<s>
Token	B-Device
Ring	I-Device
is	O
a	O
computer	B-Architecture
networking	I-Architecture
technology	O
used	O
to	O
build	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
.	O
</s>
<s>
It	O
was	O
introduced	O
by	O
IBM	O
in	O
1984	O
,	O
and	O
standardized	O
in	O
1989	O
as	O
IEEE	B-Device
802.5	I-Device
.	O
</s>
<s>
It	O
uses	O
a	O
special	O
three-byte	O
frame	B-Protocol
called	O
a	O
token	O
that	O
is	O
passed	O
around	O
a	O
logical	O
ring	O
of	O
workstations	B-Device
or	O
servers	O
.	O
</s>
<s>
This	O
token	B-Protocol
passing	I-Protocol
is	O
a	O
channel	O
access	O
method	O
providing	O
fair	O
access	O
for	O
all	O
stations	O
,	O
and	O
eliminating	O
the	O
collisions	O
of	O
contention-based	O
access	O
methods	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
was	O
a	O
successful	O
technology	O
,	O
particularly	O
in	O
corporate	O
environments	O
,	O
but	O
was	O
gradually	O
eclipsed	O
by	O
the	O
later	O
versions	O
of	O
Ethernet	O
.	O
</s>
<s>
A	O
wide	O
range	O
of	O
different	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
technologies	O
were	O
developed	O
in	O
the	O
early	O
1970s	O
,	O
of	O
which	O
one	O
,	O
the	O
Cambridge	B-General_Concept
Ring	I-General_Concept
,	O
had	O
demonstrated	O
the	O
potential	O
of	O
a	O
token	B-Protocol
passing	I-Protocol
ring	B-Architecture
topology	I-Architecture
,	O
and	O
many	O
teams	O
worldwide	O
began	O
working	O
on	O
their	O
own	O
implementations	O
.	O
</s>
<s>
At	O
the	O
IBM	O
Zurich	O
Research	O
Laboratory	O
Werner	O
Bux	O
and	O
Hans	O
Müller	O
,	O
in	O
particular	O
,	O
worked	O
on	O
the	O
design	O
and	O
development	O
of	O
IBM	O
's	O
Token	B-Device
Ring	I-Device
technology	O
,	O
while	O
early	O
work	O
at	O
MIT	O
led	O
to	O
the	O
Proteon	O
10Mbit/s	O
ProNet-10	O
Token	B-Device
Ring	I-Device
network	I-Device
in	O
1981the	O
same	O
year	O
that	O
workstation	B-Device
vendor	O
Apollo	O
Computer	O
introduced	O
their	O
proprietary	O
12Mbit/s	O
Apollo	O
Token	B-Device
Ring	I-Device
(	O
ATR	O
)	O
network	O
running	O
over	O
75-ohm	O
RG-6U	O
coaxial	O
cabling	O
.	O
</s>
<s>
Proteon	O
later	O
evolved	O
a	O
16Mbit/s	O
version	O
that	O
ran	O
on	O
unshielded	O
twisted	B-Protocol
pair	I-Protocol
cable	O
.	O
</s>
<s>
IBM	O
launched	O
their	O
own	O
proprietary	O
Token	B-Device
Ring	I-Device
product	O
on	O
October	O
15	O
,	O
1985	O
.	O
</s>
<s>
It	O
used	O
a	O
convenient	O
star-wired	O
physical	B-Architecture
topology	I-Architecture
and	O
ran	O
over	O
shielded	O
twisted-pair	O
cabling	O
.	O
</s>
<s>
Shortly	O
thereafter	O
it	O
became	O
the	O
basis	O
for	O
the	O
IEEE	B-Device
802.5	I-Device
standard	O
.	O
</s>
<s>
During	O
this	O
time	O
,	O
IBM	O
argued	O
that	O
Token	B-Device
Ring	I-Device
LANs	B-General_Concept
were	O
superior	O
to	O
Ethernet	O
,	O
especially	O
under	O
load	O
,	O
but	O
these	O
claims	O
were	O
debated	O
.	O
</s>
<s>
In	O
1988	O
the	O
faster	O
16Mbit/s	O
Token	B-Device
Ring	I-Device
was	O
standardized	O
by	O
the	O
802.5	B-Device
working	O
group	O
.	O
</s>
<s>
An	O
increase	O
to	O
100Mbit/s	O
was	O
standardized	O
and	O
marketed	O
during	O
the	O
wane	O
of	O
Token	B-Device
Ring	I-Device
's	O
existence	O
and	O
was	O
never	O
widely	O
used	O
.	O
</s>
<s>
While	O
a	O
1000Mbit/s	O
standard	O
was	O
approved	O
in	O
2001	O
,	O
no	O
products	O
were	O
ever	O
brought	O
to	O
market	O
and	O
standards	O
activity	O
came	O
to	O
a	O
standstill	O
as	O
Fast	B-Protocol
Ethernet	I-Protocol
and	O
Gigabit	O
Ethernet	O
dominated	O
the	O
local	B-General_Concept
area	I-General_Concept
networking	I-General_Concept
market	O
.	O
</s>
<s>
Ethernet	O
and	O
Token	B-Device
Ring	I-Device
have	O
some	O
notable	O
differences	O
:	O
</s>
<s>
Ethernet	O
supports	O
a	O
direct	O
cable	O
connection	O
between	O
two	O
network	O
interface	O
cards	O
by	O
the	O
use	O
of	O
a	O
crossover	B-Protocol
cable	I-Protocol
or	O
through	O
auto-sensing	O
if	O
supported	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
does	O
not	O
inherently	O
support	O
this	O
feature	O
and	O
requires	O
additional	O
software	O
and	O
hardware	O
to	O
operate	O
on	O
a	O
direct	O
cable	O
connection	O
setup	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
eliminates	O
collision	O
by	O
the	O
use	O
of	O
a	O
single-use	O
token	O
and	O
early	O
token	O
release	O
to	O
alleviate	O
the	O
down	O
time	O
.	O
</s>
<s>
Ethernet	O
alleviates	O
collision	O
by	O
carrier	O
sense	O
multiple	O
access	O
and	O
by	O
the	O
use	O
of	O
an	O
intelligent	O
switch	B-Protocol
;	O
primitive	O
Ethernet	O
devices	O
like	O
hubs	B-Protocol
can	O
precipitate	O
collisions	O
due	O
to	O
repeating	O
traffic	O
blindly	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
network	I-Device
interface	O
cards	O
contain	O
all	O
of	O
the	O
intelligence	O
required	O
for	O
speed	O
autodetection	O
,	O
routing	O
and	O
can	O
drive	O
themselves	O
on	O
many	O
Multistation	B-Device
Access	I-Device
Units	I-Device
(	O
MAUs	O
)	O
that	O
operate	O
without	O
power	O
(	O
most	O
MAUs	O
operate	O
in	O
this	O
fashion	O
,	O
only	O
requiring	O
a	O
power	O
supply	O
for	O
LEDs	O
)	O
.	O
</s>
<s>
Ethernet	O
network	O
interface	O
cards	O
can	O
theoretically	O
operate	O
on	O
a	O
passive	O
hub	B-Protocol
to	O
a	O
degree	O
,	O
but	O
not	O
as	O
a	O
large	O
LAN	B-General_Concept
and	O
the	O
issue	O
of	O
collisions	O
is	O
still	O
present	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
employs	O
access	O
priority	O
in	O
which	O
certain	O
nodes	O
can	O
have	O
priority	O
over	O
the	O
token	O
.	O
</s>
<s>
Multiple	O
identical	O
MAC	B-Protocol
addresses	O
are	O
supported	O
on	O
Token	B-Device
Ring	I-Device
(	O
a	O
feature	O
used	O
by	O
S/390	B-Device
mainframes	O
)	O
.	O
</s>
<s>
Switched	B-Protocol
Ethernet	I-Protocol
cannot	O
support	O
duplicate	O
MAC	B-Protocol
addresses	O
without	O
reprimand	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
was	O
more	O
complex	O
than	O
Ethernet	O
,	O
requiring	O
a	O
specialized	O
processor	O
and	O
licensed	O
MAC/LLC	O
firmware	O
for	O
each	O
interface	O
.	O
</s>
<s>
By	O
contrast	O
,	O
Ethernet	O
included	O
both	O
the	O
(	O
simpler	O
)	O
firmware	O
and	O
the	O
lower	O
licensing	O
cost	O
in	O
the	O
MAC	B-Protocol
chip	O
.	O
</s>
<s>
The	O
cost	O
of	O
a	O
token	B-Device
Ring	I-Device
interface	O
using	O
the	O
Texas	O
Instruments	O
TMS380C16	O
MAC	B-Protocol
and	O
PHY	O
was	O
approximately	O
three	O
times	O
that	O
of	O
an	O
Ethernet	O
interface	O
using	O
the	O
Intel	O
82586	O
MAC	B-Protocol
and	O
PHY	O
.	O
</s>
<s>
Initially	O
both	O
networks	O
used	O
expensive	O
cable	O
,	O
but	O
once	O
Ethernet	O
was	O
standardized	O
for	O
unshielded	O
twisted	B-Protocol
pair	I-Protocol
with	O
10BASE-T	B-Protocol
(	O
Cat	B-Protocol
3	I-Protocol
)	O
and	O
100BASE-TX	B-Protocol
(	O
Cat	O
5(e )	O
)	O
,	O
it	O
had	O
a	O
distinct	O
advantage	O
and	O
sales	O
of	O
it	O
increased	O
markedly	O
.	O
</s>
<s>
Even	O
more	O
significant	O
when	O
comparing	O
overall	O
system	O
costs	O
was	O
the	O
much-higher	O
cost	O
of	O
router	O
ports	O
and	O
network	O
cards	O
for	O
Token	B-Device
Ring	I-Device
vs	O
Ethernet	O
.	O
</s>
<s>
The	O
emergence	O
of	O
Ethernet	B-Protocol
switches	I-Protocol
may	O
have	O
been	O
the	O
final	O
straw	O
.	O
</s>
<s>
Stations	O
on	O
a	O
Token	B-Device
Ring	I-Device
LAN	B-General_Concept
are	O
logically	B-Architecture
organized	I-Architecture
in	O
a	O
ring	B-Architecture
topology	I-Architecture
with	O
data	O
being	O
transmitted	O
sequentially	O
from	O
one	O
ring	O
station	O
to	O
the	O
next	O
with	O
a	O
control	O
token	O
circulating	O
around	O
the	O
ring	O
controlling	O
access	O
.	O
</s>
<s>
Similar	O
token	B-Protocol
passing	I-Protocol
mechanisms	O
are	O
used	O
by	O
ARCNET	B-Protocol
,	O
token	B-Protocol
bus	I-Protocol
,	O
100VG-AnyLAN	B-Protocol
(	O
802.12	O
)	O
and	O
FDDI	B-Protocol
,	O
and	O
they	O
have	O
theoretical	O
advantages	O
over	O
the	O
CSMA/CD	O
of	O
early	O
Ethernet	O
.	O
</s>
<s>
A	O
Token	B-Device
Ring	I-Device
network	I-Device
can	O
be	O
modeled	O
as	O
a	O
polling	O
system	O
where	O
a	O
single	O
server	B-Application
provides	O
service	O
to	O
queues	O
in	O
a	O
cyclic	O
order	O
.	O
</s>
<s>
The	O
computer	O
will	O
then	O
be	O
able	O
to	O
send	O
the	O
frame	B-Protocol
.	O
</s>
<s>
The	O
frame	B-Protocol
is	O
then	O
examined	O
by	O
each	O
successive	O
workstation	B-Device
.	O
</s>
<s>
The	O
workstation	B-Device
that	O
identifies	O
itself	O
to	O
be	O
the	O
destination	O
for	O
the	O
message	O
copies	O
it	O
from	O
the	O
frame	B-Protocol
and	O
changes	O
the	O
token	O
back	O
to	O
0	O
.	O
</s>
<s>
When	O
the	O
frame	B-Protocol
gets	O
back	O
to	O
the	O
originator	O
,	O
it	O
sees	O
that	O
the	O
token	O
has	O
been	O
changed	O
to	O
0	O
and	O
that	O
the	O
message	O
has	O
been	O
copied	O
and	O
received	O
.	O
</s>
<s>
It	O
removes	O
the	O
message	O
from	O
the	O
frame	B-Protocol
.	O
</s>
<s>
The	O
frame	B-Protocol
continues	O
to	O
circulate	O
as	O
an	O
empty	O
frame	B-Protocol
,	O
ready	O
to	O
be	O
taken	O
by	O
a	O
workstation	B-Device
when	O
it	O
has	O
a	O
message	O
to	O
send	O
.	O
</s>
<s>
Physically	O
,	O
a	O
Token	B-Device
Ring	I-Device
network	I-Device
is	O
wired	O
as	O
a	O
star	B-Architecture
,	O
with	O
'	O
MAUs	O
 '	O
in	O
the	O
center	O
,	O
'	O
arms	O
 '	O
out	O
to	O
each	O
station	O
,	O
and	O
the	O
loop	O
going	O
out-and-back	O
through	O
each	O
.	O
</s>
<s>
A	O
MAU	B-Device
could	O
present	O
in	O
the	O
form	O
of	O
a	O
hub	B-Protocol
or	O
a	O
switch	B-Protocol
;	O
since	O
Token	B-Device
Ring	I-Device
had	O
no	O
collisions	O
many	O
MAUs	O
were	O
manufactured	O
as	O
hubs	B-Protocol
.	O
</s>
<s>
Although	O
Token	B-Device
Ring	I-Device
runs	O
on	O
LLC	O
,	O
it	O
includes	O
source	O
routing	O
to	O
forward	O
packets	O
beyond	O
the	O
local	B-General_Concept
network	I-General_Concept
.	O
</s>
<s>
Later	O
IBM	O
would	O
release	O
Controlled	O
Access	O
Units	O
that	O
could	O
support	O
multiple	O
MAU	B-Device
modules	O
known	O
as	O
a	O
Lobe	B-Device
Attachment	I-Device
Module	I-Device
.	O
</s>
<s>
This	O
offered	O
a	O
more	O
reliable	O
setup	O
and	O
remote	O
management	O
than	O
with	O
an	O
unmanaged	O
MAU	B-Device
hub	B-Protocol
.	O
</s>
<s>
Cabling	O
is	O
generally	O
IBM	O
"	O
Type-1	O
"	O
,	O
a	O
heavy	O
two-pair	O
150	O
Ohm	O
shielded	O
twisted	B-Protocol
pair	I-Protocol
cable	O
.	O
</s>
<s>
Connectors	O
at	O
the	O
computer	O
were	O
usually	O
DE-9	B-Protocol
female	O
.	O
</s>
<s>
In	O
later	O
implementations	O
of	O
Token	B-Device
Ring	I-Device
,	O
Cat	B-Protocol
4	I-Protocol
cabling	O
was	O
also	O
supported	O
,	O
so	O
8P8C	O
(	O
RJ45	O
)	O
connectors	O
were	O
used	O
on	O
both	O
of	O
the	O
MAUs	O
,	O
CAUs	O
and	O
NICs	O
;	O
with	O
many	O
of	O
the	O
network	O
cards	O
supporting	O
both	O
8P8C	O
and	O
DE-9	B-Protocol
for	O
backwards	O
compatibility	O
.	O
</s>
<s>
When	O
no	O
station	O
is	O
sending	O
a	O
frame	B-Protocol
,	O
a	O
special	O
token	O
frame	B-Protocol
circles	O
the	O
loop	O
.	O
</s>
<s>
This	O
special	O
token	O
frame	B-Protocol
is	O
repeated	O
from	O
station	O
to	O
station	O
until	O
arriving	O
at	O
a	O
station	O
that	O
needs	O
to	O
send	O
data	O
.	O
</s>
<s>
Starting	O
delimiter	O
Consists	O
of	O
a	O
special	O
bit	O
pattern	O
denoting	O
the	O
beginning	O
of	O
the	O
frame	B-Protocol
.	O
</s>
<s>
Since	O
Manchester	B-Protocol
encoding	I-Protocol
is	O
self-clocking	O
,	O
and	O
has	O
a	O
transition	O
for	O
every	O
encoded	O
bit	O
0	O
or	O
1	O
,	O
the	O
J	O
and	O
K	O
codings	O
violate	O
this	O
,	O
and	O
will	O
be	O
detected	O
by	O
the	O
hardware	O
.	O
</s>
<s>
Both	O
the	O
Starting	O
Delimiter	O
and	O
Ending	O
Delimiter	O
fields	O
are	O
used	O
to	O
mark	O
frame	B-Protocol
boundaries	O
.	O
</s>
<s>
The	O
P	O
bits	O
are	O
priority	O
bits	O
,	O
T	O
is	O
the	O
token	O
bit	O
which	O
when	O
set	O
specifies	O
that	O
this	O
is	O
a	O
token	O
frame	B-Protocol
,	O
M	O
is	O
the	O
monitor	O
bit	O
which	O
is	O
set	O
by	O
the	O
Active	O
Monitor	O
(	O
AM	O
)	O
station	O
when	O
it	O
sees	O
this	O
frame	B-Protocol
,	O
and	O
R	O
bits	O
are	O
reserved	O
bits	O
.	O
</s>
<s>
Frame	B-Protocol
control	O
A	O
one-byte	O
field	O
that	O
contains	O
bits	O
describing	O
the	O
data	O
portion	O
of	O
the	O
frame	B-Protocol
contents	O
which	O
indicates	O
whether	O
the	O
frame	B-Protocol
contains	O
data	O
or	O
control	O
information	O
.	O
</s>
<s>
Frame	B-Protocol
type	O
–	O
01	O
indicates	O
LLC	O
frame	B-Protocol
IEEE	O
802.2	O
(	O
data	O
)	O
and	O
ignore	O
control	O
bits	O
;	O
</s>
<s>
Data	O
A	O
variable	O
length	O
field	O
of	O
0	O
or	O
more	O
bytes	O
,	O
the	O
maximum	O
allowable	O
size	O
depending	O
on	O
ring	O
speed	O
containing	O
MAC	B-Protocol
management	O
data	O
or	O
upper	O
layer	O
information	O
.	O
</s>
<s>
Frame	B-Protocol
check	O
sequence	O
A	O
four-byte	O
field	O
used	O
to	O
store	O
the	O
calculation	O
of	O
a	O
CRC	O
for	O
frame	B-Protocol
integrity	O
verification	O
by	O
the	O
receiver	O
.	O
</s>
<s>
Ending	O
delimiter	O
The	O
counterpart	O
to	O
the	O
starting	O
delimiter	O
,	O
this	O
field	O
marks	O
the	O
end	O
of	O
the	O
frame	B-Protocol
and	O
consists	O
of	O
the	O
following	O
bits	O
from	O
most	O
significant	O
to	O
least	O
significant	O
:	O
J	O
,	O
K	O
,	O
1	O
,	O
J	O
,	O
K	O
,	O
1	O
,	O
I	O
,	O
E	O
.	O
</s>
<s>
I	O
is	O
the	O
intermediate	O
frame	B-Protocol
bit	O
and	O
E	O
is	O
the	O
error	O
bit	O
.	O
</s>
<s>
Frame	B-Protocol
status	O
A	O
one-byte	O
field	O
used	O
as	O
a	O
primitive	O
acknowledgment	O
scheme	O
on	O
whether	O
the	O
frame	B-Protocol
was	O
recognized	O
and	O
copied	O
by	O
its	O
intended	O
receiver	O
.	O
</s>
<s>
Every	O
station	O
in	O
a	O
Token	B-Device
Ring	I-Device
network	I-Device
is	O
either	O
an	O
active	O
monitor	O
(	O
AM	O
)	O
or	O
standby	O
monitor	O
(	O
SM	O
)	O
station	O
.	O
</s>
<s>
a	O
particular	O
timer	O
on	O
an	O
end	O
station	O
expires	O
such	O
as	O
the	O
case	O
when	O
a	O
station	O
has	O
n't	O
seen	O
a	O
token	O
frame	B-Protocol
in	O
the	O
past	O
7	O
seconds	O
.	O
</s>
<s>
When	O
any	O
of	O
the	O
above	O
conditions	O
take	O
place	O
and	O
a	O
station	O
decides	O
that	O
a	O
new	O
monitor	O
is	O
needed	O
,	O
it	O
will	O
transmit	O
a	O
claim	O
token	O
frame	B-Protocol
,	O
announcing	O
that	O
it	O
wants	O
to	O
become	O
the	O
new	O
monitor	O
.	O
</s>
<s>
If	O
some	O
other	O
station	O
tries	O
to	O
become	O
the	O
monitor	O
at	O
the	O
same	O
time	O
then	O
the	O
station	O
with	O
the	O
highest	O
MAC	B-Protocol
address	O
will	O
win	O
the	O
election	O
process	O
.	O
</s>
<s>
A	O
third	O
function	O
for	O
the	O
AM	O
is	O
to	O
ensure	O
that	O
exactly	O
one	O
token	O
circulates	O
whenever	O
there	O
is	O
no	O
frame	B-Protocol
being	O
transmitted	O
,	O
and	O
to	O
detect	O
a	O
broken	O
ring	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
stations	O
must	O
go	O
through	O
a	O
5-phase	O
ring	O
insertion	O
process	O
before	O
being	O
allowed	O
to	O
participate	O
in	O
the	O
ring	B-Architecture
network	I-Architecture
.	O
</s>
<s>
If	O
any	O
of	O
these	O
phases	O
fail	O
,	O
the	O
Token	B-Device
Ring	I-Device
station	O
will	O
not	O
insert	O
into	O
the	O
ring	O
and	O
the	O
Token	B-Device
Ring	I-Device
driver	O
may	O
report	O
an	O
error	O
.	O
</s>
<s>
A	O
station	O
is	O
wrapped	O
at	O
the	O
MSAU	B-Device
and	O
is	O
able	O
to	O
send	O
2000	O
test	O
frames	O
down	O
its	O
transmit	O
pair	O
which	O
will	O
loop	O
back	O
to	O
its	O
receive	O
pair	O
.	O
</s>
<s>
Phase	O
1	O
(	O
Physical	O
Insertion	O
)	O
–	O
A	O
station	O
then	O
sends	O
a	O
5-volt	O
signal	O
to	O
the	O
MSAU	B-Device
to	O
open	O
the	O
relay	O
.	O
</s>
<s>
Phase	O
2	O
(	O
Address	O
Verification	O
)	O
–	O
A	O
station	O
then	O
transmits	O
MAC	B-Protocol
frames	O
with	O
its	O
own	O
MAC	B-Protocol
address	O
in	O
the	O
destination	O
address	O
field	O
of	O
a	O
Token	B-Device
Ring	I-Device
frame	B-Protocol
.	O
</s>
<s>
When	O
the	O
frame	B-Protocol
returns	O
and	O
if	O
the	O
Address	O
Recognized	O
(	O
AR	O
)	O
and	O
Frame	B-Protocol
Copied	O
(	O
FC	O
)	O
bits	O
in	O
the	O
frame-status	O
are	O
set	O
to	O
0	O
(	O
indicating	O
that	O
no	O
other	O
station	O
currently	O
on	O
the	O
ring	O
uses	O
that	O
address	O
)	O
,	O
the	O
station	O
must	O
participate	O
in	O
the	O
periodic	O
(	O
every	O
7	O
seconds	O
)	O
ring	O
poll	O
process	O
.	O
</s>
<s>
This	O
is	O
where	O
stations	O
identify	O
themselves	O
on	O
the	O
network	O
as	O
part	O
of	O
the	O
MAC	B-Protocol
management	O
functions	O
.	O
</s>
<s>
Station	O
waits	O
until	O
it	O
receives	O
an	O
AMP	O
or	O
SMP	O
frame	B-Protocol
with	O
the	O
AR	O
and	O
FC	O
bits	O
set	O
to	O
0	O
.	O
</s>
<s>
When	O
it	O
does	O
,	O
the	O
station	O
flips	O
both	O
bits	O
(	O
AR	O
and	O
FC	O
)	O
to	O
1	O
,	O
if	O
enough	O
resources	O
are	O
available	O
,	O
and	O
queues	O
an	O
SMP	O
frame	B-Protocol
for	O
transmission	O
.	O
</s>
<s>
Phase	O
4	O
(	O
Request	O
Initialization	O
)	O
–	O
Finally	O
a	O
station	O
sends	O
out	O
a	O
special	O
request	O
to	O
a	O
parameter	O
server	B-Application
to	O
obtain	O
configuration	O
information	O
.	O
</s>
<s>
This	O
frame	B-Protocol
is	O
sent	O
to	O
a	O
special	O
functional	O
address	O
,	O
typically	O
a	O
Token	B-Device
Ring	I-Device
bridge	O
,	O
which	O
may	O
hold	O
timer	O
and	O
ring	O
number	O
information	O
the	O
new	O
station	O
needs	O
to	O
know	O
.	O
</s>
<s>
Token	B-Device
Ring	I-Device
specifies	O
an	O
optional	O
scheme	O
of	O
this	O
sort	O
,	O
as	O
does	O
the	O
CAN	B-Protocol
Bus	I-Protocol
,	O
(	O
widely	O
used	O
in	O
automotive	O
applications	O
)	O
–	O
but	O
Ethernet	O
does	O
not	O
.	O
</s>
<s>
In	O
the	O
Token	B-Device
Ring	I-Device
priority	O
MAC	B-Protocol
,	O
eight	O
priority	O
levels	O
,	O
0	O
–	O
7	O
,	O
are	O
used	O
.	O
</s>
<s>
When	O
the	O
station	O
wishing	O
to	O
transmit	O
receives	O
a	O
token	O
or	O
data	B-Protocol
frame	I-Protocol
with	O
a	O
priority	O
less	O
than	O
or	O
equal	O
to	O
the	O
station	O
's	O
requested	O
priority	O
,	O
it	O
sets	O
the	O
priority	O
bits	O
to	O
its	O
desired	O
priority	O
.	O
</s>
<s>
Upon	O
sending	O
and	O
receiving	O
its	O
own	O
data	B-Protocol
frame	I-Protocol
,	O
the	O
station	O
downgrades	O
the	O
token	O
priority	O
back	O
to	O
the	O
original	O
priority	O
.	O
</s>
<s>
Bridging	O
solutions	O
for	O
Token	B-Device
Ring	I-Device
and	O
Ethernet	O
networks	O
included	O
the	O
AT&T	O
StarWAN	O
10:4	O
Bridge	O
,	O
the	O
IBM	O
8209	O
LAN	B-General_Concept
Bridge	O
and	O
the	O
Microcom	O
LAN	B-General_Concept
Bridge	O
.	O
</s>
<s>
Alternative	O
connection	O
solutions	O
incorporated	O
a	O
router	O
that	O
could	O
be	O
configured	O
to	O
dynamically	O
filter	O
traffic	O
,	O
protocols	O
and	O
interfaces	O
,	O
such	O
as	O
the	O
IBM	O
2210-24M	O
Multiprotocol	O
Router	O
,	O
which	O
contained	O
both	O
Ethernet	O
and	O
Token	B-Device
Ring	I-Device
interfaces	O
.	O
</s>
