<s>
A	O
cloudlet	B-Operating_System
is	O
a	O
mobility-enhanced	O
small-scale	O
cloud	B-Architecture
datacenter	I-Architecture
that	O
is	O
located	O
at	O
the	O
edge	O
of	O
the	O
Internet	O
.	O
</s>
<s>
The	O
main	O
purpose	O
of	O
the	O
cloudlet	B-Operating_System
is	O
supporting	O
resource-intensive	O
and	O
interactive	O
mobile	O
applications	O
by	O
providing	O
powerful	O
computing	O
resources	O
to	O
mobile	O
devices	O
with	O
lower	O
latency	O
.	O
</s>
<s>
It	O
is	O
a	O
new	O
architectural	O
element	O
that	O
extends	O
today	O
's	O
cloud	B-Architecture
computing	I-Architecture
infrastructure	O
.	O
</s>
<s>
It	O
represents	O
the	O
middle	O
tier	O
of	O
a	O
3-tier	O
hierarchy	O
:	O
mobile	O
device	O
-	O
cloudlet	B-Operating_System
-	O
cloud	B-Architecture
.	O
</s>
<s>
A	O
cloudlet	B-Operating_System
can	O
be	O
viewed	O
as	O
a	O
data	O
center	O
in	O
a	O
box	O
whose	O
goal	O
is	O
to	O
bring	O
the	O
cloud	B-Architecture
closer	O
.	O
</s>
<s>
The	O
cloudlet	B-Operating_System
term	O
was	O
first	O
coined	O
by	O
M	O
.	O
Satyanarayanan	O
,	O
Victor	O
Bahl	O
,	O
Ramón	O
Cáceres	O
,	O
and	O
Nigel	O
Davies	O
,	O
and	O
a	O
prototype	O
implementation	O
is	O
developed	O
by	O
Carnegie	O
Mellon	O
University	O
as	O
a	O
research	O
project	O
.	O
</s>
<s>
The	O
concept	O
of	O
cloudlet	B-Operating_System
is	O
also	O
known	O
as	O
follow	O
me	O
cloud	B-Architecture
,	O
and	O
mobile	O
micro-cloud	O
.	O
</s>
<s>
Many	O
mobile	O
services	O
split	O
the	O
application	O
into	O
a	B-Architecture
front-end	I-Architecture
client	I-Architecture
program	I-Architecture
and	O
a	B-Architecture
back-end	I-Architecture
server	I-Architecture
program	I-Architecture
following	O
the	O
traditional	O
client-server	B-Operating_System
model	I-Operating_System
.	O
</s>
<s>
The	O
front-end	B-Architecture
mobile	O
application	O
offloads	O
its	O
functionality	O
to	O
the	O
back-end	B-Architecture
servers	O
for	O
various	O
reasons	O
such	O
as	O
speeding	O
up	O
processing	O
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
cloud	B-Architecture
computing	I-Architecture
,	O
the	O
back-end	B-Architecture
server	O
is	O
typically	O
hosted	O
at	O
the	O
cloud	B-Architecture
datacenter	I-Architecture
.	O
</s>
<s>
Though	O
the	O
use	O
of	O
a	O
cloud	B-Architecture
datacenter	I-Architecture
offers	O
various	O
benefits	O
such	O
as	O
scalability	O
and	O
elasticity	O
,	O
its	O
consolidation	O
and	O
centralization	O
lead	O
to	O
a	O
large	O
separation	O
between	O
a	O
mobile	O
device	O
and	O
its	O
associated	O
datacenter	O
.	O
</s>
<s>
For	O
the	O
reasons	O
of	O
latency	O
,	O
some	O
emerging	O
mobile	O
applications	O
require	O
cloud	B-Architecture
offload	O
infrastructure	O
to	O
be	O
close	O
to	O
the	O
mobile	O
device	O
to	O
achieve	O
low	O
response	O
time	O
.	O
</s>
<s>
The	O
individual	O
elements	O
of	O
this	O
offload	O
infrastructure	O
are	O
referred	O
to	O
as	O
cloudlets	B-Operating_System
.	O
</s>
<s>
Cloudlets	B-Operating_System
aim	O
to	O
support	O
mobile	O
applications	O
that	O
are	O
both	O
resource-intensive	O
and	O
interactive	O
.	O
</s>
<s>
Augmented	B-General_Concept
reality	I-General_Concept
applications	I-General_Concept
that	O
use	O
head-tracked	O
systems	O
require	O
end-to-end	O
latencies	O
of	O
less	O
than	O
16	O
ms.	O
</s>
<s>
Cloud	B-Application
games	I-Application
with	O
remote	O
rendering	O
also	O
require	O
low	O
latencies	O
and	O
high	O
bandwidth	O
.	O
</s>
<s>
Wearable	O
cognitive	O
assistance	O
systems	O
combine	O
devices	O
such	O
as	O
Google	B-Application
Glass	I-Application
with	O
cloud-based	B-Architecture
processing	O
to	O
guide	O
users	O
through	O
complex	O
tasks	O
.	O
</s>
<s>
These	O
applications	O
use	O
cloud	B-Architecture
resources	O
in	O
the	O
critical	O
path	O
of	O
real-time	O
user	O
interaction	O
.	O
</s>
<s>
Apple	B-Application
Siri	I-Application
and	O
Google	B-Application
Now	I-Application
which	O
perform	O
compute-intensive	O
speech	O
recognition	O
in	B-Architecture
the	I-Architecture
cloud	I-Architecture
,	O
are	O
further	O
examples	O
in	O
this	O
emerging	O
space	O
.	O
</s>
<s>
There	O
is	O
significant	O
overlap	O
in	O
the	O
requirements	O
for	O
cloud	B-Architecture
and	O
cloudlet	B-Operating_System
.	O
</s>
<s>
At	O
a	O
cloud	B-Architecture
datacenter	I-Architecture
,	O
these	O
requirements	O
are	O
met	O
today	O
using	O
the	O
virtual	B-Architecture
machine	I-Architecture
(	O
VM	O
)	O
abstraction	O
.	O
</s>
<s>
For	O
the	O
same	O
reasons	O
they	O
are	O
used	O
in	O
cloud	B-Architecture
computing	I-Architecture
today	O
,	O
VMs	O
are	O
used	O
as	O
an	O
abstraction	O
for	O
cloudlets	B-Operating_System
.	O
</s>
<s>
Meanwhile	O
,	O
there	O
are	O
a	O
few	O
but	O
important	O
differentiators	O
between	O
cloud	B-Architecture
and	O
cloudlet	B-Operating_System
.	O
</s>
<s>
Different	O
from	O
cloud	B-Architecture
data	O
centers	O
that	O
are	O
optimized	O
for	O
launching	O
existing	O
VM	O
images	O
in	O
their	O
storage	O
tier	O
,	O
cloudlets	B-Operating_System
need	O
to	O
be	O
much	O
more	O
agile	O
in	O
their	O
provisioning	O
.	O
</s>
<s>
A	O
user	O
from	O
far	O
away	O
may	O
unexpectedly	O
show	O
up	O
at	O
a	O
cloudlet	B-Operating_System
(	O
e.g.	O
,	O
if	O
he	O
just	O
got	O
off	O
an	O
international	O
flight	O
)	O
and	O
try	O
to	O
use	O
it	O
for	O
an	O
application	O
such	O
as	O
a	O
personalized	O
language	O
translator	O
.	O
</s>
<s>
If	O
a	O
mobile	O
device	O
user	O
moves	O
away	O
from	O
the	O
cloudlet	B-Operating_System
he	O
is	O
currently	O
using	O
,	O
the	O
interactive	O
response	O
will	O
degrade	O
as	O
the	O
logical	O
network	O
distance	O
increases	O
.	O
</s>
<s>
To	O
address	O
this	O
effect	O
of	O
user	O
mobility	O
,	O
the	O
offloaded	O
services	O
on	O
the	O
first	O
cloudlet	B-Operating_System
need	O
to	O
be	O
transferred	O
to	O
the	O
second	O
cloudlet	B-Operating_System
maintaining	O
end-to-end	O
network	O
quality	O
.	O
</s>
<s>
This	O
resembles	O
live	O
migration	O
in	O
cloud	B-Architecture
computing	I-Architecture
but	O
differs	O
considerably	O
in	O
a	O
sense	O
that	O
the	O
VM	O
handoff	O
happens	O
in	O
Wide	O
Area	O
Network	O
(	O
WAN	O
)	O
.	O
</s>
<s>
Since	O
the	O
cloudlet	B-Operating_System
model	O
requires	O
reconfiguration	O
or	O
additional	O
deployment	O
of	O
hardware/software	O
,	O
it	O
is	O
important	O
to	O
provide	O
a	O
systematic	O
way	O
to	O
incentivise	O
the	O
deployment	O
.	O
</s>
<s>
Cloudlets	B-Operating_System
need	O
practical	O
applications	O
to	O
incentivize	O
cloudlet	B-Operating_System
deployment	O
.	O
</s>
<s>
However	O
,	O
developers	O
cannot	O
heavily	O
rely	O
on	O
cloudlet	B-Operating_System
infrastructure	O
until	O
it	O
is	O
widely	O
deployed	O
.	O
</s>
<s>
To	O
break	O
this	O
deadlock	O
and	O
bootstrap	O
the	O
cloudlet	B-Operating_System
deployment	O
,	O
researchers	O
at	O
Carnegie	O
Mellon	O
University	O
proposed	O
OpenStack++	O
that	O
extends	O
OpenStack	B-Application
to	O
leverage	O
its	O
open	O
ecosystem	O
.	O
</s>
<s>
OpenStack++	O
provides	O
a	O
set	O
of	O
cloudlet-specific	O
APIs	O
as	O
OpenStack	B-Application
extensions	O
.	O
</s>
<s>
By	O
2015	O
cloudlet	B-Operating_System
based	O
applications	O
were	O
commercially	O
available	O
.	O
</s>
<s>
In	O
2017	O
the	O
National	O
Institute	O
of	O
Standards	O
and	O
Technology	O
published	O
draft	O
standards	O
for	O
fog	B-Device
computing	I-Device
in	O
which	O
cloudlets	B-Operating_System
were	O
defined	O
as	O
nodes	O
on	O
the	O
fog	O
architecture	O
.	O
</s>
