<s>
10	O
Gigabit	O
Attachment	B-Protocol
Unit	I-Protocol
Interface	I-Protocol
(	O
XAUI	B-Protocol
)	O
is	O
a	O
standard	O
for	O
extending	O
the	O
XGMII	O
(	O
10	O
Gigabit	O
Media	O
Independent	O
Interface	O
)	O
between	O
the	O
MAC	B-Protocol
and	O
PHY	O
layer	O
of	O
10	O
Gigabit	O
Ethernet	O
(	O
10GbE	O
)	O
defined	O
in	O
Clause	O
47	O
of	O
the	O
IEEE	O
802.3	O
standard	O
.	O
</s>
<s>
The	O
name	O
is	O
a	O
concatenation	O
of	O
the	O
Roman	O
numeral	O
X	O
,	O
meaning	O
ten	O
,	O
and	O
the	O
initials	O
of	O
"	O
Attachment	B-Protocol
Unit	I-Protocol
Interface	I-Protocol
"	O
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
XGMII	O
Extender	O
,	O
which	O
is	O
composed	O
of	O
an	O
XGXS	O
(	O
XGMII	O
Extender	O
Sublayer	O
)	O
at	O
the	O
MAC	B-Protocol
end	O
,	O
an	O
XGXS	O
at	O
the	O
PHY	O
end	O
and	O
a	O
XAUI	B-Protocol
between	O
them	O
,	O
is	O
to	O
extend	O
the	O
operational	O
distance	O
of	O
the	O
XGMII	O
and	O
to	O
reduce	O
the	O
number	O
of	O
interface	O
signals	O
.	O
</s>
<s>
Applications	O
include	O
extending	O
the	O
physical	O
separation	O
possible	O
between	O
MAC	B-Protocol
and	O
PHY	O
components	O
in	O
a	O
10	O
Gigabit	O
Ethernet	O
system	O
distributed	O
across	O
a	O
circuit	O
board	O
.	O
</s>
<s>
The	O
following	O
is	O
a	O
list	O
of	O
the	O
major	O
concepts	O
of	O
XGXS	O
and	O
XAUI	B-Protocol
:	O
</s>
<s>
The	O
optional	O
XGMII	O
Extender	O
can	O
be	O
inserted	O
between	O
the	O
Reconciliation	O
Sublayer	O
and	O
the	O
PHY	O
(	O
physical	B-Application
layer	I-Application
)	O
to	O
transparently	O
extend	O
the	O
physical	O
reach	O
of	O
the	O
XGMII	O
and	O
reduce	O
the	O
interface	O
pin	O
count	O
from	O
72	O
to	O
16	O
.	O
</s>
<s>
The	O
source	O
XGXS	O
converts	O
bytes	O
on	O
an	O
XGMII	O
lane	O
into	O
a	O
self	O
clocked	O
,	O
serial	O
,	O
8b/10b	B-Protocol
encoded	O
data	O
stream	O
.	O
</s>
<s>
Each	O
of	O
the	O
four	O
XGMII	O
lanes	O
is	O
transmitted	O
across	O
one	O
of	O
the	O
four	O
XAUI	B-Protocol
lanes	O
.	O
</s>
<s>
The	O
source	O
XGXS	O
converts	O
XGMII	O
Idle	O
control	O
characters	O
(	O
interframe	O
)	O
into	O
an	O
8b/10b	B-Protocol
code	O
sequence	O
.	O
</s>
<s>
The	O
destination	O
XGXS	O
recovers	O
clock	O
and	O
data	O
from	O
each	O
XAUI	B-Protocol
lane	O
and	O
deskews	O
the	O
four	O
XAUI	B-Protocol
lanes	O
into	O
the	O
single-clock	O
XGMII	O
.	O
</s>
<s>
Capabilities	O
have	O
been	O
built	O
into	O
XAUI	B-Protocol
to	O
overcome	O
the	O
inter-lane	O
signal-skewing	O
problems	O
using	O
a	O
type	O
of	O
automatic	O
de-skewing	O
.	O
</s>
<s>
Signals	O
can	O
be	O
launched	O
at	O
the	O
transmitter	O
end	O
of	O
a	O
XAUI	B-Protocol
line	O
without	O
precisely	O
matching	O
the	O
routing	B-Protocol
of	O
the	O
four	O
lanes	O
,	O
and	O
the	O
signals	O
will	O
be	O
automatically	O
de-skewed	O
at	O
the	O
receiver	O
.	O
</s>
<s>
Reduced	O
Pin	O
eXtended	O
Attachment	B-Protocol
Unit	I-Protocol
Interface	I-Protocol
(	O
RXAUI	O
)	O
is	O
a	O
proprietary	O
modification	O
created	O
by	O
Marvell	O
and	O
Dune	O
Networks	O
(	O
later	O
acquired	O
by	O
Broadcom	O
)	O
aimed	O
to	O
increase	O
the	O
port	O
density	O
by	O
decreasing	O
the	O
interface	O
pin	O
count	O
.	O
</s>
<s>
The	O
four	O
lanes	O
of	O
the	O
standard	O
XAUI	B-Protocol
running	O
at	O
3.125	O
Gbit/s	O
are	O
replaced	O
by	O
two	O
lanes	O
at	O
6.25	O
Gbit/s	O
.	O
</s>
<s>
Thus	O
16	O
pins	O
of	O
an	O
integrated	O
circuit	O
(	O
4	O
transmit	O
+	O
4	O
receive	O
differential	O
pairs	O
)	O
can	O
provide	O
either	O
one	O
XAUI	B-Protocol
port	O
or	O
two	O
RXAUI	O
ports	O
.	O
</s>
<s>
The	O
specification	O
also	O
defines	O
a	O
XAUI	B-Protocol
to	O
RXAUI	O
adapter	O
,	O
and	O
provides	O
an	O
implementation	O
as	O
Verilog	B-Language
RTL	O
code	O
.	O
</s>
<s>
FPGA	B-Architecture
vendors	O
are	O
offering	O
their	O
own	O
implementations	O
as	O
IP	O
blocks	O
.	O
</s>
<s>
The	O
implementation	O
of	O
XAUI	B-Protocol
as	O
an	O
optional	O
XGMII	O
Extender	O
is	O
primarily	O
intended	O
as	O
a	O
chip-to-chip	O
(	O
integrated	O
circuit	O
to	O
integrated	O
circuit	O
)	O
interface	O
implemented	O
with	O
traces	O
on	O
a	O
printed	O
circuit	O
board	O
.	O
</s>
<s>
The	O
10	O
Gbit/s	O
MAC	B-Protocol
data	O
stream	O
is	O
converted	O
into	O
four	O
lanes	O
at	O
the	O
XGMII	O
(	O
by	O
the	O
Reconciliation	O
Sublayer	O
for	O
transmit	O
or	O
the	O
PHY	O
for	O
receive	O
)	O
.	O
</s>
<s>
The	O
byte	O
stream	O
of	O
each	O
lane	O
is	O
8b/10b	B-Protocol
encoded	O
by	O
the	O
XGXS	O
for	O
transmission	O
across	O
the	O
XAUI	B-Protocol
at	O
a	O
nominal	O
rate	O
of	O
3.125	O
gigabaud	O
.	O
</s>
<s>
The	O
XGMII	O
Extender	O
is	O
logically	O
composed	O
of	O
two	O
XGXSs	O
interconnected	O
with	O
a	O
XAUI	B-Protocol
data	O
path	O
in	O
each	O
direction	O
.	O
</s>
<s>
One	O
XGXS	O
acts	O
as	O
the	O
source	O
to	O
the	O
XAUI	B-Protocol
data	O
path	O
in	O
the	O
DTE	O
transmit	O
path	O
and	O
as	O
the	O
destination	O
in	O
the	O
receive	O
path	O
.	O
</s>
<s>
Each	O
XAUI	B-Protocol
data	O
path	O
is	O
composed	O
of	O
four	O
serial	O
lanes	O
.	O
</s>
<s>
All	O
specifications	O
for	O
the	O
XGMII	O
Extender	O
are	O
written	O
assuming	O
conversion	O
from	O
XGMII	O
to	O
XAUI	B-Protocol
and	O
back	O
to	O
XGMII	O
,	O
but	O
other	O
techniques	O
may	O
be	O
employed	O
provided	O
that	O
the	O
result	O
is	O
that	O
the	O
XGMII	O
Extender	O
operates	O
as	O
if	O
all	O
specified	O
conversions	O
had	O
been	O
made	O
.	O
</s>
<s>
One	O
example	O
of	O
this	O
is	O
the	O
use	O
of	O
the	O
optional	O
XAUI	B-Protocol
with	O
the	O
10GBASE-LX4	O
8b/10b	B-Protocol
PHY	O
,	O
where	O
the	O
XGXS	O
interfacing	O
to	O
the	O
Reconciliation	O
Sublayer	O
provides	O
the	O
PCS	O
and	O
PMA	O
functionality	O
required	O
by	O
the	O
PHY	O
.	O
</s>
<s>
An	O
XGXS	O
layer	O
is	O
not	O
required	O
at	O
the	O
PHY	O
end	O
of	O
the	O
XAUI	B-Protocol
in	O
this	O
case	O
.	O
</s>
<s>
However	O
,	O
means	O
may	O
still	O
be	O
required	O
to	O
remove	O
jitter	O
introduced	O
on	O
the	O
XAUI	B-Protocol
in	O
order	O
to	O
meet	O
PHY	O
jitter	O
requirements	O
.	O
</s>
