<s>
Reliable	B-Error_Name
Data	I-Error_Name
Transfer	I-Error_Name
is	O
a	O
topic	O
in	O
computer	B-Architecture
networking	I-Architecture
concerning	O
the	O
transfer	O
of	O
data	O
across	O
unreliable	O
channels	O
.	O
</s>
<s>
Unreliability	O
is	O
one	O
of	O
the	O
drawbacks	O
of	O
packet	B-Protocol
switched	I-Protocol
networks	I-Protocol
such	O
as	O
the	O
modern	O
internet	O
,	O
as	O
packet	B-Protocol
loss	I-Protocol
can	O
occur	O
for	O
a	O
variety	O
of	O
reasons	O
,	O
and	O
delivery	O
of	O
packets	B-Protocol
is	O
not	O
guaranteed	O
to	O
happen	O
in	O
the	O
order	O
that	O
the	O
packets	B-Protocol
were	O
sent	O
.	O
</s>
<s>
Therefore	O
,	O
in	O
order	O
to	O
create	O
long-term	O
data	O
streams	O
over	O
the	O
internet	O
,	O
techniques	O
have	O
been	O
developed	O
to	O
provide	O
reliability	O
,	O
which	O
are	O
generally	O
implemented	O
in	O
the	O
Transport	B-Architecture
layer	I-Architecture
of	O
the	O
internet	O
protocol	O
suite	O
.	O
</s>
<s>
In	O
instructional	O
materials	O
,	O
the	O
topic	O
is	O
often	O
presented	O
in	O
the	O
form	O
of	O
theoretical	O
example	O
protocols	O
which	O
are	O
themselves	O
referred	O
to	O
as	O
"	O
RDT	O
"	O
,	O
in	O
order	O
to	O
introduce	O
students	O
to	O
the	O
problems	O
and	O
solutions	O
encountered	O
in	O
Transport	B-Architecture
layer	I-Architecture
protocols	O
such	O
as	O
the	O
Transmission	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
These	O
sources	O
often	O
describe	O
a	O
pseudo-API	O
and	O
include	O
Finite-state	B-Architecture
machine	I-Architecture
diagrams	O
to	O
illustrate	O
how	O
such	O
a	O
protocol	O
might	O
be	O
implemented	O
,	O
as	O
well	O
as	O
a	O
version	O
history	O
.	O
</s>
<s>
Sources	O
that	O
describe	O
an	O
example	O
RDT	O
protocol	O
often	O
provide	O
a	O
"	O
version	O
history	O
"	O
to	O
illustrate	O
the	O
development	O
of	O
modern	O
Transport	B-Architecture
layer	I-Architecture
techniques	O
,	O
generally	O
resembling	O
the	O
below	O
:	O
</s>
<s>
With	O
Reliable	B-Error_Name
Data	I-Error_Name
Transfer	I-Error_Name
1.0	O
,	O
the	O
data	O
can	O
only	O
be	O
transferred	O
via	O
a	O
reliable	O
data	O
channel	O
.	O
</s>
<s>
It	O
is	O
the	O
most	O
simple	O
of	O
the	O
Reliable	B-Error_Name
Data	I-Error_Name
Transfer	I-Error_Name
protocols	O
in	O
terms	O
of	O
algorithm	O
processing	O
.	O
</s>
<s>
Reliable	B-Error_Name
Data	I-Error_Name
Transfer	I-Error_Name
2.0	O
supports	O
reliable	B-Error_Name
data	I-Error_Name
transfer	I-Error_Name
in	O
unreliable	O
data	O
channels	O
.	O
</s>
<s>
Reliable	B-Error_Name
Data	I-Error_Name
Transfer	I-Error_Name
2.1	O
also	O
supports	O
reliable	B-Error_Name
data	I-Error_Name
transfers	I-Error_Name
in	O
unreliable	O
data	O
channels	O
and	O
uses	O
a	O
checksum	O
to	O
detect	O
errors	O
.	O
</s>
<s>
However	O
,	O
to	O
prevent	O
duplicate	O
messages	O
,	O
it	O
adds	O
a	O
sequence	B-Protocol
number	I-Protocol
to	O
each	O
packet	B-Protocol
.	O
</s>
<s>
Reliable	B-Error_Name
Data	I-Error_Name
Transfer	I-Error_Name
3.0	O
,	O
like	O
earlier	O
versions	O
of	O
the	O
protocol	O
,	O
supports	O
reliable	B-Error_Name
data	I-Error_Name
transfer	I-Error_Name
in	O
unreliable	O
data	O
channels	O
,	O
uses	O
checksums	O
to	O
check	O
for	O
errors	O
,	O
and	O
adds	O
sequence	B-Protocol
numbers	I-Protocol
to	O
data	B-Protocol
packets	I-Protocol
.	O
</s>
<s>
Additionally	O
,	O
it	O
includes	O
a	O
countdown	O
timer	O
to	O
detect	O
packet	B-Protocol
loss	I-Protocol
.	O
</s>
<s>
If	O
the	O
sender	O
cannot	O
acknowledge	O
specific	O
data	O
in	O
a	O
certain	O
duration	O
,	O
it	O
will	O
consider	O
as	O
packet	B-Protocol
as	O
lost	O
and	O
will	O
send	O
it	O
again	O
.	O
</s>
