<s>
Voice	B-Application
over	I-Application
Internet	I-Application
Protocol	I-Application
(	O
VoIP	B-Application
)	O
,	O
also	O
called	O
IP	B-Application
telephony	I-Application
,	O
is	O
a	O
method	O
and	O
group	O
of	O
technologies	O
for	O
the	O
delivery	O
of	O
voice	O
communications	O
and	O
multimedia	O
sessions	O
over	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
networks	O
,	O
such	O
as	O
the	O
Internet	O
.	O
</s>
<s>
The	O
terms	O
Internet	B-Application
telephony	I-Application
,	O
broadband	B-Application
telephony	I-Application
,	O
and	O
broadband	B-Application
phone	I-Application
service	I-Application
specifically	O
refer	O
to	O
the	O
provisioning	O
of	O
communications	O
services	O
(	O
voice	O
,	O
fax	O
,	O
SMS	O
,	O
voice-messaging	O
)	O
over	O
the	O
Internet	O
,	O
rather	O
than	O
via	O
the	O
public	O
switched	O
telephone	O
network	O
(	O
PSTN	O
)	O
,	O
also	O
known	O
as	O
plain	O
old	O
telephone	O
service	O
(	O
POTS	O
)	O
.	O
</s>
<s>
The	O
steps	O
and	O
principles	O
involved	O
in	O
originating	O
VoIP	B-Application
telephone	O
calls	O
are	O
similar	O
to	O
traditional	O
digital	O
telephony	O
and	O
involve	O
signaling	O
,	O
channel	O
setup	O
,	O
digitization	O
of	O
the	O
analog	O
voice	O
signals	O
,	O
and	O
encoding	O
.	O
</s>
<s>
Instead	O
of	O
being	O
transmitted	O
over	O
a	O
circuit-switched	B-Protocol
network	I-Protocol
,	O
the	O
digital	O
information	O
is	O
packetized	O
and	O
transmission	O
occurs	O
as	O
IP	O
packets	O
over	O
a	O
packet-switched	B-Protocol
network	I-Protocol
.	O
</s>
<s>
They	O
transport	O
media	O
streams	O
using	O
special	O
media	O
delivery	O
protocols	O
that	O
encode	O
audio	O
and	O
video	O
with	O
audio	B-Algorithm
codecs	I-Algorithm
and	O
video	B-Application
codecs	I-Application
.	O
</s>
<s>
Various	O
codecs	B-General_Concept
exist	O
that	O
optimize	O
the	O
media	O
stream	O
based	O
on	O
application	O
requirements	O
and	O
network	O
bandwidth	O
;	O
some	O
implementations	O
rely	O
on	O
narrowband	O
and	O
compressed	B-Application
speech	I-Application
,	O
while	O
others	O
support	O
high-fidelity	O
stereo	O
codecs	B-General_Concept
.	O
</s>
<s>
The	O
most	O
widely	O
used	O
speech	B-Application
coding	I-Application
standards	O
in	O
VoIP	B-Application
are	O
based	O
on	O
the	O
linear	B-Algorithm
predictive	I-Algorithm
coding	I-Algorithm
(	O
LPC	O
)	O
and	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
compression	O
methods	O
.	O
</s>
<s>
Popular	O
codecs	B-General_Concept
include	O
the	O
MDCT-based	O
AAC-LD	B-Algorithm
(	O
used	O
in	O
FaceTime	B-Operating_System
)	O
,	O
the	O
LPC/MDCT	O
-based	O
Opus	B-Algorithm
(	O
used	O
in	O
WhatsApp	B-Application
)	O
,	O
the	O
LPC-based	O
SILK	O
(	O
used	O
in	O
Skype	B-Application
)	O
,	O
μ-law	B-Algorithm
and	O
A-law	B-Algorithm
versions	O
of	O
G.711	B-Algorithm
,	O
G.722	B-Algorithm
,	O
and	O
an	O
open	B-Application
source	I-Application
voice	B-Application
codec	I-Application
known	O
as	O
iLBC	B-Algorithm
,	O
a	O
codec	B-General_Concept
that	O
uses	O
only	O
8kbit/s	O
each	O
way	O
called	O
G.729	B-Algorithm
.	O
</s>
<s>
Early	O
providers	O
of	O
voice-over-IP	B-Application
services	O
used	O
business	O
models	O
and	O
offered	O
technical	O
solutions	O
that	O
mirrored	O
the	O
architecture	O
of	O
the	O
legacy	O
telephone	O
network	O
.	O
</s>
<s>
Second-generation	O
providers	O
,	O
such	O
as	O
Skype	B-Application
,	O
built	O
closed	O
networks	O
for	O
private	O
user	O
bases	O
,	O
offering	O
the	O
benefit	O
of	O
free	O
calls	O
and	O
convenience	O
while	O
potentially	O
charging	O
for	O
access	O
to	O
other	O
communication	O
networks	O
,	O
such	O
as	O
the	O
PSTN	O
.	O
</s>
<s>
Third-generation	O
providers	O
,	O
such	O
as	O
Google	B-Application
Talk	I-Application
,	O
adopted	O
the	O
concept	O
of	O
federated	B-Application
VoIP	I-Application
.	O
</s>
<s>
These	O
solutions	O
typically	O
allow	O
dynamic	O
interconnection	B-Architecture
between	O
users	O
in	O
any	O
two	O
domains	O
of	O
the	O
Internet	O
,	O
when	O
a	O
user	O
wishes	O
to	O
place	O
a	O
call	O
.	O
</s>
<s>
In	O
addition	O
to	O
VoIP	B-Device
phones	I-Device
,	O
VoIP	B-Application
is	O
also	O
available	O
on	O
many	O
personal	B-Device
computers	I-Device
and	O
other	O
Internet	O
access	O
devices	O
.	O
</s>
<s>
VoIP	B-Application
provides	O
a	O
framework	O
for	O
consolidation	O
of	O
all	O
modern	O
communications	O
technologies	O
using	O
a	O
single	O
unified	B-Protocol
communications	I-Protocol
system	O
.	O
</s>
<s>
VoIP	B-Application
is	O
variously	O
pronounced	O
as	O
an	O
initialism	O
,	O
V-O-I-P	O
,	O
or	O
as	O
an	O
acronym	O
,	O
(	O
)	O
.	O
</s>
<s>
Full	O
words	O
,	O
voice	B-Application
over	I-Application
Internet	I-Application
Protocol	I-Application
,	O
or	O
voice	B-Application
over	I-Application
IP	I-Application
,	O
are	O
sometimes	O
used	O
.	O
</s>
<s>
Voice	B-Application
over	I-Application
IP	I-Application
has	O
been	O
implemented	O
with	O
proprietary	O
protocols	O
and	O
protocols	O
based	O
on	O
open	O
standards	O
in	O
applications	O
such	O
as	O
VoIP	B-Device
phones	I-Device
,	O
mobile	O
applications	O
,	O
and	O
web-based	B-Protocol
communications	I-Protocol
.	O
</s>
<s>
A	O
variety	O
of	O
functions	O
are	O
needed	O
to	O
implement	O
VoIP	B-Application
communication	O
.	O
</s>
<s>
Session	B-Protocol
management	I-Protocol
–	O
Creating	O
and	O
managing	O
a	O
session	B-Protocol
(	O
sometimes	O
glossed	O
as	O
simply	O
a	O
"	O
call	O
"	O
)	O
,	O
which	O
is	O
a	O
connection	O
between	O
two	O
or	O
more	O
peers	O
that	O
provides	O
a	O
context	O
for	O
further	O
communication	O
.	O
</s>
<s>
)	O
,	O
how	O
to	O
encode/decode	O
it	O
,	O
and	O
how	O
to	O
send/receive	O
it	O
(	O
IP	B-Protocol
addresses	I-Protocol
,	O
ports	O
,	O
etc	O
.	O
</s>
<s>
VoIP	B-Application
protocols	O
include	O
:	O
</s>
<s>
H.323	B-Protocol
,	O
one	O
of	O
the	O
first	O
VoIP	B-Application
call	I-Application
signaling	O
and	O
control	O
protocols	O
that	O
found	O
widespread	O
implementation	O
.	O
</s>
<s>
Since	O
the	O
development	O
of	O
newer	O
,	O
less	O
complex	O
protocols	O
such	O
as	O
MGCP	O
and	O
SIP	B-Application
,	O
H.323	B-Protocol
deployments	O
are	O
increasingly	O
limited	O
to	O
carrying	O
existing	O
long-haul	O
network	O
traffic	O
.	O
</s>
<s>
Session	B-Language
Description	I-Language
Protocol	I-Language
(	O
SDP	O
)	O
,	O
a	O
syntax	O
for	O
session	B-Protocol
initiation	O
and	O
announcement	O
for	O
multi-media	O
communications	O
and	O
WebSocket	B-Protocol
transports	O
.	O
</s>
<s>
Mass-market	O
VoIP	B-Application
services	O
use	O
existing	O
broadband	O
Internet	O
access	O
,	O
by	O
which	O
subscribers	O
place	O
and	O
receive	O
telephone	O
calls	O
in	O
much	O
the	O
same	O
manner	O
as	O
they	O
would	O
via	O
the	O
PSTN	O
.	O
</s>
<s>
Full-service	O
VoIP	B-Device
phone	I-Device
companies	O
provide	O
inbound	O
and	O
outbound	O
service	O
with	O
direct	B-Device
inbound	I-Device
dialing	I-Device
.	O
</s>
<s>
A	O
VoIP	B-Device
phone	I-Device
is	O
necessary	O
to	O
connect	O
to	O
a	O
VoIP	B-Application
service	O
provider	O
.	O
</s>
<s>
Dedicated	O
VoIP	B-Device
phones	I-Device
connect	O
directly	O
to	O
the	O
IP	O
network	O
using	O
technologies	O
such	O
as	O
wired	O
Ethernet	O
or	O
Wi-Fi	O
.	O
</s>
<s>
An	O
analog	B-Protocol
telephone	I-Protocol
adapter	I-Protocol
connects	O
to	O
the	O
network	O
and	O
implements	O
the	O
electronics	O
and	O
firmware	O
to	O
operate	O
a	O
conventional	O
analog	O
telephone	O
attached	O
through	O
a	O
modular	O
phone	O
jack	O
.	O
</s>
<s>
Some	O
residential	O
Internet	O
gateways	O
and	O
cablemodems	B-Device
have	O
this	O
function	O
built	O
in	O
.	O
</s>
<s>
Softphone	B-Protocol
application	O
software	O
installed	O
on	O
a	O
networked	O
computer	O
that	O
is	O
equipped	O
with	O
a	O
microphone	O
and	O
speaker	O
,	O
or	O
headset	O
.	O
</s>
<s>
It	O
is	O
increasingly	O
common	O
for	O
telecommunications	O
providers	O
to	O
use	O
VoIP	B-Application
telephony	I-Application
over	O
dedicated	O
and	O
public	O
IP	O
networks	O
as	O
a	O
backhaul	B-General_Concept
to	O
connect	O
switching	O
centers	O
and	O
to	O
interconnect	B-Architecture
with	O
other	O
telephony	O
network	O
providers	O
;	O
this	O
is	O
often	O
referred	O
to	O
as	O
IP	O
backhaul	B-General_Concept
.	O
</s>
<s>
Smartphones	B-Application
may	O
have	O
SIP	B-Application
clients	O
built	O
into	O
the	O
firmware	O
or	O
available	O
as	O
an	O
application	O
download	O
.	O
</s>
<s>
Because	O
of	O
the	O
bandwidth	O
efficiency	O
and	O
low	O
costs	O
that	O
VoIP	B-Application
technology	O
can	O
provide	O
,	O
businesses	O
are	O
migrating	O
from	O
traditional	O
copper-wire	O
telephone	O
systems	O
to	O
VoIP	B-Application
systems	O
to	O
reduce	O
their	O
monthly	O
phone	O
costs	O
.	O
</s>
<s>
In	O
2008	O
,	O
80%	O
of	O
all	O
new	O
Private	B-Device
branch	I-Device
exchange	I-Device
(	O
PBX	O
)	O
lines	O
installed	O
internationally	O
were	O
VoIP	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
in	O
the	O
United	O
States	O
,	O
the	O
Social	O
Security	O
Administration	O
is	O
converting	O
its	O
field	O
offices	O
of	O
63,000	O
workers	O
from	O
traditional	O
phone	O
installations	O
to	O
a	O
VoIP	B-Application
infrastructure	O
carried	O
over	O
its	O
existing	O
data	O
network	O
.	O
</s>
<s>
VoIP	B-Application
allows	O
both	O
voice	O
and	O
data	O
communications	O
to	O
be	O
run	O
over	O
a	O
single	O
network	O
,	O
which	O
can	O
significantly	O
reduce	O
infrastructure	O
costs	O
.	O
</s>
<s>
The	O
prices	O
of	O
extensions	O
on	O
VoIP	B-Application
are	O
lower	O
than	O
for	O
PBX	O
and	O
key	O
systems	O
.	O
</s>
<s>
VoIP	B-Application
switches	O
may	O
run	O
on	O
commodity	O
hardware	O
,	O
such	O
as	O
personal	B-Device
computers	I-Device
.	O
</s>
<s>
VoIP	B-Application
devices	O
have	O
simple	O
,	O
intuitive	O
user	O
interfaces	O
,	O
so	O
users	O
can	O
often	O
make	O
simple	O
system	O
configuration	O
changes	O
.	O
</s>
<s>
VoIP	B-Application
solutions	O
aimed	O
at	O
businesses	O
have	O
evolved	O
into	O
unified	B-Protocol
communications	I-Protocol
services	O
that	O
treat	O
all	O
communications	O
—	O
phone	O
calls	O
,	O
faxes	O
,	O
voice	O
mail	O
,	O
e-mail	O
,	O
web	O
conferences	O
,	O
and	O
more	O
—	O
as	O
discrete	O
units	O
that	O
can	O
all	O
be	O
delivered	O
via	O
any	O
means	O
and	O
to	O
any	O
handset	O
,	O
including	O
cellphones	O
.	O
</s>
<s>
Two	O
kinds	O
of	O
service	O
providers	O
are	O
operating	O
in	O
this	O
space	O
:	O
one	O
set	O
is	O
focused	O
on	O
VoIP	B-Application
for	O
medium	O
to	O
large	O
enterprises	O
,	O
while	O
another	O
is	O
targeting	O
the	O
small-to-medium	O
business	O
(	O
SMB	O
)	O
market	O
.	O
</s>
<s>
Skype	B-Application
,	O
which	O
originally	O
marketed	O
itself	O
as	O
a	O
service	O
among	O
friends	O
,	O
has	O
begun	O
to	O
cater	O
to	O
businesses	O
,	O
providing	O
free-of-charge	O
connections	O
between	O
any	O
users	O
on	O
the	O
Skype	B-Application
network	O
and	O
connecting	O
to	O
and	O
from	O
ordinary	O
PSTN	O
telephones	O
for	O
a	O
charge	O
.	O
</s>
<s>
In	O
general	O
,	O
the	O
provision	O
of	O
VoIP	B-Application
telephony	I-Application
systems	O
to	O
organizational	O
or	O
individual	O
users	O
can	O
be	O
divided	O
into	O
two	O
primary	O
delivery	O
methods	O
:	O
private	O
or	O
on-premises	O
solutions	O
,	O
or	O
externally	O
hosted	O
solutions	O
delivered	O
by	O
third-party	O
providers	O
.	O
</s>
<s>
While	O
many	O
use	O
cases	O
still	O
remain	O
for	O
private	O
or	O
on-premises	O
VoIP	B-Application
systems	O
,	O
the	O
wider	O
market	O
has	O
been	O
gradually	O
shifting	O
toward	O
Cloud	O
or	O
Hosted	O
VoIP	B-Application
solutions	O
.	O
</s>
<s>
Hosted	O
systems	O
are	O
also	O
generally	O
better	O
suited	O
to	O
smaller	O
or	O
personal	O
use	O
VoIP	B-Application
deployments	O
,	O
where	O
a	O
private	O
system	O
may	O
not	O
be	O
viable	O
for	O
these	O
scenarios	O
.	O
</s>
<s>
Hosted	O
or	O
Cloud	O
VoIP	B-Application
solutions	O
involve	O
a	O
service	O
provider	O
or	O
telecommunications	O
carrier	O
hosting	O
the	O
telephone	O
system	O
as	O
a	O
software	O
solution	O
within	O
their	O
own	O
infrastructure	O
.	O
</s>
<s>
Typically	O
this	O
will	O
be	O
one	O
or	O
more	O
datacentres	B-Operating_System
,	O
with	O
geographic	O
relevance	O
to	O
the	O
end-user(s )	O
of	O
the	O
system	O
.	O
</s>
<s>
Endpoints	B-Protocol
,	O
such	O
as	O
VoIP	B-Application
telephones	O
or	O
softphone	B-Protocol
applications	O
(	O
apps	O
running	O
on	O
a	O
computer	O
or	O
mobile	O
device	O
)	O
,	O
will	O
connect	O
to	O
the	O
VoIP	B-Application
service	O
remotely	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
a	O
private	O
VoIP	B-Application
system	O
,	O
the	O
primary	O
telephony	O
system	O
itself	O
is	O
located	O
within	O
the	O
private	O
infrastructure	O
of	O
the	O
end-user	O
organization	O
.	O
</s>
<s>
However	O
,	O
the	O
responsibility	O
for	O
ensuring	O
that	O
the	O
VoIP	B-Application
system	O
remains	O
performant	O
and	O
resilient	O
is	O
predominantly	O
vested	O
in	O
the	O
end-user	O
organization	O
.	O
</s>
<s>
This	O
is	O
not	O
the	O
case	O
with	O
a	O
Hosted	O
VoIP	B-Application
solution	O
.	O
</s>
<s>
Private	O
VoIP	B-Application
systems	O
can	O
be	O
physical	O
hardware	O
PBX	O
appliances	O
,	O
converged	O
with	O
other	O
infrastructure	O
,	O
or	O
they	O
can	O
be	O
deployed	O
as	O
software	O
applications	O
.	O
</s>
<s>
Examples	O
can	O
include	O
datacentre	B-Operating_System
collocation	O
services	O
,	O
public	O
cloud	O
,	O
or	O
private	O
cloud	O
locations	O
.	O
</s>
<s>
For	O
on-premises	O
systems	O
,	O
local	O
endpoints	B-Protocol
within	O
the	O
same	O
location	O
typically	O
connect	O
directly	O
over	O
the	O
LAN	B-General_Concept
.	O
</s>
<s>
For	O
remote	O
and	O
external	O
endpoints	B-Protocol
,	O
available	O
connectivity	O
options	O
mirror	O
those	O
of	O
Hosted	O
or	O
Cloud	O
VoIP	B-Application
solutions	O
.	O
</s>
<s>
However	O
,	O
VoIP	B-Application
traffic	O
to	O
and	O
from	O
the	O
on-premises	O
systems	O
can	O
often	O
also	O
be	O
sent	O
over	O
secure	O
private	O
links	O
.	O
</s>
<s>
Examples	O
include	O
personal	O
VPN	B-Application
,	O
site-to-site	O
VPN	B-Application
,	O
private	O
networks	O
such	O
as	O
MPLS	O
and	O
SD-WAN	O
,	O
or	O
via	O
private	O
SBCs	O
(	O
Session	B-Protocol
Border	I-Protocol
Controllers	I-Protocol
)	O
.	O
</s>
<s>
While	O
exceptions	O
and	O
private	O
peering	O
options	O
do	O
exist	O
,	O
it	O
is	O
generally	O
uncommon	O
for	O
those	O
private	O
connectivity	O
methods	O
to	O
be	O
provided	O
by	O
Hosted	O
or	O
Cloud	O
VoIP	B-Application
providers	O
.	O
</s>
<s>
Communication	O
on	O
the	O
IP	O
network	O
is	O
perceived	O
as	O
less	O
reliable	O
in	O
contrast	O
to	O
the	O
circuit-switched	B-Protocol
public	O
telephone	O
network	O
because	O
it	O
does	O
not	O
provide	O
a	O
network-based	O
mechanism	O
to	O
ensure	O
that	O
data	O
packets	O
are	O
not	O
lost	O
,	O
and	O
are	O
delivered	O
in	O
sequential	O
order	O
.	O
</s>
<s>
This	O
system	O
may	O
be	O
more	O
prone	O
to	O
data	O
loss	O
in	O
the	O
presence	O
of	O
congestion	O
than	O
traditional	O
circuit	B-Protocol
switched	I-Protocol
systems	O
;	O
a	O
circuit	B-Protocol
switched	I-Protocol
system	O
of	O
insufficient	O
capacity	O
will	O
refuse	O
new	O
connections	O
while	O
carrying	O
the	O
remainder	O
without	O
impairment	O
,	O
while	O
the	O
quality	O
of	O
real-time	O
data	O
such	O
as	O
telephone	O
conversations	O
on	O
packet-switched	B-Protocol
networks	I-Protocol
degrades	O
dramatically	O
.	O
</s>
<s>
Therefore	O
,	O
VoIP	B-Application
implementations	O
may	O
face	O
problems	O
with	O
latency	O
,	O
packet	B-Protocol
loss	I-Protocol
,	O
and	O
jitter	O
.	O
</s>
<s>
By	O
default	O
,	O
network	B-Protocol
routers	I-Protocol
handle	O
traffic	O
on	O
a	O
first-come	O
,	O
first-served	O
basis	O
.	O
</s>
<s>
Network	B-Protocol
routers	I-Protocol
on	O
high	O
volume	O
traffic	O
links	O
may	O
introduce	O
latency	O
that	O
exceeds	O
permissible	O
thresholds	O
for	O
VoIP	B-Application
.	O
</s>
<s>
Excessive	O
load	O
on	O
a	O
link	O
can	O
cause	O
congestion	O
and	O
associated	O
queueing	B-Protocol
delays	I-Protocol
and	O
packet	B-Protocol
loss	I-Protocol
.	O
</s>
<s>
This	O
signals	O
a	O
transport	O
protocol	O
like	O
TCP	B-Protocol
to	O
reduce	O
its	O
transmission	O
rate	O
to	O
alleviate	O
the	O
congestion	O
.	O
</s>
<s>
But	O
VoIP	B-Application
usually	O
uses	O
UDP	B-Protocol
not	O
TCP	B-Protocol
because	O
recovering	O
from	O
congestion	O
through	O
retransmission	O
usually	O
entails	O
too	O
much	O
latency	O
.	O
</s>
<s>
So	O
QoS	O
mechanisms	O
can	O
avoid	O
the	O
undesirable	O
loss	O
of	O
VoIP	B-Application
packets	O
by	O
immediately	O
transmitting	O
them	O
ahead	O
of	O
any	O
queued	O
bulk	O
traffic	O
on	O
the	O
same	O
link	O
,	O
even	O
when	O
the	O
link	O
is	O
congested	O
by	O
bulk	O
traffic	O
.	O
</s>
<s>
VoIP	B-Application
endpoints	B-Protocol
usually	O
have	O
to	O
wait	O
for	O
the	O
completion	O
of	O
transmission	O
of	O
previous	O
packets	O
before	O
new	O
data	O
may	O
be	O
sent	O
.	O
</s>
<s>
An	O
alternative	O
to	O
preemption	O
on	O
slower	O
links	O
,	O
such	O
as	O
dialup	O
and	O
digital	O
subscriber	O
line	O
(	O
DSL	O
)	O
,	O
is	O
to	O
reduce	O
the	O
maximum	O
transmission	O
time	O
by	O
reducing	O
the	O
maximum	B-Protocol
transmission	I-Protocol
unit	I-Protocol
.	O
</s>
<s>
Packet	B-Architecture
delay	I-Architecture
variation	I-Architecture
results	O
from	O
changes	O
in	O
queuing	B-Protocol
delay	I-Protocol
along	O
a	O
given	O
network	O
path	O
due	O
to	O
competition	O
from	O
other	O
users	O
for	O
the	O
same	O
transmission	O
links	O
.	O
</s>
<s>
VoIP	B-Application
receivers	O
accommodate	O
this	O
variation	O
by	O
storing	O
incoming	O
packets	O
briefly	O
in	O
a	O
playout	O
buffer	O
,	O
deliberately	O
increasing	O
latency	O
to	O
improve	O
the	O
chance	O
that	O
each	O
packet	O
will	O
be	O
on	O
hand	O
when	O
it	O
is	O
time	O
for	O
the	O
voice	B-Protocol
engine	I-Protocol
to	O
play	O
it	O
.	O
</s>
<s>
Although	O
jitter	O
is	O
a	O
random	O
variable	O
,	O
it	O
is	O
the	O
sum	O
of	O
several	O
other	O
random	O
variables	O
that	O
are	O
at	O
least	O
somewhat	O
independent	O
:	O
the	O
individual	O
queuing	B-Protocol
delays	I-Protocol
of	O
the	O
routers	B-Protocol
along	O
the	O
Internet	O
path	O
in	O
question	O
.	O
</s>
<s>
In	O
practice	O
,	O
the	O
variance	O
in	O
latency	O
of	O
many	O
Internet	O
paths	O
is	O
dominated	O
by	O
a	O
small	O
number	O
(	O
often	O
one	O
)	O
of	O
relatively	O
slow	O
and	O
congested	O
bottleneck	B-Application
links	I-Application
.	O
</s>
<s>
optical	O
fiber	O
)	O
and	O
the	O
routers	B-Protocol
driving	O
them	O
do	O
not	O
have	O
enough	O
buffering	O
for	O
queuing	B-Protocol
delays	I-Protocol
to	O
be	O
significant	O
.	O
</s>
<s>
A	O
number	O
of	O
protocols	O
have	O
been	O
defined	O
to	O
support	O
the	O
reporting	O
of	O
quality	O
of	O
service	O
(	O
QoS	O
)	O
and	O
quality	O
of	O
experience	O
(	O
QoE	O
)	O
for	O
VoIP	B-Application
calls	I-Application
.	O
</s>
<s>
These	O
include	O
RTP	B-Protocol
Control	I-Protocol
Protocol	I-Protocol
(	O
RTCP	B-Protocol
)	O
extended	O
reports	O
,	O
SIP	B-Application
RTCP	B-Protocol
summary	O
reports	O
,	O
H.460.9	O
Annex	O
B	O
(	O
for	O
H.323	B-Protocol
)	O
,	O
H.248.30	O
and	O
MGCP	O
extensions	O
.	O
</s>
<s>
The	O
RTCP	B-Protocol
extended	O
report	O
VoIP	B-Application
metrics	O
block	O
specified	O
by	O
is	O
generated	O
by	O
an	O
VoIP	B-Device
phone	I-Device
or	O
gateway	O
during	O
a	O
live	O
call	O
and	O
contains	O
information	O
on	O
packet	B-Protocol
loss	I-Protocol
rate	O
,	O
packet	O
discard	O
rate	O
(	O
because	O
of	O
jitter	O
)	O
,	O
packet	O
loss/discard	O
burst	O
metrics	O
(	O
burst	O
length/density	O
,	O
gap	O
length/density	O
)	O
,	O
network	O
delay	O
,	O
end	O
system	O
delay	O
,	O
signal/noise/echo	O
level	O
,	O
mean	O
opinion	O
scores	O
(	O
MOS	O
)	O
and	O
R	O
factors	O
and	O
configuration	O
information	O
related	O
to	O
the	O
jitter	O
buffer	O
.	O
</s>
<s>
VoIP	B-Application
metrics	O
reports	O
are	O
exchanged	O
between	O
IP	O
endpoints	B-Protocol
on	O
an	O
occasional	O
basis	O
during	O
a	O
call	O
,	O
and	O
an	O
end	O
of	O
call	O
message	O
sent	O
via	O
SIP	B-Application
RTCP	B-Protocol
summary	O
report	O
or	O
one	O
of	O
the	O
other	O
signaling	O
protocol	O
extensions	O
.	O
</s>
<s>
VoIP	B-Application
metrics	O
reports	O
are	O
intended	O
to	O
support	O
real-time	O
feedback	O
related	O
to	O
QoS	O
problems	O
,	O
the	O
exchange	O
of	O
information	O
between	O
the	O
endpoints	B-Protocol
for	O
improved	O
call	O
quality	O
calculation	O
and	O
a	O
variety	O
of	O
other	O
applications	O
.	O
</s>
<s>
DSL	O
modems	B-Application
typically	O
provide	O
Ethernet	O
connections	O
to	O
local	O
equipment	O
,	O
but	O
inside	O
they	O
may	O
actually	O
be	O
Asynchronous	O
Transfer	O
Mode	O
(	O
ATM	O
)	O
modems	B-Application
.	O
</s>
<s>
They	O
use	O
ATM	B-Protocol
Adaptation	I-Protocol
Layer	I-Protocol
5	I-Protocol
(	O
AAL5	B-Protocol
)	O
to	O
segment	O
each	O
Ethernet	O
packet	O
into	O
a	O
series	O
of	O
53-byte	O
ATM	O
cells	O
for	O
transmission	O
,	O
reassembling	O
them	O
back	O
into	O
Ethernet	O
frames	O
at	O
the	O
receiving	O
end	O
.	O
</s>
<s>
If	O
this	O
is	O
the	O
bottleneck	O
link	O
,	O
this	O
latency	O
is	O
probably	O
small	O
enough	O
to	O
ensure	O
good	O
VoIP	B-Application
performance	O
without	O
MTU	B-Protocol
reductions	O
or	O
multiple	O
ATM	O
VCs	O
.	O
</s>
<s>
The	O
latest	O
generations	O
of	O
DSL	O
,	O
VDSL	O
and	O
VDSL2	O
,	O
carry	O
Ethernet	O
without	O
intermediate	O
ATM/AAL5	O
layers	O
,	O
and	O
they	O
generally	O
support	O
IEEE	O
802.1p	O
priority	O
tagging	O
so	O
that	O
VoIP	B-Application
can	O
be	O
queued	O
ahead	O
of	O
less	O
time-critical	O
traffic	O
.	O
</s>
<s>
Several	O
protocols	O
are	O
used	O
in	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
and	O
physical	B-Application
layer	I-Application
for	O
quality-of-service	O
mechanisms	O
that	O
help	O
VoIP	B-Application
applications	O
work	O
well	O
even	O
in	O
the	O
presence	O
of	O
network	B-Protocol
congestion	I-Protocol
.	O
</s>
<s>
IEEE	O
802.11e	O
is	O
an	O
approved	O
amendment	O
to	O
the	O
IEEE	O
802.11	O
standard	O
that	O
defines	O
a	O
set	O
of	O
quality-of-service	O
enhancements	O
for	O
wireless	O
LAN	B-General_Concept
applications	I-General_Concept
through	O
modifications	O
to	O
the	O
Media	B-Protocol
Access	I-Protocol
Control	I-Protocol
(	O
MAC	O
)	O
layer	O
.	O
</s>
<s>
IEEE	O
802.1p	O
defines	O
8	O
different	O
classes	O
of	O
service	O
(	O
including	O
one	O
dedicated	O
to	O
voice	O
)	O
for	O
traffic	O
on	O
layer-2	B-Protocol
wired	O
Ethernet	O
.	O
</s>
<s>
The	O
ITU-T	B-General_Concept
G.hn	I-General_Concept
standard	O
,	O
which	O
provides	O
a	O
way	O
to	O
create	O
a	O
high-speed	O
(	O
up	O
to	O
1	O
gigabit	O
per	O
second	O
)	O
Local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
using	O
existing	O
home	O
wiring	O
(	O
power	B-Device
lines	I-Device
,	O
phone	O
lines	O
and	O
coaxial	B-Protocol
cables	I-Protocol
)	O
.	O
</s>
<s>
G.hn	B-General_Concept
provides	O
QoS	O
by	O
means	O
of	O
Contention-Free	O
Transmission	O
Opportunities	O
(	O
CFTXOPs	O
)	O
which	O
are	O
allocated	O
to	O
flows	O
(	O
such	O
as	O
a	O
VoIP	B-Application
call	I-Application
)	O
that	O
require	O
QoS	O
and	O
which	O
have	O
negotiated	O
a	O
contract	O
with	O
the	O
network	O
controllers	O
.	O
</s>
<s>
Such	O
metrics	O
include	O
network	O
packet	B-Protocol
loss	I-Protocol
,	O
packet	B-Architecture
jitter	I-Architecture
,	O
packet	O
latency	O
(	O
delay	O
)	O
,	O
post-dial	O
delay	O
,	O
and	O
echo	O
.	O
</s>
<s>
The	O
metrics	O
are	O
determined	O
by	O
VoIP	B-Application
performance	O
testing	O
and	O
monitoring	O
.	O
</s>
<s>
A	O
VoIP	B-Application
media	O
gateway	O
controller	O
(	O
aka	O
Class	B-Device
5	I-Device
Softswitch	B-Device
)	O
works	O
in	O
cooperation	O
with	O
a	O
media	O
gateway	O
(	O
aka	O
IP	O
Business	O
Gateway	O
)	O
and	O
connects	O
the	O
digital	O
media	O
stream	O
,	O
so	O
as	O
to	O
complete	O
the	O
path	O
for	O
voice	O
and	O
data	O
.	O
</s>
<s>
Ethernet	O
interfaces	O
are	O
also	O
included	O
in	O
the	O
modern	O
systems	O
which	O
are	O
specially	O
designed	O
to	O
link	O
calls	O
that	O
are	O
passed	O
via	O
VoIP	B-Application
.	O
</s>
<s>
Most	O
VoIP	B-Application
implementations	O
support	O
E.164	O
to	O
allow	O
calls	O
to	O
be	O
routed	O
to	O
and	O
from	O
VoIP	B-Application
subscribers	O
and	O
the	O
PSTN/PLMN	O
.	O
</s>
<s>
VoIP	B-Application
implementations	O
can	O
also	O
allow	O
other	O
identification	O
techniques	O
to	O
be	O
used	O
.	O
</s>
<s>
For	O
example	O
,	O
Skype	B-Application
allows	O
subscribers	O
to	O
choose	O
Skype	B-Application
names	O
(	O
usernames	O
)	O
whereas	O
SIP	B-Application
implementations	O
can	O
use	O
Uniform	B-Protocol
Resource	I-Protocol
Identifier	I-Protocol
(	O
URIs	B-Protocol
)	O
similar	O
to	O
email	O
addresses	O
.	O
</s>
<s>
Often	O
VoIP	B-Application
implementations	O
employ	O
methods	O
of	O
translating	O
non-E.164	O
identifiers	O
to	O
E.164	O
numbers	O
and	O
vice	O
versa	O
,	O
such	O
as	O
the	O
Skype-In	O
service	O
provided	O
by	O
Skype	B-Application
and	O
the	O
E.164	O
number	O
to	O
URI	B-Protocol
mapping	O
(	O
ENUM	O
)	O
service	O
in	O
IMS	O
and	O
SIP	B-Application
.	O
</s>
<s>
Local	O
number	O
portability	O
(	O
LNP	O
)	O
and	O
mobile	O
number	O
portability	O
(	O
MNP	O
)	O
also	O
impact	O
VoIP	B-Application
business	O
.	O
</s>
<s>
In	O
November	O
2007	O
,	O
the	O
Federal	O
Communications	O
Commission	O
in	O
the	O
United	O
States	O
released	O
an	O
order	O
extending	O
number	O
portability	O
obligations	O
to	O
interconnected	O
VoIP	B-Application
providers	O
and	O
carriers	O
that	O
support	O
VoIP	B-Application
providers	O
.	O
</s>
<s>
A	O
voice	O
call	O
originating	O
in	O
the	O
VoIP	B-Application
environment	O
also	O
faces	O
least-cost	O
routing	O
(	O
LCR	O
)	O
challenges	O
to	O
reach	O
its	O
destination	O
if	O
the	O
number	O
is	O
routed	O
to	O
a	O
mobile	O
phone	O
number	O
on	O
a	O
traditional	O
mobile	O
carrier	O
.	O
</s>
<s>
Therefore	O
,	O
VoIP	B-Application
solutions	O
also	O
need	O
to	O
handle	O
MNP	O
when	O
routing	O
a	O
voice	O
call	O
.	O
</s>
<s>
As	O
the	O
popularity	O
of	O
VoIP	B-Application
increases	O
in	O
the	O
enterprise	O
markets	O
because	O
of	O
LCR	O
options	O
,	O
VoIP	B-Application
needs	O
to	O
provide	O
a	O
certain	O
level	O
of	O
reliability	O
when	O
handling	O
calls	O
.	O
</s>
<s>
A	O
telephone	O
connected	O
to	O
a	O
land	B-Application
line	I-Application
has	O
a	O
direct	O
relationship	O
between	O
a	O
telephone	O
number	O
and	O
a	O
physical	O
location	O
,	O
which	O
is	O
maintained	O
by	O
the	O
telephone	O
company	O
and	O
available	O
to	O
emergency	O
responders	O
via	O
the	O
national	O
emergency	O
response	O
service	O
centers	O
in	O
form	O
of	O
emergency	O
subscriber	O
lists	O
.	O
</s>
<s>
In	O
IP	B-Application
telephony	I-Application
,	O
no	O
such	O
direct	O
link	O
between	O
location	O
and	O
communications	O
end	O
point	O
exists	O
.	O
</s>
<s>
Even	O
a	O
provider	O
having	O
wired	O
infrastructure	O
,	O
such	O
as	O
a	O
DSL	O
provider	O
,	O
may	O
know	O
only	O
the	O
approximate	O
location	O
of	O
the	O
device	O
,	O
based	O
on	O
the	O
IP	B-Protocol
address	I-Protocol
allocated	O
to	O
the	O
network	B-Protocol
router	I-Protocol
and	O
the	O
known	O
service	O
address	O
.	O
</s>
<s>
Some	O
ISPs	O
do	O
not	O
track	O
the	O
automatic	O
assignment	O
of	O
IP	B-Protocol
addresses	I-Protocol
to	O
customer	O
equipment	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
residential	O
broadband	O
connection	O
may	O
be	O
used	O
as	O
a	O
link	O
to	O
a	O
virtual	B-Application
private	I-Application
network	I-Application
of	O
a	O
corporate	O
entity	O
,	O
in	O
which	O
case	O
the	O
IP	B-Protocol
address	I-Protocol
being	O
used	O
for	O
customer	O
communications	O
may	O
belong	O
to	O
the	O
enterprise	O
,	O
not	O
the	O
residential	O
ISP	O
.	O
</s>
<s>
On	O
mobile	O
devices	O
,	O
e.g.	O
,	O
a	O
3G	O
handset	O
or	O
USB	O
wireless	O
broadband	O
adapter	O
,	O
the	O
IP	B-Protocol
address	I-Protocol
has	O
no	O
relationship	O
with	O
any	O
physical	O
location	O
known	O
to	O
the	O
telephony	O
service	O
provider	O
,	O
since	O
a	O
mobile	O
user	O
could	O
be	O
anywhere	O
in	O
a	O
region	O
with	O
network	O
coverage	O
,	O
even	O
roaming	O
via	O
another	O
cellular	O
company	O
.	O
</s>
<s>
At	O
the	O
VoIP	B-Application
level	O
,	O
a	O
phone	O
or	O
gateway	O
may	O
identify	O
itself	O
by	O
its	O
account	O
credentials	O
with	O
a	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	B-Application
)	O
registrar	O
.	O
</s>
<s>
In	O
such	O
cases	O
,	O
the	O
Internet	B-Protocol
telephony	I-Protocol
service	I-Protocol
provider	I-Protocol
(	O
ITSP	B-Protocol
)	O
knows	O
only	O
that	O
a	O
particular	O
user	O
's	O
equipment	O
is	O
active	O
.	O
</s>
<s>
Such	O
emergency	O
services	O
are	O
provided	O
by	O
VoIP	B-Application
vendors	O
in	O
the	O
United	O
States	O
by	O
a	O
system	O
called	O
Enhanced	O
911	O
(	O
E911	O
)	O
,	O
based	O
on	O
the	O
Wireless	O
Communications	O
and	O
Public	O
Safety	O
Act	O
.	O
</s>
<s>
The	O
VoIP	B-Application
E911	O
emergency-calling	O
system	O
associates	O
a	O
physical	O
address	O
with	O
the	O
calling	O
party	O
's	O
telephone	O
number	O
.	O
</s>
<s>
All	O
VoIP	B-Application
providers	O
that	O
provide	O
access	O
to	O
the	O
public	O
switched	O
telephone	O
network	O
are	O
required	O
to	O
implement	O
E911	O
,	O
a	O
service	O
for	O
which	O
the	O
subscriber	O
may	O
be	O
charged	O
.	O
</s>
<s>
"	O
VoIP	B-Application
providers	O
may	O
not	O
allow	O
customers	O
to	O
opt-out	O
of	O
911	O
service.	O
"	O
</s>
<s>
The	O
VoIP	B-Application
E911	O
system	O
is	O
based	O
on	O
a	O
static	O
table	O
lookup	O
.	O
</s>
<s>
Unlike	O
in	O
cellular	O
phones	O
,	O
where	O
the	O
location	O
of	O
an	O
E911	O
call	O
can	O
be	O
traced	O
using	O
assisted	O
GPS	O
or	O
other	O
methods	O
,	O
the	O
VoIP	B-Application
E911	O
information	O
is	O
accurate	O
only	O
if	O
subscribers	O
keep	O
their	O
emergency	O
address	O
information	O
current	O
.	O
</s>
<s>
Sending	O
faxes	O
over	O
VoIP	B-Application
networks	O
is	O
sometimes	O
referred	O
to	O
as	O
Fax	O
over	O
IP	O
(	O
FoIP	B-Protocol
)	O
.	O
</s>
<s>
Transmission	O
of	O
fax	O
documents	O
was	O
problematic	O
in	O
early	O
VoIP	B-Application
implementations	O
,	O
as	O
most	O
voice	O
digitization	O
and	O
compression	O
codecs	B-General_Concept
are	O
optimized	O
for	O
the	O
representation	O
of	O
the	O
human	O
voice	O
and	O
the	O
proper	O
timing	O
of	O
the	O
modem	B-Application
signals	O
cannot	O
be	O
guaranteed	O
in	O
a	O
packet-based	O
,	O
connectionless	O
network	O
.	O
</s>
<s>
A	O
standards-based	O
solution	O
for	O
reliably	O
delivering	O
fax-over-IP	O
is	O
the	O
T.38	B-Protocol
protocol	O
.	O
</s>
<s>
The	O
T.38	B-Protocol
protocol	O
is	O
designed	O
to	O
compensate	O
for	O
the	O
differences	O
between	O
traditional	O
packet-less	O
communications	O
over	O
analog	O
lines	O
and	O
packet-based	O
transmissions	O
which	O
are	O
the	O
basis	O
for	O
IP	B-Protocol
communications	I-Protocol
.	O
</s>
<s>
The	O
fax	O
machine	O
may	O
be	O
a	O
standard	O
device	O
connected	O
to	O
an	O
analog	B-Protocol
telephone	I-Protocol
adapter	I-Protocol
(	O
ATA	O
)	O
,	O
or	O
it	O
may	O
be	O
a	O
software	O
application	O
or	O
dedicated	O
network	O
device	O
operating	O
via	O
an	O
Ethernet	O
interface	O
.	O
</s>
<s>
Originally	O
,	O
T.38	B-Protocol
was	O
designed	O
to	O
use	O
UDP	B-Protocol
or	O
TCP	B-Protocol
transmission	O
methods	O
across	O
an	O
IP	O
network	O
.	O
</s>
<s>
Some	O
newer	O
high-end	O
fax	O
machines	O
have	O
built-in	O
T.38	B-Protocol
capabilities	O
which	O
are	O
connected	O
directly	O
to	O
a	O
network	O
switch	O
or	O
router	B-Protocol
.	O
</s>
<s>
In	O
T.38	B-Protocol
each	O
packet	O
contains	O
a	O
portion	O
of	O
the	O
data	O
stream	O
sent	O
in	O
the	O
previous	O
packet	O
.	O
</s>
<s>
VoIP	B-Device
phones	I-Device
and	O
VoIP	B-Application
telephone	O
adapters	O
connect	O
to	O
routers	B-Protocol
or	O
cable	B-Device
modems	I-Device
which	O
typically	O
depend	O
on	O
the	O
availability	O
of	O
mains	O
electricity	O
or	O
locally	O
generated	O
power	O
.	O
</s>
<s>
Some	O
VoIP	B-Application
service	O
providers	O
use	O
customer	O
premises	O
equipment	O
(	O
e.g.	O
,	O
cable	B-Device
modems	I-Device
)	O
with	O
battery-backed	O
power	O
supplies	O
to	O
assure	O
uninterrupted	O
service	O
for	O
up	O
to	O
several	O
hours	O
in	O
case	O
of	O
local	O
power	O
failures	O
.	O
</s>
<s>
Some	O
VoIP	B-Application
service	O
providers	O
implement	O
services	O
to	O
route	O
calls	O
to	O
other	O
telephone	O
services	O
of	O
the	O
subscriber	O
,	O
such	O
a	O
cellular	O
phone	O
,	O
in	O
the	O
event	O
that	O
the	O
customer	O
's	O
network	O
device	O
is	O
inaccessible	O
to	O
terminate	O
the	O
call	O
.	O
</s>
<s>
Secure	O
calls	O
are	O
possible	O
using	O
standardized	O
protocols	O
such	O
as	O
Secure	B-Protocol
Real-time	I-Protocol
Transport	I-Protocol
Protocol	I-Protocol
.	O
</s>
<s>
Most	O
of	O
the	O
facilities	O
of	O
creating	O
a	O
secure	O
telephone	O
connection	O
over	O
traditional	O
phone	O
lines	O
,	O
such	O
as	O
digitizing	O
and	O
digital	O
transmission	O
,	O
are	O
already	O
in	O
place	O
with	O
VoIP	B-Application
.	O
</s>
<s>
The	O
security	O
concerns	O
for	O
VoIP	B-Application
telephone	O
systems	O
are	O
similar	O
to	O
those	O
of	O
other	O
Internet-connected	O
devices	O
.	O
</s>
<s>
This	O
means	O
that	O
hackers	B-Application
with	O
knowledge	O
of	O
VoIP	B-Application
vulnerabilities	O
can	O
perform	O
denial-of-service	O
attacks	O
,	O
harvest	O
customer	O
data	O
,	O
record	O
conversations	O
,	O
and	O
compromise	O
voicemail	O
messages	O
.	O
</s>
<s>
Compromised	O
VoIP	B-Application
user	O
account	O
or	O
session	B-Protocol
credentials	O
may	O
enable	O
an	O
attacker	O
to	O
incur	O
substantial	O
charges	O
from	O
third-party	O
services	O
,	O
such	O
as	O
long-distance	O
or	O
international	O
calling	O
.	O
</s>
<s>
The	O
technical	O
details	O
of	O
many	O
VoIP	B-Application
protocols	O
create	O
challenges	O
in	O
routing	O
VoIP	B-Application
traffic	O
through	O
firewalls	B-Application
and	O
network	B-Protocol
address	I-Protocol
translators	I-Protocol
,	O
used	O
to	O
interconnect	B-Architecture
to	O
transit	O
networks	O
or	O
the	O
Internet	O
.	O
</s>
<s>
Private	O
session	B-Protocol
border	I-Protocol
controllers	I-Protocol
are	O
often	O
employed	O
to	O
enable	O
VoIP	B-Application
calls	I-Application
to	O
and	O
from	O
protected	O
networks	O
.	O
</s>
<s>
Other	O
methods	O
to	O
traverse	B-Protocol
NAT	I-Protocol
devices	O
involve	O
assistive	O
protocols	O
such	O
as	O
STUN	B-Protocol
and	O
Interactive	O
Connectivity	O
Establishment	O
(	O
ICE	O
)	O
.	O
</s>
<s>
Standards	O
for	O
securing	O
VoIP	B-Application
are	O
available	O
in	O
the	O
Secure	B-Protocol
Real-time	I-Protocol
Transport	I-Protocol
Protocol	I-Protocol
(	O
SRTP	B-Protocol
)	O
and	O
the	O
ZRTP	B-Protocol
protocol	O
for	O
analog	B-Protocol
telephony	I-Protocol
adapters	I-Protocol
,	O
as	O
well	O
as	O
for	O
some	O
softphones	B-Protocol
.	O
</s>
<s>
IPsec	B-Protocol
is	O
available	O
to	O
secure	O
point-to-point	B-Architecture
VoIP	B-Application
at	O
the	O
transport	O
level	O
by	O
using	O
opportunistic	B-Protocol
encryption	I-Protocol
.	O
</s>
<s>
Though	O
many	O
consumer	O
VoIP	B-Application
solutions	O
do	O
not	O
support	O
encryption	O
of	O
the	O
signaling	O
path	O
or	O
the	O
media	O
,	O
securing	O
a	O
VoIP	B-Device
phone	I-Device
is	O
conceptually	O
easier	O
to	O
implement	O
using	O
VoIP	B-Application
than	O
on	O
traditional	O
telephone	O
circuits	O
.	O
</s>
<s>
A	O
result	O
of	O
the	O
lack	O
of	O
widespread	O
support	O
for	O
encryption	O
is	O
that	O
it	O
is	O
relatively	O
easy	O
to	O
eavesdrop	O
on	O
VoIP	B-Application
calls	I-Application
when	O
access	O
to	O
the	O
data	O
network	O
is	O
possible	O
.	O
</s>
<s>
Free	O
open-source	B-Application
solutions	O
,	O
such	O
as	O
Wireshark	B-Language
,	O
facilitate	O
capturing	O
VoIP	B-Application
conversations	O
.	O
</s>
<s>
Government	O
and	O
military	O
organizations	O
use	O
various	O
security	O
measures	O
to	O
protect	O
VoIP	B-Application
traffic	O
,	O
such	O
as	O
voice	O
over	O
secure	O
IP	O
(	O
VoSIP	O
)	O
,	O
secure	O
voice	B-Application
over	I-Application
IP	I-Application
(	O
SVoIP	B-Application
)	O
,	O
and	O
secure	O
voice	O
over	O
secure	O
IP	O
(	O
SVoSIP	O
)	O
.	O
</s>
<s>
Secure	O
voice	O
over	O
secure	O
IP	O
may	O
be	O
implemented	O
by	O
encrypting	O
the	O
media	O
with	O
protocols	O
such	O
as	O
SRTP	B-Protocol
and	O
ZRTP	B-Protocol
.	O
</s>
<s>
Secure	O
voice	B-Application
over	I-Application
IP	I-Application
uses	O
Type	O
1	O
encryption	O
on	O
a	O
classified	O
network	O
,	O
such	O
as	O
SIPRNet	O
.	O
</s>
<s>
Public	O
Secure	O
VoIP	B-Application
is	O
also	O
available	O
with	O
free	O
GNU	O
software	O
and	O
in	O
many	O
popular	O
commercial	O
VoIP	B-Application
programs	O
via	O
libraries	O
,	O
such	O
as	O
ZRTP	B-Protocol
.	O
</s>
<s>
In	O
June	O
2021	O
,	O
the	O
National	O
Security	O
Agency	O
(	O
NSA	O
)	O
released	O
comprehensive	O
documents	O
describing	O
the	O
four	O
attack	O
planes	O
of	O
a	O
communications	O
system	O
–	O
the	O
network	O
,	O
perimeter	O
,	O
session	B-Protocol
controllers	O
and	O
endpoints	B-Protocol
–	O
and	O
explaining	O
security	O
risks	O
and	O
mitigation	O
techniques	O
for	O
each	O
of	O
them	O
.	O
</s>
<s>
Voice	B-Application
over	I-Application
IP	I-Application
protocols	O
and	O
equipment	O
provide	O
caller	O
ID	O
support	O
that	O
is	O
compatible	O
with	O
the	O
PSTN	O
.	O
</s>
<s>
Many	O
VoIP	B-Application
service	O
providers	O
also	O
allow	O
callers	O
to	O
configure	O
custom	O
caller	O
ID	O
information	O
.	O
</s>
<s>
Wireline	O
telephones	O
which	O
are	O
manufactured	O
in	O
,	O
imported	O
to	O
,	O
or	O
intended	O
to	O
be	O
used	O
in	O
the	O
US	O
with	O
Voice	B-Application
over	I-Application
IP	I-Application
service	O
,	O
on	O
or	O
after	O
February	O
28	O
,	O
2020	O
,	O
are	O
required	O
to	O
meet	O
the	O
hearing	O
aid	O
compatibility	O
requirements	O
set	O
forth	O
by	O
the	O
Federal	O
Communications	O
Commission	O
.	O
</s>
<s>
VoIP	B-Application
has	O
drastically	O
reduced	O
the	O
cost	O
of	O
communication	O
by	O
sharing	O
network	O
infrastructure	O
between	O
data	O
and	O
voice	O
.	O
</s>
<s>
As	O
the	O
popularity	O
of	O
VoIP	B-Application
grows	O
,	O
governments	O
are	O
becoming	O
more	O
interested	O
in	O
regulating	O
VoIP	B-Application
in	O
a	O
manner	O
similar	O
to	O
PSTN	O
services	O
.	O
</s>
<s>
Throughout	O
the	O
developing	O
world	O
,	O
particularly	O
in	O
countries	O
where	O
regulation	O
is	O
weak	O
or	O
captured	O
by	O
the	O
dominant	O
operator	O
,	O
restrictions	O
on	O
the	O
use	O
of	O
VoIP	B-Application
are	O
often	O
imposed	O
,	O
including	O
in	O
Panama	B-Algorithm
where	O
VoIP	B-Application
is	O
taxed	O
,	O
Guyana	O
where	O
VoIP	B-Application
is	O
prohibited	O
.	O
</s>
<s>
In	O
Ethiopia	O
,	O
where	O
the	O
government	O
is	O
nationalizing	O
telecommunication	O
service	O
,	O
it	O
is	O
a	O
criminal	O
offense	O
to	O
offer	O
services	O
using	O
VoIP	B-Application
.	O
</s>
<s>
The	O
country	O
has	O
installed	O
firewalls	B-Application
to	O
prevent	O
international	O
calls	O
from	O
being	O
made	O
using	O
VoIP	B-Application
.	O
</s>
<s>
These	O
measures	O
were	O
taken	O
after	O
the	O
popularity	O
of	O
VoIP	B-Application
reduced	O
the	O
income	O
generated	O
by	O
the	O
state-owned	O
telecommunication	O
company	O
.	O
</s>
<s>
In	O
Canada	O
,	O
the	O
Canadian	O
Radio-television	O
and	O
Telecommunications	O
Commission	O
regulates	O
telephone	O
service	O
,	O
including	O
VoIP	B-Application
telephony	I-Application
service	O
.	O
</s>
<s>
VoIP	B-Application
services	O
operating	O
in	O
Canada	O
are	O
required	O
to	O
provide	O
9-1-1	O
emergency	O
service	O
.	O
</s>
<s>
In	O
the	O
European	O
Union	O
,	O
the	O
treatment	O
of	O
VoIP	B-Application
service	O
providers	O
is	O
a	O
decision	O
for	O
each	O
national	O
telecommunications	O
regulator	O
,	O
which	O
must	O
use	O
competition	O
law	O
to	O
define	O
relevant	O
national	O
markets	O
and	O
then	O
determine	O
whether	O
any	O
service	O
provider	O
on	O
those	O
national	O
markets	O
has	O
"	O
significant	O
market	O
power	O
"	O
(	O
and	O
so	O
should	O
be	O
subject	O
to	O
certain	O
obligations	O
)	O
.	O
</s>
<s>
A	O
general	O
distinction	O
is	O
usually	O
made	O
between	O
VoIP	B-Application
services	O
that	O
function	O
over	O
managed	O
networks	O
(	O
via	O
broadband	O
connections	O
)	O
and	O
VoIP	B-Application
services	O
that	O
function	O
over	O
unmanaged	O
networks	O
(	O
essentially	O
,	O
the	O
Internet	O
)	O
.	O
</s>
<s>
The	O
relevant	O
EU	O
Directive	O
is	O
not	O
clearly	O
drafted	O
concerning	O
obligations	O
that	O
can	O
exist	O
independently	O
of	O
market	O
power	O
(	O
e.g.	O
,	O
the	O
obligation	O
to	O
offer	O
access	O
to	O
emergency	O
calls	O
)	O
,	O
and	O
it	O
is	O
impossible	O
to	O
say	O
definitively	O
whether	O
VoIP	B-Application
service	O
providers	O
of	O
either	O
type	O
are	O
bound	O
by	O
them	O
.	O
</s>
<s>
In	O
Oman	O
,	O
it	O
is	O
illegal	O
to	O
provide	O
or	O
use	O
unauthorized	O
VoIP	B-Application
services	O
,	O
to	O
the	O
extent	O
that	O
web	O
sites	O
of	O
unlicensed	O
VoIP	B-Application
providers	O
have	O
been	O
blocked	O
.	O
</s>
<s>
In	O
2009	O
,	O
police	O
raided	O
121	O
Internet	O
cafes	O
throughout	O
the	O
country	O
and	O
arrested	O
212	O
people	O
for	O
using	O
or	O
providing	O
VoIP	B-Application
services	O
.	O
</s>
<s>
In	O
September	O
2017	O
,	O
Saudi	O
Arabia	O
lifted	O
the	O
ban	O
on	O
VoIPs	B-Application
,	O
in	O
an	O
attempt	O
to	O
reduce	O
operational	O
costs	O
and	O
spur	O
digital	O
entrepreneurship	O
.	O
</s>
<s>
In	O
the	O
United	O
Arab	O
Emirates	O
(	O
UAE	O
)	O
,	O
it	O
is	O
illegal	O
to	O
provide	O
or	O
use	O
unauthorized	O
VoIP	B-Application
services	O
.	O
</s>
<s>
Web	O
sites	O
of	O
unlicensed	O
VoIP	B-Application
providers	O
have	O
been	O
blocked	O
.	O
</s>
<s>
Some	O
VoIP	B-Application
services	O
such	O
as	O
Skype	B-Application
were	O
allowed	O
.	O
</s>
<s>
In	O
January	O
2018	O
,	O
internet	O
service	O
providers	O
in	O
UAE	O
blocked	O
all	O
VoIP	B-Application
apps	O
,	O
including	O
Skype	B-Application
,	O
but	O
permitting	O
only	O
2	O
government-approved	O
VoIP	B-Application
apps	O
(	O
C’ME	O
and	O
BOTIM	O
)	O
.	O
</s>
<s>
On	O
March	O
24	O
,	O
2020	O
,	O
the	O
United	O
Arab	O
Emirates	O
loosened	O
restriction	O
on	O
VoIP	B-Application
services	O
earlier	O
prohibited	O
in	O
the	O
country	O
,	O
to	O
ease	O
communication	O
during	O
the	O
COVID-19	O
pandemic	O
.	O
</s>
<s>
However	O
,	O
popular	O
instant	O
messaging	O
applications	O
like	O
WhatsApp	B-Application
,	O
Skype	B-Application
,	O
and	O
FaceTime	B-Operating_System
remained	O
blocked	O
from	O
being	O
used	O
for	O
voice	O
and	O
video	O
calls	O
,	O
constricting	O
residents	O
to	O
use	O
paid	O
services	O
from	O
the	O
country	O
's	O
state-owned	O
telecom	O
providers	O
.	O
</s>
<s>
In	O
India	O
,	O
it	O
is	O
legal	O
to	O
use	O
VoIP	B-Application
,	O
but	O
it	O
is	O
illegal	O
to	O
have	O
VoIP	B-Protocol
gateways	I-Protocol
inside	O
India	O
.	O
</s>
<s>
This	O
effectively	O
means	O
that	O
people	O
who	O
have	O
PCs	B-Device
can	O
use	O
them	O
to	O
make	O
a	O
VoIP	B-Application
call	I-Application
to	O
other	O
computers	O
but	O
not	O
to	O
a	O
normal	O
phone	O
number	O
.	O
</s>
<s>
Foreign-based	O
VoIP	B-Application
server	O
services	O
are	O
illegal	O
to	O
use	O
in	O
India	O
.	O
</s>
<s>
Internet	B-Application
telephony	I-Application
is	O
permitted	O
to	O
the	O
ISP	O
with	O
restrictions	O
.	O
</s>
<s>
connected	O
to	O
ISP	O
node	O
with	O
static	O
IP	B-Protocol
address	I-Protocol
to	O
similar	O
device	O
/	O
Adapter	O
;	O
within	O
or	O
outside	O
India	O
.	O
</s>
<s>
Except	O
whatever	O
is	O
described	O
in	O
,	O
no	O
other	O
form	O
of	O
Internet	B-Application
Telephony	I-Application
is	O
permitted	O
.	O
</s>
<s>
In	O
India	O
no	O
Separate	O
Numbering	O
Scheme	O
is	O
provided	O
to	O
the	O
Internet	B-Application
Telephony	I-Application
.	O
</s>
<s>
Presently	O
the	O
10	O
digit	O
Numbering	O
allocation	O
based	O
on	O
E.164	O
is	O
permitted	O
to	O
the	O
Fixed	B-Application
Telephony	I-Application
,	O
GSM	O
,	O
CDMA	O
wireless	O
service	O
.	O
</s>
<s>
For	O
Internet	B-Application
Telephony	I-Application
,	O
the	O
numbering	O
scheme	O
shall	O
only	O
conform	O
to	O
IP	B-Protocol
addressing	I-Protocol
Scheme	O
of	O
Internet	O
Assigned	O
Numbers	O
Authority	O
(	O
IANA	O
)	O
.	O
</s>
<s>
Translation	O
of	O
E.164	O
number	O
/	O
private	O
number	O
to	O
IP	B-Protocol
address	I-Protocol
allotted	O
to	O
any	O
device	O
and	O
vice	O
versa	O
,	O
by	O
ISP	O
to	O
show	O
compliance	O
with	O
IANA	O
numbering	O
scheme	O
is	O
not	O
permitted	O
.	O
</s>
<s>
In	O
South	O
Korea	O
,	O
only	O
providers	O
registered	O
with	O
the	O
government	O
are	O
authorized	O
to	O
offer	O
VoIP	B-Application
services	O
.	O
</s>
<s>
Unlike	O
many	O
VoIP	B-Application
providers	O
,	O
most	O
of	O
whom	O
offer	O
flat	O
rates	O
,	O
Korean	O
VoIP	B-Application
services	O
are	O
generally	O
metered	O
and	O
charged	O
at	O
rates	O
similar	O
to	O
terrestrial	O
calling	O
.	O
</s>
<s>
Foreign	O
VoIP	B-Application
providers	O
encounter	O
high	O
barriers	O
to	O
government	O
registration	O
.	O
</s>
<s>
This	O
issue	O
came	O
to	O
a	O
head	O
in	O
2006	O
when	O
Internet	O
service	O
providers	O
providing	O
personal	O
Internet	O
services	O
by	O
contract	O
to	O
United	O
States	O
Forces	O
Korea	O
(	O
USFK	O
)	O
members	O
residing	O
on	O
USFK	O
bases	O
threatened	O
to	O
block	O
off	O
access	O
to	O
VoIP	B-Application
services	O
used	O
by	O
USFK	O
members	O
as	O
an	O
economical	O
way	O
to	O
keep	O
in	O
contact	O
with	O
their	O
families	O
in	O
the	O
United	O
States	O
,	O
on	O
the	O
grounds	O
that	O
the	O
service	O
members	O
 '	O
VoIP	B-Application
providers	O
were	O
not	O
registered	O
.	O
</s>
<s>
A	O
compromise	O
was	O
reached	O
between	O
USFK	O
and	O
Korean	O
telecommunications	O
officials	O
in	O
January	O
2007	O
,	O
wherein	O
USFK	O
service	O
members	O
arriving	O
in	O
Korea	O
before	O
June	O
1	O
,	O
2007	O
,	O
and	O
subscribing	O
to	O
the	O
ISP	O
services	O
provided	O
on	O
base	O
could	O
continue	O
to	O
use	O
their	O
US-based	O
VoIP	B-Application
subscription	O
,	O
but	O
later	O
arrivals	O
are	O
required	O
to	O
use	O
a	O
Korean-based	O
VoIP	B-Application
provider	O
,	O
which	O
by	O
contract	O
will	O
offer	O
pricing	O
similar	O
to	O
the	O
flat	O
rates	O
offered	O
by	O
US	O
VoIP	B-Application
providers	O
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
the	O
Federal	O
Communications	O
Commission	O
requires	O
all	O
interconnected	O
VoIP	B-Application
service	O
providers	O
to	O
comply	O
with	O
requirements	O
comparable	O
to	O
those	O
for	O
traditional	O
telecommunications	O
service	O
providers	O
.	O
</s>
<s>
VoIP	B-Application
operators	O
in	O
the	O
US	O
are	O
required	O
to	O
support	O
local	O
number	O
portability	O
;	O
make	O
service	O
accessible	O
to	O
people	O
with	O
disabilities	O
;	O
pay	O
regulatory	O
fees	O
,	O
universal	O
service	O
contributions	O
,	O
and	O
other	O
mandated	O
payments	O
;	O
and	O
enable	O
law	O
enforcement	O
authorities	O
to	O
conduct	O
surveillance	O
pursuant	O
to	O
the	O
Communications	O
Assistance	O
for	O
Law	O
Enforcement	O
Act	O
(	O
CALEA	O
)	O
.	O
</s>
<s>
Operators	O
of	O
Interconnected	O
VoIP	B-Application
(	O
fully	O
connected	O
to	O
the	O
PSTN	O
)	O
are	O
mandated	O
to	O
provide	O
Enhanced	O
911	O
service	O
without	O
special	O
request	O
,	O
provide	O
for	O
customer	O
location	O
updates	O
,	O
clearly	O
disclose	O
any	O
limitations	O
on	O
their	O
E-911	O
functionality	O
to	O
their	O
consumers	O
,	O
obtain	O
affirmative	O
acknowledgements	O
of	O
these	O
disclosures	O
from	O
all	O
consumers	O
,	O
and	O
may	O
not	O
allow	O
their	O
customers	O
to	O
opt-out	O
of	O
911	O
service	O
.	O
</s>
<s>
VoIP	B-Application
operators	O
also	O
receive	O
the	O
benefit	O
of	O
certain	O
US	O
telecommunications	O
regulations	O
,	O
including	O
an	O
entitlement	O
to	O
interconnection	B-Architecture
and	O
exchange	O
of	O
traffic	O
with	O
incumbent	O
local	O
exchange	O
carriers	O
via	O
wholesale	O
carriers	O
.	O
</s>
<s>
Providers	O
of	O
nomadic	O
VoIP	B-Application
service	O
—	O
those	O
who	O
are	O
unable	O
to	O
determine	O
the	O
location	O
of	O
their	O
users	O
—	O
are	O
exempt	O
from	O
state	O
telecommunications	O
regulation	O
.	O
</s>
<s>
The	O
NSA	O
is	O
not	O
authorized	O
to	O
tap	O
Americans	O
 '	O
conversations	O
without	O
a	O
warrant	O
—	O
but	O
the	O
Internet	O
,	O
and	O
specifically	O
VoIP	B-Application
does	O
not	O
draw	O
as	O
clear	O
a	O
line	O
to	O
the	O
location	O
of	O
a	O
caller	O
or	O
a	O
call	O
's	O
recipient	O
as	O
the	O
traditional	O
phone	O
system	O
does	O
.	O
</s>
<s>
As	O
VoIP	B-Application
's	O
low	O
cost	O
and	O
flexibility	O
convinces	O
more	O
and	O
more	O
organizations	O
to	O
adopt	O
the	O
technology	O
,	O
surveillance	O
for	O
law	O
enforcement	O
agencies	O
becomes	O
more	O
difficult	O
.	O
</s>
<s>
VoIP	B-Application
technology	O
has	O
also	O
increased	O
federal	O
security	O
concerns	O
because	O
VoIP	B-Application
and	O
similar	O
technologies	O
have	O
made	O
it	O
more	O
difficult	O
for	O
the	O
government	O
to	O
determine	O
where	O
a	O
target	O
is	O
physically	O
located	O
when	O
communications	O
are	O
being	O
intercepted	O
,	O
and	O
that	O
creates	O
a	O
whole	O
set	O
of	O
new	O
legal	O
challenges	O
.	O
</s>
<s>
The	O
early	O
developments	O
of	O
packet	B-Protocol
network	I-Protocol
designs	O
by	O
Paul	O
Baran	O
and	O
other	O
researchers	O
were	O
motivated	O
by	O
a	O
desire	O
for	O
a	O
higher	O
degree	O
of	O
circuit	O
redundancy	O
and	O
network	O
availability	O
in	O
the	O
face	O
of	O
infrastructure	O
failures	O
than	O
was	O
possible	O
in	O
the	O
circuit-switched	B-Protocol
networks	I-Protocol
in	O
telecommunications	O
of	O
the	O
mid-twentieth	O
century	O
.	O
</s>
<s>
Danny	O
Cohen	O
first	O
demonstrated	O
a	O
form	O
of	O
packet	B-Application
voice	I-Application
in	O
1973	O
which	O
was	O
developed	O
into	O
Network	B-Protocol
Voice	I-Protocol
Protocol	I-Protocol
which	O
operated	O
across	O
the	O
early	O
ARPANET	O
.	O
</s>
<s>
On	O
the	O
early	O
ARPANET	O
,	O
real-time	O
voice	O
communication	O
was	O
not	O
possible	O
with	O
uncompressed	B-General_Concept
pulse-code	B-Algorithm
modulation	I-Algorithm
(	O
PCM	B-Algorithm
)	O
digital	O
speech	O
packets	O
,	O
which	O
had	O
a	O
bit	O
rate	O
of	O
64kbps	O
,	O
much	O
greater	O
than	O
the	O
2.4kbps	O
bandwidth	O
of	O
early	O
modems	B-Application
.	O
</s>
<s>
The	O
solution	O
to	O
this	O
problem	O
was	O
linear	B-Algorithm
predictive	I-Algorithm
coding	I-Algorithm
(	O
LPC	O
)	O
,	O
a	O
speech	B-Application
coding	I-Application
data	B-General_Concept
compression	I-General_Concept
algorithm	I-General_Concept
that	O
was	O
first	O
proposed	O
by	O
Fumitada	O
Itakura	O
of	O
Nagoya	O
University	O
and	O
Shuzo	O
Saito	O
of	O
Nippon	O
Telegraph	O
and	O
Telephone	O
(	O
NTT	O
)	O
in	O
1966	O
.	O
</s>
<s>
LPC	O
has	O
since	O
been	O
the	O
most	O
widely	O
used	O
speech	B-Application
coding	I-Application
method	O
.	O
</s>
<s>
Code-excited	B-Algorithm
linear	I-Algorithm
prediction	I-Algorithm
(	O
CELP	B-Algorithm
)	O
,	O
a	O
type	O
of	O
LPC	O
algorithm	O
,	O
was	O
developed	O
by	O
Manfred	O
R	O
.	O
Schroeder	O
and	O
Bishnu	O
S	O
.	O
Atal	O
in	O
1985	O
.	O
</s>
<s>
LPC	O
algorithms	O
remain	O
an	O
audio	O
coding	O
standard	O
in	O
modern	O
VoIP	B-Application
technology	O
.	O
</s>
<s>
Following	O
the	O
termination	O
of	O
the	O
ARPANET	O
project	O
,	O
and	O
expansion	O
of	O
the	O
Internet	O
for	O
commercial	O
traffic	O
,	O
IP	B-Application
telephony	I-Application
was	O
tested	O
and	O
deemed	O
infeasible	O
for	O
commercial	O
use	O
until	O
the	O
introduction	O
of	O
VocalChat	O
in	O
the	O
early	O
1990s	O
and	O
then	O
in	O
Feb	O
1995	O
the	O
official	O
release	O
of	O
Internet	B-Application
Phone	I-Application
(	O
or	O
iPhone	O
for	O
short	O
)	O
commercial	O
software	O
by	O
VocalTec	O
,	O
based	O
on	O
the	O
patent	O
by	O
Lior	O
Haramaty	O
and	O
Alon	O
Cohen	O
,	O
and	O
followed	O
by	O
other	O
VoIP	B-Application
infrastructure	O
components	O
such	O
as	O
telephony	O
gateways	O
and	O
switching	O
servers	O
.	O
</s>
<s>
By	O
the	O
late	O
1990s	O
,	O
the	O
first	O
softswitches	B-Device
became	O
available	O
,	O
and	O
new	O
protocols	O
,	O
such	O
as	O
H.323	B-Protocol
,	O
MGCP	O
and	O
the	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	B-Application
)	O
gained	O
widespread	O
attention	O
.	O
</s>
<s>
In	O
the	O
early	O
2000s	O
,	O
the	O
proliferation	O
of	O
high-bandwidth	O
always-on	O
Internet	O
connections	O
to	O
residential	O
dwellings	O
and	O
businesses	O
,	O
spawned	O
an	O
industry	O
of	O
Internet	B-Protocol
telephony	I-Protocol
service	I-Protocol
providers	I-Protocol
(	O
ITSPs	B-Protocol
)	O
.	O
</s>
<s>
The	O
development	O
of	O
open-source	B-Application
telephony	O
software	O
,	O
such	O
as	O
Asterisk	B-Language
PBX	I-Language
,	O
fueled	O
widespread	O
interest	O
and	O
entrepreneurship	O
in	O
voice-over-IP	B-Application
services	O
,	O
applying	O
new	O
Internet	O
technology	O
paradigms	O
,	O
such	O
as	O
cloud	B-Architecture
services	I-Architecture
to	O
telephony	O
.	O
</s>
<s>
In	O
1999	O
,	O
a	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
audio	O
data	B-General_Concept
compression	I-General_Concept
algorithm	I-General_Concept
called	O
the	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
was	O
adopted	O
for	O
the	O
Siren	B-Algorithm
codec	I-Algorithm
,	O
used	O
in	O
the	O
G.722.1	B-Algorithm
wideband	B-Algorithm
audio	I-Algorithm
coding	O
standard	O
.	O
</s>
<s>
The	O
same	O
year	O
,	O
the	O
MDCT	O
was	O
adapted	O
into	O
the	O
LD-MDCT	O
speech	B-Application
coding	I-Application
algorithm	O
,	O
used	O
for	O
the	O
AAC-LD	B-Algorithm
format	O
and	O
intended	O
for	O
significantly	O
improved	O
audio	O
quality	O
in	O
VoIP	B-Application
applications	O
.	O
</s>
<s>
MDCT	O
has	O
since	O
been	O
widely	O
used	O
in	O
VoIP	B-Application
applications	O
,	O
such	O
as	O
the	O
G.729.1	B-Algorithm
wideband	O
codec	B-General_Concept
introduced	O
in	O
2006	O
,	O
Apple	O
's	O
FaceTime	B-Operating_System
(	O
using	O
AAC-LD	B-Algorithm
)	O
introduced	O
in	O
2010	O
,	O
the	O
CELT	B-Algorithm
codec	B-General_Concept
introduced	O
in	O
2011	O
,	O
the	O
Opus	B-Algorithm
codec	I-Algorithm
introduced	O
in	O
2012	O
,	O
and	O
WhatsApp	B-Application
's	O
voice	O
calling	O
feature	O
introduced	O
in	O
2015	O
.	O
</s>
<s>
1966	O
:	O
Linear	B-Algorithm
predictive	I-Algorithm
coding	I-Algorithm
(	O
LPC	O
)	O
proposed	O
by	O
Fumitada	O
Itakura	O
of	O
Nagoya	O
University	O
and	O
Shuzo	O
Saito	O
of	O
Nippon	O
Telegraph	O
and	O
Telephone	O
(	O
NTT	O
)	O
.	O
</s>
<s>
1973	O
:	O
Packet	B-Application
voice	I-Application
application	O
by	O
Danny	O
Cohen	O
.	O
</s>
<s>
1974	O
:	O
The	O
Institute	O
of	O
Electrical	O
and	O
Electronics	O
Engineers	O
(	O
IEEE	O
)	O
publishes	O
a	O
paper	O
entitled	O
"	O
A	O
Protocol	O
for	O
Packet	B-Protocol
Network	I-Protocol
Interconnection	B-Architecture
"	O
.	O
</s>
<s>
1974	O
:	O
Network	B-Protocol
Voice	I-Protocol
Protocol	I-Protocol
(	O
NVP	B-Protocol
)	O
tested	O
over	O
ARPANET	O
in	O
August	O
1974	O
,	O
carrying	O
barely	O
audible	O
16kpbs	O
CVSD	B-Algorithm
encoded	O
voice	O
.	O
</s>
<s>
1977	O
:	O
Danny	O
Cohen	O
and	O
Jon	O
Postel	O
of	O
the	O
USC	O
Information	O
Sciences	O
Institute	O
,	O
and	O
Vint	O
Cerf	O
of	O
the	O
Defense	O
Advanced	O
Research	O
Projects	O
Agency	O
(	O
DARPA	O
)	O
,	O
agree	O
to	O
separate	O
IP	O
from	O
TCP	B-Protocol
,	O
and	O
create	O
UDP	B-Protocol
for	O
carrying	O
real-time	O
traffic	O
.	O
</s>
<s>
1981	O
:	O
IPv4	B-Protocol
is	O
described	O
in	O
RFC	O
791	O
.	O
</s>
<s>
1985	O
:	O
Code-excited	B-Algorithm
linear	I-Algorithm
prediction	I-Algorithm
(	O
CELP	B-Algorithm
)	O
,	O
a	O
type	O
of	O
LPC	O
algorithm	O
,	O
developed	O
by	O
Manfred	O
R	O
.	O
Schroeder	O
and	O
Bishnu	O
S	O
.	O
Atal	O
.	O
</s>
<s>
1991	O
:	O
Speak	O
Freely	O
,	O
a	O
voice-over-IP	B-Application
application	O
,	O
was	O
released	O
to	O
the	O
public	O
domain	O
.	O
</s>
<s>
1992	O
:	O
InSoft	B-Protocol
Inc	I-Protocol
.	I-Protocol
announces	O
and	O
launches	O
its	O
desktop	O
conferencing	O
product	O
Communique	O
,	O
which	O
included	O
VoIP	B-Application
and	O
video	O
.	O
</s>
<s>
The	O
company	O
is	O
credited	O
with	O
developing	O
the	O
first	O
generation	O
of	O
commercial	O
,	O
US-based	O
VoIP	B-Application
,	O
Internet	O
media	O
streaming	O
and	O
real-time	O
Internet	O
telephony/collaborative	O
software	O
and	O
standards	O
that	O
would	O
provide	O
the	O
basis	O
for	O
the	O
Real	O
Time	O
Streaming	O
Protocol	O
(	O
RTSP	O
)	O
standard	O
.	O
</s>
<s>
1993	O
Release	O
of	O
VocalChat	O
,	O
a	O
commercial	O
packet	B-Protocol
network	I-Protocol
PC	O
voice	O
communication	O
software	O
from	O
VocalTec	O
.	O
</s>
<s>
1995	O
:	O
VocalTec	O
releases	O
Internet	B-Application
Phone	I-Application
commercial	O
Internet	B-Application
phone	I-Application
software	O
.	O
</s>
<s>
Beginning	O
in	O
1995	O
,	O
Intel	O
,	O
Microsoft	O
and	O
Radvision	B-Protocol
initiated	O
standardization	O
activities	O
for	O
VoIP	B-Application
communications	O
system	O
.	O
</s>
<s>
ITU-T	O
begins	O
development	O
of	O
standards	O
for	O
the	O
transmission	O
and	O
signaling	O
of	O
voice	O
communications	O
over	O
Internet	B-Protocol
Protocol	I-Protocol
networks	O
with	O
the	O
H.323	B-Protocol
standard	O
.	O
</s>
<s>
US	O
telecommunication	O
companies	O
petition	O
the	O
US	O
Congress	O
to	O
ban	O
Internet	B-Application
phone	I-Application
technology	O
.	O
</s>
<s>
G.729	B-Algorithm
speech	B-Application
codec	I-Application
introduced	O
,	O
using	O
CELP	B-Algorithm
(	O
LPC	O
)	O
algorithm	O
.	O
</s>
<s>
1997	O
:	O
Level	O
3	O
began	O
development	O
of	O
its	O
first	O
softswitch	B-Device
,	O
a	O
term	O
they	O
coined	O
in	O
1998	O
.	O
</s>
<s>
The	O
Session	B-Application
Initiation	I-Application
Protocol	I-Application
(	O
SIP	B-Application
)	O
specification	O
RFC	O
2543	O
is	O
released	O
.	O
</s>
<s>
Mark	O
Spencer	O
of	O
Digium	B-Protocol
develops	O
the	O
first	O
open	B-Application
source	I-Application
private	B-Device
branch	I-Device
exchange	I-Device
(	O
PBX	O
)	O
software	O
(	O
Asterisk	B-Language
)	O
.	O
</s>
<s>
A	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
variant	O
called	O
the	O
modified	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
MDCT	O
)	O
is	O
adopted	O
for	O
the	O
Siren	B-Algorithm
codec	I-Algorithm
,	O
used	O
in	O
the	O
G.722.1	B-Algorithm
wideband	B-Algorithm
audio	I-Algorithm
coding	O
standard	O
.	O
</s>
<s>
The	O
MDCT	O
is	O
adapted	O
into	O
the	O
LD-MDCT	O
algorithm	O
,	O
used	O
in	O
the	O
AAC-LD	B-Algorithm
standard	O
.	O
</s>
<s>
2001	O
:	O
INOC-DBA	O
,	O
first	O
inter-provider	O
SIP	B-Application
network	O
deployed	O
;	O
also	O
first	O
voice	O
network	O
to	O
reach	O
all	O
seven	O
continents	O
.	O
</s>
<s>
2003	O
:	O
First	O
released	O
in	O
August	O
2003	O
,	O
Skype	B-Application
was	O
the	O
creation	O
of	O
Niklas	O
Zennström	O
and	O
Janus	O
Friis	O
,	O
in	O
cooperation	O
with	O
four	O
Estonian	O
developers	O
.	O
</s>
<s>
It	O
quickly	O
became	O
a	O
popular	O
program	O
that	O
helped	O
democratise	O
VoIP	B-Application
.	O
</s>
<s>
2004	O
:	O
Commercial	O
VoIP	B-Application
service	O
providers	O
proliferate	O
.	O
</s>
<s>
2006	O
:	O
G.729.1	B-Algorithm
wideband	O
codec	B-General_Concept
introduced	O
,	O
using	O
MDCT	O
and	O
CELP	B-Algorithm
(	O
LPC	O
)	O
algorithms	O
.	O
</s>
<s>
2007	O
:	O
VoIP	B-Application
device	O
manufacturers	O
and	O
sellers	O
boom	O
in	O
Asia	O
,	O
specifically	O
in	O
the	O
Philippines	O
where	O
many	O
families	O
of	O
overseas	O
workers	O
reside	O
.	O
</s>
<s>
2009	O
:	O
SILK	O
codec	B-General_Concept
introduced	O
,	O
using	O
LPC	O
algorithm	O
,	O
and	O
used	O
for	O
voice	O
calling	O
in	O
Skype	B-Application
.	O
</s>
<s>
2010	O
:	O
Apple	O
introduces	O
FaceTime	B-Operating_System
,	O
which	O
uses	O
the	O
LD-MDCT-based	O
AAC-LD	B-Algorithm
codec	B-General_Concept
.	O
</s>
<s>
Rise	O
of	O
WebRTC	B-Protocol
technology	O
which	O
allows	O
VoIP	B-Application
directly	O
in	O
browsers	O
.	O
</s>
<s>
CELT	B-Algorithm
codec	B-General_Concept
introduced	O
,	O
using	O
MDCT	O
algorithm	O
.	O
</s>
<s>
2012	O
:	O
Opus	B-Algorithm
codec	I-Algorithm
introduced	O
,	O
using	O
MDCT	O
and	O
LPC	O
algorithms	O
.	O
</s>
