<s>
In	O
telecommunications	O
,	O
8b/10b	B-Protocol
is	O
a	O
line	B-Protocol
code	I-Protocol
that	O
maps	O
8-bit	O
words	O
to	O
10-bit	O
symbols	O
to	O
achieve	O
DC	O
balance	O
and	O
bounded	O
disparity	O
,	O
and	O
at	O
the	O
same	O
time	O
provide	O
enough	O
state	O
changes	O
to	O
allow	O
reasonable	O
clock	O
recovery	O
.	O
</s>
<s>
An	O
8b/10b	B-Protocol
code	O
can	O
be	O
implemented	O
in	O
various	O
ways	O
with	O
focus	O
on	O
different	O
performance	O
paramenters	O
.	O
</s>
<s>
Kees	O
Schouhamer	O
Immink	O
designed	O
an	O
8b/10b	B-Protocol
code	O
for	O
the	O
DCC	O
audio	O
recorder	O
.	O
</s>
<s>
The	O
IBM	O
implementation	O
was	O
described	O
in	O
1983	O
by	O
Al	B-Protocol
Widmer	I-Protocol
and	O
Peter	O
Franaszek	O
.	O
</s>
<s>
Standards	O
using	O
the	O
8b/10b	B-Protocol
encoding	I-Protocol
also	O
define	O
up	O
to	O
12	O
special	O
symbols	O
(	O
or	O
control	O
characters	O
)	O
that	O
can	O
be	O
sent	O
in	O
place	O
of	O
a	O
data	O
symbol	O
.	O
</s>
<s>
Because	O
8b/10b	B-Protocol
encoding	I-Protocol
uses	O
10-bit	O
symbols	O
to	O
encode	O
8-bit	O
words	O
,	O
some	O
of	O
the	O
possible	O
1024	O
(	O
10	O
bit	O
,	O
210	O
)	O
symbols	O
can	O
be	O
excluded	O
to	O
grant	O
a	O
run-length	O
limit	O
of	O
5	O
consecutive	O
equal	O
bits	O
and	O
to	O
ensure	O
the	O
difference	O
between	O
the	O
count	O
of	O
zeros	O
and	O
ones	O
to	O
be	O
no	O
more	O
than	O
two	O
.	O
</s>
<s>
This	O
permits	O
the	O
data	O
stream	O
to	O
be	O
transmitted	O
through	O
a	O
channel	O
with	O
a	O
high-pass	O
characteristic	O
,	O
for	O
example	O
Ethernet	O
's	O
transformer-coupled	O
unshielded	O
twisted	O
pair	O
or	O
optical	O
receivers	O
using	O
automatic	O
gain	O
control	O
.	O
</s>
<s>
The	O
5b/6b	O
code	O
is	O
a	O
paired	B-Protocol
disparity	I-Protocol
code	I-Protocol
,	O
and	O
so	O
is	O
the	O
3b/4b	O
code	O
.	O
</s>
<s>
8b/10b	B-Protocol
coding	O
is	O
DC-free	O
,	O
meaning	O
that	O
the	O
long-term	O
ratio	O
of	O
ones	O
and	O
zeros	O
transmitted	O
is	O
exactly	O
50%	O
.	O
</s>
<s>
The	O
control	O
symbols	O
within	O
8b/10b	B-Protocol
are	O
10b	O
symbols	O
that	O
are	O
valid	O
sequences	O
of	O
bits	O
(	O
no	O
more	O
than	O
six	O
1s	O
or	O
0s	O
)	O
but	O
do	O
not	O
have	O
a	O
corresponding	O
8b	O
data	O
byte	O
.	O
</s>
<s>
For	O
instance	O
,	O
in	O
Fibre	B-Architecture
Channel	I-Architecture
,	O
K28.5	O
is	O
used	O
at	O
the	O
beginning	O
of	O
four-byte	O
sequences	O
(	O
called	O
"	O
Ordered	O
Sets	O
"	O
)	O
that	O
perform	O
functions	O
such	O
as	O
Loop	O
Arbitration	O
,	O
Fill	O
Words	O
,	O
Link	O
Resets	O
,	O
etc	O
.	O
</s>
<s>
Comma	O
symbols	O
are	O
used	O
for	O
synchronization	O
(	O
finding	O
the	O
alignment	O
of	O
the	O
8b/10b	B-Protocol
codes	O
within	O
a	O
bit-stream	O
)	O
.	O
</s>
<s>
After	O
the	O
above-mentioned	O
IBM	O
patent	O
expired	O
,	O
the	O
scheme	O
became	O
even	O
more	O
popular	O
and	O
was	O
chosen	O
as	O
a	O
DC-free	O
line	B-Protocol
code	I-Protocol
for	O
several	O
communication	O
technologies	O
.	O
</s>
<s>
Among	O
the	O
areas	O
in	O
which	O
8b/10b	B-Protocol
encoding	I-Protocol
finds	O
application	O
are	O
the	O
following	O
:	O
</s>
<s>
The	O
FC-0	O
standard	O
defines	O
what	O
encoding	B-Protocol
scheme	I-Protocol
is	O
to	O
be	O
used	O
(	O
8b/10b	B-Protocol
or	O
64b/66b	O
)	O
in	O
a	O
Fibre	B-Architecture
Channel	I-Architecture
system	O
higher	O
speed	O
variants	O
typically	O
use	O
64b/66b	O
to	O
optimize	O
bandwidth	O
efficiency	O
(	O
since	O
bandwidth	O
overhead	O
is	O
20%	O
in	O
8b/10b	B-Protocol
versus	O
approximately	O
3%	O
(	O
~	O
2/66	O
)	O
in	O
64b/66b	O
systems	O
)	O
.	O
</s>
<s>
Thus	O
,	O
8b/10b	B-Protocol
encoding	I-Protocol
is	O
used	O
for	O
4GFC	B-Architecture
and	O
8GFC	B-Architecture
variants	O
;	O
for	O
10GFC	B-Architecture
and	O
16GFC	B-Architecture
variants	O
,	O
it	O
is	O
64b/66b	O
.	O
</s>
<s>
The	O
Fibre	B-Architecture
Channel	I-Architecture
FC1	O
data	O
link	O
layer	O
is	O
then	O
responsible	O
for	O
implementing	O
the	O
8b/10b	B-Protocol
encoding	I-Protocol
and	O
decoding	O
of	O
signals	O
.	O
</s>
<s>
The	O
Fibre	B-Architecture
Channel	I-Architecture
8b/10b	B-Protocol
coding	O
scheme	O
is	O
also	O
used	O
in	O
other	O
telecommunications	O
systems	O
.	O
</s>
<s>
This	O
mapping	O
is	O
usually	O
done	O
at	O
the	O
time	O
when	O
parallel	O
input	O
data	O
is	O
converted	O
into	O
a	O
serial	O
output	O
stream	O
for	O
transmission	O
over	O
a	O
fibre	B-Architecture
channel	I-Architecture
link	O
.	O
</s>
<s>
A	O
differing	O
but	O
related	O
scheme	O
is	O
used	O
for	O
audio	O
CDs	O
and	O
CD-ROMs	B-Device
:	O
</s>
<s>
Note	O
that	O
8b/10b	B-Protocol
is	O
the	O
encoding	B-Protocol
scheme	I-Protocol
,	O
not	O
a	O
specific	O
code	O
.	O
</s>
<s>
While	O
many	O
applications	O
do	O
use	O
the	O
same	O
code	O
,	O
there	O
exist	O
some	O
incompatible	O
implementations	O
;	O
for	O
example	O
,	O
Transition	B-Protocol
Minimized	I-Protocol
Differential	I-Protocol
Signaling	I-Protocol
,	O
which	O
also	O
expands	O
8	O
bits	O
to	O
10	O
bits	O
,	O
but	O
it	O
uses	O
a	O
completely	O
different	O
method	O
to	O
do	O
so	O
.	O
</s>
<s>
64b/66b	O
encoding	O
,	O
introduced	O
for	O
10	O
Gigabit	O
Ethernet	O
's	O
10GBASE-R	O
Physical	B-Protocol
Medium	I-Protocol
Dependent	I-Protocol
(	O
PMD	O
)	O
interfaces	O
,	O
is	O
a	O
lower-overhead	O
alternative	O
to	O
8b/10b	B-Protocol
encoding	I-Protocol
,	O
having	O
a	O
two-bit	O
overhead	O
per	O
64	O
bits	O
(	O
instead	O
of	O
eight	O
bits	O
)	O
of	O
encoded	O
data	O
.	O
</s>
<s>
This	O
scheme	O
is	O
considerably	O
different	O
in	O
design	O
from	O
8b/10b	B-Protocol
encoding	I-Protocol
,	O
and	O
does	O
not	O
explicitly	O
guarantee	O
DC	O
balance	O
,	O
short	O
run	O
length	O
,	O
and	O
transition	O
density	O
(	O
these	O
features	O
are	O
achieved	O
statistically	O
via	O
scrambling	O
)	O
.	O
</s>
<s>
64b/66b	O
encoding	O
has	O
been	O
extended	O
to	O
the	O
128b/130b	O
and	O
128b/132b	O
encoding	O
variants	O
for	O
PCI	O
Express	O
3.0	O
and	O
USB	O
3.1	O
,	O
respectively	O
,	O
replacing	O
the	O
8b/10b	B-Protocol
encoding	I-Protocol
in	O
earlier	O
revisions	O
of	O
each	O
standard	O
.	O
</s>
