<s>
Twinkle	B-Protocol
is	O
a	O
free	B-License
and	I-License
open-source	I-License
application	O
for	O
voice	O
communications	O
over	O
Voice	B-Application
over	I-Application
IP	I-Application
(	O
VoIP	B-Application
)	O
protocol	O
.	O
</s>
<s>
It	O
is	O
designed	O
for	O
Linux	B-Application
operating	I-Application
systems	I-Application
and	O
uses	O
the	O
Qt	B-Language
toolkit	I-Language
for	O
its	O
graphical	O
user	O
interface	O
.	O
</s>
<s>
For	O
call	O
signaling	O
it	O
employs	O
the	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
.	O
</s>
<s>
Media	O
streams	O
are	O
transmitted	O
via	O
the	O
Real-time	B-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
RTP	O
)	O
which	O
may	O
be	O
encrypted	O
with	O
the	O
Secure	B-Protocol
Real-time	I-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
SRTP	O
)	O
and	O
the	O
ZRTP	B-Protocol
security	O
protocols	O
.	O
</s>
<s>
Since	O
version	O
1.3.2	O
(	O
September	O
2008	O
)	O
,	O
Twinkle	B-Protocol
supports	O
message	O
exchange	O
and	O
a	O
buddy-list	O
feature	O
for	O
presence	O
notification	O
,	O
showing	O
the	O
online-status	O
of	O
predefined	O
communications	O
partners	O
(	O
provider-support	O
needed	O
)	O
.	O
</s>
