<s>
Circuit	B-Protocol
switching	I-Protocol
is	O
a	O
method	O
of	O
implementing	O
a	O
telecommunications	O
network	O
in	O
which	O
two	O
network	B-Protocol
nodes	I-Protocol
establish	O
a	O
dedicated	O
communications	O
channel	O
(	O
circuit	O
)	O
through	O
the	O
network	O
before	O
the	O
nodes	O
may	O
communicate	O
.	O
</s>
<s>
The	O
circuit	O
guarantees	O
the	O
full	O
bandwidth	O
of	O
the	O
channel	O
and	O
remains	O
connected	O
for	O
the	O
duration	O
of	O
the	O
communication	B-Protocol
session	I-Protocol
.	O
</s>
<s>
Circuit	B-Protocol
switching	I-Protocol
originated	O
in	O
analog	O
telephone	O
networks	O
where	O
the	O
network	O
created	O
a	O
dedicated	O
circuit	O
between	O
two	O
telephones	O
for	O
the	O
duration	O
of	O
a	O
telephone	O
call	O
.	O
</s>
<s>
It	O
contrasts	O
with	O
message	B-Protocol
switching	I-Protocol
and	O
packet	B-Protocol
switching	I-Protocol
used	O
in	O
modern	O
digital	O
networks	O
in	O
which	O
the	O
trunklines	O
between	O
switching	O
centers	O
carry	O
data	O
between	O
many	O
different	O
nodes	O
in	O
the	O
form	O
of	O
data	B-Protocol
packets	I-Protocol
without	O
dedicated	O
circuits	O
.	O
</s>
<s>
The	O
defining	O
example	O
of	O
a	O
circuit-switched	B-Protocol
network	I-Protocol
is	O
the	O
early	O
analog	O
telephone	O
network	O
.	O
</s>
<s>
In	O
circuit	B-Protocol
switching	I-Protocol
,	O
the	O
bit	O
delay	O
is	O
constant	O
during	O
a	O
connection	O
(	O
as	O
opposed	O
to	O
packet	B-Protocol
switching	I-Protocol
,	O
where	O
packet	B-Protocol
queues	O
may	O
cause	O
varying	O
and	O
potentially	O
indefinitely	O
long	O
packet	B-Protocol
transfer	I-Protocol
delays	I-Protocol
)	O
.	O
</s>
<s>
While	O
circuit	B-Protocol
switching	I-Protocol
is	O
commonly	O
used	O
for	O
connecting	O
voice	O
circuits	O
,	O
the	O
concept	O
of	O
a	O
dedicated	O
path	O
persisting	O
between	O
two	O
communicating	O
parties	O
or	O
nodes	O
can	O
be	O
extended	O
to	O
signal	O
content	O
other	O
than	O
voice	O
.	O
</s>
<s>
The	O
advantage	O
of	O
using	O
circuit	B-Protocol
switching	I-Protocol
is	O
that	O
it	O
provides	O
for	O
continuous	O
transfer	O
without	O
the	O
overhead	O
associated	O
with	O
packets	B-Protocol
,	O
making	O
maximal	O
use	O
of	O
available	O
bandwidth	O
for	O
that	O
communication	O
.	O
</s>
<s>
ISDN	B-Protocol
is	O
one	O
such	O
service	O
that	O
uses	O
a	O
separate	O
signalling	O
channel	O
while	O
plain	O
old	O
telephone	O
service	O
(	O
POTS	O
)	O
does	O
not	O
.	O
</s>
<s>
The	O
method	O
of	O
establishing	O
the	O
connection	O
and	O
monitoring	O
its	O
progress	O
and	O
termination	O
through	O
the	O
network	O
may	O
also	O
utilize	O
a	O
separate	O
control	O
channel	O
as	O
in	O
the	O
case	O
of	O
links	O
between	O
telephone	O
exchanges	O
which	O
use	O
CCS7	O
packet-switched	B-Protocol
signalling	O
protocol	O
to	O
communicate	O
the	O
call	O
setup	O
and	O
control	O
information	O
and	O
use	O
TDM	B-Protocol
to	O
transport	O
the	O
actual	O
circuit	O
data	O
.	O
</s>
<s>
Early	O
telephone	O
exchanges	O
were	O
a	O
suitable	O
example	O
of	O
circuit	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
In	O
circuit	B-Protocol
switching	I-Protocol
,	O
a	O
route	O
and	O
its	O
associated	O
bandwidth	O
is	O
reserved	O
from	O
source	O
to	O
destination	O
,	O
making	O
circuit	B-Protocol
switching	I-Protocol
relatively	O
inefficient	O
since	O
capacity	O
is	O
reserved	O
whether	O
or	O
not	O
the	O
connection	O
is	O
in	O
continuous	O
use	O
.	O
</s>
<s>
Circuit	B-Protocol
switching	I-Protocol
contrasts	O
with	O
message	B-Protocol
switching	I-Protocol
and	O
packet	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
Both	O
of	O
these	O
methods	O
can	O
make	O
better	O
use	O
of	O
available	O
network	O
bandwidth	O
between	O
multiple	O
communication	B-Protocol
sessions	I-Protocol
under	O
typical	O
conditions	O
in	O
data	O
communication	O
networks	O
.	O
</s>
<s>
Message	B-Protocol
switching	I-Protocol
routes	O
messages	O
in	O
their	O
entirety	O
,	O
one	O
hop	O
at	O
a	O
time	O
,	O
that	O
is	O
,	O
store	B-Protocol
and	I-Protocol
forward	I-Protocol
of	O
the	O
entire	O
message	O
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
divides	O
the	O
data	O
to	O
be	O
transmitted	O
into	O
packets	B-Protocol
transmitted	O
through	O
the	O
network	O
independently	O
.	O
</s>
<s>
Instead	O
of	O
being	O
dedicated	O
to	O
one	O
communication	B-Protocol
session	I-Protocol
at	O
a	O
time	O
,	O
network	O
links	O
are	O
shared	O
by	O
packets	B-Protocol
from	O
multiple	O
competing	O
communication	B-Protocol
sessions	I-Protocol
,	O
resulting	O
in	O
the	O
loss	O
of	O
the	O
quality	O
of	O
service	O
guarantees	O
that	O
are	O
provided	O
by	O
circuit	B-Protocol
switching	I-Protocol
.	O
</s>
<s>
Packet	B-Protocol
switching	I-Protocol
can	O
be	O
based	O
on	O
connection-oriented	B-Protocol
communication	I-Protocol
or	O
connection-less	B-Protocol
communication	I-Protocol
.	O
</s>
<s>
That	O
is	O
,	O
based	O
on	O
virtual	B-Protocol
circuits	I-Protocol
or	O
datagrams	B-Protocol
.	O
</s>
<s>
Virtual	B-Protocol
circuits	I-Protocol
use	O
packet	B-Protocol
switching	I-Protocol
technology	O
that	O
emulates	O
circuit	B-Protocol
switching	I-Protocol
,	O
in	O
the	O
sense	O
that	O
the	O
connection	O
is	O
established	O
before	O
any	O
packets	B-Protocol
are	O
transferred	O
,	O
and	O
packets	B-Protocol
are	O
delivered	O
in	O
order	O
.	O
</s>
<s>
Connection-less	B-Protocol
packet	B-Protocol
switching	I-Protocol
divides	O
the	O
data	O
to	O
be	O
transmitted	O
into	O
packets	B-Protocol
,	O
called	O
datagrams	B-Protocol
,	O
transmitted	O
through	O
the	O
network	O
independently	O
.	O
</s>
<s>
Each	O
datagram	B-Protocol
is	O
labeled	O
with	O
its	O
destination	O
and	O
a	O
sequence	O
number	O
for	O
ordering	O
related	O
packets	B-Protocol
,	O
precluding	O
the	O
need	O
for	O
a	O
dedicated	O
path	O
to	O
help	O
the	O
packet	B-Protocol
find	O
its	O
way	O
to	O
its	O
destination	O
.	O
</s>
<s>
Each	O
datagram	B-Protocol
is	O
dispatched	O
independently	O
and	O
each	O
may	O
be	O
routed	O
via	O
a	O
different	O
path	O
.	O
</s>
<s>
At	O
the	O
destination	O
,	O
the	O
original	O
message	O
is	O
reordered	O
based	O
on	O
the	O
packet	B-Protocol
number	O
to	O
reproduce	O
the	O
original	O
message	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
datagram	B-Protocol
packet	B-Protocol
switching	I-Protocol
networks	O
do	O
not	O
require	O
a	O
circuit	O
to	O
be	O
established	O
and	O
allow	O
many	O
pairs	O
of	O
nodes	O
to	O
communicate	O
concurrently	O
over	O
the	O
same	O
channel	O
.	O
</s>
<s>
Multiplexing	B-Architecture
multiple	O
telecommunications	O
connections	O
over	O
the	O
same	O
physical	O
conductor	O
has	O
been	O
possible	O
for	O
a	O
long	O
time	O
,	O
but	O
each	O
channel	O
on	O
the	O
multiplexed	B-Architecture
link	O
was	O
either	O
dedicated	O
to	O
one	O
call	O
at	O
a	O
time	O
,	O
or	O
it	O
was	O
idle	O
between	O
calls	O
.	O
</s>
