<s>
A	O
VoIP	B-Protocol
gateway	I-Protocol
is	O
a	O
gateway	B-Application
device	O
that	O
uses	O
Internet	B-Protocol
Protocols	I-Protocol
to	O
transmit	O
and	O
receive	O
voice	B-Application
communications	I-Application
(	O
VoIP	B-Application
)	O
.	O
</s>
<s>
A	O
typical	O
VoIP	B-Protocol
gateway	I-Protocol
has	O
interfaces	O
to	O
both	O
IP	O
networks	O
and	O
PSTN	O
(	O
Public	O
switched	O
telephone	O
network	O
)	O
or	O
POTS	O
(	O
Plain	O
old	O
telephone	O
service	O
)	O
telephone	O
services	O
.	O
</s>
<s>
The	O
gateway	B-Application
may	O
be	O
configured	O
to	O
use	O
these	O
in	O
several	O
ways	O
,	O
including	O
:	O
</s>
<s>
An	O
internal	O
telephone	O
instrument	O
or	O
nmnbm	O
,	O
with	O
external	O
game	O
connectivity	O
through	O
VoIP	B-Application
via	O
the	O
Internet	O
.	O
</s>
<s>
The	O
PSTN	O
interface	O
to	O
a	O
telephone	O
network	O
,	O
with	O
IP	O
connectivity	O
to	O
an	O
in-house	O
VoIP	B-Application
phone	O
system	O
.	O
</s>
<s>
Both	O
PSTN	O
and	O
VoIP	B-Application
interfaces	O
externally	O
,	O
sometimes	O
to	O
offer	O
a	O
connection	O
at	O
local	O
call	O
charges	O
to	O
a	O
remote	O
call	O
centre	O
.	O
</s>
<s>
A	O
relatively	O
potent	O
device	O
is	O
needed	O
to	O
use	O
better	O
compression	O
formats	O
,	O
such	O
as	O
G.729a	B-Algorithm
;	O
a	O
relatively	O
inexpensive	O
and	O
simple	O
device	O
can	O
easily	O
handle	O
a	O
similar	O
function	O
using	O
more	O
bandwidth	O
over	O
G.711	B-Algorithm
.	O
</s>
<s>
Any	O
device	O
capable	O
of	O
delivering	O
audio	O
in	O
G.711	B-Algorithm
via	O
Internet	O
in	O
either	O
way	O
can	O
be	O
considered	O
a	O
VOIP	B-Protocol
Gateway	I-Protocol
,	O
but	O
one	O
that	O
is	O
capable	O
of	O
sending	O
and	O
receiving	O
simultaneously	O
will	O
perform	O
better	O
.	O
</s>
<s>
One	O
with	O
support	O
for	O
more	O
codecs	B-General_Concept
will	O
usually	O
be	O
able	O
to	O
perform	O
better	O
in	O
a	O
range	O
of	O
situations	O
,	O
such	O
as	O
restricted	O
bandwidth	O
,	O
though	O
doing	O
so	O
is	O
not	O
always	O
easy	O
to	O
differentiate	O
.	O
</s>
<s>
The	O
packets	O
of	O
data	O
are	O
quickly	O
sent	O
(	O
as	O
little	O
as	O
a	O
few	O
milliseconds	O
between	O
packets	O
)	O
,	O
most	O
often	O
using	O
User	B-Protocol
Datagram	I-Protocol
Protocol	I-Protocol
(	O
UDP	O
)	O
.	O
</s>
<s>
Using	O
G.711	B-Algorithm
as	O
the	O
codec	B-General_Concept
,	O
it	O
is	O
possible	O
to	O
use	O
a	O
fax	O
machine	O
or	O
modem	O
via	O
these	O
devices	O
without	O
issues	O
.	O
</s>
<s>
This	O
is	O
mostly	O
due	O
to	O
G.711	B-Algorithm
being	O
a	O
relatively	O
simple	O
compression	O
audio	O
stream	O
.	O
</s>
<s>
Other	O
codecs	B-General_Concept
will	O
not	O
usually	O
perform	O
this	O
task	O
.	O
</s>
<s>
Any	O
modern	O
PC	O
with	O
a	O
microphone	O
and	O
speakers	O
(	O
or	O
a	O
headset	O
serving	O
both	O
those	O
tasks	O
)	O
is	O
capable	O
of	O
acting	O
as	O
a	O
VoIP	B-Protocol
gateway	I-Protocol
.	O
</s>
<s>
This	O
still	O
requires	O
an	O
Internet	O
connection	O
and	O
a	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	O
)	O
relay	O
which	O
adds	O
to	O
the	O
disadvantages	O
of	O
VoIP	B-Application
.	O
</s>
