<s>
A	O
backbone	B-General_Concept
or	O
core	B-General_Concept
network	I-General_Concept
is	O
a	O
part	O
of	O
a	O
computer	B-Architecture
network	I-Architecture
which	O
interconnects	B-Architecture
networks	O
,	O
providing	O
a	O
path	O
for	O
the	O
exchange	O
of	O
information	O
between	O
different	O
LANs	B-General_Concept
or	O
subnetworks	B-Protocol
.	O
</s>
<s>
A	O
backbone	B-General_Concept
can	O
tie	O
together	O
diverse	O
networks	O
in	O
the	O
same	O
building	O
,	O
in	O
different	O
buildings	O
in	O
a	O
campus	O
environment	O
,	O
or	O
over	O
wide	O
areas	O
.	O
</s>
<s>
Normally	O
,	O
the	O
backbone	B-General_Concept
's	O
capacity	O
is	O
greater	O
than	O
the	O
networks	O
connected	O
to	O
it	O
.	O
</s>
<s>
A	O
large	O
corporation	O
that	O
has	O
many	O
locations	O
may	O
have	O
a	O
backbone	B-General_Concept
network	I-General_Concept
that	O
ties	O
all	O
of	O
the	O
locations	O
together	O
,	O
for	O
example	O
,	O
if	O
a	O
server	O
cluster	O
needs	O
to	O
be	O
accessed	O
by	O
different	O
departments	O
of	O
a	O
company	O
that	O
are	O
located	O
at	O
different	O
geographical	O
locations	O
.	O
</s>
<s>
The	O
pieces	O
of	O
the	O
network	O
connections	O
(	O
for	O
example	O
:	O
ethernet	O
,	O
wireless	O
)	O
that	O
bring	O
these	O
departments	O
together	O
is	O
often	O
mentioned	O
as	O
network	B-General_Concept
backbone	I-General_Concept
.	O
</s>
<s>
Network	B-Protocol
congestion	I-Protocol
is	O
often	O
taken	O
into	O
consideration	O
while	O
designing	O
backbones	B-General_Concept
.	O
</s>
<s>
One	O
example	O
of	O
a	O
backbone	B-General_Concept
network	I-General_Concept
is	O
the	O
Internet	B-General_Concept
backbone	I-General_Concept
.	O
</s>
<s>
The	O
theory	O
,	O
design	O
principles	O
,	O
and	O
first	O
instantiation	O
of	O
the	O
backbone	B-General_Concept
network	I-General_Concept
came	O
from	O
the	O
telephone	O
core	B-General_Concept
network	I-General_Concept
when	O
traffic	O
was	O
purely	O
voice	O
.	O
</s>
<s>
The	O
core	B-General_Concept
network	I-General_Concept
was	O
the	O
central	O
part	O
of	O
a	O
telecommunications	O
network	O
that	O
provided	O
various	O
services	O
to	O
customers	O
who	O
were	O
connected	O
by	O
the	O
access	O
network	O
.	O
</s>
<s>
A	O
core	B-General_Concept
network	I-General_Concept
provided	O
paths	O
for	O
the	O
exchange	O
of	O
information	O
between	O
different	O
sub-networks	B-Protocol
.	O
</s>
<s>
In	O
the	O
United	O
States	O
,	O
local	O
exchange	O
core	B-General_Concept
networks	I-General_Concept
were	O
linked	O
by	O
several	O
competing	O
interexchange	O
networks	O
;	O
in	O
the	O
rest	O
of	O
the	O
world	O
,	O
the	O
core	B-General_Concept
network	I-General_Concept
has	O
been	O
extended	O
to	O
national	O
boundaries	O
.	O
</s>
<s>
Core	B-General_Concept
networks	I-General_Concept
usually	O
had	O
a	O
mesh	B-Architecture
topology	I-Architecture
that	O
provided	O
any-to-any	O
connections	O
among	O
devices	O
on	O
the	O
network	O
.	O
</s>
<s>
Backbone	B-General_Concept
networks	I-General_Concept
create	O
links	O
that	O
allow	O
long-distance	O
transmission	O
,	O
usually	O
10	O
to	O
100	O
miles	O
,	O
and	O
in	O
certain	O
cases	O
-	O
up	O
to	O
150	O
miles	O
.	O
</s>
<s>
This	O
makes	O
backbone	B-General_Concept
network	I-General_Concept
essential	O
to	O
providing	O
long-haul	O
wireless	O
solutions	O
to	O
provide	O
internet	B-Protocol
service	I-Protocol
,	O
especially	O
to	O
remote	O
areas	O
.	O
</s>
<s>
Core	B-General_Concept
networks	I-General_Concept
typically	O
provided	O
the	O
following	O
functionality	O
:	O
</s>
<s>
Customer-premises	O
equipment	O
(	O
CPE	O
)	O
do	O
not	O
normally	O
connect	O
to	O
the	O
core	B-General_Concept
networks	I-General_Concept
of	O
a	O
large	O
service	O
provider	O
.	O
</s>
<s>
switching	O
functionality	O
may	O
decide	O
based	O
on	O
the	O
"	O
called	O
number	O
"	O
that	O
the	O
call	O
be	O
routed	B-Protocol
towards	O
a	O
subscriber	O
within	O
this	O
operator	O
's	O
network	O
or	O
with	O
number	O
portability	O
more	O
prevalent	O
to	O
another	O
operator	O
's	O
network	O
.	O
</s>
<s>
Charging	O
:	O
This	O
functionality	O
of	O
the	O
collation	O
and	O
processing	O
of	O
charging	O
data	O
generated	O
by	O
various	O
network	B-Protocol
nodes	I-Protocol
.	O
</s>
<s>
Service	O
Invocation	O
:	O
Core	B-General_Concept
network	I-General_Concept
performs	O
the	O
task	O
of	O
service	O
invocation	O
for	O
its	O
subscribers	O
.	O
</s>
<s>
It	O
's	O
important	O
to	O
note	O
however	O
that	O
service	O
"	O
execution	O
"	O
may	O
or	O
may	O
not	O
be	O
a	O
core	B-General_Concept
network	I-General_Concept
functionality	O
as	O
third	O
party	O
network/nodes	O
may	O
take	O
part	O
in	O
actual	O
service	O
execution	O
.	O
</s>
<s>
Gateways	B-Application
:	O
Gateways	B-Application
shall	O
be	O
present	O
in	O
the	O
core	B-General_Concept
network	I-General_Concept
to	O
access	O
other	O
networks	O
.	O
</s>
<s>
Gateway	B-Application
functionality	O
is	O
dependent	O
on	O
the	O
type	O
of	O
network	O
it	O
interfaces	O
with	O
.	O
</s>
<s>
Physically	O
,	O
one	O
or	O
more	O
of	O
these	O
logical	O
functionalities	O
may	O
simultaneously	O
exist	O
in	O
a	O
given	O
core	B-General_Concept
network	I-General_Concept
node	B-Protocol
.	O
</s>
<s>
Besides	O
above-mentioned	O
functionalities	O
,	O
the	O
following	O
also	O
formed	O
part	O
of	O
a	O
telecommunications	O
core	B-General_Concept
network	I-General_Concept
:	O
</s>
<s>
O&M	O
:	O
Operations	O
&	O
Maintenance	O
centre	O
or	O
Operations	O
Support	O
Systems	O
to	O
configure	O
and	O
provision	O
the	O
core	B-General_Concept
network	I-General_Concept
nodes	O
.	O
</s>
<s>
Network	O
statistics	O
collection	O
(	O
Performance	O
Management	O
)	O
,	O
alarm	O
monitoring	O
(	O
Fault	O
Management	O
)	O
and	O
logging	O
of	O
various	O
network	B-Protocol
nodes	I-Protocol
actions	O
(	O
Event	O
Management	O
)	O
also	O
happens	O
in	O
the	O
O&M	O
centre	O
.	O
</s>
<s>
Subscriber	O
Database	O
:	O
Core	B-General_Concept
network	I-General_Concept
also	O
hosts	O
the	O
subscribers	O
database	O
(	O
e.g.	O
</s>
<s>
Subscriber	O
database	O
is	O
accessed	O
by	O
core	B-General_Concept
network	I-General_Concept
nodes	O
for	O
functions	O
like	O
authentication	O
,	O
profiling	O
,	O
service	O
invocation	O
etc	O
.	O
</s>
<s>
A	O
distributed	B-General_Concept
backbone	I-General_Concept
is	O
a	O
backbone	B-General_Concept
network	I-General_Concept
that	O
consists	O
of	O
a	O
number	O
of	O
connectivity	O
devices	O
connected	O
to	O
a	O
series	O
of	O
central	O
connectivity	O
devices	O
,	O
such	O
as	O
hubs	O
,	O
switches	O
,	O
or	O
routers	B-Protocol
,	O
in	O
a	O
hierarchy	O
.	O
</s>
<s>
This	O
kind	O
of	O
topology	B-Architecture
allows	O
for	O
simple	O
expansion	O
and	O
limited	O
capital	O
outlay	O
for	O
growth	O
,	O
because	O
more	O
layers	O
of	O
devices	O
can	O
be	O
added	O
to	O
existing	O
layers	O
.	O
</s>
<s>
In	O
a	O
distributed	B-General_Concept
backbone	I-General_Concept
network	O
,	O
all	O
of	O
the	O
devices	O
that	O
access	O
the	O
backbone	B-General_Concept
share	O
the	O
transmission	O
media	O
,	O
as	O
every	O
device	O
connected	O
to	O
this	O
network	O
is	O
sent	O
all	O
transmissions	O
placed	O
on	O
that	O
network	O
.	O
</s>
<s>
Distributed	B-General_Concept
backbones	I-General_Concept
,	O
in	O
all	O
practicality	O
,	O
are	O
in	O
use	O
by	O
all	O
large-scale	O
networks	O
.	O
</s>
<s>
Each	O
floor	O
or	O
department	O
possesses	O
a	O
LAN	B-General_Concept
and	O
a	O
wiring	O
closet	O
with	O
that	O
workgroup	O
's	O
main	O
hub	O
or	O
router	B-Protocol
connected	O
to	O
a	O
bus-style	O
network	O
using	O
backbone	B-General_Concept
cabling	O
.	O
</s>
<s>
Another	O
advantage	O
of	O
using	O
a	O
distributed	B-General_Concept
backbone	I-General_Concept
is	O
the	O
ability	O
for	O
network	O
administrator	O
to	O
segregate	O
workgroups	O
for	O
ease	O
of	O
management	O
.	O
</s>
<s>
The	O
distributed	B-General_Concept
backbone	I-General_Concept
must	O
be	O
designed	O
to	O
separate	O
network	O
traffic	O
circulating	O
on	O
each	O
individual	O
LAN	B-General_Concept
from	O
the	O
backbone	B-General_Concept
network	I-General_Concept
traffic	O
by	O
using	O
access	O
devices	O
such	O
as	O
routers	B-Protocol
and	O
bridges	B-Protocol
.	O
</s>
<s>
A	O
conventional	O
backbone	B-General_Concept
network	I-General_Concept
spans	O
distance	O
to	O
provide	O
interconnectivity	B-Architecture
across	O
multiple	O
locations	O
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
the	O
backbones	B-General_Concept
are	O
the	O
links	O
while	O
the	O
switching	O
or	O
routing	B-Protocol
functions	O
are	O
done	O
by	O
the	O
equipment	O
at	O
each	O
location	O
.	O
</s>
<s>
A	O
collapsed	B-General_Concept
backbone	I-General_Concept
(	O
also	O
known	O
as	O
inverted	O
backbone	B-General_Concept
or	O
backbone-in-a-box	O
)	O
is	O
a	O
type	O
of	O
backbone	B-General_Concept
network	I-General_Concept
architecture	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
a	O
collapsed	B-General_Concept
backbone	I-General_Concept
,	O
each	O
location	O
features	O
a	O
link	O
back	O
to	O
a	O
central	O
location	O
to	O
be	O
connected	O
to	O
the	O
collapsed	B-General_Concept
backbone	I-General_Concept
.	O
</s>
<s>
The	O
collapsed	B-General_Concept
backbone	I-General_Concept
can	O
be	O
a	O
cluster	O
or	O
a	O
single	O
switch	B-Protocol
or	O
router	B-Protocol
.	O
</s>
<s>
The	O
topology	B-Architecture
and	O
architecture	O
of	O
a	O
collapsed	B-General_Concept
backbone	I-General_Concept
is	O
a	O
star	B-Architecture
or	O
a	O
rooted	O
tree	O
.	O
</s>
<s>
since	O
the	O
backbone	B-General_Concept
is	O
essentially	O
the	O
back	O
plane	O
or	O
internal	O
switching	O
matrix	O
of	O
the	O
box	O
,	O
proprietary	O
,	O
high	B-Architecture
performance	I-Architecture
technology	I-Architecture
can	O
be	O
used	O
.	O
</s>
<s>
However	O
,	O
the	O
drawback	O
of	O
the	O
collapsed	B-General_Concept
backbone	I-General_Concept
is	O
that	O
if	O
the	O
box	O
housing	O
the	O
backbone	B-General_Concept
is	O
down	O
or	O
there	O
are	O
reachability	O
problem	O
to	O
the	O
central	O
location	O
,	O
the	O
entire	O
network	O
will	O
crash	O
.	O
</s>
<s>
These	O
problems	O
can	O
be	O
minimized	O
by	O
having	O
redundant	O
backbone	B-General_Concept
boxes	O
as	O
well	O
as	O
having	O
secondary/backup	O
backbone	B-General_Concept
locations	O
.	O
</s>
<s>
There	O
are	O
a	O
few	O
different	O
types	O
of	O
backbones	B-General_Concept
that	O
are	O
used	O
for	O
an	O
enterprise-wide	O
network	O
.	O
</s>
<s>
When	O
organizations	O
are	O
looking	O
for	O
a	O
very	O
strong	O
and	O
trustworthy	O
backbone	B-General_Concept
they	O
should	O
choose	O
a	O
parallel	B-General_Concept
backbone	I-General_Concept
.	O
</s>
<s>
This	O
backbone	B-General_Concept
is	O
a	O
variation	O
of	O
a	O
collapsed	B-General_Concept
backbone	I-General_Concept
in	O
that	O
it	O
uses	O
a	O
central	O
node	B-Protocol
(	O
connection	O
point	O
)	O
.	O
</s>
<s>
Although	O
,	O
with	O
a	O
parallel	B-General_Concept
backbone	I-General_Concept
,	O
it	O
allows	O
for	O
duplicate	O
connections	O
when	O
there	O
is	O
more	O
than	O
one	O
router	B-Protocol
or	O
switch	B-Protocol
.	O
</s>
<s>
Each	O
switch	B-Protocol
and	O
router	B-Protocol
are	O
connected	O
by	O
two	O
cables	O
.	O
</s>
<s>
Parallel	B-General_Concept
backbones	I-General_Concept
are	O
more	O
expensive	O
than	O
other	O
backbone	B-General_Concept
networks	I-General_Concept
because	O
they	O
require	O
more	O
cabling	O
than	O
the	O
other	O
network	B-Architecture
topologies	I-Architecture
.	O
</s>
<s>
Although	O
this	O
can	O
be	O
a	O
major	O
factor	O
when	O
deciding	O
which	O
enterprise-wide	O
topology	B-Architecture
to	O
use	O
,	O
the	O
expense	O
of	O
it	O
makes	O
up	O
for	O
the	O
efficiency	O
it	O
creates	O
by	O
adding	O
increased	O
performance	O
and	O
fault	B-General_Concept
tolerance	I-General_Concept
.	O
</s>
<s>
Most	O
organizations	O
use	O
parallel	B-General_Concept
backbones	I-General_Concept
when	O
there	O
are	O
critical	O
devices	O
on	O
the	O
network	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
there	O
is	O
important	O
data	O
,	O
such	O
as	O
payroll	O
,	O
that	O
should	O
be	O
accessed	O
at	O
all	O
times	O
by	O
multiple	O
departments	O
,	O
then	O
your	O
organization	O
should	O
choose	O
to	O
implement	O
a	O
Parallel	B-General_Concept
Backbone	I-General_Concept
to	O
make	O
sure	O
that	O
the	O
connectivity	O
is	O
never	O
lost	O
.	O
</s>
<s>
A	O
serial	B-General_Concept
backbone	I-General_Concept
is	O
the	O
simplest	O
kind	O
of	O
backbone	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Serial	B-General_Concept
backbones	I-General_Concept
consist	O
of	O
two	O
or	O
more	O
internet	O
working	O
devices	O
connected	O
to	O
each	O
other	O
by	O
a	O
single	O
cable	O
in	O
a	O
daisy-chain	O
fashion	O
.	O
</s>
<s>
However	O
,	O
hubs	O
are	O
not	O
the	O
only	O
device	O
that	O
can	O
be	O
connected	O
in	O
a	O
serial	B-General_Concept
backbone	I-General_Concept
.	O
</s>
<s>
Gateways	B-Application
,	O
routers	B-Protocol
,	O
switches	O
and	O
bridges	B-Protocol
more	O
commonly	O
form	O
part	O
of	O
the	O
backbone	B-General_Concept
.	O
</s>
<s>
The	O
serial	B-General_Concept
backbone	I-General_Concept
topology	B-Architecture
could	O
be	O
used	O
for	O
enterprise-wide	O
networks	O
,	O
though	O
it	O
is	O
rarely	O
implemented	O
for	O
that	O
purpose	O
.	O
</s>
