<s>
A	O
Wireless	B-Protocol
Data	I-Protocol
center	I-Protocol
is	O
a	O
type	O
of	O
data	B-Operating_System
center	I-Operating_System
that	O
uses	O
wireless	O
communication	O
technology	O
instead	O
of	O
cables	O
to	O
store	O
,	O
process	O
and	O
retrieve	O
data	O
for	O
enterprises	O
.	O
</s>
<s>
The	O
development	O
of	O
Wireless	B-Protocol
Data	I-Protocol
centers	I-Protocol
arose	O
as	O
a	O
solution	O
to	O
growing	O
cabling	O
complexity	O
and	O
hotspots	O
.	O
</s>
<s>
The	O
wireless	O
technology	O
was	O
introduced	O
by	O
Shin	O
et	O
al.	O
,	O
who	O
replaced	O
all	O
cables	O
with	O
60GHz	O
wireless	O
connections	O
at	O
the	O
Cayley	O
data	B-Operating_System
center	I-Operating_System
.	O
</s>
<s>
Apart	O
from	O
that	O
,	O
cables	O
can	O
additionally	O
affect	O
data	B-Operating_System
center	I-Operating_System
cooling	O
.	O
</s>
<s>
The	O
Data	B-Operating_System
Center	I-Operating_System
Network	O
(	O
DCN	O
)	O
is	O
the	O
infrastructure	O
responsible	O
to	O
provide	O
intra	O
and	O
inter-DC	O
networking	O
services	O
,	O
therefore	O
is	O
essential	O
to	O
design	O
efficient	O
high-speed/high	O
bandwidth	O
DCN	O
to	O
satisfy	O
the	O
high	O
computing	O
and	O
communication	O
demands	O
from	O
the	O
DC	O
.	O
</s>
<s>
High	O
inter-node	O
link	O
capacity	O
:	O
Online	O
services	O
,	O
such	O
as	O
MapReduce	B-Operating_System
and	O
distributed	O
file	O
systems	O
,	O
need	O
high	O
link	O
and	O
network	O
capacity	O
.	O
</s>
<s>
60	O
GHz	O
RF	O
:	O
Radios	O
in	O
the	O
license-free	O
60GHz	O
range	O
have	O
several	O
characteristics	O
that	O
make	O
them	O
more	O
suitable	O
for	O
adoption	O
in	O
data-centers	B-Operating_System
.	O
</s>
<s>
Since	O
DCNs	O
needs	O
high	O
bandwidth	O
in	O
order	O
to	O
exchange	O
big	O
amount	O
of	O
data	O
,	O
new	O
communication	O
technologies	O
must	O
be	O
capable	O
of	O
achieving	O
high	O
link	O
and	O
network	O
capacities	O
and	O
also	O
it	O
should	O
meet	O
other	O
requirements	O
of	O
a	O
data	B-Operating_System
center	I-Operating_System
network	O
.	O
</s>
<s>
Hence	O
,	O
In	O
order	O
to	O
implement	O
wireless	O
communication	O
technologies	O
in	O
data	B-Operating_System
centers	I-Operating_System
,	O
there	O
are	O
several	O
challenges	O
that	O
may	O
face	O
any	O
wireless	O
technology	O
to	O
be	O
deployed	O
in	O
DCNs	O
like	O
:	O
</s>
<s>
can	O
cause	O
changes	O
in	O
Data	B-Operating_System
center	I-Operating_System
environmental	O
control	O
,	O
e.g.	O
</s>
<s>
Obstruction-free	O
wireless	O
links	O
:	O
In	O
the	O
large-scale	O
data	B-Operating_System
centers	I-Operating_System
there	O
is	O
too	O
many	O
interconnectivity	O
between	O
the	O
racks	O
,	O
therefore	O
the	O
proposed	O
wireless	O
communication	O
technology	O
to	O
use	O
in	O
DCNs	O
must	O
be	O
able	O
to	O
meet	O
this	O
large	O
link	O
connectivity	O
in	O
DCNs	O
.	O
</s>
<s>
A	O
few	O
papers	O
discuss	O
the	O
deployment	O
of	O
60GHz	O
RF	O
and	O
FSO	O
technologies	O
in	O
the	O
containerised	O
DCN	O
(	O
also	O
known	O
as	O
Modular	O
data	B-Operating_System
center	I-Operating_System
)	O
scenario	O
.	O
</s>
<s>
In	O
the	O
concept	O
of	O
wireless	B-Protocol
data	I-Protocol
centers	I-Protocol
,	O
efficient	O
use	O
of	O
open	O
spaces	O
is	O
significant	O
in	O
order	O
to	O
optimize	O
resource	O
multiplexing	O
.	O
</s>
<s>
Since	O
the	O
maximum	O
number	O
of	O
live	O
connections	O
proportional	O
to	O
the	O
volume	O
of	O
data	B-Operating_System
center	I-Operating_System
per	O
single	O
antenna	O
beam	O
.	O
</s>
<s>
Network	O
Interface	O
Cards	O
(	O
NIC	O
)	O
that	O
are	O
used	O
in	O
traditional	O
data	B-Operating_System
centers	I-Operating_System
are	O
replaced	O
by	O
a	O
custom-built	O
Y-switch	O
with	O
transceivers	O
to	O
connect	O
the	O
server	O
's	O
system	O
bus	O
.	O
</s>
<s>
During	O
the	O
tests	O
,	O
since	O
the	O
wireless	O
transceivers	O
and	O
Y-switches	O
are	O
not	O
yet	O
available	O
in	O
the	O
market	O
,	O
estimations	O
have	O
done	O
based	O
on	O
the	O
expected	O
price	O
range	O
of	O
60GHz	O
transceivers	O
and	O
simulations	O
are	O
developed	O
for	O
performance	O
evaluations	O
of	O
Cayley	O
data	B-Operating_System
center	I-Operating_System
and	O
Conventional	O
data	B-Operating_System
centers	I-Operating_System
(	O
CDC	O
)	O
with	O
different	O
designs	O
.	O
</s>
<s>
Based	O
on	O
conducted	O
experiences	O
with	O
Cayley	O
data	B-Operating_System
center	I-Operating_System
and	O
CDC	O
that	O
are	O
configured	O
with	O
different	O
oversubscription	O
rates	O
,	O
Cayley	O
data	B-Operating_System
centers	I-Operating_System
have	O
better	O
performance	O
at	O
maximum	O
aggregate	O
bandwidth	O
compared	O
to	O
CDC	O
.	O
</s>
<s>
Cayley	O
data	B-Operating_System
centers	I-Operating_System
are	O
taking	O
advantage	O
of	O
less	O
switching	O
design	O
and	O
doubles	O
CDC	O
's	O
bandwidth	O
during	O
packet	O
delivery	O
outside	O
of	O
a	O
rack	O
.	O
</s>
<s>
Cayley	O
data	B-Operating_System
center	I-Operating_System
has	O
a	O
drawback	O
in	O
packet	O
delivery	O
latency	O
and	O
scalability	O
because	O
it	O
uses	O
multi-hop	O
routing	O
and	O
uses	O
intermediate	O
nodes	O
to	O
convey	O
packets	O
to	O
other	O
nodes	O
.	O
</s>
<s>
Cayley	O
data	B-Operating_System
centers	I-Operating_System
are	O
more	O
resilient	O
to	O
failures	O
compared	O
to	O
conventional	O
data	B-Operating_System
centers	I-Operating_System
since	O
Cayley	O
topology	O
has	O
dense	O
connectivity	O
and	O
have	O
minimized	O
the	O
number	O
of	O
switches	O
that	O
are	O
a	O
critical	O
point	O
for	O
failures	O
for	O
data	B-Operating_System
centers	I-Operating_System
.	O
</s>
<s>
Cost	O
analysis	O
of	O
Cayley	O
data	B-Operating_System
centers	I-Operating_System
has	O
been	O
done	O
based	O
on	O
assumptions	O
since	O
60GHz	O
transceivers	O
are	O
not	O
commercially	O
in	O
the	O
market	O
yet	O
.	O
</s>
<s>
In	O
the	O
case	O
,	O
the	O
cost	O
of	O
a	O
60-GHz	O
transceiver	O
less	O
than	O
$90	O
,	O
Cayley	O
data	B-Operating_System
centers	I-Operating_System
will	O
be	O
much	O
cheaper	O
.	O
</s>
<s>
Therefore	O
,	O
total	O
power	O
switch	O
packet	O
consumption	O
of	O
CDC	O
is	O
at	O
least	O
12	O
times	O
more	O
than	O
Cayley	O
data	B-Operating_System
centers	I-Operating_System
.	O
</s>
