<s>
Linphone	B-Protocol
(	O
contraction	O
of	O
Linux	B-Application
phone	O
)	O
is	O
a	O
free	O
voice	B-Application
over	I-Application
IP	I-Application
softphone	B-Protocol
,	O
SIP	B-Application
client	O
and	O
service	O
.	O
</s>
<s>
It	O
may	O
be	O
used	O
for	O
audio	O
and	O
video	O
direct	O
calls	O
and	O
calls	O
through	O
any	O
VoIP	B-Device
softswitch	I-Device
or	O
IP-PBX	O
.	O
</s>
<s>
Linphone	B-Protocol
also	O
provides	O
the	O
possibility	O
to	O
exchange	O
instant	B-Application
messages	I-Application
.	O
</s>
<s>
It	O
has	O
a	O
simple	O
multilanguage	O
interface	O
based	O
on	O
Qt	O
for	O
GUI	B-Application
and	O
can	O
also	O
be	O
run	O
as	O
a	O
console-mode	O
application	O
on	O
Linux	B-Application
.	O
</s>
<s>
The	O
softphone	B-Protocol
is	O
currently	O
developed	O
by	O
Belledonne	O
Communications	O
in	O
France	O
.	O
</s>
<s>
Linphone	B-Protocol
was	O
initially	O
developed	O
for	O
Linux	B-Application
but	O
now	O
supports	O
many	O
additional	O
platforms	O
including	O
Microsoft	B-Application
Windows	I-Application
,	O
macOS	B-Application
,	O
and	O
mobile	O
phones	O
running	O
Windows	B-Protocol
Phone	I-Protocol
,	O
iOS	B-Application
or	O
Android	B-Application
.	O
</s>
<s>
It	O
supports	O
ZRTP	B-Protocol
for	O
end-to-end	O
encrypted	O
voice	O
and	O
video	O
communication	O
.	O
</s>
<s>
Linphone	B-Protocol
is	O
licensed	O
under	O
the	O
GNU	B-License
GPL-3.0-or-later	I-License
and	O
supports	O
IPv6	B-Protocol
.	O
</s>
<s>
Linphone	B-Protocol
can	O
also	O
be	O
used	O
behind	O
network	B-Protocol
address	I-Protocol
translator	I-Protocol
(	O
NAT	O
)	O
,	O
meaning	O
it	O
can	O
run	O
behind	O
home	O
routers	O
.	O
</s>
<s>
It	O
is	O
compatible	O
with	O
telephony	O
by	O
using	O
an	O
Internet	B-Protocol
telephony	I-Protocol
service	I-Protocol
provider	I-Protocol
(	O
ITSP	B-Protocol
)	O
.	O
</s>
<s>
Linphone	B-Protocol
hosts	O
a	O
free	O
SIP	B-Application
service	O
on	O
its	O
website	O
.	O
</s>
<s>
The	O
Linphone	B-Protocol
client	O
provides	O
access	O
to	O
following	O
functionalities	O
:	O
</s>
<s>
Video	O
codec	O
support	O
:	O
MPEG-4	B-Algorithm
,	O
Theora	B-Algorithm
,	O
VP8	B-Algorithm
and	O
H.264	B-Application
(	O
with	O
a	O
plugin	O
based	O
on	O
x264	B-Language
)	O
,	O
with	O
resolutions	O
from	O
QCIF	O
(	O
176×144	O
)	O
to	O
SVGA	O
(	O
800×600	O
)	O
provided	O
that	O
network	O
bandwidth	O
and	O
CPU	O
power	O
are	O
sufficient	O
.	O
</s>
