<s>
Fiber	B-Protocol
Distributed	I-Protocol
Data	I-Protocol
Interface	I-Protocol
(	O
FDDI	B-Protocol
)	O
is	O
a	O
standard	O
for	O
data	O
transmission	O
in	O
a	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
It	O
uses	O
optical	B-Architecture
fiber	I-Architecture
as	O
its	O
standard	O
underlying	O
physical	O
medium	O
,	O
although	O
it	O
was	O
also	O
later	O
specified	O
to	O
use	O
copper	O
cable	O
,	O
in	O
which	O
case	O
it	O
may	O
be	O
called	O
CDDI	B-Protocol
(	O
Copper	B-Protocol
Distributed	I-Protocol
Data	I-Protocol
Interface	I-Protocol
)	O
,	O
standardized	O
as	O
TP-PMD	O
(	O
Twisted-Pair	O
Physical	O
Medium-Dependent	O
)	O
,	O
also	O
referred	O
to	O
as	O
TP-DDI	O
(	O
Twisted-Pair	O
Distributed	O
Data	O
Interface	O
)	O
.	O
</s>
<s>
FDDI	B-Protocol
was	O
effectively	O
made	O
obsolete	O
in	O
local	B-General_Concept
networks	I-General_Concept
by	O
Fast	B-Protocol
Ethernet	I-Protocol
which	O
offered	O
the	O
same	O
100Mbit/s	O
speeds	O
,	O
but	O
at	O
a	O
much	O
lower	O
cost	O
and	O
,	O
since	O
1998	O
,	O
by	O
Gigabit	O
Ethernet	O
due	O
to	O
its	O
speed	O
,	O
and	O
even	O
lower	O
cost	O
,	O
and	O
ubiquity	O
.	O
</s>
<s>
FDDI	B-Protocol
provides	O
a	O
100Mbit/s	O
optical	O
standard	O
for	O
data	O
transmission	O
in	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
that	O
can	O
extend	O
in	O
range	O
up	O
to	O
.	O
</s>
<s>
Although	O
FDDI	B-Protocol
logical	B-Architecture
topology	I-Architecture
is	O
a	O
ring-based	O
token	O
network	O
,	O
it	O
did	O
not	O
use	O
the	O
IEEE	B-Device
802.5	I-Device
Token	B-Device
Ring	I-Device
protocol	O
as	O
its	O
basis	O
;	O
instead	O
,	O
its	O
protocol	O
was	O
derived	O
from	O
the	O
IEEE	B-Protocol
802.4	I-Protocol
token	B-Protocol
bus	I-Protocol
timed	O
token	O
protocol	O
.	O
</s>
<s>
In	O
addition	O
to	O
covering	O
large	O
geographical	O
areas	O
,	O
FDDI	B-Protocol
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
can	O
support	O
thousands	O
of	O
users	O
.	O
</s>
<s>
FDDI	B-Protocol
offers	O
both	O
a	O
Dual-Attached	O
Station	O
(	O
DAS	O
)	O
,	O
counter-rotating	O
token	B-Device
ring	I-Device
topology	B-Architecture
and	O
a	O
Single-Attached	O
Station	O
(	O
SAS	O
)	O
,	O
token	B-Protocol
bus	I-Protocol
passing	O
ring	O
topology	B-Architecture
.	O
</s>
<s>
FDDI	B-Protocol
,	O
as	O
a	O
product	O
of	O
American	O
National	O
Standards	O
Institute	O
X3T9.5	O
(	O
now	O
X3T12	O
)	O
,	O
conforms	O
to	O
the	O
Open	O
Systems	O
Interconnection	O
(	O
OSI	O
)	O
model	O
of	O
functional	O
layering	O
using	O
other	O
protocols	O
.	O
</s>
<s>
FDDI-II	O
,	O
a	O
version	O
of	O
FDDI	B-Protocol
described	O
in	O
1989	O
,	O
added	O
circuit-switched	B-Protocol
service	I-Protocol
capability	O
to	O
the	O
network	O
so	O
that	O
it	O
could	O
also	O
handle	O
voice	O
and	O
video	O
signals	O
.	O
</s>
<s>
Work	O
started	O
to	O
connect	O
FDDI	B-Protocol
networks	O
to	O
synchronous	B-Protocol
optical	I-Protocol
networking	I-Protocol
(	O
SONET	B-Protocol
)	O
technology	O
.	O
</s>
<s>
An	O
FDDI	B-Protocol
network	O
contains	O
two	O
rings	O
,	O
one	O
as	O
a	O
secondary	O
backup	O
in	O
case	O
the	O
primary	O
ring	O
fails	O
.	O
</s>
<s>
FDDI	B-Protocol
had	O
a	O
larger	O
maximum	O
frame	O
size	O
(	O
4,352	O
bytes	O
)	O
than	O
the	O
standard	O
Ethernet	O
family	O
,	O
which	O
only	O
supports	O
a	O
maximum	O
frame	O
size	O
of	O
1,500	O
bytes	O
,	O
allowing	O
better	O
effective	O
data	O
rates	O
in	O
some	O
cases	O
.	O
</s>
<s>
Designers	O
normally	O
constructed	O
FDDI	B-Protocol
rings	I-Protocol
in	O
a	O
network	B-Architecture
topology	I-Architecture
such	O
as	O
a	O
"	O
dual	O
ring	O
of	O
trees	O
"	O
.	O
</s>
<s>
A	O
small	O
number	O
of	O
devices	O
,	O
typically	O
infrastructure	O
devices	O
such	O
as	O
routers	B-Protocol
and	O
concentrators	O
rather	O
than	O
host	O
computers	O
,	O
were	O
"	O
dual-attached	O
"	O
to	O
both	O
rings	O
.	O
</s>
<s>
Host	O
computers	O
then	O
connect	O
as	O
single-attached	O
devices	O
to	O
the	O
routers	B-Protocol
or	O
concentrators	O
.	O
</s>
<s>
Typically	O
,	O
a	O
computer-room	O
contained	O
the	O
whole	O
dual	O
ring	O
,	O
although	O
some	O
implementations	O
deployed	O
FDDI	B-Protocol
as	O
a	O
metropolitan	O
area	O
network	O
.	O
</s>
<s>
FDDI	B-Protocol
requires	O
this	O
network	B-Architecture
topology	I-Architecture
because	O
the	O
dual	O
ring	O
actually	O
passes	O
through	O
each	O
connected	O
device	O
and	O
requires	O
each	O
such	O
device	O
to	O
remain	O
continuously	O
operational	O
.	O
</s>
<s>
As	O
an	O
alternative	O
to	O
using	O
a	O
dual-attached	O
connection	O
,	O
a	O
workstation	O
can	O
obtain	O
the	O
same	O
degree	O
of	O
resilience	B-General_Concept
through	O
a	O
dual-homed	O
connection	O
made	O
simultaneously	O
to	O
two	O
separate	O
devices	O
in	O
the	O
same	O
FDDI	B-Protocol
ring	I-Protocol
.	O
</s>
<s>
The	O
frame	O
check	O
sequence	O
uses	O
the	O
same	O
cyclic	O
redundancy	O
check	O
as	O
Token	B-Device
Ring	I-Device
and	O
Ethernet	O
.	O
</s>
<s>
The	O
Internet	O
Engineering	O
Task	O
Force	O
defined	O
a	O
standard	O
for	O
transmission	O
of	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
which	O
would	O
be	O
the	O
protocol	O
data	O
unit	O
in	O
this	O
case	O
)	O
over	O
FDDI	B-Protocol
.	O
</s>
<s>
FDDI	B-Protocol
was	O
considered	O
an	O
attractive	O
campus	O
backbone	B-General_Concept
network	I-General_Concept
technology	O
in	O
the	O
early	O
to	O
mid	O
1990s	O
since	O
existing	O
Ethernet	O
networks	O
only	O
offered	O
10Mbit/s	O
data	O
rates	O
and	O
Token	B-Device
Ring	I-Device
networks	I-Device
only	O
offered	O
4Mbit/s	O
or	O
16Mbit/s	O
rates	O
.	O
</s>
<s>
FDDI	B-Protocol
installations	O
have	O
largely	O
been	O
replaced	O
by	O
Ethernet	O
deployments	O
.	O
</s>
<s>
FDDI	B-Protocol
standards	O
included	O
:	O
</s>
