<s>
RFB	O
(	O
"	O
remote	O
framebuffer	B-Algorithm
"	O
)	O
is	O
an	O
open	O
simple	O
protocol	O
for	O
remote	B-Protocol
access	I-Protocol
to	O
graphical	B-Application
user	I-Application
interfaces	I-Application
.	O
</s>
<s>
Because	O
it	O
works	O
at	O
the	O
framebuffer	B-Algorithm
level	O
it	O
is	O
applicable	O
to	O
all	O
windowing	B-Application
systems	I-Application
and	O
applications	O
,	O
including	O
Microsoft	B-Application
Windows	I-Application
,	O
macOS	B-Application
and	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
RFB	O
is	O
the	O
protocol	O
used	O
in	O
Virtual	B-Protocol
Network	I-Protocol
Computing	I-Protocol
(	O
VNC	B-Protocol
)	O
and	O
its	O
derivatives	O
.	O
</s>
<s>
By	O
default	O
,	O
a	O
viewer/client	O
uses	O
TCP	O
port	B-Protocol
5900	I-Protocol
to	O
connect	O
to	O
a	O
server	O
(	O
or	O
5800	O
for	O
browser	O
access	O
)	O
,	O
but	O
can	O
also	O
be	O
set	O
to	O
use	O
any	O
other	O
port	O
.	O
</s>
<s>
Although	O
RFB	O
started	O
as	O
a	O
relatively	O
simple	O
protocol	O
,	O
it	O
has	O
been	O
enhanced	O
with	O
additional	O
features	O
(	O
such	O
as	O
file	O
transfers	O
)	O
and	O
more	O
sophisticated	O
compression	B-General_Concept
and	O
security	O
techniques	O
as	O
it	O
has	O
developed	O
.	O
</s>
<s>
To	O
maintain	O
seamless	O
cross-compatibility	O
between	O
the	O
many	O
different	O
VNC	B-Protocol
client	O
and	O
server	O
implementations	O
,	O
the	O
clients	O
and	O
servers	O
negotiate	O
a	O
connection	O
using	O
the	O
best	O
RFB	O
version	O
,	O
and	O
the	O
most	O
appropriate	O
compression	B-General_Concept
and	O
security	O
options	O
that	O
they	O
can	O
both	O
support	O
.	O
</s>
<s>
RFB	O
was	O
originally	O
developed	O
at	O
Olivetti	O
Research	O
Laboratory	O
(	O
ORL	O
)	O
as	O
a	O
remote	O
display	O
technology	O
to	O
be	O
used	O
by	O
a	O
simple	O
thin	B-Device
client	I-Device
with	O
Asynchronous	O
Transfer	O
Mode	O
connectivity	O
called	O
a	O
Videotile	O
.	O
</s>
<s>
RFB	O
found	O
a	O
second	O
and	O
more	O
enduring	O
use	O
when	O
VNC	B-Protocol
was	O
developed	O
.	O
</s>
<s>
VNC	B-Protocol
was	O
released	O
as	O
open	B-Application
source	I-Application
software	I-Application
and	O
the	O
RFB	O
specification	O
published	O
on	O
the	O
web	O
.	O
</s>
<s>
When	O
ORL	O
was	O
closed	O
in	O
2002	O
some	O
of	O
the	O
key	O
people	O
behind	O
VNC	B-Protocol
and	O
RFB	O
formed	O
RealVNC	B-Language
,	O
Ltd.	O
,	O
in	O
order	O
to	O
continue	O
development	O
of	O
VNC	B-Protocol
and	O
to	O
maintain	O
the	O
RFB	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
The	O
current	O
RFB	B-Protocol
protocol	I-Protocol
is	O
published	O
on	O
the	O
.	O
</s>
<s>
Published	O
versions	O
of	O
the	O
RFB	B-Protocol
protocol	I-Protocol
are	O
as	O
follows	O
:	O
</s>
<s>
The	O
list	O
of	O
encoding	O
and	O
security	O
types	O
was	O
maintained	O
by	O
RealVNC	B-Language
Ltd	O
and	O
is	O
separate	O
from	O
the	O
protocol	O
specification	O
so	O
that	O
new	O
types	O
can	O
be	O
added	O
without	O
requiring	O
the	O
specification	O
to	O
be	O
reissued	O
.	O
</s>
<s>
A	O
community	O
version	O
of	O
the	O
RFB	B-Protocol
protocol	I-Protocol
specification	O
which	O
aims	O
to	O
document	O
all	O
existing	O
extensions	O
is	O
hosted	O
by	O
the	O
TigerVNC	B-Language
project	O
.	O
</s>
<s>
Tight	O
Encoding	O
,	O
a	O
mixture	O
of	O
rectangle	O
,	O
palette	O
and	O
gradient	O
filling	O
with	O
zlib	O
and	O
JPEG	O
,	O
plus	O
a	O
Zlib-plus-filter	O
"	O
basic	O
compression	B-General_Concept
"	O
.	O
</s>
<s>
Tight	O
PNG	O
Encoding	O
,	O
Tight	O
encoding	O
with	O
basic	O
compression	B-General_Concept
replaced	O
with	O
PNG	O
data	O
.	O
</s>
<s>
H.264	B-Application
has	O
been	O
researched	O
for	O
encoding	O
RFB	O
data	O
,	O
but	O
the	O
preliminary	O
results	O
(	O
using	O
Open	O
H.264	B-Application
format	O
)	O
were	O
described	O
as	O
lackluster	O
by	O
a	O
TurboVNC	B-Application
developer	O
.	O
</s>
<s>
The	O
VNC	B-Protocol
protocol	O
is	O
pixel	O
based	O
.	O
</s>
<s>
any	O
type	O
of	O
desktop	O
can	O
be	O
displayed	O
)	O
,	O
it	O
is	O
often	O
less	O
efficient	O
than	O
solutions	O
that	O
have	O
a	O
better	O
understanding	O
of	O
the	O
underlying	O
graphic	O
layout	O
like	O
X11	B-Operating_System
or	O
desktop	O
such	O
as	O
RDP	B-Protocol
.	O
</s>
<s>
The	O
VNC	B-Protocol
protocol	O
expresses	O
mouse	O
button	O
state	O
in	O
a	O
single	O
byte	O
,	O
as	O
binary	O
up/down	O
.	O
</s>
