<s>
VRPN	B-General_Concept
(	O
Virtual-Reality	B-Application
Peripheral	O
Network	O
)	O
is	O
a	O
device-independent	O
,	O
network-based	O
interface	O
for	O
accessing	O
virtual	B-Application
reality	I-Application
peripherals	O
in	O
VR	O
applications	O
.	O
</s>
<s>
VRPN	B-General_Concept
was	O
maintained	O
and	O
supported	O
by	O
Sensics	O
while	O
it	O
was	O
business	O
.	O
</s>
<s>
It	O
is	O
described	O
more	O
fully	O
at	O
and	O
in	O
VRPN-VRST	O
.	O
</s>
<s>
The	O
purpose	O
of	O
VRPN	B-General_Concept
is	O
to	O
provide	O
a	O
unified	O
interface	O
to	O
input	O
devices	O
,	O
like	O
motion	B-Application
trackers	I-Application
or	O
joystick	B-Device
controllers	O
.	O
</s>
<s>
The	O
VRPN	B-General_Concept
system	O
consists	O
of	O
programming	O
interfaces	O
for	O
both	O
the	O
client	O
application	O
and	O
the	O
hardware	O
drivers	O
and	O
a	O
server	O
application	O
that	O
communicates	O
with	O
the	O
hardware	O
devices	O
.	O
</s>
<s>
The	O
client	O
interfaces	O
are	O
written	O
in	O
C++	B-Language
but	O
have	O
been	O
wrapped	O
in	O
C#	O
,	O
Python	B-Language
and	O
Java	B-Language
.	O
</s>
<s>
A	O
typical	O
application	O
of	O
VRPN	B-General_Concept
is	O
to	O
encode	O
and	O
send	O
6DoF	O
motion	B-Application
capture	I-Application
data	O
through	O
the	O
network	O
in	O
real	O
time	O
.	O
</s>
<s>
A	O
VRPN	B-General_Concept
client	O
can	O
establish	O
a	O
connection	O
with	O
a	O
VRPN	B-General_Concept
server	O
(	O
the	O
device	O
providing	O
the	O
data	O
)	O
in	O
two	O
ways	O
:	O
either	O
over	O
TCP	B-Protocol
(	O
reliable	O
,	O
but	O
less	O
efficient	O
)	O
,	O
or	O
over	O
UDP	B-Protocol
(	O
unreliable	O
,	O
but	O
lower-latency	O
and	O
more	O
efficient	O
)	O
.	O
</s>
<s>
The	O
"	O
unreliable	O
"	O
connection	O
initialization	O
sequence	O
makes	O
use	O
of	O
both	O
the	O
TCP	B-Protocol
and	O
UDP	B-Protocol
protocols	I-Protocol
.	O
</s>
<s>
the	O
client	O
opens	O
a	O
TCP	B-Protocol
socket	I-Protocol
for	O
listening	O
on	O
an	O
arbitrary	O
port	O
;	O
</s>
<s>
the	O
client	O
sends	O
the	O
port	O
number	O
of	O
this	O
socket	B-Protocol
,	O
along	O
with	O
its	O
own	O
machine	O
name	O
,	O
in	O
a	O
UDP	B-Protocol
datagram	O
directed	O
to	O
a	O
well	O
known	O
port	O
of	O
the	O
VRPN	B-General_Concept
server	O
(	O
the	O
default	O
is	O
3883	O
)	O
;	O
</s>
<s>
the	O
server	O
opens	O
a	O
TCP	B-Protocol
connection	O
with	O
the	O
client	O
,	O
to	O
the	O
port	O
number	O
communicated	O
at	O
step	O
2	O
;	O
</s>
<s>
if	O
the	O
TCP	B-Protocol
connection	O
is	O
established	O
,	O
each	O
device	O
tells	O
to	O
the	O
other	O
the	O
supported	O
VRPN	B-General_Concept
version	O
;	O
</s>
<s>
otherwise	O
,	O
each	O
device	O
begins	O
to	O
listen	O
on	O
a	O
new	O
UDP	B-Protocol
port	O
(	O
different	O
from	O
those	O
used	O
before	O
)	O
and	O
sends	O
the	O
port	O
number	O
to	O
the	O
other	O
device	O
,	O
by	O
using	O
the	O
previously	O
created	O
TCP	B-Protocol
connection	O
;	O
</s>
<s>
from	O
now	O
on	O
,	O
all	O
the	O
data	O
is	O
sent	O
over	O
the	O
two	O
UDP	B-Protocol
ports	O
opened	O
at	O
step	O
6	O
.	O
</s>
<s>
However	O
,	O
the	O
"	O
unreliable	O
"	O
connection	O
initialization	O
protocol	O
does	O
not	O
honor	O
the	O
strict	O
layering	O
protocol	O
design	O
principle	O
,	O
as	O
the	O
application-level	B-Application
VRPN	B-General_Concept
payload	O
leaks	O
information	O
about	O
lower	O
levels	O
in	O
the	O
network	O
stack	O
,	O
namely	O
the	O
machine	O
names	O
and	O
TCP/UDP	O
port	O
numbers	O
.	O
</s>
<s>
Because	O
of	O
this	O
design	O
choice	O
,	O
it	O
is	O
impossible	O
to	O
establish	O
a	O
VRPN	B-General_Concept
connection	O
between	O
two	O
devices	O
connected	O
through	O
a	O
NAT	B-Protocol
:	O
the	O
router	O
would	O
need	O
to	O
translate	O
not	O
only	O
the	O
layer-3	O
information	O
in	O
the	O
packet	O
headers	O
,	O
but	O
also	O
the	O
references	O
to	O
IP	O
addresses	O
and	O
port	O
numbers	O
inside	O
the	O
VRPN	B-General_Concept
payload	O
.	O
</s>
<s>
To	O
deal	O
with	O
this	O
problem	O
,	O
VRPN	B-General_Concept
offers	O
a	O
second	O
"	O
reliable	O
"	O
,	O
TCP-only	O
connection	O
initialization	O
mode	O
,	O
which	O
is	O
a	O
standard	O
TCP	B-Protocol
server-client	O
interaction	O
:	O
the	O
VRPN	B-General_Concept
server	O
listens	O
on	O
a	O
well-known	O
TCP	B-Protocol
port	O
and	O
the	O
client	O
initiates	O
a	O
connection	O
.	O
</s>
<s>
In	O
this	O
mode	O
,	O
all	O
the	O
data	O
is	O
sent	O
on	O
the	O
same	O
TCP	B-Protocol
connection	O
,	O
and	O
no	O
UDP	B-Protocol
communication	O
is	O
required	O
.	O
</s>
<s>
Analog	O
devices	O
used	O
as	O
a	O
tracker	O
(	O
Magellan	O
,	O
CerealBox	O
with	O
joysticks	B-Device
attached	O
,	O
Radamec	O
SPI	O
,	O
Mouse	O
,	O
...	O
)	O
.	O
</s>
<s>
ARToolkit	O
VRPN	B-General_Concept
tracker	O
available	O
from	O
Universidad	O
de	O
los	O
Andes	O
.	O
</s>
<s>
Microsoft	B-Algorithm
Kinect	I-Algorithm
(	O
two	O
different	O
VRPN	B-General_Concept
servers	O
available	O
.	O
)	O
</s>
<s>
Novint	B-Device
force-feedback	O
device	O
.	O
</s>
<s>
OptiTrack	O
Motive	O
(	O
was	O
NaturalPoint	O
OptiTrack	O
Tracking	O
Tools	O
)	O
(	O
VRPN	B-General_Concept
server	O
is	O
built	O
into	O
vendor	O
server	O
)	O
.	O
</s>
<s>
Other	O
InterSense	O
trackers	O
(	O
using	O
InterSense	O
native	O
library	O
,	O
even	O
USB-based	O
ones	O
)	O
;	O
there	O
is	O
currently	O
a	O
discussion	O
on	O
the	O
VRPN	B-General_Concept
email	O
list	O
about	O
whether	O
the	O
position	O
and	O
orientation	O
information	O
are	O
returned	O
consistently	O
when	O
using	O
this	O
interface	O
.	O
</s>
<s>
Razer	B-Device
Hydra	I-Device
game	O
controller	O
.	O
</s>
<s>
Vicon	O
(	O
VRPN	B-General_Concept
server	O
is	O
built	O
into	O
the	O
vendor	O
's	O
server	O
)	O
.	O
</s>
<s>
Wintracker	O
III	O
magnetic	O
tracking	O
system	O
from	O
Virtual	B-Application
Realities	I-Application
Ltd	O
.	O
</s>
<s>
zSpace	O
immersive	O
interactive	O
hardware	O
and	O
software	O
platform	O
(	O
VRPN	B-General_Concept
server	O
built	O
into	O
vendor	O
server	O
)	O
.	O
</s>
<s>
B&G	O
systems	O
CerealBox	O
button/dial/slider/joystick	O
controllers	O
plugged	O
into	O
any	O
server-capable	O
machine	O
.	O
</s>
<s>
DirectInput	O
enabled	O
joysticks	B-Device
(	O
including	O
force-feedback	O
joysticks	B-Device
)	O
on	O
Windows	O
(	O
see	O
howto	O
)	O
.	O
</s>
<s>
Joystick	B-Device
controllers	O
:	O
Contour	O
ShuttleXpress	O
,	O
Futaba	O
InterLink	O
Elite	O
,	O
Griffin	O
PowerMate	O
,	O
Logitech	O
Extreme	O
3D	O
Pro	O
,	O
Saitek	O
ST290	O
Pro	O
,	O
Microsoft	O
SideWinder	O
Precision	O
2	O
,	O
Microsoft	O
SideWinder	O
,	O
Microsoft	O
Xbox	O
S	O
(	O
raw	O
controller	O
on	O
all	O
O/S	O
)	O
,	O
Microsoft	O
Xbox	O
360	O
(	O
raw	O
controller	O
on	O
all	O
O/S	O
)	O
,	O
Afterglow	O
Ax1	O
For	O
Xbox	O
360	O
(	O
raw	O
controller	O
on	O
all	O
O/S	O
)	O
.	O
</s>
<s>
Other	O
joysticks	B-Device
on	O
Windows	O
.	O
</s>
<s>
PC	O
joysticks	B-Device
running	O
under	O
Linux	O
.	O
</s>
<s>
Engineering	O
:	O
the	O
Desktop	O
,	O
Professional	O
,	O
Jog&Shuttle	O
,	O
Joystick	B-Device
,	O
and	O
foot	O
pedal	O
.	O
</s>
