<s>
SpaceWire	B-Architecture
is	O
a	O
spacecraft	O
communication	O
network	O
based	O
in	O
part	O
on	O
the	O
IEEE	O
1355	O
standard	O
of	O
communications	O
.	O
</s>
<s>
Within	O
a	O
SpaceWire	B-Architecture
network	O
the	O
nodes	O
are	O
connected	O
through	O
low-cost	O
,	O
low-latency	O
,	O
full-duplex	O
,	O
point-to-point	B-Architecture
serial	O
links	O
,	O
and	O
packet	B-Protocol
switching	I-Protocol
wormhole	B-Protocol
routing	I-Protocol
routers	O
.	O
</s>
<s>
SpaceWire	B-Architecture
covers	O
two	O
(	O
physical	O
and	O
data-link	O
)	O
of	O
the	O
seven	O
layers	O
of	O
the	O
OSI	O
model	O
for	O
communications	O
.	O
</s>
<s>
SpaceWire	B-Architecture
's	O
modulation	O
and	O
data	O
formats	O
generally	O
follow	O
the	O
data	B-Protocol
strobe	I-Protocol
encoding	I-Protocol
-	O
differential	O
ended	O
signaling	O
(	O
DS-DE	O
)	O
part	O
of	O
the	O
IEEE	O
Std	O
1355-1995	O
.	O
</s>
<s>
SpaceWire	B-Architecture
utilizes	O
asynchronous	O
communication	O
and	O
allows	O
speeds	O
between	O
2	O
Mbit/s	O
and	O
200	O
Mbit/s	O
,	O
with	O
initial	O
signalling	O
rate	O
of	O
10Mbit/s	O
.	O
</s>
<s>
DS-DE	O
is	O
well-favored	O
because	O
it	O
describes	O
modulation	O
,	O
bit	O
formats	O
,	O
routing	O
,	O
flow	O
control	O
,	O
and	O
error	B-Error_Name
detection	I-Error_Name
in	O
hardware	O
,	O
with	O
little	O
need	O
for	O
software	O
.	O
</s>
<s>
SpaceWire	B-Architecture
also	O
has	O
very	O
low	O
error	O
rates	O
,	O
deterministic	O
system	O
behavior	O
,	O
and	O
relatively	O
simple	O
digital	O
electronics	O
.	O
</s>
<s>
SpaceWire	B-Architecture
replaced	O
old	O
PECL	B-General_Concept
differential	O
drivers	O
in	O
the	O
physical	O
layer	O
of	O
IEEE	O
1355	O
DS-DE	O
by	O
low-voltage	B-Architecture
differential	I-Architecture
signaling	I-Architecture
(	O
LVDS	B-Architecture
)	O
.	O
</s>
<s>
SpaceWire	B-Architecture
also	O
proposes	O
the	O
use	O
of	O
space-qualified	O
9-pin	O
connectors	O
.	O
</s>
<s>
SpaceWire	B-Architecture
and	O
IEEE	O
1355	O
DS-DE	O
allows	O
for	O
a	O
wider	O
set	O
of	O
speeds	O
for	O
data	O
transmission	O
,	O
and	O
some	O
new	O
features	O
for	O
automatic	O
failover	B-General_Concept
.	O
</s>
<s>
The	O
fail-over	B-General_Concept
features	O
let	O
data	O
find	O
alternate	O
routes	O
,	O
so	O
a	O
spacecraft	O
can	O
have	O
multiple	O
data	O
buses	O
,	O
and	O
be	O
made	O
fault-tolerant	B-General_Concept
.	O
</s>
<s>
SpaceWire	B-Architecture
also	O
allows	O
the	O
propagation	O
of	O
time	O
interrupts	O
over	O
SpaceWire	B-Architecture
links	O
,	O
eliminating	O
the	O
need	O
for	O
separate	O
time	O
discretes	O
.	O
</s>
<s>
The	O
hardware	O
devices	O
may	O
be	O
connected	O
either	O
directly	O
,	O
or	O
via	O
a	O
SpaceWire	B-Architecture
router	O
.	O
</s>
<s>
In	O
the	O
former	O
case	O
,	O
usually	O
pairs	O
of	O
devices	O
are	O
used	O
to	O
guarantee	O
a	O
fail-safe	B-General_Concept
operation	O
-	O
which	O
is	O
however	O
handled	O
by	O
the	O
software	O
.	O
</s>
<s>
A	O
SpaceWire	B-Architecture
router	O
is	O
usually	O
a	O
crossbar	O
switch-type	O
device	O
,	O
operating	O
in	O
wormhole	B-Protocol
switching	I-Protocol
mode	O
.	O
</s>
<s>
SpaceWire	B-Architecture
is	O
used	O
all	O
around	O
the	O
globe	O
.	O
</s>
<s>
SpaceWire	B-Architecture
initiatives	O
are	O
being	O
coordinated	O
between	O
several	O
Space	O
Agencies	O
in	O
the	O
frame	O
of	O
CCSDS	O
in	O
order	O
to	O
extend	O
its	O
communication	O
model	O
to	O
the	O
Network	O
and	O
Transport	O
Layers	O
of	O
the	O
OSI	O
model	O
.	O
</s>
<s>
SpaceWire	B-Architecture
supports	O
highly	O
fault-tolerant	B-General_Concept
networks	O
and	O
systems	O
,	O
which	O
is	O
one	O
reason	O
for	O
its	O
popularity	O
.	O
</s>
