<s>
Integrated	B-Protocol
Services	I-Protocol
Digital	I-Protocol
Network	I-Protocol
(	O
ISDN	B-Protocol
)	O
is	O
a	O
set	O
of	O
communication	O
standards	O
for	O
simultaneous	O
digital	B-General_Concept
transmission	O
of	O
voice	O
,	O
video	B-Application
,	O
data	O
,	O
and	O
other	O
network	O
services	O
over	O
the	O
digitalised	O
circuits	O
of	O
the	O
public	O
switched	O
telephone	O
network	O
.	O
</s>
<s>
By	O
the	O
time	O
the	O
standard	O
was	O
released	O
,	O
newer	O
networking	O
systems	O
with	O
much	O
greater	O
speeds	O
were	O
available	O
,	O
and	O
ISDN	B-Protocol
saw	O
relatively	O
little	O
uptake	O
in	O
the	O
wider	O
market	O
.	O
</s>
<s>
One	O
estimate	O
suggests	O
ISDN	B-Protocol
use	O
peaked	O
at	O
a	O
worldwide	O
total	O
of	O
25	O
million	O
subscribers	O
at	O
a	O
time	O
when	O
1.3	O
billion	O
analog	O
lines	O
were	O
in	O
use	O
.	O
</s>
<s>
ISDN	B-Protocol
has	O
largely	O
been	O
replaced	O
with	O
digital	B-General_Concept
subscriber	B-Architecture
line	I-Architecture
(	O
DSL	O
)	O
systems	O
of	O
much	O
higher	O
performance	O
.	O
</s>
<s>
Prior	O
to	O
ISDN	B-Protocol
,	O
the	O
telephone	O
system	O
consisted	O
of	O
digital	B-General_Concept
links	O
like	O
T1/E1	B-Protocol
on	O
the	O
long-distance	O
lines	O
between	O
telephone	O
company	O
offices	O
and	O
analog	O
signals	O
on	O
copper	O
telephone	O
wires	O
to	O
the	O
customers	O
,	O
the	O
"	O
last	B-Protocol
mile	I-Protocol
"	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
the	O
network	O
was	O
viewed	O
as	O
a	O
way	O
to	O
transport	O
voice	O
,	O
with	O
some	O
special	O
services	O
available	O
for	O
data	O
using	O
additional	O
equipment	O
like	O
modems	B-Application
or	O
by	O
providing	O
a	O
T1	B-Protocol
on	O
the	O
customer	O
's	O
location	O
.	O
</s>
<s>
What	O
became	O
ISDN	B-Protocol
started	O
as	O
an	O
effort	O
to	O
digitize	O
the	O
last	B-Protocol
mile	I-Protocol
,	O
originally	O
under	O
the	O
name	O
"	O
Public	O
Switched	O
Digital	B-General_Concept
Capacity	O
"	O
(	O
PSDC	O
)	O
.	O
</s>
<s>
This	O
would	O
allow	O
call	O
routing	O
to	O
be	O
completed	O
in	O
an	O
all-digital	O
system	O
,	O
while	O
also	O
offering	O
a	O
separate	O
data	O
line	O
.	O
</s>
<s>
The	O
Basic	B-Protocol
Rate	I-Protocol
Interface	I-Protocol
,	O
or	O
BRI	O
,	O
is	O
the	O
standard	O
last-mile	O
connection	O
in	O
the	O
ISDN	B-Protocol
system	O
,	O
offering	O
two	O
64kbit/s	O
"	O
bearer	O
"	O
lines	O
and	O
a	O
single	O
16kbit/s	O
"	O
delta	O
"	O
channel	O
for	O
commands	O
and	O
data	O
.	O
</s>
<s>
Although	O
ISDN	B-Protocol
found	O
a	O
number	O
of	O
niche	O
roles	O
and	O
some	O
wider	O
uptake	O
in	O
specific	O
locales	O
,	O
the	O
system	O
was	O
largely	O
ignored	O
and	O
garnered	O
the	O
industry	O
nickname	O
"	O
innovation	O
subscribers	O
did	O
n't	O
need.	O
"	O
</s>
<s>
It	O
found	O
a	O
use	O
for	O
a	O
time	O
for	O
small-office	O
digital	B-General_Concept
connection	O
,	O
using	O
the	O
voice	O
lines	O
for	O
data	O
at	O
64kbit/s	O
,	O
sometimes	O
"	O
bonded	B-Architecture
"	O
to	O
128kbit/s	O
,	O
but	O
the	O
introduction	O
of	O
56kbit/s	O
modems	B-Application
undercut	O
its	O
value	O
in	O
many	O
roles	O
.	O
</s>
<s>
It	O
also	O
found	O
use	O
in	O
videoconference	B-Application
systems	O
,	O
where	O
the	O
direct	O
end-to-end	O
connection	O
was	O
desirable	O
.	O
</s>
<s>
The	O
H.320	B-Application
standard	O
was	O
designed	O
around	O
its	O
64kbit/s	O
data	O
rate	O
.	O
</s>
<s>
The	O
underlying	O
ISDN	B-Protocol
concepts	O
found	O
wider	O
use	O
as	O
a	O
replacement	O
for	O
the	O
T1/E1	B-Protocol
lines	O
it	O
was	O
originally	O
intended	O
to	O
extend	O
,	O
roughly	O
doubling	O
the	O
performance	O
of	O
those	O
lines	O
.	O
</s>
<s>
Bell	O
Labs	O
 '	O
seminal	O
work	O
on	O
digital	B-General_Concept
encoding	O
of	O
voice	O
led	O
to	O
the	O
use	O
of	O
64kbit/s	O
as	O
a	O
standard	O
for	O
voice	O
lines	O
(	O
or	O
56kbit/s	O
in	O
some	O
systems	O
)	O
.	O
</s>
<s>
In	O
1962	O
,	O
Robert	O
Aaron	O
of	O
Bell	O
introduced	O
the	O
T1	B-Protocol
system	O
,	O
which	O
carried	O
1.544Mbit/s	O
of	O
data	O
on	O
a	O
pair	O
of	O
twisted	O
pair	O
lines	O
over	O
a	O
distance	O
of	O
about	O
one	O
mile	O
.	O
</s>
<s>
This	O
was	O
used	O
in	O
the	O
Bell	O
network	O
to	O
carry	O
traffic	O
between	O
local	O
switch	O
offices	O
,	O
with	O
24	O
voice	O
lines	O
at	O
64	O
kbit/s	O
and	O
a	O
separate	O
8	O
kbit/s	O
line	O
for	O
signaling	O
commands	O
like	O
connecting	O
or	O
hanging	O
up	O
a	O
call	O
.	O
</s>
<s>
T1	B-Protocol
used	O
a	O
very	O
simple	O
encoding	O
scheme	O
,	O
alternate	O
mark	O
inversion	O
(	O
AMI	O
)	O
,	O
which	O
reached	O
only	O
a	O
few	O
percent	O
of	O
the	O
theoretical	O
capacity	O
of	O
the	O
line	O
but	O
was	O
appropriate	O
for	O
1960s	O
electronics	O
.	O
</s>
<s>
By	O
the	O
late	O
1970s	O
,	O
T1	B-Protocol
lines	I-Protocol
and	O
their	O
faster	O
counterparts	O
,	O
along	O
with	O
all-digital	O
switching	O
systems	O
,	O
had	O
replaced	O
the	O
earlier	O
analog	O
systems	O
for	O
most	O
of	O
the	O
western	O
world	O
,	O
leaving	O
only	O
the	O
customer	O
's	O
equipment	O
and	O
their	O
local	O
end	B-Device
office	I-Device
using	O
analog	O
systems	O
.	O
</s>
<s>
Digitizing	O
this	O
"	O
last	B-Protocol
mile	I-Protocol
"	O
was	O
increasingly	O
seen	O
as	O
the	O
next	O
problem	O
that	O
needed	O
to	O
be	O
solved	O
.	O
</s>
<s>
However	O
,	O
these	O
connections	O
now	O
represented	O
over	O
99%	O
of	O
the	O
total	O
telephony	O
network	O
,	O
as	O
the	O
upstream	O
links	O
had	O
increasingly	O
been	O
aggregated	O
into	O
a	O
smaller	O
number	O
of	O
much	O
higher	O
performance	O
systems	O
,	O
especially	O
after	O
the	O
introduction	O
of	O
fiber	B-Architecture
optic	I-Architecture
lines	O
.	O
</s>
<s>
If	O
the	O
system	O
was	O
to	O
become	O
all-digital	O
,	O
a	O
new	O
standard	O
would	O
be	O
needed	O
that	O
was	O
appropriate	O
for	O
the	O
existing	O
customer	O
lines	O
,	O
which	O
might	O
be	O
miles	O
long	O
and	O
of	O
widely	O
varying	O
quality	O
.	O
</s>
<s>
They	O
studied	O
a	O
number	O
of	O
derivatives	O
of	O
the	O
T1	B-Protocol
's	O
AMI	O
concept	O
and	O
concluded	O
that	O
a	O
customer-side	O
line	O
could	O
reliably	O
carry	O
about	O
160kbit/s	O
of	O
data	O
over	O
a	O
distance	O
of	O
.	O
</s>
<s>
That	O
would	O
be	O
enough	O
to	O
carry	O
two	O
voice-quality	O
lines	O
at	O
64kbit/s	O
as	O
well	O
as	O
a	O
separate	O
16kbit/s	O
line	O
for	O
data	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
modems	B-Application
were	O
normally	O
300bps	O
and	O
1200bit/s	O
would	O
not	O
become	O
common	O
until	O
the	O
early	O
1980s	O
and	O
the	O
2400bit/s	O
standard	O
would	O
not	O
be	O
completed	O
until	O
1984	O
.	O
</s>
<s>
In	O
this	O
market	O
,	O
16kbit/s	O
represented	O
a	O
significant	O
advance	O
in	O
performance	O
in	O
addition	O
to	O
being	O
a	O
separate	O
channel	O
that	O
coexists	O
with	O
voice	O
channels	O
.	O
</s>
<s>
A	O
key	O
problem	O
was	O
that	O
the	O
customer	O
might	O
only	O
have	O
a	O
single	O
twisted	O
pair	O
line	O
to	O
the	O
location	O
of	O
the	O
handset	O
,	O
so	O
the	O
solution	O
used	O
in	O
T1	B-Protocol
with	O
separate	O
upstream	O
and	O
downstream	O
connections	O
was	O
not	O
universally	O
available	O
.	O
</s>
<s>
John	O
Cioffi	O
had	O
recently	O
demonstrated	O
echo	O
cancellation	O
would	O
work	O
at	O
these	O
speeds	O
,	O
and	O
further	O
suggested	O
that	O
they	O
should	O
consider	O
moving	O
directly	O
to	O
1.5Mbit/s	O
performance	O
using	O
this	O
concept	O
.	O
</s>
<s>
As	O
the	O
new	O
standard	O
was	O
to	O
be	O
international	O
,	O
this	O
was	O
even	O
more	O
contentious	O
as	O
several	O
regional	O
digital	B-General_Concept
standards	O
had	O
emerged	O
in	O
the	O
1960s	O
and	O
70s	O
and	O
merging	O
them	O
was	O
not	O
going	O
to	O
be	O
easy	O
.	O
</s>
<s>
This	O
standard	O
used	O
an	O
80kHz	O
base	O
frequency	O
and	O
encoded	O
two	O
bits	O
per	O
baud	O
to	O
produce	O
the	O
160kbit/s	O
base	O
rate	O
.	O
</s>
<s>
From	O
an	O
economic	O
perspective	O
,	O
the	O
European	O
Commission	O
sought	O
to	O
liberalize	O
and	O
regulate	O
ISDN	B-Protocol
across	O
the	O
European	O
Economic	O
Community	O
.	O
</s>
<s>
With	O
digital-quality	O
voice	O
made	O
possible	O
by	O
ISDN	B-Protocol
,	O
two	O
separate	O
lines	O
and	O
all-the-time	O
data	O
,	O
the	O
telephony	O
world	O
was	O
convinced	O
there	O
would	O
be	O
high	O
customer	O
demand	O
for	O
such	O
systems	O
in	O
both	O
the	O
home	O
and	O
office	O
.	O
</s>
<s>
In	O
the	O
office	O
,	O
multi-line	O
digital	B-General_Concept
switches	O
like	O
the	O
Meridian	B-Device
Norstar	I-Device
took	O
over	O
telephone	O
lines	O
while	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
like	O
Ethernet	O
provided	O
performance	O
around	O
10Mbit/s	O
which	O
had	O
become	O
the	O
baseline	O
for	O
inter-computer	O
connections	O
in	O
offices	O
.	O
</s>
<s>
ISDN	B-Protocol
offered	O
no	O
real	O
advantages	O
in	O
the	O
voice	O
role	O
and	O
was	O
far	O
from	O
competitive	O
in	O
data	O
.	O
</s>
<s>
Additionally	O
,	O
modems	B-Application
had	O
continued	O
improving	O
,	O
introducing	O
9600bit/s	O
systems	O
in	O
the	O
late	O
1980s	O
and	O
14.4kbit/s	O
in	O
1991	O
,	O
which	O
significantly	O
eroded	O
ISDN	B-Protocol
's	O
value	O
proposition	O
for	O
the	O
home	O
customer	O
.	O
</s>
<s>
Meanwhile	O
,	O
Lechleider	O
had	O
proposed	O
using	O
ISDN	B-Protocol
's	O
echo	O
cancellation	O
and	O
2B1Q	O
encoding	O
on	O
existing	O
T1	B-Protocol
connections	O
so	O
that	O
the	O
distance	O
between	O
repeaters	O
could	O
be	O
doubled	O
to	O
about	O
.	O
</s>
<s>
Another	O
standards	O
war	O
broke	O
out	O
,	O
but	O
in	O
1991	O
Lechleider	O
's	O
1.6Mbit/s	O
"	O
High-Speed	O
Digital	B-General_Concept
Subscriber	B-Architecture
Line	I-Architecture
"	O
eventually	O
won	O
this	O
process	O
as	O
well	O
,	O
after	O
Starr	O
drove	O
it	O
through	O
the	O
ANSI	O
T1E1.4	O
group	O
.	O
</s>
<s>
A	O
similar	O
standard	O
emerged	O
in	O
Europe	O
to	O
replace	O
their	O
E1	O
lines	O
,	O
increasing	O
the	O
sampling	O
range	O
from	O
80	O
to	O
100kHz	O
to	O
achieve	O
2.048Mbit/s	O
.	O
</s>
<s>
By	O
the	O
mid-1990s	O
,	O
these	O
Primary	B-Protocol
Rate	I-Protocol
Interface	I-Protocol
(	O
PRI	O
)	O
lines	O
had	O
largely	O
replaced	O
T1	B-Protocol
and	O
E1	O
between	O
telephone	O
company	O
offices	O
.	O
</s>
<s>
Lechleider	O
also	O
believed	O
this	O
higher-speed	O
standard	O
would	O
be	O
much	O
more	O
attractive	O
to	O
customers	O
than	O
ISDN	B-Protocol
had	O
proven	O
.	O
</s>
<s>
An	O
early	O
supporter	O
of	O
the	O
concept	O
was	O
Alcatel	O
,	O
who	O
jumped	O
on	O
ADSL	O
while	O
many	O
other	O
companies	O
were	O
still	O
devoted	O
to	O
ISDN	B-Protocol
.	O
</s>
<s>
They	O
introduced	O
the	O
first	O
DSL	O
Access	O
Multiplexers	O
(	O
DSLAM	O
)	O
,	O
the	O
large	O
multi-modem	O
systems	O
used	O
at	O
the	O
telephony	O
offices	O
,	O
and	O
later	O
introduced	O
customer	O
ADSL	O
modems	B-Application
under	O
the	O
Thomson	O
brand	O
.	O
</s>
<s>
ADSL	O
quickly	O
replaced	O
ISDN	B-Protocol
as	O
the	O
customer-facing	O
solution	O
for	O
last-mile	O
connectivity	O
.	O
</s>
<s>
ISDN	B-Protocol
has	O
largely	O
disappeared	O
on	O
the	O
customer	O
side	O
,	O
remaining	O
in	O
use	O
only	O
in	O
niche	O
roles	O
like	O
dedicated	O
teleconferencing	O
systems	O
and	O
similar	O
legacy	O
systems	O
.	O
</s>
<s>
Integrated	O
services	O
refers	O
to	O
ISDN	B-Protocol
's	O
ability	O
to	O
deliver	O
at	O
minimum	O
two	O
simultaneous	O
connections	O
,	O
in	O
any	O
combination	O
of	O
data	O
,	O
voice	O
,	O
video	B-Application
,	O
and	O
fax	O
,	O
over	O
a	O
single	B-Architecture
line	I-Architecture
.	O
</s>
<s>
That	O
means	O
an	O
ISDN	B-Protocol
line	I-Protocol
can	O
take	O
care	O
of	O
what	O
were	O
expected	O
to	O
be	O
most	O
people	O
's	O
complete	O
communications	O
needs	O
(	O
apart	O
from	O
broadband	O
Internet	O
access	O
and	O
entertainment	O
television	O
)	O
at	O
a	O
much	O
higher	O
transmission	O
rate	O
,	O
without	O
forcing	O
the	O
purchase	O
of	O
multiple	O
analog	O
phone	O
lines	O
.	O
</s>
<s>
In	O
ISDN	B-Protocol
,	O
there	O
are	O
two	O
types	O
of	O
channels	O
,	O
B	O
(	O
for	O
"	O
bearer	O
"	O
)	O
and	O
D	O
(	O
for	O
"	O
data	O
"	O
)	O
.	O
</s>
<s>
B	B-Protocol
channels	I-Protocol
are	O
used	O
for	O
data	O
(	O
which	O
may	O
include	O
voice	O
)	O
,	O
and	O
D	B-Protocol
channels	I-Protocol
are	O
intended	O
for	O
signaling	O
and	O
control	O
(	O
but	O
can	O
also	O
be	O
used	O
for	O
data	O
)	O
.	O
</s>
<s>
There	O
are	O
two	O
ISDN	B-Protocol
implementations	O
.	O
</s>
<s>
Basic	B-Protocol
Rate	I-Protocol
Interface	I-Protocol
(	O
BRI	O
)	O
,	O
also	O
called	O
basic	B-Protocol
rate	I-Protocol
access	I-Protocol
(	O
BRA	O
)	O
—	O
consists	O
of	O
two	O
B	B-Protocol
channels	I-Protocol
,	O
each	O
with	O
bandwidth	O
of	O
64	O
kbit/s	O
,	O
and	O
one	O
D	B-Protocol
channel	I-Protocol
with	O
a	O
bandwidth	O
of	O
16	O
kbit/s	O
.	O
</s>
<s>
Together	O
these	O
three	O
channels	O
can	O
be	O
designated	O
as	O
2B+D	B-Protocol
.	O
</s>
<s>
Primary	B-Protocol
Rate	I-Protocol
Interface	I-Protocol
(	O
PRI	O
)	O
,	O
also	O
called	O
primary	B-Protocol
rate	I-Protocol
access	I-Protocol
(	O
PRA	O
)	O
in	O
Europe	O
—	O
contains	O
a	O
greater	O
number	O
of	O
B	B-Protocol
channels	I-Protocol
and	O
a	O
D	B-Protocol
channel	I-Protocol
with	O
a	O
bandwidth	O
of	O
64	O
kbit/s	O
.	O
</s>
<s>
The	O
number	O
of	O
B	B-Protocol
channels	I-Protocol
for	O
PRI	O
varies	O
according	O
to	O
the	O
nation	O
:	O
in	O
North	O
America	O
and	O
Japan	O
it	O
is	O
23B+1D	O
,	O
with	O
an	O
aggregate	O
bit	O
rate	O
of	O
1.544	O
Mbit/s	O
(	O
T1	B-Protocol
)	O
;	O
in	O
Europe	O
,	O
India	O
and	O
Australia	O
it	O
is	O
30B+2D	O
,	O
with	O
an	O
aggregate	O
bit	O
rate	O
of	O
2.048	O
Mbit/s	O
(	O
E1	O
)	O
.	O
</s>
<s>
Broadband	B-Protocol
Integrated	I-Protocol
Services	I-Protocol
Digital	I-Protocol
Network	I-Protocol
(	O
BISDN	B-Protocol
)	O
is	O
another	O
ISDN	B-Protocol
implementation	O
and	O
it	O
is	O
able	O
to	O
manage	O
different	O
types	O
of	O
services	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
It	O
is	O
primarily	O
used	O
within	O
network	B-General_Concept
backbones	I-General_Concept
and	O
employs	O
ATM	O
.	O
</s>
<s>
Another	O
alternative	O
ISDN	B-Protocol
configuration	O
can	O
be	O
used	O
in	O
which	O
the	O
B	B-Protocol
channels	I-Protocol
of	O
an	O
ISDN	B-Protocol
BRI	I-Protocol
line	O
are	O
bonded	B-Architecture
to	O
provide	O
a	O
total	O
duplex	O
bandwidth	O
of	O
128	O
kbit/s	O
.	O
</s>
<s>
The	O
B	B-Protocol
channels	I-Protocol
of	O
several	O
BRIs	O
can	O
be	O
bonded	B-Architecture
,	O
a	O
typical	O
use	O
is	O
a	O
384K	O
videoconferencing	B-Application
channel	O
.	O
</s>
<s>
Using	O
bipolar	B-Protocol
with	I-Protocol
eight-zero	I-Protocol
substitution	I-Protocol
encoding	O
technique	O
,	O
call	O
data	O
is	O
transmitted	O
over	O
the	O
data	O
(	O
B	O
)	O
channels	O
,	O
with	O
the	O
signaling	O
(	O
D	O
)	O
channels	O
used	O
for	O
call	O
setup	O
and	O
management	O
.	O
</s>
<s>
Once	O
a	O
call	O
is	O
set	O
up	O
,	O
there	O
is	O
a	O
simple	O
64	O
kbit/s	O
synchronous	O
bidirectional	O
data	O
channel	O
(	O
actually	O
implemented	O
as	O
two	O
simplex	O
channels	O
,	O
one	O
in	O
each	O
direction	O
)	O
between	O
the	O
end	O
parties	O
,	O
lasting	O
until	O
the	O
call	O
is	O
terminated	O
.	O
</s>
<s>
Bearer	O
channels	O
may	O
also	O
be	O
multiplexed	B-Architecture
into	O
what	O
may	O
be	O
considered	O
single	O
,	O
higher-bandwidth	O
channels	O
via	O
a	O
process	O
called	O
B	B-Protocol
channel	I-Protocol
BONDING	B-Architecture
,	O
or	O
via	O
use	O
of	O
Multi-Link	O
PPP	O
"	O
bundling	O
"	O
or	O
by	O
using	O
an	O
H0	O
,	O
H11	O
,	O
or	O
H12	O
channel	O
on	O
a	O
PRI	O
.	O
</s>
<s>
The	O
D	B-Protocol
channel	I-Protocol
can	O
also	O
be	O
used	O
for	O
sending	O
and	O
receiving	O
X.25	B-Protocol
data	O
packets	O
,	O
and	O
connection	O
to	O
X.25	B-Protocol
packet	O
network	O
,	O
this	O
is	O
specified	O
in	O
X.31	O
.	O
</s>
<s>
A	O
set	O
of	O
reference	O
points	O
are	O
defined	O
in	O
the	O
ISDN	B-Protocol
standard	O
to	O
refer	O
to	O
certain	O
points	O
between	O
the	O
telco	O
and	O
the	O
end	O
user	O
ISDN	B-Protocol
equipment	O
.	O
</s>
<s>
T	B-Protocol
–	O
defines	O
the	O
point	O
between	O
the	O
NT2	O
and	O
network	B-Protocol
termination	I-Protocol
1	I-Protocol
(	O
NT1	O
)	O
devices	O
.	O
</s>
<s>
Most	O
NT-1	O
devices	O
can	O
perform	O
the	O
functions	O
of	O
the	O
NT2	O
as	O
well	O
,	O
and	O
so	O
the	O
S	B-Protocol
and	O
T	B-Protocol
reference	O
points	O
are	O
generally	O
collapsed	O
into	O
the	O
S/T	O
reference	O
point	O
.	O
</s>
<s>
In	O
North	O
America	O
,	O
the	O
NT1	O
device	O
is	O
considered	O
customer	O
premises	O
equipment	O
(	O
CPE	O
)	O
and	O
must	O
be	O
maintained	O
by	O
the	O
customer	O
,	O
thus	O
,	O
the	O
U	B-Protocol
interface	I-Protocol
is	O
provided	O
to	O
the	O
customer	O
.	O
</s>
<s>
In	O
other	O
locations	O
,	O
the	O
NT1	O
device	O
is	O
maintained	O
by	O
the	O
telco	O
,	O
and	O
the	O
S/T	O
interface	O
is	O
provided	O
to	O
the	O
customer	O
.	O
</s>
<s>
In	O
India	O
,	O
service	O
providers	O
provide	O
U	B-Protocol
interface	I-Protocol
and	O
an	O
NT1	O
may	O
be	O
supplied	O
by	O
Service	O
provider	O
as	O
part	O
of	O
service	O
offering	O
.	O
</s>
<s>
The	O
entry	O
level	O
interface	O
to	O
ISDN	B-Protocol
is	O
the	O
Basic	B-Protocol
Rate	I-Protocol
Interface	I-Protocol
(	O
BRI	O
)	O
,	O
a	O
128	O
kbit/s	O
service	O
delivered	O
over	O
a	O
pair	O
of	O
standard	O
telephone	O
copper	O
wires	O
.	O
</s>
<s>
The	O
144	O
kbit/s	O
overall	O
payload	O
rate	O
is	O
divided	O
into	O
two	O
64	O
kbit/s	O
bearer	O
channels	O
( 	O
 '	O
B	O
 '	O
channels	O
)	O
and	O
one	O
16	O
kbit/s	O
signaling	O
channel	O
( 	O
 '	O
D	O
 '	O
channel	O
or	O
data	O
channel	O
)	O
.	O
</s>
<s>
This	O
is	O
sometimes	O
referred	O
to	O
as	O
2B+D	B-Protocol
.	O
</s>
<s>
The	O
U	B-Protocol
interface	I-Protocol
is	O
a	O
two-wire	O
interface	O
between	O
the	O
exchange	O
and	O
a	O
network	O
terminating	O
unit	O
,	O
which	O
is	O
usually	O
the	O
demarcation	B-Architecture
point	I-Architecture
in	O
non-North	O
American	O
networks	O
.	O
</s>
<s>
The	O
T	B-Protocol
interface	I-Protocol
is	O
a	O
serial	O
interface	O
between	O
a	O
computing	O
device	O
and	O
a	O
terminal	B-Protocol
adapter	I-Protocol
,	O
which	O
is	O
the	O
digital	B-General_Concept
equivalent	O
of	O
a	O
modem	B-Application
.	O
</s>
<s>
The	O
S	B-Protocol
interface	I-Protocol
is	O
a	O
four-wire	O
bus	O
that	O
ISDN	B-Protocol
consumer	O
devices	O
plug	O
into	O
;	O
the	O
S	B-Protocol
&	O
T	B-Protocol
reference	O
points	O
are	O
commonly	O
implemented	O
as	O
a	O
single	O
interface	O
labeled	O
'	O
S/T	O
'	O
on	O
a	O
Network	B-Protocol
termination	I-Protocol
1	I-Protocol
(	O
NT1	O
)	O
.	O
</s>
<s>
The	O
R	O
interface	O
defines	O
the	O
point	O
between	O
a	O
non-ISDN	O
device	O
and	O
a	O
terminal	B-Protocol
adapter	I-Protocol
(	O
TA	O
)	O
which	O
provides	O
translation	O
to	O
and	O
from	O
such	O
a	O
device	O
.	O
</s>
<s>
BRI-ISDN	O
is	O
very	O
popular	O
in	O
Europe	O
but	O
is	O
much	O
less	O
common	O
in	O
North	O
America	O
.	O
</s>
<s>
The	O
other	O
ISDN	B-Protocol
access	O
available	O
is	O
the	O
Primary	B-Protocol
Rate	I-Protocol
Interface	I-Protocol
(	O
PRI	O
)	O
,	O
which	O
is	O
carried	O
over	O
T-carrier	O
(	O
T1	B-Protocol
)	O
with	O
24	O
time	O
slots	O
(	O
channels	O
)	O
in	O
North	O
America	O
,	O
and	O
over	O
E-carrier	O
(	O
E1	O
)	O
with	O
32	O
channels	O
in	O
most	O
other	O
countries	O
.	O
</s>
<s>
Each	O
channel	O
provides	O
transmission	O
at	O
a	O
64	O
kbit/s	O
data	O
rate	O
.	O
</s>
<s>
In	O
North	O
America	O
,	O
PRI	O
service	O
is	O
delivered	O
via	O
T1	B-Protocol
carriers	O
with	O
only	O
one	O
data	O
channel	O
,	O
often	O
referred	O
to	O
as	O
23B+D	O
,	O
and	O
a	O
total	O
data	O
rate	O
of	O
1544	O
kbit/s	O
.	O
</s>
<s>
Non-Facility	B-Protocol
Associated	I-Protocol
Signalling	I-Protocol
(	O
NFAS	O
)	O
allows	O
two	O
or	O
more	O
PRI	O
circuits	O
to	O
be	O
controlled	O
by	O
a	O
single	O
D	B-Protocol
channel	I-Protocol
,	O
which	O
is	O
sometimes	O
called	O
23B+D	O
+	O
n*24B	O
.	O
</s>
<s>
D-channel	B-Protocol
backup	O
allows	O
for	O
a	O
second	O
D	B-Protocol
channel	I-Protocol
in	O
case	O
the	O
primary	O
fails	O
.	O
</s>
<s>
NFAS	O
is	O
commonly	O
used	O
on	O
a	O
Digital	B-General_Concept
Signal	O
3	O
(	O
DS3/T3	O
)	O
.	O
</s>
<s>
PRI-ISDN	O
is	O
popular	O
throughout	O
the	O
world	O
,	O
especially	O
for	O
connecting	O
private	B-Device
branch	I-Device
exchanges	I-Device
to	O
the	O
public	O
switched	O
telephone	O
network	O
(	O
PSTN	O
)	O
.	O
</s>
<s>
Even	O
though	O
many	O
network	O
professionals	O
use	O
the	O
term	O
ISDN	B-Protocol
to	O
refer	O
to	O
the	O
lower-bandwidth	O
BRI	O
circuit	O
,	O
in	O
North	O
America	O
BRI	O
is	O
relatively	O
uncommon	O
whilst	O
PRI	O
circuits	O
serving	O
PBXs	O
are	O
commonplace	O
.	O
</s>
<s>
The	O
bearer	O
channel	O
(	O
B	O
)	O
is	O
a	O
standard	O
64	O
kbit/s	O
voice	O
channel	O
of	O
8	O
bits	O
sampled	O
at	O
8kHz	O
with	O
G.711	B-Algorithm
encoding	O
.	O
</s>
<s>
B-channels	O
can	O
also	O
be	O
used	O
to	O
carry	O
data	O
,	O
since	O
they	O
are	O
nothing	O
more	O
than	O
digital	B-General_Concept
channels	O
.	O
</s>
<s>
Most	O
B	B-Protocol
channels	I-Protocol
can	O
carry	O
a	O
64kbit/s	O
signal	O
,	O
but	O
some	O
were	O
limited	O
to	O
56K	O
because	O
they	O
traveled	O
over	O
RBS	O
lines	O
.	O
</s>
<s>
X.25	B-Protocol
can	O
be	O
carried	O
over	O
the	O
B	O
or	O
D	B-Protocol
channels	I-Protocol
of	O
a	O
BRI	O
line	O
,	O
and	O
over	O
the	O
B	B-Protocol
channels	I-Protocol
of	O
a	O
PRI	B-Protocol
line	I-Protocol
.	O
</s>
<s>
X.25	B-Protocol
over	O
the	O
D	B-Protocol
channel	I-Protocol
is	O
used	O
at	O
many	O
point-of-sale	O
(	O
credit	O
card	O
)	O
terminals	O
because	O
it	O
eliminates	O
the	O
modem	B-Application
setup	O
,	O
and	O
because	O
it	O
connects	O
to	O
the	O
central	O
system	O
over	O
a	O
B	B-Protocol
channel	I-Protocol
,	O
thereby	O
eliminating	O
the	O
need	O
for	O
modems	B-Application
and	O
making	O
much	O
better	O
use	O
of	O
the	O
central	O
system	O
's	O
telephone	O
lines	O
.	O
</s>
<s>
X.25	B-Protocol
was	O
also	O
part	O
of	O
an	O
ISDN	B-Protocol
protocol	O
called	O
"	O
Always	O
On/Dynamic	O
ISDN	B-Protocol
"	O
,	O
or	O
AO/DI	O
.	O
</s>
<s>
This	O
allowed	O
a	O
user	O
to	O
have	O
a	O
constant	O
multi-link	O
PPP	O
connection	O
to	O
the	O
internet	O
over	O
X.25	B-Protocol
on	O
the	O
D	B-Protocol
channel	I-Protocol
,	O
and	O
brought	O
up	O
one	O
or	O
two	O
B	B-Protocol
channels	I-Protocol
as	O
needed	O
.	O
</s>
<s>
In	O
theory	O
,	O
Frame	B-Protocol
Relay	I-Protocol
can	O
operate	O
over	O
the	O
D	B-Protocol
channel	I-Protocol
of	O
BRIs	O
and	O
PRIs	O
,	O
but	O
it	O
is	O
seldom	O
,	O
if	O
ever	O
,	O
used	O
.	O
</s>
<s>
ISDN	B-Protocol
is	O
a	O
core	O
technology	O
in	O
the	O
telephone	O
industry	O
.	O
</s>
<s>
The	O
common	O
electrical	O
specification	O
for	O
the	O
signals	O
on	O
these	O
wires	O
is	O
T1	B-Protocol
or	O
E1	O
.	O
</s>
<s>
Normally	O
,	O
a	O
PBX	O
is	O
connected	O
via	O
a	O
T1	B-Protocol
with	O
robbed	O
bit	O
signaling	O
to	O
indicate	O
on-hook	O
or	O
off-hook	O
conditions	O
and	O
MF	O
and	O
DTMF	O
tones	O
to	O
encode	O
the	O
destination	O
number	O
.	O
</s>
<s>
ISDN	B-Protocol
is	O
much	O
better	O
because	O
messages	O
can	O
be	O
sent	O
much	O
more	O
quickly	O
than	O
by	O
trying	O
to	O
encode	O
numbers	O
as	O
long	O
(	O
100	O
ms	O
per	O
digit	O
)	O
tone	O
sequences	O
.	O
</s>
<s>
In	O
common	O
use	O
,	O
ISDN	B-Protocol
is	O
often	O
limited	O
to	O
usage	O
to	O
Q.931	O
and	O
related	O
protocols	O
,	O
which	O
are	O
a	O
set	O
of	O
signaling	O
protocols	O
establishing	O
and	O
breaking	O
circuit-switched	O
connections	O
,	O
and	O
for	O
advanced	O
calling	O
features	O
for	O
the	O
user	O
.	O
</s>
<s>
Another	O
usage	O
was	O
the	O
deployment	O
of	O
videoconference	B-Application
systems	O
,	O
where	O
a	O
direct	O
end-to-end	O
connection	O
is	O
desirable	O
.	O
</s>
<s>
ISDN	B-Protocol
uses	O
the	O
H.320	B-Application
standard	O
for	O
audio	O
coding	O
and	O
video	B-Algorithm
coding	I-Algorithm
.	O
</s>
<s>
ISDN	B-Protocol
is	O
also	O
used	O
as	O
a	O
smart-network	O
technology	O
intended	O
to	O
add	O
new	O
services	O
to	O
the	O
public	O
switched	O
telephone	O
network	O
(	O
PSTN	O
)	O
by	O
giving	O
users	O
direct	O
access	O
to	O
end-to-end	O
circuit-switched	O
digital	B-General_Concept
services	O
and	O
as	O
a	O
backup	O
or	O
failsafe	O
circuit	O
solution	O
for	O
critical	O
use	O
data	O
circuits	O
.	O
</s>
<s>
One	O
of	O
ISDNs	B-Protocol
successful	O
use-cases	O
was	O
in	O
the	O
videoconference	B-Application
field	O
,	O
where	O
even	O
small	O
improvements	O
in	O
data	O
rates	O
are	O
useful	O
,	O
but	O
more	O
importantly	O
,	O
its	O
direct	O
end-to-end	O
connection	O
offers	O
lower	O
latency	O
and	O
better	O
reliability	O
than	O
packet-switched	O
networks	O
of	O
the	O
1990s	O
.	O
</s>
<s>
The	O
H.320	B-Application
standard	O
for	O
audio	O
coding	O
and	O
video	B-Algorithm
coding	I-Algorithm
was	O
designed	O
with	O
ISDN	B-Protocol
in	O
mind	O
,	O
and	O
more	O
specifically	O
its	O
64kbit/s	O
basic	O
data	O
rate	O
.	O
</s>
<s>
including	O
audio	B-Algorithm
codecs	I-Algorithm
such	O
as	O
G.711	B-Algorithm
(	O
PCM	B-Algorithm
)	O
and	O
G.728	B-Algorithm
(	O
CELP	B-Algorithm
)	O
,	O
and	O
discrete	B-General_Concept
cosine	I-General_Concept
transform	I-General_Concept
(	O
DCT	B-General_Concept
)	O
video	B-Application
codecs	I-Application
such	O
as	O
H.261	B-Algorithm
and	O
H.263	B-Algorithm
.	O
</s>
<s>
ISDN	B-Protocol
is	O
used	O
heavily	O
by	O
the	O
broadcast	O
industry	O
as	O
a	O
reliable	O
way	O
of	O
switching	O
low-latency	O
,	O
high-quality	O
,	O
long-distance	O
audio	O
circuits	O
.	O
</s>
<s>
In	O
conjunction	O
with	O
an	O
appropriate	O
codec	B-General_Concept
using	O
MPEG	O
or	O
various	O
manufacturers	O
 '	O
proprietary	O
algorithms	O
,	O
an	O
ISDN	B-Protocol
BRI	I-Protocol
can	O
be	O
used	O
to	O
send	O
stereo	O
bi-directional	O
audio	O
coded	O
at	O
128	O
kbit/s	O
with	O
20Hz	O
–	O
20kHz	O
audio	O
bandwidth	O
,	O
although	O
commonly	O
the	O
G.722	B-Algorithm
algorithm	O
is	O
used	O
with	O
a	O
single	O
64	O
kbit/s	O
B	B-Protocol
channel	I-Protocol
to	O
send	O
much	O
lower	O
latency	O
mono	O
audio	O
at	O
the	O
expense	O
of	O
audio	O
quality	O
.	O
</s>
<s>
Where	O
very	O
high	O
quality	O
audio	O
is	O
required	O
multiple	O
ISDN	B-Protocol
BRIs	I-Protocol
can	O
be	O
used	O
in	O
parallel	O
to	O
provide	O
a	O
higher	O
bandwidth	O
circuit	O
switched	O
connection	O
.	O
</s>
<s>
BBC	O
Radio	O
3	O
commonly	O
makes	O
use	O
of	O
three	O
ISDN	B-Protocol
BRIs	I-Protocol
to	O
carry	O
320	O
kbit/s	O
audio	O
stream	O
for	O
live	O
outside	O
broadcasts	O
.	O
</s>
<s>
ISDN	B-Protocol
BRI	I-Protocol
services	O
are	O
used	O
to	O
link	O
remote	O
studios	O
,	O
sports	O
grounds	O
and	O
outside	O
broadcasts	O
into	O
the	O
main	O
broadcast	O
studio	O
.	O
</s>
<s>
ISDN	B-Protocol
via	O
satellite	O
is	O
used	O
by	O
field	O
reporters	O
around	O
the	O
world	O
.	O
</s>
<s>
It	O
is	O
also	O
common	O
to	O
use	O
ISDN	B-Protocol
for	O
the	O
return	O
audio	O
links	O
to	O
remote	O
satellite	O
broadcast	O
vehicles	O
.	O
</s>
<s>
In	O
many	O
countries	O
,	O
such	O
as	O
the	O
UK	O
and	O
Australia	O
,	O
ISDN	B-Protocol
has	O
displaced	O
the	O
older	O
technology	O
of	O
equalised	O
analogue	O
landlines	O
,	O
with	O
these	O
circuits	O
being	O
phased	O
out	O
by	O
telecommunications	O
providers	O
.	O
</s>
<s>
Use	O
of	O
IP-based	O
streaming	O
codecs	B-General_Concept
such	O
as	O
Comrex	O
ACCESS	O
and	O
ipDTL	O
is	O
becoming	O
more	O
widespread	O
in	O
the	O
broadcast	O
sector	O
,	O
using	O
broadband	O
internet	O
to	O
connect	O
remote	O
studios	O
.	O
</s>
<s>
Providing	O
a	O
backup	O
line	O
for	O
business	O
's	O
inter-office	O
and	O
internet	O
connectivity	O
was	O
a	O
popular	O
use	O
of	O
the	O
technology	O
.	O
</s>
<s>
A	O
study	O
of	O
the	O
German	O
Department	O
of	O
Science	O
shows	O
the	O
following	O
spread	O
of	O
ISDN-channels	O
per	O
1,000	O
inhabitants	O
in	O
2005	O
:	O
</s>
<s>
Telstra	O
provides	O
the	O
business	O
customer	O
with	O
the	O
ISDN	B-Protocol
services	O
.	O
</s>
<s>
There	O
are	O
five	O
types	O
of	O
ISDN	B-Protocol
services	O
which	O
are	O
ISDN2	O
,	O
ISDN2	O
Enhanced	O
,	O
ISDN10	O
,	O
ISDN20	O
and	O
ISDN30	B-Protocol
.	O
</s>
<s>
In	O
general	O
,	O
there	O
are	O
two	O
group	O
of	O
ISDN	B-Protocol
service	O
types	O
;	O
The	O
Basic	B-Protocol
Rate	I-Protocol
services	O
–	O
ISDN	B-Protocol
2	O
or	O
ISDN	B-Protocol
2	O
Enhanced	O
.	O
</s>
<s>
Another	O
group	O
of	O
types	O
are	O
the	O
Primary	B-Protocol
Rate	I-Protocol
services	O
,	O
ISDN	B-Protocol
10/20/30	O
.	O
</s>
<s>
Telstra	O
announced	O
that	O
the	O
new	O
sales	O
of	O
ISDN	B-Protocol
product	O
would	O
be	O
unavailable	O
as	O
of	O
31	O
January	O
2018	O
.	O
</s>
<s>
The	O
final	O
exit	O
date	O
of	O
ISDN	B-Protocol
service	O
and	O
migration	O
to	O
the	O
new	O
service	O
would	O
be	O
confirmed	O
by	O
2022	O
.	O
</s>
<s>
France	O
Telecom	O
offers	O
ISDN	B-Protocol
services	O
under	O
their	O
product	O
name	O
Numeris	O
(	O
2	O
B+D	O
)	O
,	O
of	O
which	O
a	O
professional	O
Duo	O
and	O
home	O
Itoo	O
version	O
is	O
available	O
.	O
</s>
<s>
ISDN	B-Protocol
is	O
generally	O
known	O
as	O
RNIS	O
in	O
France	O
and	O
has	O
widespread	O
availability	O
.	O
</s>
<s>
The	O
introduction	O
of	O
ADSL	O
is	O
reducing	O
ISDN	B-Protocol
use	O
for	O
data	O
transfer	O
and	O
Internet	O
access	O
,	O
although	O
it	O
is	O
still	O
common	O
in	O
more	O
rural	O
and	O
outlying	O
areas	O
,	O
and	O
for	O
applications	O
such	O
as	O
business	B-Device
voice	I-Device
and	O
point-of-sale	O
terminals	O
.	O
</s>
<s>
In	O
Germany	O
,	O
ISDN	B-Protocol
was	O
very	O
popular	O
with	O
an	O
installed	O
base	O
of	O
25	O
million	O
channels	O
(	O
29%	O
of	O
all	O
subscriber	B-Architecture
lines	I-Architecture
in	O
Germany	O
as	O
of	O
2003	O
and	O
20%	O
of	O
all	O
ISDN	B-Protocol
channels	O
worldwide	O
)	O
.	O
</s>
<s>
Due	O
to	O
the	O
success	O
of	O
ISDN	B-Protocol
,	O
the	O
number	O
of	O
installed	O
analog	O
lines	O
was	O
decreasing	O
.	O
</s>
<s>
Competing	O
phone	O
companies	O
often	O
offered	O
ISDN	B-Protocol
only	O
and	O
no	O
analog	O
lines	O
.	O
</s>
<s>
However	O
,	O
these	O
operators	O
generally	O
offered	O
free	O
hardware	O
that	O
also	O
allows	O
the	O
use	O
of	O
POTS	O
equipment	O
,	O
such	O
as	O
NTBAs	B-Protocol
(	O
"	O
Network	O
Termination	O
for	O
ISDN	B-Protocol
Basic	B-Protocol
rate	I-Protocol
Access	I-Protocol
"	O
:	O
small	O
devices	O
that	O
bridge	O
the	O
two-wire	O
UK0	O
line	O
to	O
the	O
four-wire	O
S0	O
bus	O
)	O
with	O
integrated	O
terminal	B-Protocol
adapters	I-Protocol
.	O
</s>
<s>
Because	O
of	O
the	O
widespread	O
availability	O
of	O
ADSL	O
services	O
,	O
ISDN	B-Protocol
was	O
primarily	O
used	O
for	O
voice	O
and	O
fax	O
traffic	O
.	O
</s>
<s>
Until	O
2007	O
ISDN	B-Protocol
(	O
BRI	O
)	O
and	O
ADSL/VDSL	O
were	O
often	O
bundled	O
on	O
the	O
same	O
line	O
,	O
mainly	O
because	O
the	O
combination	O
of	O
DSL	O
with	O
an	O
analog	O
line	O
had	O
no	O
cost	O
advantage	O
over	O
a	O
combined	O
ISDN-DSL	O
line	O
.	O
</s>
<s>
This	O
practice	O
turned	O
into	O
an	O
issue	O
for	O
the	O
operators	O
when	O
vendors	O
of	O
ISDN	B-Protocol
technology	O
stopped	O
manufacturing	O
it	O
and	O
spare	O
parts	O
became	O
hard	O
to	O
come	O
by	O
.	O
</s>
<s>
Since	O
then	O
phone	O
companies	O
started	O
introducing	O
cheaper	O
xDSL-only	O
products	O
using	O
VoIP	B-Application
for	O
telephony	O
,	O
also	O
in	O
an	O
effort	O
to	O
reduce	O
their	O
costs	O
by	O
operating	O
separate	O
data	O
&	O
voice	O
networks	O
.	O
</s>
<s>
Since	O
approximately	O
2010	O
,	O
most	O
German	O
operators	O
have	O
offered	O
more	O
and	O
more	O
VoIP	B-Application
on	O
top	O
of	O
DSL	O
lines	O
and	O
ceased	O
offering	O
ISDN	B-Protocol
lines	I-Protocol
.	O
</s>
<s>
New	O
ISDN	B-Protocol
lines	I-Protocol
have	O
been	O
no	O
longer	O
available	O
in	O
Germany	O
since	O
2018	O
,	O
existing	O
ISDN	B-Protocol
lines	I-Protocol
were	O
phased	O
out	O
from	O
2016	O
onwards	O
and	O
existing	O
customers	O
were	O
encouraged	O
to	O
move	O
to	O
DSL-based	O
VoIP	B-Application
products	O
.	O
</s>
<s>
OTE	O
,	O
the	O
incumbent	O
telecommunications	O
operator	O
,	O
offers	O
ISDN	B-Protocol
BRI	I-Protocol
(	O
BRA	O
)	O
services	O
in	O
Greece	O
.	O
</s>
<s>
Following	O
the	O
launch	O
of	O
ADSL	O
in	O
2003	O
,	O
the	O
importance	O
of	O
ISDN	B-Protocol
for	O
data	O
transfer	O
began	O
to	O
decrease	O
and	O
is	O
today	O
limited	O
to	O
niche	O
business	O
applications	O
with	O
point-to-point	O
requirements	O
.	O
</s>
<s>
Bharat	O
Sanchar	O
Nigam	O
Limited	O
,	O
Reliance	O
Communications	O
and	O
Bharti	O
Airtel	O
are	O
the	O
largest	O
communication	O
service	O
providers	O
,	O
and	O
offer	O
both	O
ISDN	B-Protocol
BRI	I-Protocol
and	O
PRI	O
services	O
across	O
the	O
country	O
.	O
</s>
<s>
ISDN	B-Protocol
continues	O
to	O
be	O
an	O
important	O
backup	O
network	O
for	O
point-to-point	O
leased	O
line	O
customers	O
such	O
as	O
banks	O
,	O
Eseva	O
Centers	O
,	O
Life	O
Insurance	O
Corporation	O
of	O
India	O
,	O
and	O
SBI	O
ATMs	O
.	O
</s>
<s>
On	O
April	O
19	O
,	O
1988	O
,	O
Japanese	O
telecommunications	O
company	O
NTT	O
began	O
offering	O
nationwide	O
ISDN	B-Protocol
services	O
trademarked	O
INS	O
Net	O
64	O
,	O
and	O
INS	O
Net	O
1500	O
,	O
a	O
fruition	O
of	O
NTT	O
's	O
independent	O
research	O
and	O
trial	O
from	O
the	O
1970s	O
of	O
what	O
it	O
referred	O
to	O
the	O
INS	O
(	O
Information	O
Network	O
System	O
)	O
.	O
</s>
<s>
Previously	O
,	O
in	O
April	O
1985	O
,	O
Japanese	O
digital	B-General_Concept
telephone	O
exchange	O
hardware	O
made	O
by	O
Fujitsu	O
was	O
used	O
to	O
experimentally	O
deploy	O
the	O
world	O
's	O
first	O
I	O
interface	O
ISDN	B-Protocol
.	O
</s>
<s>
The	O
I	O
interface	O
,	O
unlike	O
the	O
older	O
and	O
incompatible	O
Y	O
interface	O
,	O
is	O
what	O
modern	O
ISDN	B-Protocol
services	O
use	O
today	O
.	O
</s>
<s>
Since	O
2000	O
,	O
NTT	O
's	O
ISDN	B-Protocol
offering	O
have	O
been	O
known	O
as	O
FLET	O
's	O
ISDN	B-Protocol
,	O
incorporating	O
the	O
"	O
FLET	O
's	O
"	O
brand	O
that	O
NTT	O
uses	O
for	O
all	O
of	O
its	O
ISP	O
offerings	O
.	O
</s>
<s>
In	O
Japan	O
,	O
the	O
number	O
of	O
ISDN	B-Protocol
subscribers	O
dwindled	O
as	O
alternative	O
technologies	O
such	O
as	O
ADSL	O
,	O
cable	B-Device
Internet	I-Device
access	I-Device
,	O
and	O
fiber	B-Architecture
to	I-Architecture
the	I-Architecture
home	I-Architecture
gained	O
greater	O
popularity	O
.	O
</s>
<s>
On	O
November	O
2	O
,	O
2010	O
,	O
NTT	O
announced	O
plans	O
to	O
migrate	O
their	O
backend	O
from	O
PSTN	O
to	O
the	O
IP	B-Protocol
network	I-Protocol
from	O
around	O
2020	O
to	O
around	O
2025	O
.	O
</s>
<s>
For	O
this	O
migration	O
,	O
ISDN	B-Protocol
services	O
will	O
be	O
retired	O
,	O
and	O
fiber	B-Architecture
optic	I-Architecture
services	O
are	O
recommended	O
as	O
an	O
alternative	O
.	O
</s>
<s>
On	O
April	O
19	O
,	O
1988	O
,	O
Norwegian	O
telecommunications	O
company	O
Telenor	O
began	O
offering	O
nationwide	O
ISDN	B-Protocol
services	O
trademarked	O
INS	O
Net	O
64	O
,	O
and	O
INS	O
Net	O
1500	O
,	O
a	O
fruition	O
of	O
NTT	O
's	O
independent	O
research	O
and	O
trial	O
from	O
the	O
1970s	O
of	O
what	O
it	O
referred	O
to	O
the	O
INS	O
(	O
Information	O
Network	O
System	O
)	O
.	O
</s>
<s>
In	O
the	O
United	O
Kingdom	O
,	O
British	O
Telecom	O
(	O
BT	O
)	O
provides	O
ISDN2e	B-Protocol
(	O
BRI	O
)	O
as	O
well	O
as	O
ISDN30	B-Protocol
(	O
PRI	O
)	O
.	O
</s>
<s>
Until	O
April	O
2006	O
,	O
they	O
also	O
offered	O
services	O
named	O
Home	O
Highway	O
and	O
Business	O
Highway	O
,	O
which	O
were	O
BRI	O
ISDN-based	O
services	O
that	O
offered	O
integrated	O
analogue	O
connectivity	O
as	O
well	O
as	O
ISDN	B-Protocol
.	O
</s>
<s>
Later	O
versions	O
of	O
the	O
Highway	O
products	O
also	O
included	O
built-in	O
USB	B-Protocol
sockets	O
for	O
direct	O
computer	O
access	O
.	O
</s>
<s>
In	O
early	O
2015	O
,	O
BT	O
announced	O
their	O
intention	O
to	O
retire	O
the	O
UK	O
's	O
ISDN	B-Protocol
infrastructure	O
by	O
2025	O
.	O
</s>
<s>
ISDN-BRI	O
never	O
gained	O
popularity	O
as	O
a	O
general	O
use	O
telephone	O
access	O
technology	O
in	O
Canada	O
and	O
the	O
US	O
,	O
and	O
remains	O
a	O
niche	O
product	O
.	O
</s>
<s>
ISDN	B-Protocol
has	O
long	O
been	O
known	O
by	O
derogatory	O
backronyms	O
highlighting	O
these	O
issues	O
,	O
such	O
as	O
It	O
Still	O
Does	O
Nothing	O
,	O
Innovations	O
Subscribers	O
Do	O
n't	O
Need	O
,	O
and	O
I	O
Still	O
Do	O
n't	O
kNow	O
,	O
or	O
,	O
from	O
the	O
supposed	O
standpoint	O
of	O
telephone	O
companies	O
,	O
I	O
Smell	O
Dollars	O
Now	O
.	O
</s>
<s>
Although	O
various	O
minimum	O
bandwidths	O
have	O
been	O
used	O
in	O
definitions	O
of	O
Broadband	O
Internet	O
access	O
,	O
ranging	O
up	O
from	O
64	O
kbit/s	O
up	O
to	O
1.0	O
Mbit/s	O
,	O
the	O
2006	O
OECD	O
report	O
is	O
typical	O
by	O
defining	O
broadband	O
as	O
having	O
download	O
data	O
transfer	O
rates	O
equal	O
to	O
or	O
faster	O
than	O
256	O
kbit/s	O
,	O
while	O
the	O
United	O
States	O
FCC	O
,	O
as	O
of	O
2008	O
,	O
defines	O
broadband	O
as	O
anything	O
above	O
768	O
kbit/s	O
.	O
</s>
<s>
Once	O
the	O
term	O
"	O
broadband	O
"	O
came	O
to	O
be	O
associated	O
with	O
data	O
rates	O
incoming	O
to	O
the	O
customer	O
at	O
256	O
kbit/s	O
or	O
more	O
,	O
and	O
alternatives	O
like	O
ADSL	O
grew	O
in	O
popularity	O
,	O
the	O
consumer	O
market	O
for	O
BRI	O
did	O
not	O
develop	O
.	O
</s>
<s>
Widespread	O
use	O
of	O
BRI	O
is	O
further	O
stymied	O
by	O
some	O
small	O
North	O
American	O
CLECs	O
such	O
as	O
CenturyTel	B-Application
having	O
given	O
up	O
on	O
it	O
and	O
not	O
providing	O
Internet	O
access	O
using	O
it	O
.	O
</s>
<s>
However	O
,	O
AT&T	O
in	O
most	O
states	O
(	O
especially	O
the	O
former	O
SBC/SWB	O
territory	O
)	O
will	O
still	O
install	O
an	O
ISDN	B-Protocol
BRI	I-Protocol
line	O
anywhere	O
a	O
normal	O
analog	O
line	O
can	O
be	O
placed	O
and	O
the	O
monthly	O
charge	O
is	O
roughly	O
$55	O
.	O
</s>
<s>
ISDN-BRI	O
is	O
currently	O
primarily	O
used	O
in	O
industries	O
with	O
specialized	O
and	O
very	O
specific	O
needs	O
.	O
</s>
<s>
High-end	O
videoconferencing	B-Application
hardware	O
can	O
bond	O
up	O
to	O
8	O
B-channels	O
together	O
(	O
using	O
a	O
BRI	O
circuit	O
for	O
every	O
2	O
channels	O
)	O
to	O
provide	O
digital	B-General_Concept
,	O
circuit-switched	O
video	B-Application
connections	O
to	O
almost	O
anywhere	O
in	O
the	O
world	O
.	O
</s>
<s>
Most	O
modern	O
non-VoIP	O
PBXs	O
use	O
ISDN-PRI	O
circuits	O
.	O
</s>
<s>
These	O
are	O
connected	O
via	O
T1	B-Protocol
lines	I-Protocol
with	O
the	O
central	O
office	O
switch	O
,	O
replacing	O
older	O
analog	O
two-way	O
and	O
direct	B-Device
inward	I-Device
dialing	I-Device
(	O
DID	O
)	O
trunks	O
.	O
</s>
<s>
PRI	O
is	O
capable	O
of	O
delivering	O
Calling	O
Line	O
Identification	O
(	O
CLID	O
)	O
in	O
both	O
directions	O
so	O
that	O
the	O
telephone	O
number	O
of	O
an	O
extension	O
,	O
rather	O
than	O
a	O
company	O
's	O
main	O
number	O
,	O
can	O
be	O
sent	O
.	O
</s>
<s>
The	O
ISDN	B-Protocol
protocol	O
delivers	O
channelized	O
,	O
not-over-the-Internet	O
service	O
,	O
powerful	O
call	O
setup	O
and	O
routing	O
features	O
,	O
faster	O
setup	O
and	O
tear	O
down	O
,	O
superior	O
audio	O
fidelity	O
as	O
compared	O
to	O
plain	O
old	O
telephone	O
service	O
(	O
POTS	O
)	O
,	O
lower	O
delay	O
and	O
,	O
at	O
higher	O
densities	O
,	O
lower	O
cost	O
.	O
</s>
<s>
In	O
2013	O
,	O
Verizon	B-Application
announced	O
it	O
would	O
no	O
longer	O
take	O
orders	O
for	O
ISDN	B-Protocol
service	O
in	O
the	O
Northeastern	O
United	O
States	O
.	O
</s>
