<s>
In	O
the	O
seven-layer	O
OSI	O
model	O
of	O
computer	B-Architecture
networking	I-Architecture
,	O
the	O
physical	B-Application
layer	I-Application
or	O
layer	B-Application
1	I-Application
is	O
the	O
first	O
and	O
lowest	O
layer	O
:	O
the	O
layer	O
most	O
closely	O
associated	O
with	O
the	O
physical	O
connection	O
between	O
devices	O
.	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
provides	O
an	O
electrical	O
,	O
mechanical	O
,	O
and	O
procedural	O
interface	O
to	O
the	O
transmission	O
medium	O
.	O
</s>
<s>
The	O
shapes	O
and	O
properties	O
of	O
the	O
electrical	B-Protocol
connectors	I-Protocol
,	O
the	O
frequencies	O
to	O
broadcast	O
on	O
,	O
the	O
line	B-Protocol
code	I-Protocol
to	O
use	O
and	O
similar	O
low-level	O
parameters	O
,	O
are	O
specified	O
by	O
the	O
physical	B-Application
layer	I-Application
.	O
</s>
<s>
At	O
the	O
electrical	O
layer	O
,	O
the	O
physical	B-Application
layer	I-Application
is	O
commonly	O
implemented	O
by	O
dedicated	O
PHY	O
chip	O
or	O
,	O
in	O
electronic	O
design	O
automation	O
(	O
EDA	O
)	O
,	O
by	O
a	O
design	B-Architecture
block	I-Architecture
.	O
</s>
<s>
In	O
mobile	O
computing	O
,	O
the	O
MIPI	O
Alliance	O
*	B-Protocol
-PHY	I-Protocol
family	O
of	O
interconnect	O
protocols	O
are	O
widely	O
used	O
.	O
</s>
<s>
Historically	O
,	O
the	O
OSI	O
model	O
is	O
closely	O
associated	O
with	O
internetworking	O
,	O
such	O
as	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
and	O
Ethernet	O
,	O
which	O
were	O
developed	O
in	O
the	O
same	O
era	O
,	O
along	O
similar	O
lines	O
,	O
though	O
with	O
somewhat	O
different	O
abstractions	O
.	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
defines	O
the	O
means	O
of	O
transmitting	O
a	O
stream	O
of	O
raw	O
bits	O
over	O
a	O
physical	O
data	O
link	O
connecting	O
network	B-Protocol
nodes	I-Protocol
.	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
consists	O
of	O
the	O
electronic	O
circuit	O
transmission	O
technologies	O
of	O
a	O
network	O
.	O
</s>
<s>
Within	O
the	O
semantics	O
of	O
the	O
OSI	O
model	O
,	O
the	O
physical	B-Application
layer	I-Application
translates	O
logical	O
communications	O
requests	O
from	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
into	O
hardware-specific	O
operations	O
to	O
cause	O
transmission	O
or	O
reception	O
of	O
electronic	O
(	O
or	O
other	O
)	O
signals	O
.	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
supports	O
higher	O
layers	O
responsible	O
for	O
generation	O
of	O
logical	O
data	B-Protocol
packets	I-Protocol
.	O
</s>
<s>
interfaces	O
with	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
's	O
medium	B-Protocol
access	I-Protocol
control	I-Protocol
(	O
MAC	O
)	O
sublayer	O
,	O
</s>
<s>
The	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
,	O
as	O
defined	O
in	O
and	O
,	O
is	O
a	O
high-level	O
networking	O
description	O
used	O
for	O
the	O
Internet	O
and	O
similar	O
networks	O
.	O
</s>
<s>
The	O
major	O
functions	O
and	O
services	O
performed	O
by	O
the	O
physical	B-Application
layer	I-Application
are	O
:	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
performs	O
bit-by-bit	O
or	O
symbol-by-symbol	O
data	O
delivery	O
over	O
a	O
physical	O
transmission	O
medium	O
.	O
</s>
<s>
It	O
provides	O
a	O
standardized	O
interface	O
to	O
the	O
transmission	O
medium	O
,	O
including	O
a	O
mechanical	O
specification	O
of	O
electrical	B-Protocol
connectors	I-Protocol
and	O
cables	O
,	O
for	O
example	O
maximum	O
cable	O
length	O
,	O
an	O
electrical	O
specification	O
of	O
transmission	O
line	O
signal	O
level	O
and	O
impedance	O
.	O
</s>
<s>
The	O
physical	B-Application
layer	I-Application
is	O
responsible	O
for	O
electromagnetic	O
compatibility	O
including	O
electromagnetic	O
spectrum	O
frequency	B-Algorithm
allocation	I-Algorithm
and	O
specification	O
of	O
signal	O
strength	O
,	O
analog	B-Algorithm
bandwidth	I-Algorithm
,	O
etc	O
.	O
</s>
<s>
The	O
transmission	O
medium	O
may	O
be	O
electrical	O
or	O
optical	O
over	O
optical	B-Architecture
fiber	I-Architecture
or	O
a	O
wireless	O
communication	O
link	O
such	O
as	O
free-space	O
optical	O
communication	O
or	O
radio	O
.	O
</s>
<s>
Line	B-Protocol
coding	I-Protocol
is	O
used	O
to	O
convert	O
data	O
into	O
a	O
pattern	O
of	O
electrical	O
fluctuations	O
which	O
may	O
be	O
modulated	B-Application
onto	O
a	O
carrier	O
wave	O
or	O
infrared	O
light	O
.	O
</s>
<s>
The	O
flow	O
of	O
data	O
is	O
managed	O
with	O
bit	O
synchronization	O
in	O
synchronous	O
serial	B-Protocol
communication	I-Protocol
or	O
start-stop	O
signalling	O
and	O
flow	O
control	O
in	O
asynchronous	O
serial	B-Protocol
communication	I-Protocol
.	O
</s>
<s>
Sharing	O
of	O
the	O
transmission	O
medium	O
among	O
multiple	O
network	O
participants	O
can	O
be	O
handled	O
by	O
simple	O
circuit	B-Protocol
switching	I-Protocol
or	O
multiplexing	B-Architecture
.	O
</s>
<s>
More	O
complex	O
medium	B-Protocol
access	I-Protocol
control	I-Protocol
protocols	O
for	O
sharing	O
the	O
transmission	O
medium	O
may	O
use	O
carrier	O
sense	O
and	O
collision	O
detection	O
such	O
as	O
in	O
Ethernet	O
's	O
Carrier-sense	O
multiple	O
access	O
with	O
collision	O
detection	O
(	O
CSMA/CD	O
)	O
.	O
</s>
<s>
To	O
optimize	O
reliability	O
and	O
efficiency	O
,	O
signal	O
processing	O
techniques	O
such	O
as	O
equalization	B-Algorithm
,	O
training	O
sequences	O
and	O
pulse	B-Algorithm
shaping	I-Algorithm
may	O
be	O
used	O
.	O
</s>
<s>
Error	B-Error_Name
correction	I-Error_Name
codes	I-Error_Name
and	O
techniques	O
including	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
may	O
be	O
applied	O
to	O
further	O
improve	O
reliability	O
.	O
</s>
<s>
A	O
PHY	O
,	O
an	O
abbreviation	O
for	O
"	O
physical	B-Application
layer	I-Application
"	O
,	O
is	O
an	O
electronic	O
circuit	O
,	O
usually	O
implemented	O
as	O
an	O
integrated	O
circuit	O
,	O
required	O
to	O
implement	O
physical	B-Application
layer	I-Application
functions	O
of	O
the	O
OSI	O
model	O
in	O
a	O
network	B-Protocol
interface	I-Protocol
controller	I-Protocol
.	O
</s>
<s>
A	O
PHY	O
connects	O
a	O
link	B-Protocol
layer	I-Protocol
device	O
(	O
often	O
called	O
MAC	O
as	O
an	O
acronym	O
for	O
medium	B-Protocol
access	I-Protocol
control	I-Protocol
)	O
to	O
a	O
physical	O
medium	O
such	O
as	O
an	O
optical	B-Architecture
fiber	I-Architecture
or	O
copper	O
cable	O
.	O
</s>
<s>
A	O
PHY	O
device	O
typically	O
includes	O
both	O
physical	B-Protocol
coding	I-Protocol
sublayer	I-Protocol
(	O
PCS	O
)	O
and	O
physical	B-Protocol
medium	I-Protocol
dependent	I-Protocol
(	O
PMD	B-Protocol
)	O
layer	O
functionality	O
.	O
</s>
<s>
-PHY	O
may	O
also	O
be	O
used	O
as	O
a	O
suffix	O
to	O
form	O
a	O
short	O
name	O
referencing	O
a	O
specific	O
physical	B-Application
layer	I-Application
protocol	O
,	O
for	O
example	O
M-PHY	B-Protocol
.	O
</s>
<s>
Modular	O
transceivers	O
for	O
fiber-optic	B-Application
communication	I-Application
(	O
like	O
the	O
SFP	B-Protocol
family	O
)	O
complement	O
a	O
PHY	O
chip	O
and	O
form	O
the	O
PMD	B-Protocol
sublayer	O
.	O
</s>
<s>
The	O
Ethernet	O
PHY	O
is	O
a	O
component	O
that	O
operates	O
at	O
the	O
physical	B-Application
layer	I-Application
of	O
the	O
OSI	O
network	O
model	O
.	O
</s>
<s>
It	O
implements	O
the	O
physical	B-Application
layer	I-Application
portion	O
of	O
the	O
Ethernet	O
.	O
</s>
<s>
It	O
is	O
usually	O
interfaced	O
with	O
a	O
media-independent	B-Protocol
interface	I-Protocol
(	O
MII	O
)	O
to	O
a	O
MAC	O
chip	O
in	O
a	O
microcontroller	B-Architecture
or	O
another	O
system	O
that	O
takes	O
care	O
of	O
the	O
higher	O
layer	O
functions	O
.	O
</s>
<s>
More	O
specifically	O
,	O
the	O
Ethernet	O
PHY	O
is	O
a	O
chip	O
that	O
implements	O
the	O
hardware	O
send	O
and	O
receive	O
function	O
of	O
Ethernet	O
frames	O
;	O
it	O
interfaces	O
between	O
the	O
analog	O
domain	O
of	O
Ethernet	O
's	O
line	O
modulation	B-Application
and	O
the	O
digital	O
domain	O
of	O
link-layer	B-Protocol
packet	B-Protocol
signaling	I-Protocol
.	O
</s>
<s>
The	O
PHY	O
usually	O
does	O
not	O
handle	O
MAC	O
addressing	O
,	O
as	O
that	O
is	O
the	O
link	B-Protocol
layer	I-Protocol
's	O
job	O
.	O
</s>
<s>
Similarly	O
,	O
Wake-on-LAN	B-Protocol
and	O
Boot	B-Device
ROM	I-Device
functionality	O
is	O
implemented	O
in	O
the	O
network	B-Protocol
interface	I-Protocol
card	I-Protocol
(	O
NIC	O
)	O
,	O
which	O
may	O
have	O
PHY	O
,	O
MAC	O
,	O
and	O
other	O
functionality	O
integrated	O
into	O
one	O
chip	O
or	O
as	O
separate	O
chips	O
.	O
</s>
<s>
Wireless	B-Architecture
LAN	I-Architecture
or	O
Wi-Fi	O
:	O
The	O
PHY	O
portion	O
consists	O
of	O
the	O
RF	O
,	O
mixed-signal	O
and	O
analog	O
portions	O
,	O
that	O
are	O
often	O
called	O
transceivers	O
,	O
and	O
the	O
digital	O
baseband	O
portion	O
that	O
use	O
digital	B-Architecture
signal	I-Architecture
processor	I-Architecture
(	O
DSP	O
)	O
and	O
communication	O
algorithm	O
processing	O
,	O
including	O
channel	O
codes	O
.	O
</s>
<s>
It	O
is	O
common	O
that	O
these	O
PHY	O
portions	O
are	O
integrated	O
with	O
the	O
medium	B-Protocol
access	I-Protocol
control	I-Protocol
(	O
MAC	O
)	O
layer	O
in	O
system-on-a-chip	B-Architecture
(	O
SOC	O
)	O
implementations	O
.	O
</s>
<s>
Similar	O
wireless	O
applications	O
include	O
3G/4G/LTE/5G	O
,	O
WiMAX	O
and	O
UWB	O
.	O
</s>
<s>
Universal	B-Protocol
Serial	I-Protocol
Bus	I-Protocol
(	O
USB	B-Protocol
)	O
:	O
A	O
PHY	O
chip	O
is	O
integrated	O
into	O
most	O
USB	B-Protocol
controllers	O
in	O
hosts	O
or	O
embedded	B-Architecture
systems	I-Architecture
and	O
provides	O
the	O
bridge	O
between	O
the	O
digital	O
and	O
modulated	B-Application
parts	O
of	O
the	O
interface	O
.	O
</s>
<s>
IrDA	O
:	O
The	O
Infrared	O
Data	O
Association	O
's	O
(	O
IrDA	O
)	O
specification	O
includes	O
an	O
IrPHY	O
specification	O
for	O
the	O
physical	B-Application
layer	I-Application
of	O
the	O
data	O
transport	O
.	O
</s>
<s>
Serial	B-Protocol
ATA	O
(	O
SATA	O
)	O
:	O
Serial	B-Protocol
ATA	O
controllers	O
use	O
a	O
PHY	O
.	O
</s>
<s>
The	O
following	O
technologies	O
provide	O
physical	B-Application
layer	I-Application
services	O
:	O
</s>
