<s>
IEC	B-General_Concept
61334	I-General_Concept
,	O
known	O
as	O
Distribution	O
automation	O
using	O
distribution	O
line	O
carrier	O
systems	O
,	O
is	O
a	O
standard	O
for	O
low-speed	O
reliable	O
power	B-Device
line	I-Device
communications	I-Device
by	O
electricity	O
meters	O
,	O
water	O
meters	O
and	O
SCADA	O
.	O
</s>
<s>
It	O
is	O
also	O
known	O
as	O
spread	B-General_Concept
frequency-shift	I-General_Concept
keying	I-General_Concept
(	O
S-FSK	B-General_Concept
)	O
and	O
was	O
formerly	O
known	O
as	O
IEC	B-General_Concept
1334	I-General_Concept
before	O
IEC	O
's	O
most	O
recent	O
renumbering	O
.	O
</s>
<s>
Internet	B-Protocol
Protocol	I-Protocol
over	O
S-FSK	B-General_Concept
)	O
,	O
but	O
not	O
the	O
higher	O
layers	O
.	O
</s>
<s>
S-FSK	B-General_Concept
centers	O
tones	O
around	O
the	O
time	O
when	O
the	O
AC	O
line	O
passes	O
through	O
zero	O
voltage	O
.	O
</s>
<s>
S-FSK	B-General_Concept
(	O
spread	B-General_Concept
frequency-shift	I-General_Concept
keying	I-General_Concept
)	O
is	O
a	O
modulation	B-Application
scheme	O
that	O
combines	O
some	O
of	O
the	O
advantages	O
of	O
classical	O
spread-spectrum	B-Architecture
modulation	B-Application
(	O
immunity	O
against	O
narrow-band	O
interference	O
)	O
with	O
some	O
of	O
the	O
advantages	O
of	O
classical	O
frequency-shift	O
keying	O
(	O
FSK	O
is	O
low	O
complexity	O
)	O
.	O
</s>
<s>
The	O
difference	O
between	O
S-FSK	B-General_Concept
and	O
classical	O
FSK	O
is	O
that	O
in	O
S-FSK	B-General_Concept
,	O
the	O
mark	O
frequency	O
is	O
placed	O
far	O
from	O
the	O
space	O
frequency	O
.	O
</s>
