<s>
An	O
Internet	B-Protocol
telephony	I-Protocol
service	I-Protocol
provider	I-Protocol
(	O
ITSP	B-Protocol
)	O
offers	O
digital	O
telecommunications	O
services	O
based	O
on	O
Voice	B-Application
over	I-Application
Internet	I-Application
Protocol	I-Application
(	O
VoIP	B-Application
)	O
that	O
are	O
provisioned	O
via	O
the	O
Internet	O
.	O
</s>
<s>
ITSPs	B-Protocol
provide	O
services	O
to	O
end-users	O
directly	O
or	O
as	O
whole-sale	O
suppliers	O
to	O
other	O
ITSPs	B-Protocol
.	O
</s>
<s>
ITSPs	B-Protocol
use	O
a	O
variety	O
of	O
signaling	O
and	O
multimedia	O
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
Megaco	O
,	O
and	O
the	O
H.323	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
H.323	B-Protocol
is	O
one	O
of	O
the	O
earliest	O
VoIP	B-Application
protocols	O
,	O
but	O
its	O
use	O
is	O
declining	O
and	O
it	O
is	O
rarely	O
used	O
for	O
consumer	O
products	O
.	O
</s>
<s>
Retail	O
customers	O
of	O
an	O
ITSP	B-Protocol
may	O
use	O
traditional	O
analog	O
telephone	O
sets	O
attached	O
to	O
an	O
analog	B-Protocol
telephony	I-Protocol
adapter	I-Protocol
(	O
ATA	O
)	O
to	O
connect	O
to	O
the	O
service	O
provider	O
's	O
network	O
via	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
,	O
they	O
may	O
use	O
an	O
IP	O
phone	O
,	O
or	O
they	O
may	O
connect	O
a	O
private	O
branch	O
exchange	O
(	O
PBX	O
)	O
system	O
to	O
the	O
service	O
via	O
media	O
gateways	O
.	O
</s>
<s>
ITSPs	B-Protocol
are	O
also	O
known	O
as	O
voice	O
service	O
providers	O
(	O
VSP	O
)	O
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
net2Phone	B-Protocol
began	O
offering	O
consumer	O
VoIP	B-Application
service	O
in	O
1995	O
.	O
</s>
<s>
Usually	O
,	O
ITSPs	B-Protocol
negotiate	O
agreements	O
for	O
route	O
termination	O
to	O
various	O
parts	O
of	O
the	O
world	O
from	O
multiple	O
VoIP	B-Application
providers	O
.	O
</s>
<s>
ITSP	B-Protocol
customers	O
may	O
be	O
able	O
to	O
choose	O
a	O
VoIP	B-Application
provider	O
for	O
their	O
VoIP	B-Application
calls	I-Application
.	O
</s>
<s>
The	O
ITSP	B-Protocol
routing	O
software	O
searches	O
for	O
the	O
wholesale	O
VoIP	B-Application
providers	O
who	O
meet	O
the	O
customer	O
specification	O
and	O
attempt	O
to	O
route	O
the	O
customer	O
call	O
to	O
the	O
providers	O
starting	O
with	O
the	O
one	O
have	O
the	O
lowest	O
quoted	O
price	O
.	O
</s>
<s>
Pricing	O
to	O
different	O
parts	O
of	O
the	O
world	O
depend	O
on	O
several	O
factors	O
,	O
such	O
as	O
the	O
routing	O
via	O
a	O
white	B-Protocol
route	I-Protocol
or	O
a	O
black	B-Protocol
route	I-Protocol
,	O
wholesaler	O
's	O
margin	O
,	O
and	O
the	O
country	O
's	O
regulations	O
.	O
</s>
