<s>
In	O
telecommunication	O
,	O
a	O
paired	B-Protocol
disparity	I-Protocol
code	I-Protocol
is	O
a	O
line	B-Protocol
code	I-Protocol
in	O
which	O
at	O
least	O
one	O
of	O
the	O
data	O
characters	O
is	O
represented	O
by	O
two	O
codewords	O
of	O
opposite	O
disparity	O
that	O
are	O
used	O
in	O
sequence	O
so	O
as	O
to	O
minimize	O
the	O
total	O
disparity	O
of	O
a	O
longer	O
sequence	O
of	O
digits	O
.	O
</s>
<s>
A	O
particular	O
codeword	O
of	O
any	O
line	B-Protocol
code	I-Protocol
can	O
either	O
have	O
no	O
disparity	O
(	O
the	O
average	O
weight	O
of	O
the	O
codeword	O
is	O
zero	O
)	O
,	O
negative	O
disparity	O
(	O
the	O
average	O
weight	O
of	O
the	O
codeword	O
is	O
negative	O
)	O
,	O
or	O
positive	O
disparity	O
(	O
the	O
average	O
weight	O
of	O
the	O
codeword	O
is	O
positive	O
)	O
.	O
</s>
<s>
In	O
a	O
paired	B-Protocol
disparity	I-Protocol
code	I-Protocol
,	O
every	O
codeword	O
that	O
averages	O
to	O
a	O
negative	O
level	O
(	O
negative	O
disparity	O
)	O
is	O
paired	O
with	O
some	O
other	O
codeword	O
that	O
averages	O
to	O
a	O
positive	O
level	O
(	O
positive	O
disparity	O
)	O
.	O
</s>
<s>
In	O
a	O
system	O
that	O
uses	O
a	O
paired	B-Protocol
disparity	I-Protocol
code	I-Protocol
,	O
the	O
transmitter	O
must	O
keep	O
track	O
of	O
the	O
running	O
DC	O
buildup	O
the	O
running	O
disparity	O
and	O
always	O
pick	O
the	O
codeword	O
that	O
pushes	O
the	O
DC	O
level	O
back	O
towards	O
zero	O
.	O
</s>
<s>
Most	O
line	B-Protocol
codes	I-Protocol
use	O
either	O
a	O
paired	B-Protocol
disparity	I-Protocol
code	I-Protocol
or	O
a	O
constant-weight	B-Error_Name
code	I-Error_Name
.	O
</s>
<s>
The	O
simplest	O
paired	B-Protocol
disparity	I-Protocol
code	I-Protocol
is	O
alternate	O
mark	O
inversion	O
signal	O
.	O
</s>
<s>
Other	O
paired	B-Protocol
disparity	I-Protocol
codes	I-Protocol
include	O
8b/10b	B-Protocol
,	O
8B12B	O
,	O
the	O
modified	B-Protocol
AMI	I-Protocol
codes	I-Protocol
,	O
coded	B-Protocol
mark	I-Protocol
inversion	I-Protocol
,	O
and	O
4B3T	B-Protocol
.	O
</s>
