<s>
OpenBTS	B-Language
(	O
Open	O
Base	O
Transceiver	O
Station	O
)	O
is	O
a	O
software-based	O
GSM	O
access	O
point	O
,	O
allowing	O
standard	O
GSM-compatible	O
mobile	O
phones	O
to	O
be	O
used	O
as	O
SIP	B-Application
endpoints	O
in	O
Voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
networks	O
.	O
</s>
<s>
OpenBTS	B-Language
is	O
open-source	O
software	O
developed	O
and	O
maintained	O
by	O
Range	O
Networks	O
.	O
</s>
<s>
The	O
public	O
release	O
of	O
OpenBTS	B-Language
is	O
notable	O
for	O
being	O
the	O
first	O
free-software	B-Application
implementation	O
of	O
the	O
lower	O
three	O
layers	O
of	O
the	O
industry-standard	O
GSM	O
protocol	B-Protocol
stack	I-Protocol
.	O
</s>
<s>
It	O
is	O
written	O
in	O
C++	B-Language
and	O
released	O
as	O
free	B-Application
software	I-Application
under	O
the	O
terms	O
of	O
version	O
3	O
of	O
the	O
GNU	B-Application
Affero	I-Application
General	I-Application
Public	I-Application
License	I-Application
.	O
</s>
<s>
OpenBTS	B-Language
replaces	O
the	O
conventional	O
GSM	O
operator	O
core	O
network	O
infrastructure	O
from	O
layer	O
3	O
upwards	O
.	O
</s>
<s>
Instead	O
of	O
relying	O
on	O
external	O
base	O
station	O
controllers	O
for	O
radio	B-Protocol
resource	I-Protocol
management	I-Protocol
,	O
OpenBTS	B-Language
units	O
perform	O
this	O
function	O
internally	O
.	O
</s>
<s>
Instead	O
of	O
forwarding	O
call	O
traffic	O
through	O
to	O
an	O
operator	O
's	O
mobile	B-Device
switching	I-Device
center	I-Device
,	O
OpenBTS	B-Language
delivers	O
calls	O
via	O
SIP	B-Application
to	O
a	O
VOIP	B-Application
soft	O
switch	O
(	O
such	O
as	O
FreeSWITCH	B-Language
or	O
yate	B-Language
)	O
or	O
PBX	O
(	O
such	O
as	O
Asterisk	B-Language
)	O
.	O
</s>
<s>
This	O
VOIP	B-Application
switch	O
or	O
PBX	O
software	O
can	O
be	O
installed	O
on	O
the	O
same	O
computer	O
used	O
to	O
run	O
OpenBTS	B-Language
itself	O
,	O
forming	O
a	O
self-contained	O
cellular	O
network	O
in	O
a	O
single	O
computer	O
system	O
.	O
</s>
<s>
The	O
OpenBTS	B-Language
Um	O
air	O
interface	O
uses	O
a	O
software-defined	B-Architecture
radio	I-Architecture
transceiver	O
with	O
no	O
specialized	O
GSM	O
hardware	O
.	O
</s>
<s>
The	O
original	O
implementation	O
used	O
a	O
Universal	O
Software	B-Architecture
Radio	I-Architecture
Peripheral	O
from	O
Ettus	O
Research	O
,	O
but	O
has	O
since	O
been	O
expanded	O
to	O
support	O
several	O
digital	O
radios	O
in	O
implementations	O
ranging	O
from	O
full-scale	O
base	O
stations	O
to	O
embedded	O
femtocells	O
.	O
</s>
<s>
On	O
September	O
14	O
,	O
2010	O
,	O
at	O
the	O
Fall	O
2010	O
DEMO	O
conference	O
,	O
the	O
original	O
authors	O
launched	O
Range	O
Networks	O
as	O
a	O
start	O
up	O
company	O
to	O
commercialize	O
OpenBTS-based	O
products	O
.	O
</s>
<s>
In	O
September	O
2013	O
,	O
Burgess	O
left	O
Range	O
Networks	O
and	O
started	O
a	O
new	O
venture	O
called	O
Legba	O
and	O
started	O
a	O
close	O
collaboration	O
with	O
Null	O
Team	O
SRL	O
,	O
the	O
developers	O
of	O
Yate	B-Language
.	O
</s>
<s>
In	O
February	O
2014	O
,	O
Legba	O
and	O
Null	O
announced	O
the	O
release	O
of	O
YateBTS	O
,	O
a	O
fork	O
of	O
the	O
OpenBTS	B-Language
project	O
that	O
uses	O
Yate	B-Language
for	O
its	O
control	O
layers	O
and	O
network	O
interfaces	O
.	O
</s>
<s>
A	O
large	O
number	O
of	O
experimental	O
installations	O
have	O
shown	O
that	O
OpenBTS	B-Language
can	O
run	O
on	O
extremely	O
low	O
overhead	O
platforms	O
.	O
</s>
<s>
These	O
including	O
some	O
CDMA	B-Protocol
handsets	O
-	O
making	O
a	O
GSM	O
gateway	O
to	O
a	O
CDMA	B-Protocol
network	O
.	O
</s>
<s>
Computer	O
security	O
researcher	O
Chris	O
Paget	O
reported	O
that	O
a	O
handheld	O
device	O
,	O
such	O
as	O
an	O
Android	B-Application
phone	I-Application
,	O
could	O
act	O
as	O
a	O
gateway	O
base	O
station	O
to	O
which	O
handsets	O
can	O
connect	O
;	O
the	O
Android	B-Application
device	O
then	O
connects	O
calls	O
using	O
an	O
on-board	O
Asterisk	B-Language
server	O
and	O
routes	O
them	O
to	O
the	O
PSTN	O
via	O
SIP	B-Application
over	O
an	O
existing	O
3G	B-Architecture
network	I-Architecture
.	O
</s>
<s>
At	O
the	O
2010	O
DEF	O
CON	O
conference	O
,	O
it	O
was	O
demonstrated	O
with	O
OpenBTS	B-Language
that	O
GSM	O
calls	O
can	O
be	O
intercepted	O
because	O
in	O
GSM	O
the	O
handset	O
does	O
not	O
authenticate	O
the	O
base	O
station	O
prior	O
to	O
accessing	O
the	O
network	O
.	O
</s>
<s>
OpenBTS	B-Language
has	O
been	O
used	O
by	O
the	O
security	O
research	O
community	O
to	O
mount	O
attacks	O
on	O
cellular	O
phone	O
baseband	O
processors	O
.	O
</s>
<s>
Large	O
scale	O
live	O
tests	O
of	O
OpenBTS	B-Language
have	O
been	O
conducted	O
in	O
the	O
United	O
States	O
in	O
Nevada	O
and	O
northern	O
California	O
using	O
temporary	O
radio	O
licenses	O
applied	O
for	O
through	O
Kestrel	O
Signal	O
Processing	O
and	O
Range	O
Networks	O
,	O
Inc	O
.	O
</s>
<s>
Although	O
this	O
test	O
had	O
not	O
been	O
intended	O
to	O
be	O
open	O
to	O
Burning	O
Man	O
attendees	O
in	O
general	O
,	O
a	O
number	O
of	O
individuals	O
in	O
the	O
vicinity	O
succeeded	O
in	O
making	O
out-going	O
calls	O
after	O
a	O
mis-configured	O
Asterisk	B-Language
PBX	I-Language
installation	O
allowed	O
through	O
test	O
calls	O
prefixed	O
with	O
an	O
international	O
code	O
.	O
</s>
<s>
At	O
the	O
2011	O
festival	O
,	O
the	O
OpenBTS	B-Language
project	O
set	O
up	O
a	O
3-site	O
network	O
with	O
VSAT	O
gateway	O
and	O
worked	O
in	O
conjunction	O
with	O
the	O
Voice	B-Application
over	I-Application
IP	I-Application
services	O
company	O
Voxeo	O
to	O
provide	O
much	O
of	O
the	O
off-site	O
call	O
routing	O
.	O
</s>
<s>
Range	O
Networks	O
operated	O
OpenBTS	B-Language
test	O
networks	O
at	O
the	O
RELIEF	O
exercises	O
in	O
November	O
2011	O
and	O
February	O
2012	O
.	O
</s>
<s>
In	O
2010	O
,	O
an	O
OpenBTS	B-Language
system	O
was	O
installed	O
on	O
the	O
island	O
of	O
Niue	O
and	O
became	O
the	O
first	O
installation	O
to	O
be	O
connected	O
and	O
tested	O
by	O
a	O
telecommunication	O
company	O
.	O
</s>
<s>
The	O
cost	O
structure	O
of	O
OpenBTS	B-Language
suited	O
Niue	O
,	O
which	O
required	O
a	O
mobile	O
phone	O
service	O
but	O
did	O
not	O
have	O
the	O
volume	O
of	O
potential	O
customers	O
to	O
justify	O
buying	O
and	O
supporting	O
a	O
conventional	O
GSM	O
basestation	O
system	O
.	O
</s>
<s>
The	O
OpenBTS	B-Language
installation	O
was	O
later	O
decommissioned	O
~	O
February	O
2011	O
by	O
Niue	O
Telecom	O
,	O
a	O
commercial	O
grade	O
GSM	O
900	O
network	O
with	O
Edge	O
support	O
was	O
instead	O
launched	O
few	O
months	O
later	O
(	O
3x	O
sites	O
in	O
Kaimiti	O
O2	O
,	O
Sekena	O
S2/2/2	O
and	O
Avatele	O
S2/2/2	O
)	O
this	O
provided	O
full	O
coverage	O
around	O
the	O
island	O
and	O
around	O
the	O
reef	O
,	O
the	O
installation	O
included	O
a	O
pre-pay	O
system	O
,	O
USSD	O
,	O
Int	O
.	O
</s>
<s>
It	O
used	O
OpenBTS	B-Language
and	O
served	O
a	O
small	O
network	O
of	O
650	O
GSM	O
phones	O
with	O
custom	O
SIM	O
cards	O
.	O
</s>
