<s>
A	O
leased	B-Architecture
line	I-Architecture
is	O
a	O
private	O
telecommunications	O
circuit	O
between	O
two	O
or	O
more	O
locations	O
provided	O
according	O
to	O
a	O
commercial	O
contract	O
.	O
</s>
<s>
It	O
is	O
sometimes	O
also	O
known	O
as	O
a	O
private	B-Architecture
circuit	I-Architecture
,	O
and	O
as	O
a	O
data	B-Architecture
line	I-Architecture
in	O
the	O
UK	O
.	O
</s>
<s>
Typically	O
,	O
leased	B-Architecture
lines	I-Architecture
are	O
used	O
by	O
businesses	O
to	O
connect	O
geographically	O
distant	O
offices	O
.	O
</s>
<s>
Unlike	O
traditional	O
telephone	O
lines	O
in	O
the	O
public	O
switched	O
telephone	O
network	O
(	O
PSTN	O
)	O
leased	B-Architecture
lines	I-Architecture
are	O
generally	O
not	O
switched	O
circuits	O
,	O
and	O
therefore	O
do	O
not	O
have	O
an	O
associated	O
telephone	O
number	O
.	O
</s>
<s>
Leased	B-Architecture
lines	I-Architecture
can	O
be	O
used	O
for	O
telephone	O
,	O
Internet	O
,	O
or	O
other	O
data	O
communication	O
services	O
.	O
</s>
<s>
Some	O
are	O
ringdown	O
services	O
,	O
and	O
some	O
connect	O
to	O
a	O
private	B-Device
branch	I-Device
exchange	I-Device
(	O
PBX	B-Device
)	O
or	O
network	B-Protocol
router	I-Protocol
.	O
</s>
<s>
The	O
primary	O
factors	O
affecting	O
the	O
recurring	O
lease	O
fees	O
are	O
the	O
distance	O
between	O
end	B-Protocol
stations	I-Protocol
and	O
the	O
bandwidth	O
of	O
the	O
circuit	O
.	O
</s>
<s>
An	O
Internet	O
leased	B-Architecture
line	I-Architecture
is	O
a	O
premium	O
Internet	O
connectivity	O
product	O
,	O
normally	O
delivered	O
over	O
fiber	O
,	O
which	O
provides	O
uncontended	O
,	O
symmetrical	O
bandwidth	O
with	O
full-duplex	O
traffic	O
.	O
</s>
<s>
It	O
is	O
also	O
known	O
as	O
an	O
Ethernet	O
leased	B-Architecture
line	I-Architecture
,	O
dedicated	B-Protocol
line	I-Protocol
,	O
data	O
circuit	O
or	O
private	O
line	O
.	O
</s>
<s>
Leased	B-Architecture
line	I-Architecture
services	O
(	O
or	O
private	O
line	O
services	O
)	O
became	O
digital	O
in	O
the	O
1970s	O
with	O
the	O
conversion	O
of	O
the	O
Bell	O
backbone	B-General_Concept
network	I-General_Concept
from	O
analog	O
to	O
digital	O
circuits	O
.	O
</s>
<s>
This	O
allowed	O
AT&T	O
to	O
offer	O
Dataphone	O
Digital	O
Services	O
(	O
later	O
re-branded	O
digital	O
data	O
services	O
)	O
that	O
started	O
the	O
deployment	O
of	O
ISDN	B-Protocol
and	O
T1	B-Protocol
lines	I-Protocol
to	O
customer	O
premises	O
to	O
connect	O
.	O
</s>
<s>
Leased	B-Architecture
lines	I-Architecture
were	O
used	O
to	O
connect	O
mainframe	B-Architecture
computers	I-Architecture
with	O
terminals	O
and	O
remote	O
sites	O
,	O
via	O
IBM	O
's	O
Systems	B-Architecture
Network	I-Architecture
Architecture	I-Architecture
(	O
created	O
in	O
1974	O
)	O
or	O
DEC	O
's	O
DECnet	B-Protocol
(	O
created	O
in	O
1975	O
)	O
.	O
</s>
<s>
With	O
the	O
extension	O
of	O
digital	O
services	O
in	O
the	O
1980s	O
,	O
leased	B-Architecture
lines	I-Architecture
were	O
used	O
to	O
connect	O
customer	O
premises	O
to	O
Frame	B-Protocol
Relay	I-Protocol
or	O
ATM	O
networks	O
.	O
</s>
<s>
Access	O
data	O
rates	O
increased	O
from	O
the	O
original	O
T1	B-Protocol
option	O
with	O
maximum	O
transmission	O
speed	O
of	O
1.544Mbit/s	O
up	O
to	O
T3	O
circuits	O
.	O
</s>
<s>
In	O
the	O
1990s	O
,	O
with	O
the	O
advances	O
of	O
the	O
Internet	O
,	O
leased	B-Architecture
lines	I-Architecture
were	O
also	O
used	O
to	O
connect	O
customer	O
premises	O
to	O
ISP	O
point	O
of	O
presence	O
whilst	O
the	O
following	O
decade	O
saw	O
a	O
convergence	O
of	O
the	O
aforementioned	O
services	O
(	O
frame	B-Protocol
relay	I-Protocol
,	O
ATM	O
,	O
Internet	O
for	O
businesses	O
)	O
with	O
the	O
MPLS	B-Protocol
integrated	O
offerings	O
.	O
</s>
<s>
Leased	B-Architecture
lines	I-Architecture
are	O
used	O
to	O
build	O
up	O
private	O
networks	O
,	O
private	O
telephone	O
networks	O
(	O
by	O
interconnecting	O
PBXs	O
)	O
or	O
access	O
the	O
internet	O
or	O
a	O
partner	O
network	O
(	O
extranet	B-Architecture
)	O
.	O
</s>
<s>
Here	O
is	O
a	O
review	O
of	O
the	O
leased-line	O
applications	O
in	O
network	B-Architecture
designs	I-Architecture
over	O
time	O
:	O
</s>
<s>
Terminating	O
a	O
leased	B-Architecture
line	I-Architecture
with	O
two	O
routers	B-Protocol
can	O
extend	O
network	O
capabilities	O
across	O
sites	O
.	O
</s>
<s>
Leased	B-Architecture
lines	I-Architecture
were	O
first	O
used	O
in	O
the	O
1970s	O
by	O
enterprise	O
with	O
proprietary	O
protocols	O
such	O
as	O
IBM	O
System	B-Architecture
Network	I-Architecture
Architecture	I-Architecture
and	O
Digital	O
Equipment	O
DECnet	B-Protocol
,	O
and	O
with	O
TCP/IP	B-Protocol
in	O
University	O
and	O
Research	O
networks	O
before	O
the	O
Internet	O
became	O
widely	O
available	O
.	O
</s>
<s>
Note	O
that	O
other	O
Layer	B-Application
3	I-Application
protocols	O
were	O
used	O
such	O
as	O
Novell	O
IPX	O
on	O
enterprise	O
networks	O
until	O
TCP/IP	B-Protocol
became	O
ubiquitous	O
in	O
the	O
2000s	O
.	O
</s>
<s>
Today	O
,	O
point	O
to	O
point	O
data	O
circuits	O
are	O
typically	O
provisioned	O
as	O
either	O
TDM	B-Protocol
,	O
Ethernet	O
,	O
or	O
Layer	B-Application
3	I-Application
MPLS	B-Protocol
.	O
</s>
<s>
Terminating	O
a	O
leased	B-Architecture
line	I-Architecture
with	O
two	O
PBX	B-Device
allowed	O
customers	O
to	O
by-pass	O
PSTN	O
for	O
inter-site	O
telephony	O
.	O
</s>
<s>
This	O
allowed	O
the	O
customers	O
to	O
manage	O
their	O
own	O
dial	O
plan	O
(	O
and	O
to	O
use	O
short	O
extensions	O
for	O
internal	O
telephone	O
number	O
)	O
as	O
well	O
as	O
to	O
make	O
significant	O
savings	O
if	O
enough	O
voice	O
traffic	O
was	O
carried	O
across	O
the	O
line	O
(	O
especially	O
when	O
the	O
savings	O
on	O
the	O
telephone	O
bill	O
exceeded	O
the	O
fixed	O
cost	O
of	O
the	O
leased	B-Architecture
line	I-Architecture
)	O
.	O
</s>
<s>
As	O
demand	O
grew	O
on	O
data	O
network	O
telcos	O
started	O
to	O
build	O
more	O
advanced	O
networks	O
using	O
packet	B-Protocol
switching	I-Protocol
on	O
top	O
of	O
their	O
infrastructure	O
.	O
</s>
<s>
Thus	O
,	O
a	O
number	O
of	O
telecommunication	O
companies	O
added	O
ATM	O
,	O
Frame-relay	B-Protocol
or	O
ISDN	B-Protocol
offerings	O
to	O
their	O
services	O
portfolio	O
.	O
</s>
<s>
Leased	B-Architecture
lines	I-Architecture
were	O
used	O
to	O
connect	O
the	O
customer	O
site	O
to	O
the	O
telco	O
network	O
access	O
point	O
.	O
</s>
<s>
An	O
international	B-Architecture
private	I-Architecture
leased	I-Architecture
circuit	I-Architecture
(	O
IPLC	B-Architecture
)	O
functions	O
as	O
a	O
point-to-point	O
private	O
line	O
.	O
</s>
<s>
IPLCs	B-Architecture
are	O
usually	O
time-division	B-Protocol
multiplexing	I-Protocol
(	O
TDM	B-Protocol
)	O
circuits	O
that	O
utilize	O
the	O
same	O
circuit	O
amongst	O
many	O
customers	O
.	O
</s>
<s>
The	O
nature	O
of	O
TDM	B-Protocol
requires	O
the	O
use	O
of	O
a	O
CSU/DSU	O
and	O
a	O
router	B-Protocol
.	O
</s>
<s>
Usually	O
the	O
router	B-Protocol
will	O
include	O
the	O
CSU/DSU	O
.	O
</s>
<s>
Then	O
came	O
the	O
Internet	O
(	O
in	O
the	O
mid-1990s	O
)	O
and	O
since	O
then	O
the	O
most	O
common	O
application	O
for	O
leased	B-Architecture
line	I-Architecture
is	O
to	O
connect	O
a	O
customer	O
to	O
its	O
ISP	O
point	O
of	O
presence	O
.	O
</s>
<s>
With	O
the	O
changes	O
that	O
the	O
Internet	O
brought	O
in	O
the	O
networking	O
world	O
other	O
technologies	O
were	O
developed	O
to	O
propose	O
alternatives	O
to	O
frame-relay	B-Protocol
or	O
ATM	O
networks	O
such	O
as	O
VPNs	B-Application
(	O
hardware	O
and	O
software	O
)	O
and	O
MPLS	B-Protocol
networks	O
(	O
that	O
are	O
in	O
effect	O
an	O
upgrade	O
to	O
TCP/IP	B-Protocol
of	O
existing	O
ATM/frame	O
-relay	O
infrastructures	O
)	O
.	O
</s>
<s>
In	O
the	O
UK	O
,	O
leased	B-Architecture
lines	I-Architecture
are	O
available	O
at	O
speeds	O
from	O
64kbit/s	O
increasing	O
in	O
64kbit/s	O
increments	O
to	O
2.048Mbit/s	O
over	O
a	O
channelised	O
E1	O
tail	O
circuit	O
and	O
at	O
speeds	O
between	O
2.048Mbit/s	O
to	O
34.368Mbit/s	O
via	O
channelised	O
E3	O
tail	O
circuits	O
.	O
</s>
<s>
The	O
NTE	O
will	O
terminate	O
the	O
circuit	O
and	O
provide	O
the	O
requested	O
presentation	O
most	O
frequently	O
X.21	B-Protocol
however	O
higher	O
speed	O
interfaces	O
are	O
available	O
such	O
as	O
G.703	O
or	O
10BASE-T	B-Protocol
.	O
</s>
<s>
Some	O
ISPs	O
however	O
use	O
the	O
term	O
more	O
loosely	O
,	O
defining	O
a	O
leased	B-Architecture
line	I-Architecture
as	O
“	O
any	O
dedicated	O
bandwidth	O
service	O
delivered	O
over	O
a	O
leased	O
fibre	O
connection	O
"	O
.	O
</s>
<s>
As	O
of	O
March	O
2018	O
,	O
Leased	B-Architecture
Line	I-Architecture
services	O
are	O
most	O
commonly	O
available	O
in	O
the	O
region	O
of	O
100	O
Mbit/s	O
to	O
1	O
Gbit/s	O
.	O
</s>
<s>
In	O
the	O
U.S.	O
,	O
low-speed	O
leased	B-Architecture
lines	I-Architecture
(	O
56	O
kbit/s	O
and	O
below	O
)	O
are	O
usually	O
provided	O
using	O
analog	O
modems	O
.	O
</s>
<s>
Higher-speed	O
leased	B-Architecture
lines	I-Architecture
are	O
usually	O
presented	O
using	O
FT1	B-Architecture
(	O
Fractional	B-Architecture
T1	I-Architecture
)	O
:	O
a	O
T1	B-Protocol
bearer	O
circuit	O
with	O
1	O
to	O
24	O
,	O
56k	O
or	O
64k	O
timeslots	O
.	O
</s>
<s>
In	O
Hong	O
Kong	O
,	O
leased	B-Architecture
lines	I-Architecture
are	O
usually	O
available	O
at	O
speeds	O
of	O
64k	O
,	O
128k	O
,	O
256k	O
,	O
512k	O
,	O
T1	B-Protocol
(	O
channelized	O
or	O
not	O
)	O
or	O
E1	O
(	O
less	O
common	O
)	O
.	O
</s>
<s>
In	O
India	O
,	O
leased	B-Architecture
lines	I-Architecture
are	O
available	O
at	O
speeds	O
of	O
64kbit/s	O
,	O
128kbit/s	O
,	O
256kbit/s	O
,	O
512kbit/s	O
,	O
1Mbit/s	O
,	O
2Mbit/s	O
,	O
4Mbit/s	O
,	O
8Mbit/s	O
,	O
1000Mbit/s	O
T1( 	O
1.544Mbit/s	O
)	O
or	O
E1( 	O
2.048Mbit/s	O
)	O
and	O
up	O
to	O
622Mbit/s	O
.	O
</s>
<s>
Customers	O
are	O
connected	O
either	O
through	O
OFC	B-Architecture
,	O
telephone	O
lines	O
,	O
ADSL	O
,	O
or	O
through	O
Wi-Fi	O
.	O
</s>
<s>
In	O
Italy	O
,	O
leased	B-Architecture
lines	I-Architecture
are	O
available	O
at	O
speeds	O
of	O
64kbit/s	O
(	O
terminated	O
by	O
DCE2	O
or	O
DCE2plus	O
modem	O
)	O
or	O
multiple	O
of	O
64kbit/s	O
from	O
128kbit/s	O
up	O
to	O
framed	O
or	O
unframed	O
E1	O
(	O
DCE3	O
modem	O
)	O
in	O
digital	O
form	O
(	O
PDH	O
service	O
,	O
known	O
as	O
CDN	O
,	O
Circuito	O
Diretto	O
Numerico	O
)	O
.	O
</s>
<s>
Local	O
telephone	O
companies	O
also	O
may	O
provide	O
CDA	O
(	O
Circuito	O
Diretto	O
Analogico	O
)	O
,	O
that	O
are	O
plain	O
copper	O
dry	B-Architecture
pair	I-Architecture
between	O
two	O
buildings	O
,	O
without	O
any	O
line	O
termination	O
:	O
in	O
the	O
past	O
(	O
pre-2002	O
)	O
a	O
full	O
analog	O
base	O
band	O
was	O
provided	O
,	O
giving	O
an	O
option	O
to	O
customer	O
to	O
deploy	O
xDSL	O
technology	O
between	O
sites	O
:	O
nowadays	O
everything	O
is	O
limited	O
at	O
4kHz	O
of	O
bearer	O
channel	O
,	O
so	O
the	O
service	O
is	O
just	O
a	O
POTS	O
connection	O
without	O
any	O
setup	O
channel	O
.	O
</s>
<s>
For	O
many	O
purposes	O
,	O
leased	B-Architecture
lines	I-Architecture
are	O
gradually	O
being	O
replaced	O
by	O
DSL	O
and	O
metro	B-Protocol
Ethernet	I-Protocol
.	O
</s>
<s>
Leased	B-Architecture
lines	I-Architecture
are	O
more	O
expensive	O
than	O
alternative	O
connectivity	O
services	O
including	O
(	O
ADSL	O
,	O
SDSL	O
,	O
etc	O
.	O
)	O
</s>
<s>
While	O
a	O
leased	B-Architecture
line	I-Architecture
is	O
full-duplex	O
,	O
most	O
leased	B-Architecture
line	I-Architecture
alternatives	O
provide	O
only	O
half-duplex	O
or	O
in	O
many	O
cases	O
asymmetrical	O
service	O
.	O
</s>
