<s>
A	O
web	B-Application
accelerator	I-Application
is	O
a	O
proxy	B-Application
server	I-Application
that	O
reduces	O
website	O
access	O
time	O
.	O
</s>
<s>
Web	B-Application
accelerators	I-Application
may	O
be	O
installed	O
on	O
the	O
client	B-Protocol
computer	I-Protocol
or	O
mobile	O
device	O
,	O
on	O
ISP	O
servers	O
,	O
on	O
the	O
server	O
computer/network	O
,	O
or	O
a	O
combination	O
.	O
</s>
<s>
Accelerating	O
delivery	O
through	O
compression	O
requires	O
some	O
type	O
of	O
host-based	O
server	B-Application
to	O
collect	O
,	O
compress	B-General_Concept
and	O
then	O
deliver	O
content	O
to	O
a	O
client	B-Protocol
computer	I-Protocol
.	O
</s>
<s>
Web	B-Application
accelerators	I-Application
may	O
use	O
several	O
techniques	O
to	O
achieve	O
this	O
reduction	O
in	O
access	O
time	O
:	O
</s>
<s>
cache	B-Protocol
recently	O
or	O
frequently	O
accessed	O
documents	B-Protocol
so	O
they	O
may	O
be	O
sent	O
to	O
the	O
client	B-Protocol
with	O
less	O
latency	O
or	O
at	O
a	O
faster	O
transfer	O
rate	O
than	O
the	O
remote	O
server	B-Application
could	O
.	O
</s>
<s>
freshen	O
objects	O
in	O
the	O
cache	B-Protocol
ensuring	O
that	O
frequently	O
accessed	O
content	O
is	O
readily	O
available	O
for	O
display	O
.	O
</s>
<s>
preemptively	O
resolve	B-Protocol
hostnames	I-Protocol
present	O
in	O
a	O
document	O
(	O
HTML	B-Language
or	O
JavaScript	B-Language
)	O
in	O
order	O
to	O
reduce	O
latency	O
.	O
</s>
<s>
prefetch	B-Protocol
documents	B-Protocol
that	O
are	O
likely	O
to	O
be	O
accessed	O
in	O
the	O
near	O
future	O
.	O
</s>
<s>
compress	B-General_Concept
documents	B-Protocol
to	O
a	O
smaller	O
size	O
,	O
for	O
example	O
by	O
reducing	O
the	O
quality	O
of	O
images	B-Algorithm
or	O
by	O
sending	O
only	O
what	O
's	O
changed	O
since	O
the	O
document	O
was	O
last	O
requested	O
.	O
</s>
<s>
optimize	O
the	O
code	O
from	O
certain	O
documents	B-Protocol
(	O
such	O
as	O
HTML	B-Language
or	O
JavaScript	B-Language
)	O
.	O
</s>
<s>
filter	B-Application
out	O
ads	O
and	O
other	O
undesirable	O
objects	O
so	O
they	O
are	O
not	O
sent	O
to	O
the	O
client	B-Protocol
at	O
all	O
.	O
</s>
<s>
maintain	O
persistent	O
TCP	B-Protocol
connections	O
between	O
the	O
client	B-Protocol
and	O
the	O
proxy	B-Application
server	I-Application
.	O
</s>
<s>
improve	O
the	O
performance	O
via	O
protocol	O
level	O
accelerations	O
,	O
such	O
as	O
TCP	B-Protocol
acceleration	O
.	O
</s>
<s>
These	O
techniques	O
align	O
with	O
best	O
practices	O
which	O
are	O
typically	O
recommended	O
to	O
improve	O
the	O
performance	O
of	O
web	B-Application
applications	I-Application
.	O
</s>
<s>
Introduced	O
in	O
2001-2002	O
,	O
these	O
applications	O
generally	O
serve	O
to	O
improve	O
dial-up	O
,	O
broadband	B-General_Concept
and	O
other	O
connections	O
from	O
which	O
users	O
may	O
not	O
be	O
getting	O
the	O
best	O
speed	O
.	O
</s>
<s>
Many	O
Dialup	O
ISPs	O
offer	O
web	B-Application
accelerators	I-Application
as	O
a	O
part	O
of	O
their	O
services	O
.	O
</s>
<s>
Typically	O
,	O
website	O
text	O
is	O
compacted	O
to	O
5%	O
,	O
thus	O
increasing	O
effective	O
dialup	O
throughput	O
to	O
approximately	O
1000	O
kbit/s	O
,	O
and	O
JPEG/GIF/PNG	O
images	B-Algorithm
are	O
lossy-compressed	O
to	O
15	O
–	O
20%	O
,	O
increasing	O
effective	O
throughput	O
to	O
300	O
kbit/s	O
.	O
</s>
<s>
The	O
drawback	O
of	O
this	O
approach	O
is	O
a	O
loss	O
in	O
quality	O
,	O
where	O
the	O
graphics	O
acquire	O
compression	B-Algorithm
artifacts	I-Algorithm
taking	O
on	O
a	O
blurry	O
or	O
colorless	O
appearance	O
.	O
</s>
<s>
If	O
desired	O
,	O
the	O
user	O
may	O
choose	O
to	O
view	O
uncompressed	B-General_Concept
images	B-Algorithm
instead	O
,	O
but	O
at	O
a	O
much	O
slower	O
load	O
rate	O
.	O
</s>
<s>
Web	B-Application
accelerators	I-Application
are	O
typically	O
designed	O
for	O
web	O
browsing	O
and	O
,	O
sometimes	O
,	O
for	O
e-mailing	O
and	O
can	O
not	O
improve	O
speeds	O
of	O
streaming	O
,	O
gaming	O
,	O
P2P	O
downloads	O
or	O
many	O
other	O
Internet	O
applications	O
.	O
</s>
<s>
However	O
,	O
there	O
is	O
substantial	O
work	O
being	O
done	O
on	O
client-side	O
Web	B-Application
Accelerators	I-Application
for	O
Application	O
Delivery	O
Networks	O
by	O
several	O
companies	O
including	O
Cisco	O
Systems	O
and	O
F5	O
Networks	O
as	O
the	O
demand	O
for	O
SaaS	B-Architecture
and	O
PaaS	B-Application
look	O
set	O
to	O
grow	O
among	O
small	O
and	O
medium	O
enterprises	O
.	O
</s>
<s>
Other	O
web	B-Application
accelerators	I-Application
are	O
targeted	O
at	O
the	O
web	O
site	O
or	O
web	B-Application
application	I-Application
owners	O
.	O
</s>
<s>
This	O
type	O
of	O
web	B-Application
accelerator	I-Application
is	O
installed	O
in	O
front	O
of	O
web	B-Application
servers	I-Application
and	O
application	O
servers	O
and	O
use	O
a	O
variety	O
of	O
the	O
above	O
techniques	O
to	O
improve	O
performance	O
to	O
all	O
users	O
accessing	O
the	O
accelerated	O
web	O
sites	O
or	O
web	B-Application
applications	I-Application
.	O
</s>
<s>
Web	B-Application
server	I-Application
accelerators	O
are	O
sometimes	O
referred	O
to	O
as	O
reverse	B-General_Concept
proxies	I-General_Concept
or	O
Application	B-Protocol
Delivery	I-Protocol
Controllers	I-Protocol
.	O
</s>
<s>
This	O
type	O
of	O
server	B-Application
side	O
accelerator	O
has	O
the	O
added	O
benefit	O
of	O
off-loading	O
transactions	O
and	O
connection	O
managements	O
from	O
the	O
web	O
or	O
applications	O
servers	O
and	O
hence	O
,	O
reducing	O
its	O
CPU	O
utilization	O
and	O
increasing	O
web	B-Application
server	I-Application
or	O
application	O
scalability	O
to	O
handle	O
more	O
users	O
with	O
less	O
bandwidth	O
.	O
</s>
<s>
There	O
may	O
be	O
two	O
sections	O
to	O
the	O
proxy	O
as	O
well	O
-	O
a	O
server	B-Application
portion	O
sits	O
in	O
front	O
of	O
the	O
web	B-Application
server	I-Application
and	O
captures	O
the	O
input	O
and	O
output	O
from	O
the	O
server	B-Application
and	O
a	O
client	B-Protocol
portion	O
sits	O
in	O
front	O
of	O
the	O
end-user	O
'	O
s	O
web	B-Application
browser	I-Application
to	O
capture	O
the	O
input	O
and	O
output	O
from	O
the	O
browser	B-Application
.	O
</s>
<s>
An	O
example	O
would	O
be	O
Opera	B-Application
Turbo	I-Application
.	O
</s>
