<s>
Go-Back-N	B-Error_Name
ARQ	I-Error_Name
is	O
a	O
specific	O
instance	O
of	O
the	O
automatic	B-Error_Name
repeat	I-Error_Name
request	I-Error_Name
(	O
ARQ	O
)	O
protocol	O
,	O
in	O
which	O
the	O
sending	O
process	O
continues	O
to	O
send	O
a	O
number	O
of	O
frames	B-Protocol
specified	O
by	O
a	O
window	O
size	O
even	O
without	O
receiving	O
an	O
acknowledgement	B-Protocol
(	O
ACK	B-Protocol
)	O
packet	O
from	O
the	O
receiver	O
.	O
</s>
<s>
It	O
can	O
transmit	O
frames	B-Protocol
to	O
the	O
peer	O
before	O
requiring	O
an	O
ACK	B-Protocol
.	O
</s>
<s>
It	O
will	O
discard	O
any	O
frame	O
that	O
does	O
not	O
have	O
the	O
exact	O
sequence	O
number	O
it	O
expects	O
(	O
either	O
a	O
duplicate	O
frame	O
it	O
already	O
acknowledged	O
,	O
or	O
an	O
out-of-order	O
frame	O
it	O
expects	O
to	O
receive	O
later	O
)	O
and	O
will	O
send	O
an	O
ACK	B-Protocol
for	O
the	O
last	O
correct	O
in-order	O
frame	O
.	O
</s>
<s>
Once	O
the	O
sender	O
has	O
sent	O
all	O
of	O
the	O
frames	B-Protocol
in	O
its	O
window	O
,	O
it	O
will	O
detect	O
that	O
all	O
of	O
the	O
frames	B-Protocol
since	O
the	O
first	O
lost	O
frame	O
are	O
outstanding	O
,	O
and	O
will	O
go	O
back	O
to	O
the	O
sequence	O
number	O
of	O
the	O
last	O
ACK	B-Protocol
it	O
received	O
from	O
the	O
receiver	O
process	O
and	O
fill	O
its	O
window	O
starting	O
with	O
that	O
frame	O
and	O
continue	O
the	O
process	O
over	O
again	O
.	O
</s>
<s>
Go-Back-N	B-Error_Name
ARQ	I-Error_Name
is	O
a	O
more	O
efficient	O
use	O
of	O
a	O
connection	O
than	O
Stop-and-wait	B-Error_Name
ARQ	I-Error_Name
,	O
since	O
unlike	O
waiting	O
for	O
an	O
acknowledgement	B-Protocol
for	O
each	O
packet	O
,	O
the	O
connection	O
is	O
still	O
being	O
utilized	O
as	O
packets	O
are	O
being	O
sent	O
.	O
</s>
<s>
However	O
,	O
this	O
method	O
also	O
results	O
in	O
sending	O
frames	B-Protocol
multiple	O
times	O
if	O
any	O
frame	O
was	O
lost	O
or	O
damaged	O
,	O
or	O
the	O
ACK	B-Protocol
acknowledging	O
them	O
was	O
lost	O
or	O
damaged	O
,	O
then	O
that	O
frame	O
and	O
all	O
following	O
frames	B-Protocol
in	O
the	O
send	O
window	O
(	O
even	O
if	O
they	O
were	O
received	O
without	O
error	O
)	O
will	O
be	O
re-sent	O
.	O
</s>
<s>
To	O
avoid	O
this	O
,	O
Selective	B-Error_Name
Repeat	I-Error_Name
ARQ	I-Error_Name
can	O
be	O
used	O
.	O
</s>
<s>
must	O
be	O
smaller	O
than	O
the	O
number	O
of	O
sequence	O
numbers	O
(	O
if	O
they	O
are	O
numbered	O
from	O
zero	O
to	O
)	O
to	O
verify	O
transmission	O
in	O
cases	O
of	O
any	O
packet	O
(	O
any	O
data	O
or	O
ACK	B-Protocol
packet	O
)	O
being	O
dropped	O
.	O
</s>
