<s>
FAST	B-Protocol
TCP	I-Protocol
(	O
also	O
written	O
FastTCP	B-Protocol
)	O
is	O
a	O
TCP	O
congestion	O
avoidance	O
algorithm	O
especially	O
targeted	O
at	O
long-distance	O
,	O
high	O
latency	O
links	O
,	O
developed	O
at	O
the	O
Netlab	O
,	O
California	O
Institute	O
of	O
Technology	O
and	O
now	O
being	O
commercialized	O
by	O
FastSoft	O
.	O
</s>
<s>
FastSoft	O
was	O
acquired	O
by	O
Akamai	B-Application
Technologies	I-Application
in	O
2012	O
.	O
</s>
<s>
FastTCP	B-Protocol
is	O
compatible	O
with	O
existing	O
TCP	O
algorithms	O
,	O
requiring	O
modification	O
only	O
to	O
the	O
computer	O
which	O
is	O
sending	O
data	O
.	O
</s>
<s>
Like	O
TCP	B-Protocol
Vegas	I-Protocol
,	O
FAST	B-Protocol
TCP	I-Protocol
uses	O
queueing	B-Protocol
delay	I-Protocol
instead	O
of	O
loss	B-Protocol
probability	I-Protocol
as	O
a	O
congestion	O
signal	O
.	O
</s>
<s>
Most	O
current	O
congestion	O
control	O
algorithms	O
detect	O
congestion	O
and	O
slow	O
down	O
when	O
they	O
discover	O
that	O
packets	O
are	O
being	O
dropped	O
,	O
so	O
that	O
the	O
average	O
sending	O
rate	O
depends	O
on	O
the	O
loss	B-Protocol
probability	I-Protocol
.	O
</s>
<s>
First	O
,	O
low	O
loss	O
probabilities	O
are	O
required	O
to	O
sustain	O
high	O
data	O
rates	O
;	O
in	O
the	O
case	O
of	O
TCP	O
Reno	O
,	O
very	O
low	O
loss	O
probabilities	O
are	O
required	O
,	O
but	O
even	O
new	O
congestion	O
avoidance	O
algorithms	O
such	O
as	O
H-TCP	B-Protocol
,	O
BIC	B-Protocol
TCP	I-Protocol
and	O
HSTCP	B-Protocol
require	O
loss	O
rates	O
lower	O
than	O
those	O
provided	O
by	O
most	O
wireless	O
wide	O
area	O
networks	O
.	O
</s>
<s>
Moreover	O
,	O
packet	B-Protocol
loss	I-Protocol
only	O
provides	O
a	O
single	O
bit	O
of	O
information	O
about	O
the	O
congestion	O
level	O
,	O
whereas	O
delay	O
is	O
a	O
continuous	O
quantity	O
and	O
in	O
principle	O
provides	O
more	O
information	O
about	O
the	O
network	O
.	O
</s>
<s>
A	O
FAST	B-Protocol
TCP	I-Protocol
flow	O
seeks	O
to	O
maintain	O
a	O
constant	O
number	O
of	O
packets	O
in	O
queues	O
throughout	O
the	O
network	O
.	O
</s>
<s>
In	O
this	O
respect	O
,	O
it	O
is	O
a	O
direct	O
descendant	O
of	O
TCP	B-Protocol
Vegas	I-Protocol
.	O
</s>
<s>
The	O
difference	O
between	O
TCP	B-Protocol
Vegas	I-Protocol
and	O
FAST	B-Protocol
TCP	I-Protocol
lies	O
in	O
the	O
way	O
in	O
which	O
the	O
rate	O
is	O
adjusted	O
when	O
the	O
number	O
of	O
packets	O
stored	O
is	O
too	O
small	O
or	O
large	O
.	O
</s>
<s>
TCP	B-Protocol
Vegas	I-Protocol
makes	O
fixed	O
size	O
adjustments	O
to	O
the	O
rate	O
,	O
independent	O
of	O
how	O
far	O
the	O
current	O
rate	O
is	O
from	O
the	O
target	O
rate	O
.	O
</s>
<s>
FAST	B-Protocol
TCP	I-Protocol
makes	O
larger	O
steps	O
when	O
the	O
system	O
is	O
further	O
from	O
equilibrium	O
and	O
smaller	O
steps	O
near	O
equilibrium	O
.	O
</s>
<s>
Delay	O
measurements	O
are	O
also	O
subject	O
to	O
jitter	O
as	O
a	O
result	O
of	O
operating	B-General_Concept
system	I-General_Concept
scheduling	O
,	O
or	O
bus	B-General_Concept
contention	O
.	O
</s>
<s>
In	O
a	O
clean	O
network	O
,	O
the	O
queueing	B-Protocol
delay	I-Protocol
maintained	O
by	O
existing	O
FAST	O
flows	O
may	O
be	O
mistaken	O
as	O
part	O
of	O
the	O
propagation	O
delay	O
by	O
new	O
flows	O
that	O
join	O
later	O
,	O
as	O
shown	O
in	O
ns-2	O
simulations	O
in	O
.	O
</s>
<s>
FAST	B-Protocol
TCP	I-Protocol
has	O
been	O
shown	O
to	O
be	O
promising	O
in	O
terms	O
of	O
system	O
stability	O
,	O
throughput	O
and	O
fairness	O
.	O
</s>
<s>
the	O
new	O
algorithm	O
Generalized	O
FAST	B-Protocol
TCP	I-Protocol
.	O
</s>
<s>
better	O
than	O
standard	O
FAST	B-Protocol
TCP	I-Protocol
.	O
</s>
<s>
Unlike	O
most	O
TCP	O
congestion	O
avoidance	O
algorithms	O
,	O
FAST	B-Protocol
TCP	I-Protocol
is	O
protected	O
by	O
several	O
patents	O
.	O
</s>
