<s>
Asterisk	B-Language
is	O
a	O
software	O
implementation	O
of	O
a	O
private	B-Device
branch	I-Device
exchange	I-Device
(	O
PBX	O
)	O
.	O
</s>
<s>
In	O
conjunction	O
with	O
suitable	O
telephony	O
hardware	O
interfaces	O
and	O
network	O
applications	O
,	O
Asterisk	B-Language
is	O
used	O
to	O
establish	O
and	O
control	O
telephone	O
calls	O
between	O
telecommunication	O
endpoints	O
,	O
such	O
as	O
customary	O
telephone	O
sets	O
,	O
destinations	O
on	O
the	O
public	O
switched	O
telephone	O
network	O
(	O
PSTN	O
)	O
,	O
and	O
devices	O
or	O
services	O
on	O
voice	B-Application
over	I-Application
Internet	I-Application
Protocol	I-Application
(	O
VoIP	B-Application
)	O
networks	O
.	O
</s>
<s>
Its	O
name	O
comes	O
from	O
the	O
asterisk	B-Language
( *	O
)	O
symbol	O
for	O
a	O
signal	O
used	O
in	O
dual-tone	O
multi-frequency	O
(	O
DTMF	O
)	O
dialing	O
.	O
</s>
<s>
Asterisk	B-Language
was	O
created	O
in	O
1999	O
by	O
Mark	O
Spencer	O
of	O
Digium	B-Protocol
,	O
which	O
since	O
2018	O
is	O
a	O
division	O
of	O
Sangoma	O
Technologies	O
Corporation	O
.	O
</s>
<s>
Originally	O
designed	O
for	O
Linux	B-Application
,	O
Asterisk	B-Language
runs	O
on	O
a	O
variety	O
of	O
operating	B-General_Concept
systems	I-General_Concept
,	O
including	O
NetBSD	B-Device
,	O
OpenBSD	B-Operating_System
,	O
FreeBSD	B-Operating_System
,	O
macOS	B-Application
,	O
and	O
Solaris	B-Application
,	O
and	O
can	O
be	O
installed	O
in	O
embedded	O
systems	O
based	O
on	O
OpenWrt	B-Application
.	O
</s>
<s>
The	O
Asterisk	B-Language
software	O
includes	O
many	O
features	O
available	O
in	O
commercial	O
and	O
proprietary	O
PBX	O
systems	O
:	O
voice	O
mail	O
,	O
conference	O
calling	O
,	O
interactive	O
voice	O
response	O
(	O
phone	O
menus	O
)	O
,	O
and	O
automatic	O
call	O
distribution	O
.	O
</s>
<s>
Users	O
can	O
create	O
new	O
functionality	O
by	O
writing	O
dial	O
plan	O
scripts	O
in	O
several	O
of	O
Asterisk	B-Language
's	O
own	O
extensions	O
languages	O
,	O
by	O
adding	O
custom	O
loadable	O
modules	O
written	O
in	O
PHP	O
or	O
C	B-Language
,	O
or	O
by	O
implementing	O
Asterisk	B-Protocol
Gateway	I-Protocol
Interface	I-Protocol
(	O
AGI	O
)	O
programs	O
using	O
any	O
programming	O
language	O
capable	O
of	O
communicating	O
via	O
the	O
standard	O
streams	O
system	O
(	O
stdin	O
and	O
stdout	O
)	O
or	O
by	O
network	O
TCP	O
sockets	O
.	O
</s>
<s>
Asterisk	B-Language
supports	O
several	O
standard	O
VOIP	B-Application
protocols	O
,	O
including	O
the	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
,	O
the	O
Media	B-Protocol
Gateway	I-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
MGCP	O
)	O
,	O
and	O
H.323	B-Protocol
.	O
</s>
<s>
Asterisk	B-Language
supports	O
most	O
SIP	O
telephones	O
,	O
acting	O
both	O
as	O
registrar	O
and	O
back-to-back	B-Protocol
user	I-Protocol
agent	I-Protocol
.	O
</s>
<s>
The	O
Inter-Asterisk	B-Protocol
eXchange	I-Protocol
(	O
IAX	B-Protocol
)	O
protocol	O
,	O
RFC	O
5456	O
,	O
native	O
to	O
Asterisk	B-Language
,	O
provides	O
efficient	O
trunking	O
of	O
calls	O
between	O
Asterisk	B-Language
PBX	I-Language
systems	O
,	O
in	O
addition	O
to	O
distributing	O
some	O
configuration	O
logic	O
.	O
</s>
<s>
Many	O
VoIP	B-Application
service	O
providers	O
support	O
it	O
for	O
call	O
completion	O
into	O
the	O
PSTN	O
,	O
often	O
because	O
they	O
themselves	O
have	O
deployed	O
Asterisk	B-Language
or	O
offer	O
it	O
as	O
a	O
hosted	O
application	O
.	O
</s>
<s>
Some	O
telephones	O
also	O
support	O
the	O
IAX	B-Protocol
protocol	O
.	O
</s>
<s>
By	O
supporting	O
a	O
variety	O
of	O
traditional	O
and	O
VoIP	B-Application
telephony	I-Application
services	O
,	O
Asterisk	B-Language
allows	O
deployers	O
to	O
build	O
telephone	O
systems	O
,	O
or	O
migrate	O
existing	O
systems	O
to	O
new	O
technologies	O
.	O
</s>
<s>
Some	O
sites	O
are	O
using	O
Asterisk	B-Language
to	O
replace	O
proprietary	O
PBXes	O
,	O
others	O
provide	O
additional	O
features	O
,	O
such	O
as	O
voice	O
mail	O
or	O
voice	O
response	O
menus	O
,	O
or	O
virtual	O
call	O
shops	O
,	O
or	O
to	O
reduce	O
cost	O
by	O
carrying	O
both	O
local	O
and	O
long-distance	O
calls	O
over	O
the	O
Internet	O
.	O
</s>
<s>
In	O
addition	O
to	O
VoIP	B-Application
protocols	O
,	O
Asterisk	B-Language
supports	O
traditional	O
circuit-switching	O
protocols	O
such	O
as	O
ISDN	B-Protocol
and	O
SS7	O
.	O
</s>
<s>
In	O
Asterisk	B-Language
release	O
14	O
the	O
Opus	B-Algorithm
audio	I-Algorithm
codec	I-Algorithm
is	O
supported	O
.	O
</s>
<s>
While	O
initially	O
developed	O
in	O
the	O
United	O
States	O
,	O
Asterisk	B-Language
has	O
become	O
a	O
popular	O
VoIP	B-Application
PBX	O
worldwide	O
.	O
</s>
<s>
Several	O
sets	O
of	O
prompts	O
for	O
the	O
interactive	O
voice	O
response	O
and	O
voice	O
mail	O
features	O
are	O
included	O
with	O
Asterisk	B-Language
:	O
American	O
,	O
British	O
,	O
and	O
Australian	O
English	O
,	O
Canadian	O
French	O
,	O
Japanese	O
,	O
Russian	O
,	O
Mexican	O
Spanish	O
and	O
Swedish	O
.	O
</s>
<s>
A	O
few	O
novelty	O
prompts	O
are	O
offered	O
,	O
such	O
as	O
jokes	O
and	O
a	O
themed	O
"	O
zombie	O
apocalypse	O
"	O
message	O
for	O
Halloween	B-Application
.	O
</s>
<s>
The	O
default	O
set	O
of	O
English-language	O
Asterisk	B-Language
prompts	O
are	O
recorded	O
by	O
professional	O
telephone	O
voice	O
Allison	O
Smith	O
.	O
</s>
<s>
Asterisk	B-Language
is	O
a	O
core	O
component	O
in	O
many	O
commercial	O
products	O
and	O
open-source	O
projects	O
.	O
</s>
<s>
AskoziaPBX	B-Protocol
,	O
a	O
fork	O
of	O
the	O
m0n0wall	B-Protocol
project	O
,	O
uses	O
Asterisk	B-Language
PBX	I-Language
software	O
to	O
realize	O
all	O
telephony	O
functions	O
.	O
</s>
<s>
LinuxMCE	B-Application
bundles	O
Asterisk	B-Language
to	O
provide	O
telephony	O
;	O
there	O
is	O
also	O
an	O
embedded	O
version	O
of	O
Asterisk	B-Language
for	O
OpenWrt	B-Application
routers	O
.	O
</s>
<s>
PBX	O
in	O
a	O
Flash/Incredible	O
PBX	O
and	O
trixbox	B-Protocol
are	O
software	O
PBXes	O
based	O
on	O
Asterisk	B-Language
.	O
</s>
<s>
Elastix	B-Algorithm
previously	O
used	O
Asterisk	B-Language
,	O
HylaFAX	B-Device
,	O
Openfire	B-Language
and	O
Postfix	B-Application
to	O
offer	O
PBX	O
,	O
fax	O
,	O
instant	O
messaging	O
and	O
email	O
functions	O
,	O
respectively	O
,	O
before	O
switching	O
to	O
3CX	O
.	O
</s>
<s>
Issabel	B-Protocol
is	O
an	O
open-source	O
Unified	B-Protocol
Communications	I-Protocol
software	O
which	O
uses	O
Asterisk	B-Language
for	O
telephony	O
functions	O
.	O
</s>
<s>
It	O
was	O
forked	O
from	O
the	O
open-source	O
versions	O
of	O
Elastix	B-Algorithm
when	O
3CX	O
acquired	O
it	O
.	O
</s>
<s>
*	O
astTECS	O
uses	O
Asterisk	B-Language
in	O
its	O
VoIP	B-Application
and	O
mobile	O
gateways	O
.	O
</s>
<s>
Various	O
add-on	O
products	O
,	O
often	O
commercial	O
,	O
are	O
available	O
that	O
extend	O
Asterisk	B-Language
features	O
and	O
capabilities	O
.	O
</s>
<s>
Other	O
add-ons	O
provide	O
fax	O
support	O
,	O
text-to-speech	O
,	O
additional	O
codecs	B-General_Concept
and	O
new	O
features	O
.	O
</s>
<s>
Some	O
third-party	O
add-ons	O
are	O
free	O
;	O
a	O
few	O
even	O
support	O
embedded	O
platforms	O
such	O
as	O
the	O
Raspberry	B-Operating_System
Pi	I-Operating_System
.	O
</s>
