<s>
SPI-4.2	B-Protocol
is	O
a	O
version	O
of	O
the	O
System	B-Protocol
Packet	I-Protocol
Interface	I-Protocol
published	O
by	O
the	O
Optical	O
Internetworking	O
Forum	O
.	O
</s>
<s>
It	O
was	O
designed	O
to	O
be	O
used	O
in	O
systems	O
that	O
support	O
OC-192	O
SONET	B-Protocol
interfaces	O
and	O
is	O
sometimes	O
used	O
in	O
10	O
Gigabit	O
Ethernet	O
based	O
systems	O
.	O
</s>
<s>
SPI-4	O
is	O
an	O
interface	O
for	O
packet	O
and	O
cell	O
transfer	O
between	O
a	O
physical	B-Application
layer	I-Application
(	O
PHY	O
)	O
device	O
and	O
a	O
link	B-Protocol
layer	I-Protocol
device	O
,	O
for	O
aggregate	O
bandwidths	O
of	O
OC-192	O
Asynchronous	O
Transfer	O
Mode	O
and	O
Packet	B-Protocol
over	I-Protocol
SONET/SDH	I-Protocol
(	O
POS	O
)	O
,	O
as	O
well	O
as	O
10	O
Gigabit	O
Ethernet	O
applications	O
.	O
</s>
<s>
The	O
transmit	O
and	O
receive	O
FIFO	B-Operating_System
status	O
channels	O
include	O
(	O
TSCLK	O
,	O
TSTAT[1:0]	O
)	O
and	O
(	O
RSCLK	O
,	O
RSTAT[1:0]	O
)	O
respectively	O
.	O
</s>
<s>
A	O
typical	O
application	O
of	O
SPI-4.2	B-Protocol
is	O
to	O
connect	O
a	O
framer	O
device	O
to	O
a	O
network	B-General_Concept
processor	I-General_Concept
.	O
</s>
<s>
Implementations	O
of	O
SPI-4.2	B-Protocol
have	O
been	O
produced	O
which	O
allow	O
somewhat	O
higher	O
clock	O
rates	O
.	O
</s>
<s>
PMC-Sierra	O
made	O
the	O
original	O
OIF	O
contribution	O
for	O
SPI-4.2	B-Protocol
.	O
</s>
<s>
That	O
contribution	O
was	O
based	O
on	O
the	O
PL-4	B-Protocol
specification	O
that	O
was	O
developed	O
by	O
PMC-Sierra	O
in	O
conjunction	O
with	O
the	O
SATURN	O
Development	O
Group	O
.	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
of	O
SPI-4.2	B-Protocol
is	O
very	O
similar	O
to	O
the	O
HyperTransport	B-Device
1.x	O
interface	O
,	O
although	O
the	O
logical	O
layers	O
are	O
very	O
different	O
.	O
</s>
