<s>
In	O
computing	O
,	O
Chord	B-Application
is	O
a	O
protocol	O
and	O
algorithm	O
for	O
a	O
peer-to-peer	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
.	O
</s>
<s>
A	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
stores	O
key-value	B-Application
pairs	I-Application
by	O
assigning	O
keys	O
to	O
different	O
computers	O
(	O
known	O
as	O
"	O
nodes	O
"	O
)	O
;	O
a	O
node	O
will	O
store	O
the	O
values	O
for	O
all	O
the	O
keys	O
for	O
which	O
it	O
is	O
responsible	O
.	O
</s>
<s>
Chord	B-Application
specifies	O
how	O
keys	O
are	O
assigned	O
to	O
nodes	O
,	O
and	O
how	O
a	O
node	O
can	B-Protocol
discover	O
the	O
value	O
for	O
a	O
given	O
key	O
by	O
first	O
locating	O
the	O
node	O
responsible	O
for	O
that	O
key	O
.	O
</s>
<s>
Chord	B-Application
is	O
one	O
of	O
the	O
four	O
original	O
distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
protocols	O
,	O
along	O
with	O
CAN	B-Protocol
,	O
Tapestry	O
,	O
and	O
Pastry	O
.	O
</s>
<s>
The	O
2001	O
Chord	B-Application
paper	O
won	O
an	O
ACM	O
SIGCOMM	O
Test	O
of	O
Time	O
award	O
in	O
2011	O
.	O
</s>
<s>
Subsequent	O
research	O
by	O
Pamela	O
Zave	O
has	O
shown	O
that	O
the	O
original	O
Chord	B-Application
algorithm	I-Application
(	O
as	O
specified	O
in	O
the	O
2001	O
SIGCOMM	O
paper	O
,	O
the	O
2001	O
Technical	O
report	O
,	O
</s>
<s>
)	O
can	B-Protocol
mis-order	O
the	O
ring	O
,	O
produce	O
several	O
rings	O
,	O
and	O
break	O
the	O
ring	O
.	O
</s>
<s>
Nodes	O
and	O
keys	O
are	O
assigned	O
an	O
-bit	O
identifier	O
using	O
consistent	B-Algorithm
hashing	I-Algorithm
.	O
</s>
<s>
The	O
SHA-1	B-Algorithm
algorithm	O
is	O
the	O
base	O
hashing	B-Error_Name
function	I-Error_Name
for	O
consistent	B-Algorithm
hashing	I-Algorithm
.	O
</s>
<s>
Consistent	B-Algorithm
hashing	I-Algorithm
is	O
integral	O
to	O
the	O
robustness	O
and	O
performance	O
of	O
Chord	B-Application
because	O
both	O
keys	O
and	O
nodes	O
(	O
in	O
fact	O
,	O
their	O
IP	B-Protocol
addresses	I-Protocol
)	O
are	O
uniformly	O
distributed	O
in	O
the	O
same	O
identifier	O
space	O
with	O
a	O
negligible	O
possibility	O
of	O
collision	B-Algorithm
.	O
</s>
<s>
Using	O
the	O
Chord	B-Application
lookup	O
protocol	O
,	O
nodes	O
and	O
keys	O
are	O
arranged	O
in	O
an	O
identifier	O
circle	O
that	O
has	O
at	O
most	O
nodes	O
,	O
ranging	O
from	O
to	O
.	O
</s>
<s>
(	O
should	O
be	O
large	O
enough	O
to	O
avoid	O
collision	B-Algorithm
.	O
)	O
</s>
<s>
The	O
concept	O
of	O
successor	O
can	B-Protocol
be	O
used	O
for	O
keys	O
as	O
well	O
.	O
</s>
<s>
The	O
core	O
usage	O
of	O
the	O
Chord	B-Application
protocol	O
is	O
to	O
query	O
a	O
key	O
from	O
a	O
client	O
(	O
generally	O
a	O
node	O
as	O
well	O
)	O
,	O
i.e.	O
</s>
<s>
To	O
avoid	O
the	O
linear	O
search	O
above	O
,	O
Chord	B-Application
implements	O
a	O
faster	O
search	O
method	O
by	O
requiring	O
each	O
node	O
to	O
keep	O
a	O
finger	O
table	O
containing	O
up	O
to	O
entries	O
,	O
recall	O
that	O
is	O
the	O
number	O
of	O
bits	O
in	O
the	O
hash	B-Error_Name
key	O
.	O
</s>
<s>
The	O
predecessor	O
of	O
can	B-Protocol
be	O
easily	O
obtained	O
from	O
the	O
predecessor	O
of	O
(	O
in	O
the	O
previous	O
circle	O
)	O
.	O
</s>
<s>
Cooperative	O
Mirroring	O
:	O
A	O
load	B-Application
balancing	I-Application
mechanism	O
by	O
a	O
local	O
network	O
hosting	O
information	O
available	O
to	O
computers	O
outside	O
of	O
the	O
local	O
network	O
.	O
</s>
<s>
With	O
high	O
probability	O
,	O
Chord	B-Application
contacts	O
nodes	O
to	O
find	O
a	O
successor	O
in	O
an	O
-node	O
network	O
.	O
</s>
<s>
The	O
pseudocode	O
to	O
stabilize	O
the	O
chord	B-Application
ring/circle	O
after	O
node	O
joins	O
and	O
departures	O
is	O
as	O
follows	O
:	O
</s>
<s>
//	O
create	O
a	O
new	O
Chord	B-Application
ring	O
.	O
</s>
<s>
//	O
join	O
a	O
Chord	B-Application
ring	O
containing	O
node	O
n	O
 '	O
.	O
</s>
