<s>
The	O
Elektronisches	O
Wählsystem	O
Digital	O
(	O
EWSD	B-Device
)	O
,	O
translated	O
to	O
Electronic	O
Digital	O
Switching	O
System	O
in	O
English	O
,	O
is	O
a	O
widely	O
installed	O
German	O
telephone	O
exchange	O
system	O
,	O
originally	O
introduced	O
in	O
1975	O
by	O
Siemens	O
AG	O
,	O
but	O
discontinued	O
in	O
2017	O
.	O
</s>
<s>
EWSD	B-Device
can	O
operate	O
as	O
a	O
local	O
end-office	O
switch	O
,	O
a	O
tandem	O
switch	O
,	O
or	O
in	O
a	O
combined	O
configuration	O
for	O
landline	B-Application
or	O
mobile	O
telephone	O
service	O
.	O
</s>
<s>
Siemens	O
claims	O
that	O
EWSD	B-Device
switches	O
perform	O
switching	O
for	O
over	O
160	O
million	O
subscriber	O
lines	O
in	O
more	O
than	O
one	O
hundred	O
countries	O
.	O
</s>
<s>
EWSD	B-Device
was	O
introduced	O
in	O
1975	O
as	O
a	O
successor	O
of	O
the	O
EWSA	B-Device
(	O
Elektronisches	O
Wählsystem	O
Analog	O
)	O
,	O
which	O
was	O
using	O
analogue	O
technology	O
.	O
</s>
<s>
DeTeWe	O
bought	O
its	O
first	O
EWSD	B-Device
under	O
license	O
in	O
1985	O
for	O
remote	O
switching	O
.	O
</s>
<s>
Bosch	O
built	O
its	O
first	O
EWSD	B-Device
as	O
a	O
local	O
exchange	O
in	O
1986	O
.	O
</s>
<s>
Deutsche	O
Telekom	O
,	O
formerly	O
Deutsche	O
Bundespost	O
,	O
the	O
largest	O
German	O
telephone	O
company	O
,	O
uses	O
EWSD	B-Device
and	O
System	O
12	O
(	O
Alcatel	O
)	O
,	O
the	O
former	O
more	O
than	O
the	O
latter	O
.	O
</s>
<s>
In	O
2007	O
,	O
Siemens	O
AG	O
and	O
Nokia	O
Corporation	O
jointly	O
formed	O
a	O
new	O
company	O
called	O
Nokia	O
Siemens	O
Networks	O
,	O
and	O
transferred	O
responsibility	O
of	O
further	O
development	O
and	O
shipments	O
of	O
the	O
EWSD	B-Device
system	O
to	O
the	O
new	O
company	O
.	O
</s>
<s>
The	O
major	O
six	O
subsystems	O
of	O
EWSD	B-Device
are	O
the	O
Coordination	O
Processor	O
(	O
CP	O
)	O
,	O
the	O
Common	O
Channel	O
Network	O
Control	O
(	O
CCNC	O
)	O
,	O
the	O
Line	O
Trunk	O
Group	O
(	O
LTG	O
)	O
,	O
the	O
Digital	O
Line	O
Unit	O
(	O
DLU	O
)	O
,	O
the	O
Switching	O
Network	O
(	O
SN	O
)	O
,	O
and	O
the	O
ISDN	B-Protocol
Primary	O
Access	O
Unit	O
(	O
PH	O
)	O
.	O
</s>
<s>
DLU	O
handles	O
analog	O
and	O
ISDN	B-Protocol
lines	I-Protocol
and	O
includes	O
codecs	O
for	O
analog	O
lines	O
,	O
one	O
of	O
the	O
BORSCHT	B-Device
functions	O
for	O
subscriber	O
lines	O
.	O
</s>
<s>
DLU	O
concentrates	O
traffic	O
onto	O
an	O
LTG-B	O
unit	O
,	O
as	O
well	O
as	O
Primary	O
Rate	O
ISDN	B-Protocol
and	O
V5.2	B-Protocol
connections	O
.	O
</s>
<s>
For	O
PCM30	B-Protocol
(	O
E-1	O
)	O
connections	O
to	O
other	O
exchanges	O
,	O
LTG-C	O
Units	O
are	O
used	O
,	O
which	O
also	O
handle	O
signalling	O
including	O
SS7	O
,	O
MFC	O
R2	O
signalling	O
,	O
IKZ	O
(	O
dial	O
pulse	O
)	O
,	O
and	O
E&M	O
.	O
</s>
<s>
The	O
software	O
of	O
EWSD	B-Device
is	O
called	O
the	O
Automatic	O
Program	O
System	O
(	O
APS	O
)	O
.	O
</s>
<s>
It	O
is	O
predominantly	O
written	O
in	O
the	O
CHILL	B-Language
language	O
.	O
</s>
