<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
the	O
link	B-Protocol
layer	I-Protocol
is	O
the	O
lowest	O
layer	B-Architecture
in	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
,	O
the	O
networking	O
architecture	O
of	O
the	O
Internet	O
.	O
</s>
<s>
The	O
link	B-Protocol
layer	I-Protocol
is	O
the	O
group	O
of	O
methods	O
and	O
communications	O
protocols	O
confined	O
to	O
the	O
link	O
that	O
a	O
host	O
is	O
physically	O
connected	O
to	O
.	O
</s>
<s>
The	O
link	O
is	O
the	O
physical	O
and	O
logical	O
network	O
component	O
used	O
to	O
interconnect	O
hosts	B-Device
or	O
nodes	B-Protocol
in	O
the	O
network	O
and	O
a	O
link	O
protocol	O
is	O
a	O
suite	O
of	O
methods	O
and	O
standards	O
that	O
operate	O
only	O
between	O
adjacent	O
network	B-Protocol
nodes	I-Protocol
of	O
a	O
network	B-Protocol
segment	I-Protocol
.	O
</s>
<s>
Despite	O
the	O
different	O
semantics	O
of	O
layering	O
between	O
the	O
Internet	B-Protocol
protocol	I-Protocol
suite	I-Protocol
and	O
OSI	O
model	O
,	O
the	O
link	B-Protocol
layer	I-Protocol
is	O
sometimes	O
described	O
as	O
a	O
combination	O
of	O
the	O
OSI	O
's	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
(	O
layer	B-Protocol
2	I-Protocol
)	O
and	O
physical	B-Application
layer	I-Application
(	O
layer	B-Application
1	I-Application
)	O
.	O
</s>
<s>
The	O
link	B-Protocol
layer	I-Protocol
is	O
described	O
in	O
and	O
.	O
</s>
<s>
Wi-Fi	O
)	O
,	O
and	O
framing	O
protocols	O
such	O
as	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
to	O
belong	O
to	O
the	O
link	B-Protocol
layer	I-Protocol
.	O
</s>
<s>
Local	O
area	O
networking	O
standards	O
such	O
as	O
Ethernet	O
and	O
IEEE	O
802.3	O
specifications	O
use	O
terminology	O
from	O
the	O
seven-layer	O
OSI	O
model	O
rather	O
than	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
.	O
</s>
<s>
The	O
TCP/IP	B-Protocol
model	I-Protocol
,	O
in	O
general	O
,	O
does	O
not	O
consider	O
physical	O
specifications	O
,	O
rather	O
it	O
assumes	O
a	O
working	O
network	B-Architecture
infrastructure	I-Architecture
that	O
can	O
deliver	O
media-level	O
frames	O
on	O
the	O
link	O
.	O
</s>
<s>
Therefore	O
,	O
RFC	O
1122	O
and	O
RFC	O
1123	O
,	O
the	O
definition	O
of	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
,	O
do	O
not	O
discuss	O
hardware	O
issues	O
and	O
physical	O
data	O
transmission	O
and	O
set	O
no	O
standards	O
for	O
those	O
aspects	O
.	O
</s>
<s>
Some	O
textbook	O
authors	O
have	O
supported	O
the	O
interpretation	O
that	O
physical	O
data	O
transmission	O
aspects	O
are	O
part	O
of	O
the	O
link	B-Protocol
layer	I-Protocol
.	O
</s>
<s>
Others	O
assumed	O
that	O
physical	O
data	O
transmission	O
standards	O
are	O
not	O
considered	O
communication	O
protocols	O
,	O
and	O
are	O
not	O
part	O
of	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
.	O
</s>
<s>
These	O
authors	O
assume	O
a	O
hardware	O
layer	B-Architecture
or	O
physical	B-Application
layer	I-Application
below	O
the	O
link	B-Protocol
layer	I-Protocol
,	O
and	O
several	O
of	O
them	O
adopt	O
the	O
OSI	O
term	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
instead	O
of	O
link	B-Protocol
layer	I-Protocol
in	O
a	O
modified	O
description	O
of	O
layering	O
.	O
</s>
<s>
In	O
the	O
predecessor	O
to	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
,	O
the	O
ARPAnet	O
Reference	O
Model	O
(	O
RFC	O
908	O
,	O
1982	O
)	O
,	O
aspects	O
of	O
the	O
link	B-Protocol
layer	I-Protocol
are	O
referred	O
to	O
by	O
several	O
poorly	O
defined	O
terms	O
,	O
such	O
as	O
network-access	O
layer	B-Architecture
,	O
network-access	O
protocol	O
,	O
as	O
well	O
as	O
network	O
layer	B-Architecture
,	O
while	O
the	O
next	O
higher	O
layer	B-Architecture
is	O
called	O
internetwork	O
layer	B-Architecture
.	O
</s>
<s>
In	O
some	O
modern	O
textbooks	O
,	O
network-interface	O
layer	B-Architecture
,	O
host-to-network	B-Protocol
layer	I-Protocol
and	O
network-access	O
layer	B-Architecture
occur	O
as	O
synonyms	O
either	O
to	O
the	O
link	B-Protocol
layer	I-Protocol
or	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
,	O
often	O
including	O
the	O
physical	B-Application
layer	I-Application
.	O
</s>
<s>
The	O
link	B-Protocol
layer	I-Protocol
in	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
is	O
a	O
descriptive	O
realm	O
of	O
networking	O
protocols	O
that	O
operate	O
only	O
on	O
the	O
local	O
network	B-Protocol
segment	I-Protocol
(	O
link	O
)	O
that	O
a	O
host	O
is	O
connected	O
to	O
.	O
</s>
<s>
The	O
link	B-Protocol
layer	I-Protocol
includes	O
the	O
protocols	O
that	O
define	O
communication	O
between	O
local	O
(	O
on-link	O
)	O
network	B-Protocol
nodes	I-Protocol
which	O
fulfill	O
the	O
purpose	O
of	O
maintaining	O
link	O
states	O
between	O
the	O
local	O
nodes	B-Protocol
,	O
such	O
as	O
the	O
local	O
network	O
topology	O
,	O
and	O
that	O
usually	O
use	O
protocols	O
that	O
are	O
based	O
on	O
the	O
framing	O
of	O
packets	O
specific	O
to	O
the	O
link	O
types	O
.	O
</s>
<s>
The	O
core	O
protocols	O
specified	O
by	O
the	O
Internet	O
Engineering	O
Task	O
Force	O
(	O
IETF	O
)	O
in	O
this	O
layer	B-Architecture
are	O
the	O
Address	O
Resolution	O
Protocol	O
(	O
ARP	O
)	O
,	O
the	O
Reverse	B-Protocol
Address	I-Protocol
Resolution	I-Protocol
Protocol	I-Protocol
(	O
RARP	B-Protocol
)	O
,	O
and	O
the	O
Neighbor	B-Protocol
Discovery	I-Protocol
Protocol	I-Protocol
(	O
NDP	O
)	O
,	O
which	O
is	O
a	O
facility	O
delivering	O
similar	O
functionality	O
as	O
ARP	O
for	O
IPv6	B-Protocol
.	O
</s>
<s>
The	O
link	B-Protocol
layer	I-Protocol
of	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
is	O
often	O
compared	O
directly	O
with	O
the	O
combination	O
of	O
the	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
and	O
the	O
physical	B-Application
layer	I-Application
in	O
the	O
Open	O
Systems	O
Interconnection	O
(	O
OSI	O
)	O
protocol	O
stack	O
.	O
</s>
<s>
The	O
link	B-Protocol
layer	I-Protocol
in	O
TCP/IP	B-Protocol
is	O
still	O
wider	O
in	O
scope	O
and	O
in	O
principle	O
a	O
different	O
concept	O
and	O
terminology	O
of	O
classification	O
.	O
</s>
<s>
This	O
may	O
be	O
observed	O
when	O
certain	O
protocols	O
,	O
such	O
as	O
ARP	O
,	O
which	O
is	O
confined	O
to	O
the	O
link	B-Protocol
layer	I-Protocol
in	O
the	O
TCP/IP	B-Protocol
model	I-Protocol
,	O
is	O
often	O
said	O
to	O
fit	O
between	O
OSI	O
's	O
data	B-Protocol
link	I-Protocol
layer	I-Protocol
and	O
the	O
network	O
layer	B-Architecture
.	O
</s>
<s>
In	O
general	O
,	O
direct	O
or	O
strict	O
comparisons	O
should	O
be	O
avoided	O
,	O
because	O
the	O
layering	O
in	O
TCP/IP	B-Protocol
is	O
not	O
a	O
principal	O
design	O
criterion	O
and	O
in	O
general	O
,	O
is	O
considered	O
to	O
be	O
"	O
harmful	O
"	O
(	O
RFC	O
3439	O
)	O
.	O
</s>
<s>
Another	O
term	O
sometimes	O
encountered	O
,	O
network	B-Protocol
access	I-Protocol
layer	I-Protocol
,	O
tries	O
to	O
suggest	O
the	O
closeness	O
of	O
this	O
layer	B-Architecture
to	O
the	O
physical	O
network	O
.	O
</s>
<s>
However	O
,	O
this	O
use	O
is	O
misleading	O
and	O
non-standard	O
,	O
since	O
the	O
link	B-Protocol
layer	I-Protocol
implies	O
functions	O
that	O
are	O
wider	O
in	O
scope	O
than	O
just	O
network	O
access	O
.	O
</s>
<s>
Important	O
link	B-Protocol
layer	I-Protocol
protocols	O
are	O
used	O
to	O
probe	O
the	O
topology	O
of	O
the	O
local	O
network	O
,	O
discover	O
routers	O
and	O
neighboring	O
hosts	B-Device
,	O
i.e.	O
</s>
