<s>
The	O
term	O
half-open	O
refers	O
to	O
TCP	B-Protocol
connections	O
whose	O
state	O
is	O
out	O
of	O
synchronization	O
between	O
the	O
two	O
communicating	O
hosts	O
,	O
possibly	O
due	O
to	O
a	O
crash	O
of	O
one	O
side	O
.	O
</s>
<s>
A	O
connection	O
which	O
is	O
in	O
the	O
process	O
of	O
being	O
established	O
is	O
also	O
known	O
as	O
embryonic	B-Protocol
connection	I-Protocol
.	O
</s>
<s>
According	O
to	O
RFC	O
793	O
,	O
a	O
TCP	B-Protocol
connection	O
is	O
referred	O
to	O
as	O
half-open	O
when	O
the	O
host	O
at	O
one	O
end	O
of	O
that	O
TCP	B-Protocol
connection	O
has	O
crashed	O
,	O
or	O
has	O
otherwise	O
removed	O
the	O
socket	O
without	O
notifying	O
the	O
other	O
end	O
.	O
</s>
<s>
Nowadays	O
,	O
however	O
,	O
the	O
term	O
half-open	B-Protocol
connection	I-Protocol
is	O
most	O
often	O
used	O
to	O
describe	O
an	O
embryonic	B-Protocol
connection	I-Protocol
,	O
i.e.	O
</s>
<s>
a	O
TCP	B-Protocol
connection	O
which	O
is	O
in	O
the	O
process	O
of	O
being	O
established	O
.	O
</s>
<s>
TCP	B-Protocol
has	O
a	O
three	O
state	O
system	O
for	O
opening	O
a	O
connection	O
.	O
</s>
<s>
First	O
,	O
the	O
originating	O
endpoint	O
(	O
A	O
)	O
sends	O
a	O
SYN	B-Protocol
packet	I-Protocol
to	O
the	O
destination	O
(	O
B	O
)	O
.	O
</s>
