<s>
Virtual	B-Protocol
Network	I-Protocol
Computing	I-Protocol
(	O
VNC	B-Protocol
)	O
is	O
a	O
graphical	O
desktop-sharing	O
system	O
that	O
uses	O
the	O
Remote	B-Protocol
Frame	I-Protocol
Buffer	I-Protocol
protocol	I-Protocol
(	O
RFB	O
)	O
to	O
remotely	O
control	O
another	O
computer	O
.	O
</s>
<s>
It	O
transmits	O
the	O
keyboard	B-Device
and	O
mouse	B-Device
input	I-Device
from	O
one	O
computer	O
to	O
another	O
,	O
relaying	O
the	O
graphical-screen	O
updates	O
,	O
over	O
a	O
network	B-Architecture
.	O
</s>
<s>
VNC	B-Protocol
is	O
platform-independent	O
–	O
there	O
are	O
clients	O
and	O
servers	O
for	O
many	O
GUI-based	O
operating	O
systems	O
and	O
for	O
Java	B-Language
.	O
</s>
<s>
Multiple	O
clients	O
may	O
connect	O
to	O
a	O
VNC	B-Protocol
server	I-Protocol
at	O
the	O
same	O
time	O
.	O
</s>
<s>
VNC	B-Protocol
was	O
originally	O
developed	O
at	O
the	O
Olivetti	O
&	O
Oracle	B-Application
Research	O
Lab	O
in	O
Cambridge	O
,	O
United	O
Kingdom	O
.	O
</s>
<s>
The	O
original	O
VNC	B-Protocol
source	O
code	O
and	O
many	O
modern	O
derivatives	O
are	O
open	B-Application
source	I-Application
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
variants	O
of	O
VNC	B-Protocol
which	O
offer	O
their	O
own	O
particular	O
functionality	O
;	O
e.g.	O
,	O
some	O
optimised	O
for	O
Microsoft	B-Application
Windows	I-Application
,	O
or	O
offering	O
file	O
transfer	O
(	O
not	O
part	O
of	O
VNC	B-Protocol
proper	O
)	O
,	O
etc	O
.	O
</s>
<s>
Many	O
are	O
compatible	O
(	O
without	O
their	O
added	O
features	O
)	O
with	O
VNC	B-Protocol
proper	O
in	O
the	O
sense	O
that	O
a	O
viewer	O
of	O
one	O
flavour	O
can	O
connect	O
with	O
a	O
server	B-Application
of	O
another	O
;	O
others	O
are	O
based	O
on	O
VNC	B-Protocol
code	O
but	O
not	O
compatible	O
with	O
standard	O
VNC	B-Protocol
.	O
</s>
<s>
VNC	B-Protocol
and	O
RFB	O
are	O
registered	O
trademarks	O
of	O
RealVNC	B-Language
Ltd	O
.	O
in	O
the	O
US	O
and	O
some	O
other	O
countries	O
.	O
</s>
<s>
The	O
Olivetti	O
&	O
Oracle	B-Application
Research	O
Lab	O
(	O
ORL	O
)	O
at	O
Cambridge	O
in	O
the	O
UK	O
developed	O
VNC	B-Protocol
at	O
a	O
time	O
when	O
Olivetti	O
and	O
Oracle	B-Application
Corporation	I-Application
owned	O
the	O
lab	O
.	O
</s>
<s>
Developers	O
who	O
worked	O
on	O
VNC	B-Protocol
while	O
still	O
at	O
the	O
AT&T	O
Research	O
Lab	O
include	O
:	O
</s>
<s>
Following	O
the	O
closure	O
of	O
ORL	O
in	O
2002	O
,	O
several	O
members	O
of	O
the	O
development	O
team	O
(	O
including	O
Richardson	O
,	O
Harter	O
,	O
Weatherall	O
and	O
Hopper	O
)	O
formed	O
RealVNC	B-Language
in	O
order	O
to	O
continue	O
working	O
on	O
open-source	B-Application
and	O
commercial	O
VNC	B-Protocol
software	O
under	O
that	O
name	O
.	O
</s>
<s>
The	O
original	O
GPLed	O
source	O
code	O
has	O
fed	O
into	O
several	O
other	O
versions	O
of	O
VNC	B-Protocol
.	O
</s>
<s>
Such	O
forking	B-Application
has	O
not	O
led	O
to	O
compatibility	O
problems	O
because	O
the	O
RFB	B-Protocol
protocol	I-Protocol
is	O
designed	O
to	O
be	O
extensible	O
.	O
</s>
<s>
VNC	B-Protocol
clients	O
and	O
servers	O
negotiate	O
their	O
capabilities	O
with	O
handshaking	B-Protocol
in	O
order	O
to	O
use	O
the	O
most	O
appropriate	O
options	O
supported	O
at	O
both	O
ends	O
.	O
</s>
<s>
,	O
RealVNC	B-Language
Ltd	O
claims	O
the	O
term	O
"	O
VNC	B-Protocol
"	O
as	O
a	O
registered	O
trademark	O
in	O
the	O
United	O
States	O
and	O
in	O
other	O
countries	O
.	O
</s>
<s>
The	O
name	O
Virtual	O
Network	O
Computer/Computing	O
(	O
VNC	B-Protocol
)	O
originated	O
with	O
ORL	O
's	O
work	O
on	O
a	O
thin	B-Device
client	I-Device
called	O
the	O
Videotile	O
,	O
which	O
also	O
used	O
the	O
RFB	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
The	O
Videotile	O
had	O
an	O
LCD	O
display	O
with	O
pen	O
input	O
and	O
a	O
fast	O
ATM	O
connection	O
to	O
the	O
network	B-Architecture
.	O
</s>
<s>
At	O
the	O
time	O
,	O
network	B-Operating_System
computer	I-Operating_System
was	O
commonly	O
used	O
as	O
a	O
synonym	O
for	O
a	O
thin	B-Device
client	I-Device
;	O
VNC	B-Protocol
is	O
essentially	O
a	O
software-only	O
(	O
i.e.	O
</s>
<s>
virtual	O
)	O
network	B-Operating_System
computer	I-Operating_System
.	O
</s>
<s>
The	O
VNC	B-Protocol
server	I-Protocol
is	O
the	O
program	O
on	O
the	O
machine	O
that	O
shares	O
some	O
screen	B-Device
(	O
and	O
may	O
not	O
be	O
related	O
to	O
a	O
physical	O
display	O
–	O
the	O
server	B-Application
can	O
be	O
"	B-Application
headless	I-Application
"	I-Application
)	O
,	O
and	O
allows	O
the	O
client	B-Protocol
to	O
share	O
control	O
of	O
it	O
.	O
</s>
<s>
The	O
VNC	B-Protocol
client	B-Protocol
(	O
or	O
viewer	O
)	O
is	O
the	O
program	O
that	O
represents	O
the	O
screen	B-Device
data	O
originating	O
from	O
the	O
server	B-Application
,	O
receives	O
updates	O
from	O
it	O
,	O
and	O
presumably	O
controls	O
it	O
by	O
informing	O
the	O
server	B-Application
of	O
collected	O
local	O
input	O
.	O
</s>
<s>
The	O
VNC	B-Protocol
protocol	O
(	O
RFB	B-Protocol
protocol	I-Protocol
)	O
is	O
very	O
simple	O
,	O
based	O
on	O
transmitting	O
one	O
graphic	O
primitive	O
from	O
server	B-Application
to	O
client	B-Protocol
(	O
"	O
Put	O
a	O
rectangle	O
of	O
pixel	B-Algorithm
data	O
at	O
the	O
specified	O
X	B-Operating_System
,	O
Y	O
position	O
"	O
)	O
and	O
event	B-Application
messages	I-Application
from	O
client	B-Protocol
to	O
server	B-Application
.	O
</s>
<s>
In	O
the	O
normal	O
method	O
of	O
operation	O
a	O
viewer	O
connects	O
to	O
a	O
port	O
on	O
the	O
server	B-Application
(	O
default	O
port	O
:	O
5900	O
)	O
.	O
</s>
<s>
Alternatively	O
(	O
depending	O
on	O
the	O
implementation	O
)	O
a	O
browser	O
can	O
connect	O
to	O
the	O
server	B-Application
(	O
default	O
port	O
:	O
5800	O
)	O
.	O
</s>
<s>
And	O
a	O
server	B-Application
can	O
connect	O
to	O
a	O
viewer	O
in	O
"	O
listening	O
mode	O
"	O
on	O
port	O
5500	O
.	O
</s>
<s>
One	O
advantage	O
of	O
listening	O
mode	O
is	O
that	O
the	O
server	B-Application
site	O
does	O
not	O
have	O
to	O
configure	O
its	O
firewall	B-Application
to	O
allow	O
access	O
on	O
port	B-Protocol
5900	I-Protocol
(	O
or	O
5800	O
)	O
;	O
the	O
duty	O
is	O
on	O
the	O
viewer	O
,	O
which	O
is	O
useful	O
if	O
the	O
server	B-Application
site	O
has	O
no	O
computer	O
expertise	O
and	O
the	O
viewer	O
user	O
is	O
more	O
knowledgeable	O
.	O
</s>
<s>
The	O
server	B-Application
sends	O
small	O
rectangles	O
of	O
the	O
framebuffer	B-Algorithm
to	O
the	O
client	B-Protocol
.	O
</s>
<s>
In	O
its	O
simplest	O
form	O
,	O
the	O
VNC	B-Protocol
protocol	O
can	O
use	O
a	O
lot	O
of	O
bandwidth	O
,	O
so	O
various	O
methods	O
have	O
been	O
devised	O
to	O
reduce	O
the	O
communication	O
overhead	O
.	O
</s>
<s>
The	O
VNC	B-Protocol
protocol	O
allows	O
the	O
client	B-Protocol
and	O
server	B-Application
to	O
negotiate	O
which	O
encoding	O
they	O
will	O
use	O
.	O
</s>
<s>
The	O
simplest	O
encoding	O
,	O
supported	O
by	O
all	O
clients	O
and	O
servers	O
,	O
is	O
raw	O
encoding	O
,	O
which	O
sends	O
pixel	B-Algorithm
data	O
in	O
left-to-right	O
scanline	B-Algorithm
order	O
,	O
and	O
after	O
the	O
original	O
full	O
screen	B-Device
has	O
been	O
transmitted	O
,	O
transfers	O
only	O
rectangles	O
that	O
change	O
.	O
</s>
<s>
This	O
encoding	O
works	O
very	O
well	O
if	O
only	O
a	O
small	O
portion	O
of	O
the	O
screen	B-Device
changes	O
from	O
one	O
frame	O
to	O
the	O
next	O
(	O
as	O
when	O
a	O
mouse	B-Device
pointer	O
moves	O
across	O
a	O
desktop	O
,	O
or	O
when	O
text	O
is	O
written	O
at	O
the	O
cursor	O
)	O
,	O
but	O
bandwidth	O
demands	O
get	O
very	O
high	O
if	O
a	O
lot	O
of	O
pixels	B-Algorithm
change	O
at	O
the	O
same	O
time	O
(	O
such	O
as	O
when	O
scrolling	O
a	O
window	O
or	O
viewing	O
full-screen	O
video	O
)	O
.	O
</s>
<s>
VNC	B-Protocol
by	O
default	O
uses	O
TCP	B-Protocol
port	I-Protocol
5900+N	O
,	O
where	O
N	O
is	O
the	O
display	O
number	O
(	O
usually	O
:0	O
for	O
a	O
physical	O
display	O
)	O
.	O
</s>
<s>
Several	O
implementations	O
also	O
start	O
a	O
basic	O
HTTP	B-Application
server	I-Application
on	O
port	O
5800+N	O
to	O
provide	O
a	O
VNC	B-Protocol
viewer	O
as	O
a	O
Java	B-Application
applet	I-Application
,	O
allowing	O
easy	O
connection	O
through	O
any	O
Java-enabled	O
web-browser	O
.	O
</s>
<s>
Different	O
port	O
assignments	O
can	O
be	O
used	O
as	O
long	O
as	O
both	O
client	B-Protocol
and	O
server	B-Application
are	O
configured	O
accordingly	O
.	O
</s>
<s>
A	O
HTML5	O
VNC	B-Protocol
client	B-Protocol
implementation	O
for	O
modern	O
browsers	O
(	O
no	O
plugins	O
required	O
)	O
exists	O
too	O
.	O
</s>
<s>
Although	O
possible	O
even	O
on	O
low	O
bandwidth	O
,	O
using	O
VNC	B-Protocol
over	O
the	O
Internet	O
is	O
facilitated	O
if	O
the	O
user	O
has	O
a	O
broadband	B-General_Concept
connection	O
at	O
both	O
ends	O
.	O
</s>
<s>
However	O
,	O
it	O
may	O
require	O
advanced	O
network	B-Protocol
address	I-Protocol
translation	I-Protocol
(	O
NAT	O
)	O
,	O
firewall	B-Application
and	O
router	B-Protocol
configuration	O
such	O
as	O
port	O
forwarding	O
in	O
order	O
for	O
the	O
connection	O
to	O
go	O
through	O
.	O
</s>
<s>
Users	O
may	O
establish	O
communication	O
through	O
virtual	B-Application
private	I-Application
network	I-Application
(	O
VPN	B-Application
)	O
technologies	O
to	O
ease	O
usage	O
over	O
the	O
Internet	O
,	O
or	O
as	O
a	O
LAN	O
connection	O
if	O
VPN	B-Application
is	O
used	O
as	O
a	O
proxy	O
,	O
or	O
through	O
a	O
VNC	B-Protocol
repeater	O
(	O
useful	O
in	O
presence	O
of	O
a	O
NAT	O
)	O
.	O
</s>
<s>
Xvnc	O
is	O
the	O
Unix	B-Application
VNC	B-Protocol
server	I-Protocol
,	O
which	O
is	O
based	O
on	O
a	O
standard	O
X	B-Operating_System
server	I-Operating_System
.	O
</s>
<s>
To	O
applications	O
,	O
Xvnc	O
appears	O
as	O
an	O
X	B-Operating_System
"	O
server	B-Application
"	O
(	O
i.e.	O
,	O
it	O
displays	O
client	B-Protocol
windows	O
)	O
,	O
and	O
to	O
remote	O
VNC	B-Protocol
users	O
it	O
is	O
a	O
VNC	B-Protocol
server	I-Protocol
.	O
</s>
<s>
Applications	O
can	O
display	O
themselves	O
on	O
Xvnc	O
as	O
if	O
it	O
were	O
a	O
normal	O
X	B-Operating_System
display	O
,	O
but	O
they	O
will	O
appear	O
on	O
any	O
connected	O
VNC	B-Protocol
viewers	O
rather	O
than	O
on	O
a	O
physical	O
screen	B-Device
.	O
</s>
<s>
Alternatively	O
,	O
a	O
machine	O
(	O
which	O
may	O
be	O
a	O
workstation	O
or	O
a	O
network	B-Application
server	I-Application
)	O
with	O
screen	B-Device
,	O
keyboard	B-Device
,	O
and	O
mouse	B-Device
can	O
be	O
set	O
up	O
to	O
boot	O
and	O
run	O
the	O
VNC	B-Protocol
server	I-Protocol
as	O
a	O
service	O
or	O
daemon	O
,	O
then	O
the	O
screen	B-Device
,	O
keyboard	B-Device
,	O
and	O
mouse	B-Device
can	O
be	O
removed	O
and	O
the	O
machine	O
stored	O
in	O
an	O
out-of-the	O
way	O
location	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
display	O
that	O
is	O
served	O
by	O
VNC	B-Protocol
is	O
not	O
necessarily	O
the	O
same	O
display	O
seen	O
by	O
a	O
user	O
on	O
the	O
server	B-Application
.	O
</s>
<s>
On	O
Unix/Linux	O
computers	O
that	O
support	O
multiple	O
simultaneous	O
X11	B-Operating_System
sessions	O
,	O
VNC	B-Protocol
may	O
be	O
set	O
to	O
serve	O
a	O
particular	O
existing	O
X11	B-Operating_System
session	O
,	O
or	O
to	O
start	O
one	O
of	O
its	O
own	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
run	O
multiple	O
VNC	B-Protocol
sessions	O
from	O
the	O
same	O
computer	O
.	O
</s>
<s>
On	O
Microsoft	B-Application
Windows	I-Application
the	O
VNC	B-Protocol
session	O
served	O
is	O
always	O
the	O
current	O
user	O
session	O
.	O
</s>
<s>
Users	O
commonly	O
deploy	O
VNC	B-Protocol
as	O
a	O
cross-platform	O
remote	O
desktop	O
system	O
.	O
</s>
<s>
For	O
example	O
,	O
Apple	B-Operating_System
Remote	I-Operating_System
Desktop	I-Operating_System
for	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
(	O
and	O
more	O
recently	O
,	O
"	O
Back	B-Operating_System
to	I-Operating_System
My	I-Operating_System
Mac	I-Operating_System
"	O
in	O
'	O
Leopard	O
 '	O
-	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
10.5	O
)	O
interoperates	O
with	O
VNC	B-Protocol
and	O
will	O
connect	O
to	O
a	O
Unix	B-Application
user	O
's	O
current	O
desktop	O
if	O
it	O
is	O
served	O
with	O
x11vnc	B-Application
,	O
or	O
to	O
a	O
separate	O
X11	B-Operating_System
session	O
if	O
one	O
is	O
served	O
with	O
TightVNC	B-Language
.	O
</s>
<s>
From	O
Unix	B-Application
,	O
TightVNC	B-Language
will	O
connect	O
to	O
a	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
session	O
served	O
by	O
Apple	B-Operating_System
Remote	I-Operating_System
Desktop	I-Operating_System
if	O
the	O
VNC	B-Protocol
option	O
is	O
enabled	O
,	O
or	O
to	O
a	O
VNC	B-Protocol
server	I-Protocol
running	O
on	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
In	O
July	O
2014	O
RealVNC	B-Language
published	O
a	O
Wayland	B-Language
developer	O
preview	O
.	O
</s>
<s>
While	O
passwords	O
are	O
not	O
sent	O
in	O
plain-text	O
(	O
as	O
in	O
telnet	B-Protocol
)	O
,	O
cracking	O
could	O
prove	O
successful	O
if	O
both	O
the	O
encryption	O
key	O
and	O
encoded	O
password	O
were	O
sniffed	B-Protocol
from	O
a	O
network	B-Architecture
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
there	O
is	O
also	O
an	O
8-character	O
limit	O
on	O
some	O
versions	O
of	O
VNC	B-Protocol
;	O
if	O
a	O
password	O
is	O
sent	O
exceeding	O
8	O
characters	O
,	O
the	O
excess	O
characters	O
are	O
removed	O
and	O
the	O
truncated	O
string	O
is	O
compared	O
to	O
the	O
password	O
.	O
</s>
<s>
UltraVNC	B-Language
supports	O
the	O
use	O
of	O
an	O
open-source	B-Application
encryption	O
plugin	O
which	O
encrypts	O
the	O
entire	O
VNC	B-Protocol
session	O
including	O
password	O
authentication	O
and	O
data	O
transfer	O
.	O
</s>
<s>
It	O
also	O
allows	O
authentication	O
to	O
be	O
performed	O
based	O
on	O
NTLM	O
and	O
Active	B-Protocol
Directory	I-Protocol
user	O
accounts	O
.	O
</s>
<s>
However	O
,	O
use	O
of	O
such	O
encryption	O
plugins	O
makes	O
it	O
incompatible	O
with	O
other	O
VNC	B-Protocol
programs	O
.	O
</s>
<s>
RealVNC	B-Language
offers	O
high-strength	O
AES	B-Algorithm
encryption	I-Algorithm
as	O
part	O
of	O
its	O
commercial	O
package	O
,	O
along	O
with	O
integration	O
with	O
Active	B-Protocol
Directory	I-Protocol
.	O
</s>
<s>
Workspot	B-Operating_System
released	O
AES	B-Algorithm
encryption	I-Algorithm
patches	O
for	O
VNC	B-Protocol
.	O
</s>
<s>
According	O
to	O
TightVNC	B-Language
,	O
TightVNC	B-Language
is	O
not	O
secure	O
as	O
picture	O
data	O
is	O
transmitted	O
without	O
encryption	O
.	O
</s>
<s>
To	O
circumvent	O
this	O
,	O
it	O
should	O
be	O
tunneled	O
through	O
an	O
SSH	B-Protocol
connection	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
VNC	B-Protocol
may	O
be	O
tunneled	O
over	O
an	O
SSH	B-Protocol
or	O
VPN	B-Application
connection	O
which	O
would	O
add	O
an	O
extra	O
security	O
layer	O
with	O
stronger	O
encryption	O
.	O
</s>
<s>
SSH	B-Protocol
clients	O
are	O
available	O
for	O
most	O
platforms	O
;	O
SSH	B-Protocol
tunnels	O
can	O
be	O
created	O
from	O
UNIX	B-Application
clients	O
,	O
Microsoft	B-Application
Windows	I-Application
clients	O
,	O
Mac	B-Device
clients	O
(	O
including	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
and	O
System	B-Operating_System
7	I-Operating_System
and	O
up	O
)	O
and	O
many	O
others	O
.	O
</s>
<s>
There	O
are	O
also	O
freeware	B-License
applications	O
that	O
create	O
instant	O
VPN	B-Application
tunnels	O
between	O
computers	O
.	O
</s>
<s>
An	O
additional	O
security	O
concern	O
for	O
the	O
use	O
of	O
VNC	B-Protocol
is	O
to	O
check	O
whether	O
the	O
version	O
used	O
requires	O
authorization	O
from	O
the	O
remote	O
computer	O
owner	O
before	O
someone	O
takes	O
control	O
of	O
their	O
device	O
.	O
</s>
