<s>
With	O
the	O
help	O
of	O
a	O
simple	O
two-level	O
architecture	O
,	O
it	O
achieves	O
much	O
better	O
prediction	O
accuracy	O
then	O
the	O
representative	O
Vivaldi	B-Protocol
coordinates	I-Protocol
,	O
and	O
it	O
is	O
incrementally	O
deployable	O
.	O
</s>
<s>
Vivaldi	B-Protocol
is	O
the	O
most	O
common	O
distributed	O
NC	O
system	O
,	O
and	O
it	O
is	O
deployed	O
in	O
many	O
well-known	O
internet	O
systems	O
,	O
such	O
as	O
Bamboo	O
DHT	O
(	O
Distributed	B-Operating_System
hash	I-Operating_System
table	I-Operating_System
)	O
,	O
Stream-Based	O
Overlay	O
Network	O
(	O
SBON	O
)	O
and	O
Azureus	B-Application
BitTorrent	B-Protocol
.	O
</s>
<s>
The	O
Vivaldi	B-Protocol
algorithm	O
is	O
applied	O
to	O
both	O
the	O
base	O
overlay	O
and	O
the	O
local	O
cluster	O
.	O
</s>
<s>
The	O
experimental	O
results	O
show	O
that	O
Pharos	O
greatly	O
outperforms	O
Vivaldi	B-Protocol
in	O
internet	O
distance	O
prediction	O
without	O
adding	O
any	O
significant	O
overhead	O
.	O
</s>
<s>
Fully	O
compatible	O
with	O
Vivaldi	B-Protocol
,	O
the	O
most	O
widely	O
deployed	O
NC	O
system	O
.	O
</s>
<s>
For	O
every	O
host	O
where	O
the	O
Vivaldi	B-Protocol
client	O
has	O
been	O
deployed	O
,	O
it	O
just	O
needs	O
to	O
run	O
classic	O
Vivaldi	B-Protocol
NC	O
algorithm	O
to	O
join	O
global	O
overlay	O
and	O
local	O
cluster	O
,	O
without	O
deploying	O
another	O
NC	O
client	O
.	O
</s>
<s>
The	O
anchors	O
in	O
Pharos	O
is	O
different	O
from	O
landmarks	O
in	O
Global	B-Protocol
network	I-Protocol
positioning	I-Protocol
(	O
GNP	O
)	O
,	O
which	O
not	O
only	O
has	O
to	O
reply	O
the	O
ICMP	O
ping	O
but	O
also	O
need	O
to	O
reply	O
the	O
queries	O
from	O
all	O
clients	O
by	O
sending	O
their	O
latest	O
NCs	O
.	O
</s>
