<s>
DECbit	B-Protocol
is	O
a	O
TCP	O
congestion	B-Protocol
control	O
technique	O
implemented	O
in	O
routers	B-Protocol
to	O
avoid	O
congestion	B-Protocol
.	O
</s>
<s>
Its	O
utility	O
is	O
to	O
predict	O
possible	O
congestion	B-Protocol
and	O
prevent	O
it	O
.	O
</s>
<s>
When	O
a	O
router	B-Protocol
wants	O
to	O
signal	O
congestion	B-Protocol
to	O
the	O
sender	O
,	O
it	O
adds	O
a	O
bit	O
in	O
the	O
header	B-General_Concept
of	I-General_Concept
packets	I-General_Concept
sent	O
.	O
</s>
<s>
When	O
a	O
packet	O
arrives	O
at	O
the	O
router	B-Protocol
,	O
the	O
router	B-Protocol
calculates	O
the	O
average	O
queue	B-Application
length	O
for	O
the	O
last	O
(	O
busy	O
+	O
idle	O
)	O
period	O
plus	O
the	O
current	O
busy	O
period	O
.	O
</s>
<s>
(	O
The	O
router	B-Protocol
is	O
busy	O
when	O
it	O
is	O
transmitting	O
packets	O
,	O
and	O
idle	O
otherwise	O
)	O
.	O
</s>
<s>
When	O
the	O
average	O
queue	B-Application
length	O
exceeds	O
1	O
,	O
then	O
the	O
router	B-Protocol
sets	O
the	O
congestion	B-Protocol
indication	O
bit	O
in	O
the	O
packet	B-General_Concept
header	I-General_Concept
of	O
arriving	O
packets	O
.	O
</s>
<s>
When	O
the	O
destination	O
replies	O
,	O
the	O
corresponding	O
ACK	B-Protocol
includes	O
a	O
set	O
congestion	B-Protocol
bit	O
.	O
</s>
<s>
The	O
sender	O
receives	O
the	O
ACK	B-Protocol
and	O
calculates	O
how	O
many	O
packets	O
it	O
received	O
with	O
the	O
congestion	B-Protocol
indication	O
bit	O
set	O
to	O
one	O
.	O
</s>
<s>
If	O
less	O
than	O
half	O
of	O
the	O
packets	O
in	O
the	O
last	O
window	O
had	O
the	O
congestion	B-Protocol
indication	O
bit	O
set	O
,	O
then	O
the	O
window	O
is	O
increased	O
linearly	O
.	O
</s>
<s>
This	O
technique	O
dynamically	O
manages	O
the	O
window	O
to	O
avoid	O
congestion	B-Protocol
and	O
increasing	O
freight	O
if	O
it	O
detects	O
congestion	B-Protocol
and	O
tries	O
to	O
balance	O
bandwidth	O
with	O
respect	O
to	O
the	O
delay	O
.	O
</s>
<s>
Besides	O
,	O
the	O
fact	O
that	O
the	O
tail	O
has	O
increased	O
in	O
size	O
from	O
one	O
cycle	O
to	O
another	O
does	O
not	O
always	O
mean	O
there	O
is	O
congestion	B-Protocol
.	O
</s>
