<s>
Encapsulation	B-Protocol
is	O
the	O
computer-networking	B-Architecture
process	O
of	O
concatenating	O
layer-specific	O
headers	B-General_Concept
or	O
tailers	B-Device
with	O
a	O
service	O
data	O
unit	O
(	O
i.e.	O
</s>
<s>
a	O
payload	O
)	O
for	O
transmitting	O
information	O
over	O
computer	B-Architecture
networks	I-Architecture
.	O
</s>
<s>
Deencapsulation	O
(	O
or	O
de-encapsulation	O
)	O
is	O
the	O
reverse	O
computer-networking	B-Architecture
process	O
for	O
receiving	O
information	O
;	O
it	O
removes	O
from	O
the	O
protocol	B-Protocol
data	I-Protocol
unit	I-Protocol
(	O
PDU	O
)	O
a	O
previously	O
concatenated	O
header	B-General_Concept
or	O
tailer	O
that	O
an	O
underlying	O
communications	O
layer	O
transmitted	O
.	O
</s>
<s>
Encapsulation	B-Protocol
and	O
deencapsulation	O
allow	O
the	O
design	O
of	O
modular	O
communication	O
protocols	O
so	O
to	O
logically	O
separate	O
the	O
function	O
of	O
each	O
communications	O
layer	O
,	O
and	O
abstract	B-Application
the	O
structure	O
of	O
the	O
communicated	O
information	O
over	O
the	O
other	O
communications	O
layers	O
.	O
</s>
<s>
These	O
two	O
processes	O
are	O
common	O
features	O
of	O
the	O
computer-networking	B-Architecture
models	O
and	O
protocol	O
suites	O
,	O
like	O
in	O
the	O
OSI	O
model	O
and	O
internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
.	O
</s>
<s>
However	O
,	O
encapsulation/deencapsulation	O
processes	O
can	O
also	O
serve	O
as	O
malicious	O
features	O
like	O
in	O
the	O
tunneling	B-Protocol
protocols	I-Protocol
.	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
is	O
responsible	O
for	O
physical	O
transmission	O
of	O
the	O
data	O
,	O
link	O
encapsulation	B-Protocol
allows	O
local	B-General_Concept
area	I-General_Concept
networking	I-General_Concept
,	O
IP	B-Protocol
provides	O
global	O
addressing	O
of	O
individual	O
computers	O
,	O
and	O
TCP	B-Protocol
selects	O
the	O
process	O
or	O
application	O
(	O
i.e.	O
,	O
the	O
TCP	B-Protocol
or	I-Protocol
UDP	I-Protocol
port	I-Protocol
)	O
that	O
specifies	O
the	O
service	O
such	O
as	O
a	O
Web	B-Application
or	O
TFTP	B-Device
server	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
IP	B-Protocol
suite	I-Protocol
,	O
the	O
contents	O
of	O
a	O
web	B-Application
page	O
are	O
encapsulated	O
with	O
an	O
HTTP	B-Protocol
header	I-Protocol
,	O
then	O
by	O
a	O
TCP	B-Protocol
header	I-Protocol
,	O
an	O
IP	B-Protocol
header	B-General_Concept
,	O
and	O
,	O
finally	O
,	O
by	O
a	O
frame	O
header	B-General_Concept
and	O
trailer	B-Device
.	O
</s>
<s>
The	O
frame	O
is	O
forwarded	O
to	O
the	O
destination	O
node	O
as	O
a	O
stream	B-General_Concept
of	O
bits	O
,	O
where	O
it	O
is	O
decapsulated	O
into	O
the	O
respective	O
PDUs	O
and	O
interpreted	O
at	O
each	O
layer	O
by	O
the	O
receiving	O
node	O
.	O
</s>
<s>
The	O
result	O
of	O
encapsulation	B-Protocol
is	O
that	O
each	O
lower-layer	O
provides	O
a	O
service	O
to	O
the	O
layer	O
or	O
layers	O
above	O
it	O
,	O
while	O
at	O
the	O
same	O
time	O
each	O
layer	O
communicates	O
with	O
its	O
corresponding	O
layer	O
on	O
the	O
receiving	O
node	O
.	O
</s>
<s>
In	O
discussions	O
of	O
encapsulation	B-Protocol
,	O
the	O
more	O
abstract	B-Application
layer	O
is	O
often	O
called	O
the	O
upper-layer	O
protocol	O
while	O
the	O
more	O
specific	O
layer	O
is	O
called	O
the	O
lower-layer	O
protocol	O
.	O
</s>
<s>
Sometimes	O
,	O
however	O
,	O
the	O
terms	O
upper-layer	O
protocols	O
and	O
lower-layer	O
protocols	O
are	O
used	O
to	O
describe	O
the	O
layers	O
above	O
and	O
below	O
IP	B-Protocol
.	O
</s>
