<s>
TCP	B-Protocol
tuning	I-Protocol
techniques	O
adjust	O
the	O
network	O
congestion	O
avoidance	O
parameters	O
of	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
TCP	B-Protocol
)	O
connections	O
over	O
high-bandwidth	O
,	O
high-latency	O
networks	O
.	O
</s>
<s>
Bandwidth-delay	O
product	O
(	O
BDP	O
)	O
is	O
a	O
term	O
primarily	O
used	O
in	O
conjunction	O
with	O
TCP	B-Protocol
to	O
refer	O
to	O
the	O
number	O
of	O
bytes	B-Application
necessary	O
to	O
fill	O
a	O
TCP	B-Protocol
"	O
path	O
"	O
,	O
i.e.	O
</s>
<s>
The	O
original	O
TCP	B-Protocol
configurations	O
supported	O
TCP	B-Protocol
receive	I-Protocol
window	I-Protocol
size	O
buffers	B-General_Concept
of	O
up	O
to	O
65,535	O
(	O
64	O
KiB	O
-	O
1	O
)	O
bytes	B-Application
,	O
which	O
was	O
adequate	O
for	O
slow	O
links	O
or	O
links	O
with	O
small	O
RTTs	O
.	O
</s>
<s>
Larger	O
buffers	B-General_Concept
are	O
required	O
by	O
the	O
high	O
performance	O
options	O
described	O
below	O
.	O
</s>
<s>
In	O
general	O
,	O
buffer	B-General_Concept
size	O
will	O
need	O
to	O
be	O
scaled	O
proportionally	O
to	O
the	O
amount	O
of	O
data	O
"	O
in	O
flight	O
"	O
at	O
any	O
time	O
.	O
</s>
<s>
Maximum	O
achievable	O
throughput	O
for	O
a	O
single	O
TCP	B-Protocol
connection	O
is	O
determined	O
by	O
different	O
factors	O
.	O
</s>
<s>
But	O
there	O
are	O
also	O
other	O
,	O
less	O
obvious	O
limits	O
for	O
TCP	B-Protocol
throughput	O
.	O
</s>
<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
RWIN	B-Protocol
(	O
TCP	B-Protocol
Receive	I-Protocol
Window	I-Protocol
)	O
is	O
the	O
amount	O
of	O
data	O
that	O
a	O
computer	O
can	O
accept	O
without	O
acknowledging	O
the	O
sender	O
.	O
</s>
<s>
If	O
the	O
sender	O
has	O
not	O
received	O
acknowledgement	O
for	O
the	O
first	O
packet	B-Protocol
it	O
sent	O
,	O
it	O
will	O
stop	O
and	O
wait	O
and	O
if	O
this	O
wait	O
exceeds	O
a	O
certain	O
limit	O
,	O
it	O
may	O
even	O
retransmit	B-Protocol
.	O
</s>
<s>
This	O
is	O
how	O
TCP	B-Protocol
achieves	O
reliable	O
data	O
transmission	O
.	O
</s>
<s>
Even	O
if	O
there	O
is	O
no	O
packet	B-Protocol
loss	I-Protocol
in	O
the	O
network	O
,	O
windowing	O
can	O
limit	O
throughput	O
.	O
</s>
<s>
Because	O
TCP	B-Protocol
transmits	O
data	O
up	O
to	O
the	O
window	O
size	O
before	O
waiting	O
for	O
the	O
acknowledgements	O
,	O
the	O
full	O
bandwidth	O
of	O
the	O
network	O
may	O
not	O
always	O
get	O
used	O
.	O
</s>
<s>
where	O
RWIN	B-Protocol
is	O
the	O
TCP	B-Protocol
Receive	I-Protocol
Window	I-Protocol
and	O
RTT	O
is	O
the	O
round-trip	O
time	O
for	O
the	O
path	O
.	O
</s>
<s>
At	O
any	O
given	O
time	O
,	O
the	O
window	O
advertised	O
by	O
the	O
receive	O
side	O
of	O
TCP	B-Protocol
corresponds	O
to	O
the	O
amount	O
of	O
free	O
receive	O
memory	O
it	O
has	O
allocated	O
for	O
this	O
connection	O
.	O
</s>
<s>
Otherwise	O
it	O
would	O
risk	O
dropping	O
received	O
packets	B-Protocol
due	O
to	O
lack	O
of	O
space	O
.	O
</s>
<s>
When	O
packet	B-Protocol
loss	I-Protocol
occurs	O
in	O
the	O
network	O
,	O
an	O
additional	O
limit	O
is	O
imposed	O
on	O
the	O
connection	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
light	O
to	O
moderate	O
packet	B-Protocol
loss	I-Protocol
when	O
the	O
TCP	B-Protocol
rate	O
is	O
limited	O
by	O
the	O
congestion	O
avoidance	O
algorithm	O
,	O
the	O
limit	O
can	O
be	O
calculated	O
according	O
to	O
the	O
formula	O
(	O
Mathis	O
,	O
et	O
al	O
.	O
</s>
<s>
where	O
MSS	O
is	O
the	O
maximum	O
segment	O
size	O
and	O
Ploss	O
is	O
the	O
probability	O
of	O
packet	B-Protocol
loss	I-Protocol
.	O
</s>
<s>
If	O
packet	B-Protocol
loss	I-Protocol
is	O
so	O
rare	O
that	O
the	O
TCP	B-Protocol
window	I-Protocol
becomes	O
regularly	O
fully	O
extended	O
,	O
this	O
formula	O
does	O
n't	O
apply	O
.	O
</s>
<s>
A	O
number	O
of	O
extensions	O
have	O
been	O
made	O
to	O
TCP	B-Protocol
over	O
the	O
years	O
to	O
increase	O
its	O
performance	O
over	O
fast	O
high-RTT	O
links	O
(	O
"	O
long	O
fat	O
networks	O
"	O
or	O
LFNs	O
)	O
.	O
</s>
<s>
TCP	B-Protocol
timestamps	O
(	O
RFC	O
1323	O
)	O
play	O
a	O
double	O
role	O
:	O
they	O
avoid	O
ambiguities	O
due	O
to	O
the	O
32-bit	O
sequence	B-Protocol
number	I-Protocol
field	O
wrapping	O
around	O
,	O
and	O
they	O
allow	O
more	O
precise	O
RTT	O
estimation	O
in	O
the	O
presence	O
of	O
multiple	O
losses	O
per	O
RTT	O
.	O
</s>
<s>
With	O
those	O
improvements	O
,	O
it	O
becomes	O
reasonable	O
to	O
increase	O
the	O
TCP	B-Protocol
window	I-Protocol
beyond	O
64	O
kB	O
,	O
which	O
can	O
be	O
done	O
using	O
the	O
window	B-Protocol
scaling	I-Protocol
option	O
(	O
RFC	O
1323	O
)	O
.	O
</s>
<s>
The	O
TCP	B-Protocol
selective	O
acknowledgment	O
option	O
(	O
SACK	O
,	O
RFC	O
2018	O
)	O
allows	O
a	O
TCP	B-Protocol
receiver	O
to	O
precisely	O
inform	O
the	O
TCP	B-Protocol
sender	O
about	O
which	O
segments	O
have	O
been	O
lost	O
.	O
</s>
<s>
Path	B-Protocol
MTU	I-Protocol
Discovery	I-Protocol
avoids	O
the	O
need	O
for	O
in-network	O
fragmentation	B-Protocol
,	O
increasing	O
the	O
performance	O
in	O
the	O
presence	O
of	O
packet	B-Protocol
loss	I-Protocol
.	O
</s>
<s>
Imagine	O
a	O
Wi-Fi	B-Architecture
base	I-Architecture
station	I-Architecture
having	O
a	O
speed	O
of	O
20	O
Mbit/s	O
and	O
an	O
average	O
packet	B-Protocol
size	O
of	O
750	O
byte	B-Application
.	O
</s>
<s>
A	O
voice	B-Application
over	I-Application
IP	I-Application
client	O
should	O
be	O
able	O
to	O
transmit	O
a	O
packet	B-Protocol
every	O
20	O
ms.	O
</s>
<s>
The	O
estimated	O
maximum	O
number	O
of	O
packets	B-Protocol
in	O
transit	O
would	O
then	O
be	O
:	O
</s>
