
what	O
extent	O
the	O
caching	B-General_Concept
is	O
beneficial	O
depends	O
on	O
how	O
similar	O
the	O
content	O
interests	O
of	O
ISP	O
's	O
customers	O
.	O
</s>
<s>
Due	O
to	O
relatively	O
small	O
number	O
of	O
content	O
shared	O
in	O
P2P	O
systems	O
(	O
compared	O
to	O
Web	O
)	O
and	O
semantic	O
,	O
geographic	O
,	O
and	O
organization	O
interests	O
of	O
users	O
sharing	O
ratio	O
in	O
P2P	O
can	O
be	O
significantly	O
higher	O
than	O
HTTP/Web	O
caching	B-General_Concept
.	O
</s>
<s>
P2P	B-Protocol
caching	I-Protocol
typically	O
works	O
with	O
a	O
network	O
traffic-mitigation	O
technology	O
called	O
Deep	B-Application
Packet	I-Application
Inspection	I-Application
(	O
DPI	O
)	O
.	O
</s>
<s>
DPI	O
products	O
identify	O
and	O
pass	O
P2P	O
packets	B-Protocol
to	O
the	O
P2P	B-Protocol
caching	I-Protocol
system	O
so	O
it	O
can	O
cache	B-General_Concept
the	O
traffic	O
and	O
accelerate	O
it	O
.	O
</s>
<s>
Peerapp	O
Ltd	O
.	O
holds	O
the	O
first	O
patent	O
for	O
P2P	B-Protocol
caching	I-Protocol
technology	O
,	O
which	O
was	O
filed	O
in	O
2000	O
.	O
</s>
<s>
These	O
statistics	O
may	O
be	O
explained	O
by	O
the	O
popularization	O
of	O
Video	B-Application
on	I-Application
Demand	I-Application
services	I-Application
,	O
which	O
have	O
(	O
until	O
the	O
moment	O
)	O
used	O
a	O
centralized	O
architecture	O
for	O
data	O
distribution	O
.	O
</s>
<s>
The	O
difficulty	O
is	O
that	O
P2P	O
packets	B-Protocol
are	O
becoming	O
harder	O
and	O
harder	O
to	O
identify	O
,	O
especially	O
with	O
the	O
introduction	O
of	O
encryption	O
(	O
such	O
as	O
BitTorrent	B-Protocol
protocol	I-Protocol
encryption	I-Protocol
)	O
.	O
</s>
<s>
Implement	O
a	O
form	O
of	O
P2P	B-Protocol
caching	I-Protocol
.	O
</s>
<s>
Caching	B-General_Concept
releases	O
the	O
bandwidth	O
demand	O
on	O
critical	O
Internet	O
links	O
and	O
improves	O
the	O
experience	O
for	O
all	O
users	O
–	O
P2P	O
users	O
whose	O
file	O
sharing	O
is	O
improved	O
through	O
using	O
the	O
cache	B-General_Concept
,	O
and	O
non-P2P	O
users	O
who	O
experience	O
better	O
performance	O
from	O
networks	O
un-congested	O
from	O
P2P	O
traffic	O
.	O
</s>
<s>
The	O
initial	O
adopters	O
of	O
P2P	B-Protocol
caching	I-Protocol
have	O
been	O
ISPs	O
in	O
Asia	O
,	O
the	O
Pacific	O
Rim	O
,	O
Latin	O
America	O
,	O
the	O
Caribbean	O
and	O
the	O
Middle	O
East	O
,	O
whose	O
subscribers	O
are	O
heavy	O
users	O
of	O
P2P	O
networks	O
and	O
where	O
providing	O
the	O
additional	O
bandwidth	O
to	O
handle	O
P2P	O
data	O
is	O
very	O
costly	O
due	O
to	O
the	O
expense	O
of	O
international	O
transit	O
links	O
.	O
</s>
<s>
P2P	B-Protocol
caching	I-Protocol
is	O
expected	O
to	O
become	O
an	O
increasingly	O
essential	O
technology	O
for	O
ISPs	O
and	O
MSOs	O
(	O
multiple	O
system	O
operators	O
)	O
worldwide	O
,	O
particularly	O
with	O
the	O
growing	O
popularity	O
of	O
P2P	O
content	O
among	O
broadband	O
subscribers	O
and	O
the	O
adoption	O
of	O
P2P	O
as	O
a	O
content-distribution	O
strategy	O
by	O
mainstream	O
content	O
providers	O
such	O
as	O
the	O
BBC	O
.	O
</s>
<s>
Corelli	O
is	O
a	O
community-based	O
P2P	B-Protocol
caching	I-Protocol
system	O
that	O
operates	O
in	O
a	O
decentralized	O
way	O
across	O
multiple	O
peers	O
.	O
</s>
<s>
This	O
allows	O
a	O
caching	B-General_Concept
service	O
to	O
be	O
realised	O
in	O
environments	O
that	O
do	O
not	O
possess	O
fixed	O
caching	B-General_Concept
infrastructure	O
,	O
e.g.	O
</s>
<s>
a	O
Wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Community	O
Caching	B-General_Concept
is	O
a	O
P2P	O
community-interest-aware	O
,	O
distributed	O
caching	B-General_Concept
solution	O
for	O
structured	O
(	O
DHT-based	O
)	O
P2P	O
systems	O
.	O
</s>
