<s>
When	O
customers	O
of	O
a	O
public	O
switched	O
telephone	O
network	O
make	O
telephone	O
calls	O
,	O
they	O
utilize	O
a	O
telecommunications	O
network	O
called	O
a	O
switched-circuit	B-Protocol
network	O
.	O
</s>
<s>
In	O
a	O
switched-circuit	B-Protocol
network	O
,	O
devices	O
known	O
as	O
switches	O
are	O
used	O
to	O
connect	O
the	O
calling	O
party	O
to	O
the	O
called	O
party	O
.	O
</s>
<s>
In	O
a	O
modern	O
circuit-switched	B-Protocol
network	I-Protocol
,	O
switches	O
can	O
connect	O
any	O
inlet	O
to	O
any	O
outlet	O
;	O
this	O
is	O
known	O
as	O
full	B-Device
availability	I-Device
.	O
</s>
