<s>
In	O
computing	O
,	O
network	B-Protocol
virtualization	I-Protocol
is	O
the	O
process	O
of	O
combining	O
hardware	O
and	O
software	O
network	O
resources	O
and	O
network	O
functionality	O
into	O
a	O
single	O
,	O
software-based	O
administrative	O
entity	O
,	O
a	O
virtual	B-Protocol
network	I-Protocol
.	O
</s>
<s>
Network	B-Protocol
virtualization	I-Protocol
involves	O
platform	B-General_Concept
virtualization	I-General_Concept
,	O
often	O
combined	O
with	O
resource	O
virtualization	O
.	O
</s>
<s>
Network	B-Protocol
virtualization	I-Protocol
is	O
categorized	O
as	O
either	O
external	O
virtualization	O
,	O
combining	O
many	O
networks	O
or	O
parts	O
of	O
networks	O
into	O
a	O
virtual	O
unit	O
,	O
or	O
internal	O
virtualization	O
,	O
providing	O
network-like	O
functionality	O
to	O
software	B-Application
containers	I-Application
on	O
a	O
single	O
network	B-Application
server	I-Application
.	O
</s>
<s>
In	O
software	O
testing	O
,	O
software	O
developers	O
use	O
network	B-Protocol
virtualization	I-Protocol
to	O
test	O
software	O
which	O
are	O
under	O
development	O
in	O
a	O
simulation	O
of	O
the	O
network	O
environments	O
in	O
which	O
the	O
software	O
is	O
intended	O
to	O
operate	O
.	O
</s>
<s>
As	O
a	O
component	O
of	O
application	B-Application
performance	I-Application
engineering	I-Application
,	O
network	B-Protocol
virtualization	I-Protocol
enables	O
developers	O
to	O
emulate	O
connections	O
between	O
applications	O
,	O
services	O
,	O
dependencies	O
,	O
and	O
end	O
users	O
in	O
a	O
test	O
environment	O
without	O
having	O
to	O
physically	O
test	O
the	O
software	O
on	O
all	O
possible	O
hardware	O
or	O
system	O
software	O
.	O
</s>
<s>
The	O
validity	O
of	O
the	O
test	O
depends	O
on	O
the	O
accuracy	O
of	O
the	O
network	B-Protocol
virtualization	I-Protocol
in	O
emulating	O
real	O
hardware	O
and	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Various	O
equipment	O
and	O
software	O
vendors	O
offer	O
network	B-Protocol
virtualization	I-Protocol
by	O
combining	O
any	O
of	O
the	O
following	O
:	O
</s>
<s>
External	O
network	B-Protocol
virtualization	I-Protocol
combines	O
or	O
subdivides	O
one	O
or	O
more	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
into	O
virtual	B-Protocol
networks	I-Protocol
to	O
improve	O
a	O
large	O
network	O
's	O
or	O
data	O
center	O
's	O
efficiency	O
.	O
</s>
<s>
A	O
virtual	B-General_Concept
local	I-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
VLAN	B-General_Concept
)	O
and	O
network	B-Protocol
switch	I-Protocol
comprise	O
the	O
key	O
components	O
.	O
</s>
<s>
Using	O
this	O
technology	O
,	O
a	O
system	B-Application
administrator	I-Application
can	O
configure	O
systems	O
physically	O
attached	O
to	O
the	O
same	O
local	B-General_Concept
network	I-General_Concept
into	O
separate	O
virtual	B-Protocol
networks	I-Protocol
.	O
</s>
<s>
Conversely	O
,	O
an	O
administrator	O
can	O
combine	O
systems	O
on	O
separate	O
local	B-General_Concept
area	I-General_Concept
networks	I-General_Concept
(	O
LANs	B-General_Concept
)	O
into	O
a	O
single	O
VLAN	B-General_Concept
spanning	O
segments	O
of	O
a	O
large	O
network	O
.	O
</s>
<s>
Internal	O
network	B-Protocol
virtualization	I-Protocol
configures	O
a	O
single	O
system	O
with	O
software	B-Application
containers	I-Application
,	O
such	O
as	O
Xen	B-Operating_System
hypervisor	I-Operating_System
control	O
programs	O
,	O
or	O
pseudo-interfaces	O
,	O
such	O
as	O
a	O
VNIC	B-Protocol
,	O
to	O
emulate	O
a	O
physical	O
network	O
with	O
software	O
.	O
</s>
<s>
This	O
can	O
improve	O
a	O
single	O
system	O
's	O
efficiency	O
by	O
isolating	O
applications	O
to	O
separate	O
containers	B-Application
or	O
pseudo-interfaces	O
.	O
</s>
<s>
Citrix	B-Application
and	O
Vyatta	B-Protocol
have	O
built	O
a	O
virtual	B-Protocol
network	I-Protocol
protocol	B-Protocol
stack	I-Protocol
combining	O
Vyatta	B-Protocol
's	O
routing	O
,	O
firewall	O
,	O
and	O
VPN	B-Application
functions	O
with	O
Citrix	B-Application
's	O
Netscaler	O
load	B-Application
balancer	I-Application
,	O
branch	O
repeater	O
wide	O
area	O
network	O
(	O
WAN	O
)	O
optimization	O
,	O
and	O
secure	B-Protocol
sockets	I-Protocol
layer	I-Protocol
VPN	B-Application
.	O
</s>
<s>
OpenSolaris	B-Operating_System
network	B-Protocol
virtualization	I-Protocol
provides	O
a	O
so-called	O
"	O
network	O
in	O
a	O
box	O
"	O
(	O
see	O
OpenSolaris	B-Protocol
Network	I-Protocol
Virtualization	I-Protocol
and	I-Protocol
Resource	I-Protocol
Control	I-Protocol
)	O
.	O
</s>
<s>
Microsoft	B-General_Concept
Virtual	I-General_Concept
Server	I-General_Concept
uses	O
virtual	B-Architecture
machines	I-Architecture
to	O
make	O
a	O
"	O
network	O
in	O
a	O
box	O
"	O
for	O
x86	B-Operating_System
systems	O
.	O
</s>
<s>
These	O
containers	B-Application
can	O
run	O
different	O
operating	B-General_Concept
systems	I-General_Concept
,	O
such	O
as	O
Microsoft	B-Application
Windows	I-Application
or	O
Linux	B-Application
,	O
either	O
associated	O
with	O
or	O
independent	O
of	O
a	O
specific	O
network	B-Protocol
interface	I-Protocol
controller	I-Protocol
(	O
NIC	O
)	O
.	O
</s>
<s>
Network	B-Protocol
virtualization	I-Protocol
may	O
be	O
used	O
in	O
application	O
development	O
and	O
testing	O
to	O
mimic	O
real-world	O
hardware	O
and	O
system	O
software	O
.	O
</s>
<s>
In	O
application	B-Application
performance	I-Application
engineering	I-Application
,	O
network	B-Protocol
virtualization	I-Protocol
enables	O
emulation	O
of	O
connections	O
between	O
applications	O
,	O
services	O
,	O
dependencies	O
,	O
and	O
end	O
users	O
for	O
software	O
testing	O
.	O
</s>
<s>
Wireless	O
network	B-Protocol
virtualization	I-Protocol
can	O
have	O
a	O
very	O
broad	O
scope	O
ranging	O
from	O
spectrum	O
sharing	O
,	O
infrastructure	O
virtualization	O
,	O
to	O
air	O
interface	O
virtualization	O
.	O
</s>
<s>
Similar	O
to	O
wired	O
network	B-Protocol
virtualization	I-Protocol
,	O
in	O
which	O
physical	O
infrastructure	O
owned	O
by	O
one	O
or	O
more	O
providers	O
can	O
be	O
shared	O
among	O
multiple	O
service	O
providers	O
,	O
wireless	O
network	B-Protocol
virtualization	I-Protocol
needs	O
the	O
physical	O
wireless	O
infrastructure	O
and	O
radio	O
resources	O
to	O
be	O
abstracted	O
and	O
isolated	O
to	O
a	O
number	O
of	O
virtual	O
resources	O
,	O
which	O
then	O
can	O
be	O
offered	O
to	O
different	O
service	O
providers	O
.	O
</s>
<s>
Furthermore	O
,	O
wireless	O
network	B-Protocol
virtualization	I-Protocol
depends	O
on	O
specific	O
access	O
technologies	O
,	O
and	O
wireless	O
network	O
contains	O
much	O
more	O
access	O
technologies	O
compared	O
to	O
wired	O
network	B-Protocol
virtualization	I-Protocol
and	O
each	O
access	O
technology	O
has	O
its	O
particular	O
characteristics	O
,	O
which	O
makes	O
convergence	O
,	O
sharing	O
and	O
abstraction	O
difficult	O
to	O
achieve	O
.	O
</s>
<s>
Therefore	O
,	O
it	O
may	O
be	O
inaccurate	O
to	O
consider	O
wireless	O
network	B-Protocol
virtualization	I-Protocol
as	O
a	O
subset	O
of	O
network	B-Protocol
virtualization	I-Protocol
.	O
</s>
<s>
Until	O
1Gbit/s	O
networks	O
,	O
network	B-Protocol
virtualization	I-Protocol
was	O
not	O
suffering	O
from	O
the	O
overhead	O
of	O
the	O
software	O
layers	O
or	O
hypervisor	B-Operating_System
layers	O
providing	O
the	O
interconnects	O
.	O
</s>
<s>
With	O
the	O
rise	O
of	O
high	O
bandwidth	O
,	O
10Gbit/s	O
and	O
beyond	O
,	O
the	O
rates	O
of	O
packets	O
exceed	O
the	O
capabilities	O
of	O
processing	O
of	O
the	O
networking	B-Protocol
stacks	I-Protocol
.	O
</s>
<s>
In	O
order	O
to	O
keep	O
offering	O
high	O
throughput	O
processing	O
,	O
some	O
combinations	O
of	O
software	O
and	O
hardware	O
helpers	O
are	O
deployed	O
in	O
the	O
so-called	O
"	O
network	O
in	O
a	O
box	O
"	O
associated	O
with	O
either	O
a	O
hardware-dependent	O
network	B-Protocol
interface	I-Protocol
controller	I-Protocol
(	O
NIC	O
)	O
using	O
SRIOV	B-Protocol
extensions	O
of	O
the	O
hypervisor	B-Operating_System
or	O
either	O
using	O
a	O
fast	B-General_Concept
path	I-General_Concept
technology	O
between	O
the	O
NIC	O
and	O
the	O
payloads	O
(	O
virtual	B-Architecture
machines	I-Architecture
or	O
containers	B-Application
)	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
case	O
of	O
Openstack	B-Application
,	O
network	O
is	O
provided	O
by	O
Neutron	O
which	O
leverages	O
many	O
features	O
from	O
the	O
Linux	B-Application
kernel	O
for	O
networking	O
:	O
iptables	O
,	O
iproute2	O
,	O
L2	O
bridge	O
,	O
L3	O
routing	O
or	O
OVS	O
.	O
</s>
<s>
Since	O
the	O
Linux	B-Application
kernel	O
cannot	O
sustain	O
the	O
10G	O
packet	O
rate	O
,	O
then	O
some	O
bypass	O
technologies	O
for	O
a	O
fast	B-General_Concept
path	I-General_Concept
are	O
used	O
.	O
</s>
<s>
The	O
main	O
bypass	O
technologies	O
are	O
either	O
based	O
on	O
a	O
limited	O
set	O
of	O
features	O
such	O
as	O
Open	B-Language
vSwitch	I-Language
(	O
OVS	O
)	O
with	O
its	O
DPDK	B-Application
user	B-Operating_System
space	I-Operating_System
implementation	O
or	O
based	O
on	O
a	O
full	O
feature	O
and	O
offload	O
of	O
Linux	B-Application
processing	O
such	O
as	O
6WIND	O
virtual	O
accelerator	O
.	O
</s>
