<s>
The	O
Hierarchical	B-Protocol
internetworking	I-Protocol
model	I-Protocol
is	O
a	O
three-layer	B-Operating_System
model	O
for	O
network	B-Architecture
design	I-Architecture
first	O
proposed	O
by	O
Cisco	O
.	O
</s>
<s>
It	O
divides	O
enterprise	B-General_Concept
networks	I-General_Concept
into	O
three	B-Operating_System
layers	I-Operating_System
:	O
core	O
,	O
distribution	O
,	O
and	O
access	O
layer	O
.	O
</s>
<s>
Access	O
layer	O
devices	O
are	O
usually	O
commodity	O
switching	O
platforms	O
,	O
and	O
may	O
or	O
may	O
not	O
provide	O
layer	B-Application
3	I-Application
switching	O
services	O
.	O
</s>
<s>
The	O
distribution	O
layer	O
is	O
the	O
smart	O
layer	O
in	O
the	O
three-layer	B-Operating_System
model	O
.	O
</s>
<s>
Core	O
switches	O
and	O
routers	O
are	O
usually	O
the	O
most	O
powerful	O
,	O
in	O
terms	O
of	O
raw	O
forwarding	O
power	O
,	O
in	O
the	O
enterprise	O
;	O
core	O
network	O
devices	O
manage	O
the	O
highest-speed	O
connections	O
,	O
such	O
as	O
10	O
Gigabit	O
Ethernet	O
or	O
100	B-Protocol
Gigabit	I-Protocol
Ethernet	I-Protocol
.	O
</s>
