<s>
A	O
network	B-Protocol
interface	I-Protocol
controller	I-Protocol
(	O
NIC	O
,	O
also	O
known	O
as	O
a	O
network	B-Protocol
interface	I-Protocol
card	I-Protocol
,	O
network	B-Protocol
adapter	I-Protocol
,	O
LAN	B-Protocol
adapter	I-Protocol
or	O
physical	B-Protocol
network	I-Protocol
interface	I-Protocol
,	O
and	O
by	O
similar	O
terms	O
)	O
is	O
a	O
computer	B-Architecture
hardware	I-Architecture
component	O
that	O
connects	O
a	O
computer	O
to	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
Early	O
network	B-Protocol
interface	I-Protocol
controllers	I-Protocol
were	O
commonly	O
implemented	O
on	O
expansion	B-Device
cards	I-Device
that	O
plugged	O
into	O
a	O
computer	B-General_Concept
bus	I-General_Concept
.	O
</s>
<s>
The	O
low	O
cost	O
and	O
ubiquity	O
of	O
the	O
Ethernet	O
standard	O
means	O
that	O
most	O
newer	O
computers	O
have	O
a	O
network	O
interface	O
built	O
into	O
the	O
motherboard	B-Device
,	O
or	O
is	O
contained	O
into	O
a	O
USB-connected	O
dongle	B-Device
.	O
</s>
<s>
Modern	O
network	B-Protocol
interface	I-Protocol
controllers	I-Protocol
offer	O
advanced	O
features	O
such	O
as	O
interrupt	B-Application
and	O
DMA	B-General_Concept
interfaces	O
to	O
the	O
host	O
processors	O
,	O
support	O
for	O
multiple	O
receive	O
and	O
transmit	O
queues	B-Application
,	O
partitioning	O
into	O
multiple	O
logical	O
interfaces	O
,	O
and	O
on-controller	O
network	O
traffic	O
processing	O
such	O
as	O
the	O
TCP	B-Protocol
offload	I-Protocol
engine	I-Protocol
.	O
</s>
<s>
The	O
network	B-Protocol
controller	I-Protocol
implements	O
the	O
electronic	O
circuitry	O
required	O
to	O
communicate	O
using	O
a	O
specific	O
physical	B-Application
layer	I-Application
and	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
standard	O
such	O
as	O
Ethernet	O
or	O
Wi-Fi	O
.	O
</s>
<s>
This	O
provides	O
a	O
base	O
for	O
a	O
full	O
network	B-Protocol
protocol	I-Protocol
stack	I-Protocol
,	O
allowing	O
communication	O
among	O
computers	O
on	O
the	O
same	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
and	O
large-scale	O
network	O
communications	O
through	O
routable	O
protocols	O
,	O
such	O
as	O
Internet	B-Protocol
Protocol	I-Protocol
(	O
IP	O
)	O
.	O
</s>
<s>
The	O
NIC	O
allows	O
computers	O
to	O
communicate	O
over	O
a	O
computer	B-Architecture
network	I-Architecture
,	O
either	O
by	O
using	O
cables	O
or	O
wirelessly	O
.	O
</s>
<s>
The	O
NIC	O
is	O
both	O
a	O
physical	B-Application
layer	I-Application
and	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
device	O
,	O
as	O
it	O
provides	O
physical	O
access	O
to	O
a	O
networking	O
medium	O
and	O
,	O
for	O
IEEE	O
802	O
and	O
similar	O
networks	O
,	O
provides	O
a	O
low-level	O
addressing	O
system	O
through	O
the	O
use	O
of	O
MAC	O
addresses	O
that	O
are	O
uniquely	O
assigned	O
to	O
network	O
interfaces	O
.	O
</s>
<s>
Network	B-Protocol
controllers	I-Protocol
were	O
originally	O
implemented	O
as	O
expansion	B-Device
cards	I-Device
that	O
plugged	O
into	O
a	O
computer	B-General_Concept
bus	I-General_Concept
.	O
</s>
<s>
The	O
low	O
cost	O
and	O
ubiquity	O
of	O
the	O
Ethernet	O
standard	O
means	O
that	O
most	O
new	O
computers	O
have	O
a	O
network	B-Protocol
interface	I-Protocol
controller	I-Protocol
built	O
into	O
the	O
motherboard	B-Device
.	O
</s>
<s>
Newer	O
server	B-Application
motherboards	B-Device
may	O
have	O
multiple	O
network	O
interfaces	O
built-in	O
.	O
</s>
<s>
The	O
Ethernet	O
capabilities	O
are	O
either	O
integrated	O
into	O
the	O
motherboard	B-Device
chipset	B-Device
or	O
implemented	O
via	O
a	O
low-cost	O
dedicated	O
Ethernet	O
chip	O
.	O
</s>
<s>
A	O
separate	O
network	B-Protocol
card	I-Protocol
is	O
typically	O
no	O
longer	O
required	O
unless	O
additional	O
independent	O
network	O
connections	O
are	O
needed	O
or	O
some	O
non-Ethernet	O
type	O
of	O
network	O
is	O
used	O
.	O
</s>
<s>
A	O
general	O
trend	O
in	O
computer	B-Architecture
hardware	I-Architecture
is	O
towards	O
integrating	B-Architecture
the	I-Architecture
various	I-Architecture
components	I-Architecture
of	I-Architecture
systems	I-Architecture
on	I-Architecture
a	I-Architecture
chip	I-Architecture
,	O
and	O
this	O
is	O
also	O
applied	O
to	O
network	B-Protocol
interface	I-Protocol
cards	I-Protocol
.	O
</s>
<s>
An	O
Ethernet	O
network	B-Protocol
controller	I-Protocol
typically	O
has	O
an	O
8P8C	O
socket	O
where	O
the	O
network	O
cable	O
is	O
connected	O
.	O
</s>
<s>
Older	O
NICs	O
also	O
supplied	O
BNC	B-Protocol
,	O
or	O
AUI	B-Protocol
connections	O
.	O
</s>
<s>
Ethernet	O
network	B-Protocol
controllers	I-Protocol
typically	O
support	O
10Mbit/s	O
Ethernet	O
,	O
100	O
Mbit/s	O
Ethernet	O
,	O
and	O
1000	O
Mbit/s	O
Ethernet	O
varieties	O
.	O
</s>
<s>
Such	O
controllers	O
are	O
designated	O
as	O
10/100/1000	B-Protocol
,	O
meaning	O
that	O
they	O
can	O
support	O
data	O
rates	O
of	O
10	O
,	O
100	O
or	O
1000Mbit/s	O
.	O
</s>
<s>
10	O
Gigabit	O
Ethernet	B-Protocol
NICs	I-Protocol
are	O
also	O
available	O
,	O
and	O
,	O
,	O
are	O
beginning	O
to	O
be	O
available	O
on	O
computer	B-Device
motherboards	I-Device
.	O
</s>
<s>
Modular	O
designs	O
like	O
SFP	B-Protocol
and	I-Protocol
SFP+	I-Protocol
are	O
highly	O
popular	O
,	O
especially	O
for	O
fiber-optic	B-Application
communication	I-Application
.	O
</s>
<s>
The	O
NIC	O
may	O
use	O
one	O
or	O
more	O
of	O
the	O
following	O
techniques	O
to	O
indicate	O
the	O
availability	O
of	O
packets	B-Protocol
to	O
transfer	O
:	O
</s>
<s>
Polling	B-General_Concept
is	O
where	O
the	O
CPU	B-Device
examines	O
the	O
status	O
of	O
the	O
peripheral	O
under	O
program	O
control	O
.	O
</s>
<s>
Interrupt-driven	O
I/O	O
is	O
where	O
the	O
peripheral	O
alerts	O
the	O
CPU	B-Device
that	O
it	O
is	O
ready	O
to	O
transfer	O
data	O
.	O
</s>
<s>
NICs	O
may	O
use	O
one	O
or	O
more	O
of	O
the	O
following	O
techniques	O
to	O
transfer	O
packet	B-Protocol
data	I-Protocol
:	O
</s>
<s>
Programmed	B-General_Concept
input/output	I-General_Concept
,	O
where	O
the	O
CPU	B-Device
moves	O
the	O
data	O
to	O
or	O
from	O
the	O
NIC	O
to	O
memory	O
.	O
</s>
<s>
Direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
DMA	B-General_Concept
)	O
,	O
where	O
a	O
device	O
other	O
than	O
the	O
CPU	B-Device
assumes	O
control	O
of	O
the	O
system	B-Architecture
bus	I-Architecture
to	O
move	O
data	O
to	O
or	O
from	O
the	O
NIC	O
to	O
memory	O
.	O
</s>
<s>
This	O
removes	O
load	O
from	O
the	O
CPU	B-Device
but	O
requires	O
more	O
logic	O
on	O
the	O
card	O
.	O
</s>
<s>
In	O
addition	O
,	O
a	O
packet	B-Protocol
buffer	O
on	O
the	O
NIC	O
may	O
not	O
be	O
required	O
and	O
latency	O
can	O
be	O
reduced	O
.	O
</s>
<s>
Multiqueue	O
NICs	O
provide	O
multiple	O
transmit	O
and	O
receive	O
queues	B-Application
,	O
allowing	O
packets	B-Protocol
received	O
by	O
the	O
NIC	O
to	O
be	O
assigned	O
to	O
one	O
of	O
its	O
receive	O
queues	B-Application
.	O
</s>
<s>
The	O
NIC	O
may	O
distribute	O
incoming	O
traffic	O
between	O
the	O
receive	O
queues	B-Application
using	O
a	O
hash	B-Error_Name
function	I-Error_Name
.	O
</s>
<s>
Each	O
receive	O
queue	B-Application
is	O
assigned	O
to	O
a	O
separate	O
interrupt	B-Application
;	O
by	O
routing	O
each	O
of	O
those	O
interrupts	B-Application
to	O
different	O
CPUs	B-Device
or	O
CPU	B-Architecture
cores	I-Architecture
,	O
processing	O
of	O
the	O
interrupt	B-General_Concept
requests	I-General_Concept
triggered	O
by	O
the	O
network	O
traffic	O
received	O
by	O
a	O
single	O
NIC	O
can	O
be	O
distributed	O
improving	O
performance	O
.	O
</s>
<s>
The	O
hardware-based	O
distribution	O
of	O
the	O
interrupts	B-Application
,	O
described	O
above	O
,	O
is	O
referred	O
to	O
as	O
receive-side	O
scaling	O
(	O
RSS	O
)	O
.	O
</s>
<s>
Purely	O
software	O
implementations	O
also	O
exist	O
,	O
such	O
as	O
the	O
receive	O
packet	B-Protocol
steering	O
(	O
RPS	O
)	O
and	O
receive	O
flow	O
steering	O
(	O
RFS	O
)	O
.	O
</s>
<s>
Further	O
performance	O
improvements	O
can	O
be	O
achieved	O
by	O
routing	O
the	O
interrupt	B-General_Concept
requests	I-General_Concept
to	O
the	O
CPUs	B-Device
or	O
cores	O
executing	O
the	O
applications	O
that	O
are	O
the	O
ultimate	O
destinations	O
for	O
network	B-Protocol
packets	I-Protocol
that	O
generated	O
the	O
interrupts	B-Application
.	O
</s>
<s>
This	O
technique	O
improves	O
Locality	B-General_Concept
of	I-General_Concept
reference	I-General_Concept
and	O
results	O
in	O
higher	O
overall	O
performance	O
,	O
reduced	O
latency	O
and	O
better	O
hardware	B-Architecture
utilization	O
because	O
of	O
the	O
higher	O
utilization	O
of	O
CPU	B-General_Concept
caches	I-General_Concept
and	O
fewer	O
required	O
context	B-Operating_System
switches	I-Operating_System
.	O
</s>
<s>
With	O
multi-queue	O
NICs	O
,	O
additional	O
performance	O
improvements	O
can	O
be	O
achieved	O
by	O
distributing	O
outgoing	O
traffic	O
among	O
different	O
transmit	O
queues	B-Application
.	O
</s>
<s>
By	O
assigning	O
different	O
transmit	O
queues	B-Application
to	O
different	O
CPUs	B-Device
or	O
CPU	B-Architecture
cores	I-Architecture
,	O
internal	O
operating	O
system	O
contentions	O
can	O
be	O
avoided	O
.	O
</s>
<s>
This	O
approach	O
is	O
usually	O
referred	O
to	O
as	O
transmit	O
packet	B-Protocol
steering	O
(	O
XPS	O
)	O
.	O
</s>
<s>
Some	O
products	O
feature	O
NIC	O
partitioning	O
(	O
NPAR	O
,	O
also	O
known	O
as	O
port	O
partitioning	O
)	O
that	O
uses	O
SR-IOV	B-Protocol
virtualization	O
to	O
divide	O
a	O
single	O
10	O
Gigabit	O
Ethernet	B-Protocol
NIC	I-Protocol
into	O
multiple	O
discrete	O
virtual	O
NICs	O
with	O
dedicated	O
bandwidth	O
,	O
which	O
are	O
presented	O
to	O
the	O
firmware	O
and	O
operating	O
system	O
as	O
separate	O
PCI	B-Protocol
device	O
functions	O
.	O
</s>
<s>
TCP	B-Protocol
offload	I-Protocol
engine	I-Protocol
is	O
a	O
technology	O
used	O
in	O
some	O
NICs	O
to	O
offload	O
processing	O
of	O
the	O
entire	O
TCP/IP	B-Protocol
stack	I-Protocol
to	O
the	O
network	B-Protocol
controller	I-Protocol
.	O
</s>
<s>
It	O
is	O
primarily	O
used	O
with	O
high-speed	O
network	O
interfaces	O
,	O
such	O
as	O
Gigabit	O
Ethernet	O
and	O
10	O
Gigabit	O
Ethernet	O
,	O
for	O
which	O
the	O
processing	O
overhead	O
of	O
the	O
network	B-Protocol
stack	I-Protocol
becomes	O
significant	O
.	O
</s>
<s>
Some	O
NICs	O
offer	O
integrated	O
field-programmable	B-Architecture
gate	I-Architecture
arrays	I-Architecture
(	O
FPGAs	B-Architecture
)	O
for	O
user-programmable	O
processing	O
of	O
network	O
traffic	O
before	O
it	O
reaches	O
the	O
host	O
computer	O
,	O
allowing	O
for	O
significantly	O
reduced	O
latencies	O
in	O
time-sensitive	O
workloads	O
.	O
</s>
<s>
Moreover	O
,	O
some	O
NICs	O
offer	O
complete	O
low-latency	O
TCP/IP	B-Protocol
stacks	I-Protocol
running	O
on	O
integrated	O
FPGAs	B-Architecture
in	O
combination	O
with	O
userspace	B-Operating_System
libraries	O
that	O
intercept	O
networking	O
operations	O
usually	O
performed	O
by	O
the	O
operating	B-Operating_System
system	I-Operating_System
kernel	I-Operating_System
;	O
Solarflare	O
's	O
open-source	O
OpenOnload	O
network	B-Protocol
stack	I-Protocol
that	O
runs	O
on	O
Linux	B-Application
is	O
an	O
example	O
.	O
</s>
<s>
This	O
kind	O
of	O
functionality	O
is	O
usually	O
referred	O
to	O
as	O
user-level	B-Operating_System
networking	O
.	O
</s>
