<s>
A	O
network	B-Protocol
segment	I-Protocol
is	O
a	O
portion	O
of	O
a	O
computer	B-Architecture
network	I-Architecture
.	O
</s>
<s>
According	O
to	O
the	O
defining	O
IEEE	O
802.3	O
standards	O
for	O
Ethernet	O
,	O
a	O
network	B-Protocol
segment	I-Protocol
is	O
an	O
electrical	O
connection	O
between	O
networked	O
devices	O
using	O
a	O
shared	B-Protocol
medium	I-Protocol
.	O
</s>
<s>
At	O
this	O
point	O
in	O
the	O
evolution	O
of	O
Ethernet	O
,	O
multiple	O
network	B-Protocol
segments	I-Protocol
could	O
be	O
connected	O
with	O
repeaters	O
(	O
in	O
accordance	O
with	O
the	O
5-4-3	B-Protocol
rule	I-Protocol
for	O
10	O
Mbit	O
Ethernet	O
)	O
to	O
form	O
a	O
larger	O
collision	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
With	O
twisted-pair	B-Protocol
Ethernet	I-Protocol
,	O
electrical	O
segments	O
can	O
be	O
joined	O
together	O
using	O
repeaters	O
or	O
repeater	B-Protocol
hubs	I-Protocol
as	O
can	O
other	O
varieties	O
of	O
Ethernet	O
.	O
</s>
<s>
This	O
corresponds	O
to	O
the	O
extent	O
of	O
an	O
OSI	B-Application
layer	I-Application
1	I-Application
network	O
and	O
is	O
equivalent	O
to	O
the	O
collision	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
The	O
5-4-3	B-Protocol
rule	I-Protocol
applies	O
to	O
this	O
collision	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
Using	O
switches	B-Protocol
or	O
bridges	B-Protocol
,	O
multiple	O
layer-1	B-Application
segments	O
can	O
be	O
combined	O
to	O
a	O
common	O
layer-2	B-Protocol
segment	O
,	O
i.e.	O
</s>
<s>
all	O
nodes	B-Protocol
can	O
communicate	O
with	O
each	O
other	O
through	O
MAC	O
addressing	O
or	O
broadcasts	B-Operating_System
.	O
</s>
<s>
A	O
layer-2	B-Protocol
segment	O
is	O
equivalent	O
to	O
a	O
broadcast	B-Architecture
domain	I-Architecture
.	O
</s>
<s>
Traffic	O
within	O
a	O
layer-2	B-Protocol
segment	O
can	O
be	O
separated	O
into	O
virtually	O
distinct	O
partitions	O
by	O
using	O
VLANs	B-General_Concept
.	O
</s>
<s>
Each	O
VLAN	B-General_Concept
forms	O
its	O
own	O
logical	O
layer-2	B-Protocol
segment	O
.	O
</s>
<s>
A	O
layer-3	B-Application
segment	O
in	O
an	O
IP	B-Protocol
network	I-Protocol
is	O
called	O
a	O
subnetwork	B-Protocol
,	O
formed	O
by	O
all	O
nodes	B-Protocol
sharing	O
the	O
same	O
network	O
prefix	O
as	O
defined	O
by	O
their	O
IP	O
addresses	O
and	O
the	O
network	O
mask	O
.	O
</s>
<s>
Communication	O
between	O
layer-3	B-Application
subnets	B-Protocol
requires	O
a	O
router	B-Protocol
.	O
</s>
<s>
Hosts	O
on	O
a	O
subnet	B-Protocol
communicate	O
directly	O
using	O
the	O
layer-2	B-Protocol
segment	O
that	O
connects	O
them	O
.	O
</s>
<s>
Most	O
often	O
a	O
subnetwork	B-Protocol
corresponds	O
exactly	O
with	O
the	O
underlying	O
layer-2	B-Protocol
segment	O
but	O
it	O
is	O
also	O
possible	O
to	O
run	O
multiple	O
subnets	B-Protocol
on	O
a	O
single	O
layer-2	B-Protocol
segment	O
.	O
</s>
