<s>
Dynamic	B-Protocol
Site	I-Protocol
Acceleration	I-Protocol
(	O
DSA	O
)	O
is	O
a	O
group	O
of	O
technologies	O
which	O
make	O
the	O
delivery	O
of	O
dynamic	O
websites	O
more	O
efficient	O
.	O
</s>
<s>
Manufacturers	O
of	O
application	B-Protocol
delivery	I-Protocol
controllers	I-Protocol
and	O
content	B-Operating_System
delivery	I-Operating_System
networks	I-Operating_System
(	O
CDNs	O
)	O
use	O
a	O
host	O
of	O
techniques	O
to	O
accelerate	O
dynamic	O
sites	O
,	O
including	O
:	O
</s>
<s>
An	O
edge	O
device	O
,	O
either	O
an	O
ADC	B-Protocol
or	O
a	O
CDN	O
,	O
is	O
capable	O
of	O
TCP	O
multiplexing	B-Architecture
which	O
can	O
be	O
placed	O
between	O
web	O
servers	O
and	O
clients	O
to	O
offload	O
origin	O
servers	O
and	O
accelerate	O
content	O
delivery	O
.	O
</s>
<s>
With	O
TCP	O
multiplexing	B-Architecture
,	O
the	O
situation	O
is	O
different	O
.	O
</s>
<s>
HTTP	B-Protocol
has	O
a	O
built-in	O
system	O
for	O
cache	B-Protocol
control	I-Protocol
,	O
using	O
headers	O
such	O
as	O
ETag	B-Protocol
,	O
"	O
expires	O
"	O
and	O
"	O
last	O
modified	O
"	O
.	O
</s>
<s>
Many	O
CDNs	O
and	O
ADCs	O
that	O
claim	O
to	O
have	O
DSA	O
,	O
have	O
replaced	O
this	O
with	O
their	O
system	O
,	O
calling	O
it	O
dynamic	O
caching	O
or	O
dynamic	O
cache	B-Protocol
control	I-Protocol
.	O
</s>
<s>
It	O
gives	O
them	O
more	O
options	O
to	O
invalidate	O
and	O
bypass	O
the	O
cache	O
over	O
the	O
standard	O
HTTP	B-Protocol
cache	I-Protocol
control	O
.	O
</s>
<s>
The	O
purpose	O
of	O
dynamic	O
cache	B-Protocol
control	I-Protocol
is	O
to	O
increase	O
the	O
cache-hit	O
ratio	O
of	O
a	O
website	O
,	O
which	O
is	O
the	O
rate	O
between	O
requests	O
served	O
by	O
the	O
cache	O
and	O
those	O
served	O
by	O
the	O
normal	O
server	O
.	O
</s>
<s>
Due	O
to	O
the	O
dynamic	O
nature	O
of	O
web	O
2.0	O
websites	O
,	O
it	O
is	O
difficult	O
to	O
use	O
static	O
web	B-Protocol
caching	I-Protocol
.	O
</s>
<s>
Dynamic	O
cache	B-Protocol
control	I-Protocol
has	O
more	O
options	O
to	O
configure	O
caching	O
,	O
such	O
as	O
cookie-based	B-Application
cache	B-Protocol
control	I-Protocol
,	O
that	O
allows	O
serving	O
content	O
from	O
cache	O
based	O
on	O
the	O
presence	O
or	O
lack	O
of	O
specific	O
cookies	B-Application
.	O
</s>
<s>
A	O
cookie	B-Application
stores	O
the	O
unique	O
identifier-key	O
of	O
a	O
logged-in	O
user	O
on	O
their	O
device	O
and	O
it	O
's	O
already	O
implemented	O
for	O
authenticating	O
users	O
upon	O
execution	O
of	O
any	O
page	O
that	O
opens	O
a	O
session	O
,	O
in	O
a	O
dynamic	O
caching	O
system	O
,	O
the	O
caches	O
are	O
referred	O
to	O
by	O
URL	O
as	O
well	O
as	O
the	O
cookie	B-Application
keys	O
,	O
allowing	O
to	O
simply	O
enable	O
serving	O
of	O
default	O
caches	O
to	O
anonymous	O
users	O
and	O
personalized	O
caches	O
to	O
logged-in	O
users	O
(	O
without	O
forcing	O
you	O
to	O
modify	O
the	O
code	O
,	O
to	O
make	O
it	O
append	O
additional	O
user	O
identifiers	O
to	O
the	O
URL	O
,	O
like	O
in	O
a	O
static	O
caching	O
system	O
)	O
.	O
</s>
<s>
This	O
differs	O
from	O
caching	O
as	O
prefetched	O
responses	O
are	O
only	O
served	O
once	O
,	O
being	O
especially	O
useful	O
for	O
accelerating	O
responses	O
of	O
third-party	O
APIs	B-Application
,	O
such	O
as	O
advertisements	O
.	O
</s>
<s>
dropping	O
the	O
quality	O
of	O
images	O
)	O
,	O
minification	B-Language
,	O
resource	O
consolidation	O
and	O
inlining	O
Because	O
FEO	O
changes	O
the	O
actual	O
traffic	O
,	O
configuration	O
tends	O
to	O
be	O
more	O
difficult	O
,	O
as	O
there	O
is	O
a	O
risk	O
of	O
affecting	O
the	O
user-experience	O
,	O
by	O
serving	O
content	O
that	O
was	O
incorrectly	O
changed	O
.	O
</s>
