<s>
In	O
telecommunications	O
,	O
an	O
electronic	B-Device
switching	I-Device
system	I-Device
(	O
ESS	B-Device
)	O
is	O
a	O
telephone	O
switch	O
that	O
uses	O
solid-state	O
electronics	O
,	O
such	O
as	O
digital	O
electronics	O
and	O
computerized	O
common	B-Device
control	I-Device
,	O
to	O
interconnect	O
telephone	B-Architecture
circuits	I-Architecture
for	O
the	O
purpose	O
of	O
establishing	O
telephone	O
calls	O
.	O
</s>
<s>
The	O
first	O
generation	O
of	O
electronic	B-Device
switching	I-Device
systems	I-Device
in	O
the	O
1960s	O
were	O
not	O
entirely	O
digital	O
in	O
nature	O
,	O
but	O
used	O
reed	O
relay-operated	O
metallic	O
paths	O
or	O
crossbar	O
switches	O
operated	O
by	O
stored	B-Device
program	I-Device
control	I-Device
(	O
SPC	O
)	O
systems	O
.	O
</s>
<s>
The	O
first	O
large-scale	O
electronic	B-Device
switching	I-Device
system	I-Device
was	O
the	O
Number	B-Device
One	I-Device
Electronic	I-Device
Switching	I-Device
System	I-Device
(	O
1ESS	B-Device
)	O
of	O
the	O
Bell	O
System	O
,	O
cut	O
over	O
in	O
Succasunna	O
,	O
New	O
Jersey	O
,	O
in	O
May	O
1965	O
.	O
</s>
<s>
The	O
adoption	O
of	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
(	O
MOS	O
)	O
and	O
pulse-code	B-Algorithm
modulation	I-Algorithm
(	O
PCM	B-Algorithm
)	O
technologies	O
in	O
the	O
1970s	O
led	O
to	O
the	O
transition	O
from	O
analog	O
to	O
digital	B-General_Concept
telephony	I-General_Concept
.	O
</s>
<s>
Later	O
electronic	B-Device
switching	I-Device
systems	I-Device
implemented	O
the	O
digital	O
representation	O
of	O
the	O
electrical	O
audio	O
signals	O
on	O
subscriber	B-Architecture
loops	I-Architecture
by	O
digitizing	O
the	O
analog	O
signals	O
and	O
processing	O
the	O
resulting	O
data	O
for	O
transmission	O
between	O
central	O
offices	O
.	O
</s>
<s>
Time-division	B-Protocol
multiplexing	I-Protocol
(	O
TDM	O
)	O
technology	O
permitted	O
the	O
simultaneous	O
transmission	O
of	O
multiple	O
telephone	O
calls	O
on	O
a	O
single	O
wire	O
connection	O
between	O
central	O
offices	O
or	O
other	O
electronic	O
switches	O
,	O
resulting	O
in	O
dramatic	O
capacity	O
improvements	O
of	O
the	O
telephone	O
network	O
.	O
</s>
<s>
In	O
the	O
late	O
20th	O
century	O
most	O
telephone	O
exchanges	O
without	O
TDM	O
processing	O
were	O
eliminated	O
and	O
the	O
term	O
electronic	B-Device
switching	I-Device
system	I-Device
became	O
largely	O
a	O
historical	O
distinction	O
for	O
the	O
older	O
SPC	O
systems	O
.	O
</s>
