<s>
TCP	B-Protocol
Gender	I-Protocol
Changer	I-Protocol
is	O
a	O
method	O
in	O
computer	O
networking	O
for	O
making	O
an	O
internal	O
TCP/IP	B-Protocol
based	O
network	B-Application
server	I-Application
accessible	O
beyond	O
its	O
protective	O
firewall	B-Application
.	O
</s>
<s>
It	O
consists	O
of	O
two	O
nodes	O
,	O
one	O
resides	O
on	O
the	O
internal	O
the	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
where	O
it	O
can	O
access	O
the	O
desired	O
server	O
,	O
and	O
the	O
other	O
node	O
runs	O
outside	O
of	O
the	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
,	O
where	O
the	O
client	O
can	O
access	O
it	O
.	O
</s>
<s>
The	O
Listen-Listen	O
node	O
,	O
however	O
,	O
passively	O
Listens	O
on	O
two	O
TCP/IP	B-Protocol
ports	O
,	O
one	O
to	O
receive	O
a	O
connection	O
from	O
CC	O
and	O
the	O
other	O
one	O
for	O
an	O
incoming	O
connection	O
from	O
the	O
client	O
.	O
</s>
<s>
One	O
of	O
the	O
cases	O
where	O
it	O
can	O
be	O
very	O
useful	O
is	O
to	O
connect	O
to	O
a	O
desktop	O
machine	O
behind	O
a	O
firewall	B-Application
running	O
VNC	B-Protocol
,	O
which	O
would	O
make	O
the	O
desktop	O
remotely	O
accessible	O
over	O
the	O
network	O
and	O
beyond	O
the	O
firewall	B-Application
.	O
</s>
<s>
Another	O
useful	O
scenario	O
would	O
be	O
to	O
create	O
a	O
VPN	B-Application
using	O
PPP	B-Protocol
over	O
SSH	B-Protocol
,	O
or	O
even	O
simply	O
using	O
SSH	B-Protocol
to	O
connect	O
to	O
an	O
internal	O
Unix	B-Application
based	O
server	O
.	O
</s>
