<s>
An	O
Ethernet	B-Protocol
hub	I-Protocol
,	O
active	B-Protocol
hub	I-Protocol
,	O
network	O
hub	B-Protocol
,	O
repeater	B-Protocol
hub	I-Protocol
,	O
multiport	B-Protocol
repeater	I-Protocol
,	O
or	O
simply	O
hub	B-Protocol
is	O
a	O
network	B-Device
hardware	I-Device
device	O
for	O
connecting	O
multiple	O
Ethernet	O
devices	O
together	O
and	O
making	O
them	O
act	O
as	O
a	O
single	O
network	B-Protocol
segment	I-Protocol
.	O
</s>
<s>
It	O
has	O
multiple	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
ports	O
,	O
in	O
which	O
a	O
signal	O
introduced	O
at	O
the	O
input	O
of	O
any	O
port	B-Protocol
appears	O
at	O
the	O
output	O
of	O
every	O
port	B-Protocol
except	O
the	O
original	O
incoming	O
.	O
</s>
<s>
A	O
hub	B-Protocol
works	O
at	O
the	O
physical	B-Application
layer	I-Application
(	O
layer	B-Application
1	I-Application
)	O
of	O
the	O
OSI	O
model	O
.	O
</s>
<s>
A	O
repeater	B-Protocol
hub	I-Protocol
also	O
participates	O
in	O
collision	O
detection	O
,	O
forwarding	O
a	O
jam	O
signal	O
to	O
all	O
ports	O
if	O
it	O
detects	O
a	O
collision	O
.	O
</s>
<s>
In	O
addition	O
to	O
standard	O
8P8C	O
(	O
"	O
RJ45	O
"	O
)	O
ports	O
,	O
some	O
hubs	B-Protocol
may	O
also	O
come	O
with	O
a	O
BNC	B-Protocol
or	O
an	O
Attachment	B-Protocol
Unit	I-Protocol
Interface	I-Protocol
(	O
AUI	O
)	O
connector	O
to	O
allow	O
connection	O
to	O
legacy	O
10BASE2	O
or	O
10BASE5	O
network	B-Protocol
segments	I-Protocol
.	O
</s>
<s>
Hubs	B-Protocol
are	O
now	O
largely	O
obsolete	O
,	O
having	O
been	O
replaced	O
by	O
network	B-Protocol
switches	I-Protocol
except	O
in	O
very	O
old	O
installations	O
or	O
specialized	O
applications	O
.	O
</s>
<s>
As	O
of	O
2011	O
,	O
connecting	O
network	B-Protocol
segments	I-Protocol
by	O
repeaters	O
or	O
hubs	B-Protocol
is	O
deprecated	O
by	O
IEEE	O
802.3	O
.	O
</s>
<s>
A	O
layer	B-Application
1	I-Application
network	B-Device
device	I-Device
such	O
as	O
a	O
hub	B-Protocol
transfers	O
data	O
but	O
does	O
not	O
manage	O
any	O
of	O
the	O
traffic	O
coming	O
through	O
it	O
.	O
</s>
<s>
Any	O
packet	O
entering	O
a	O
port	B-Protocol
is	O
repeated	O
to	O
the	O
output	O
of	O
every	O
other	O
port	B-Protocol
except	O
for	O
the	O
port	B-Protocol
of	O
entry	O
.	O
</s>
<s>
A	O
repeater	B-Protocol
hub	I-Protocol
can	O
therefore	O
only	O
receive	O
and	O
forward	O
at	O
a	O
single	O
speed	O
.	O
</s>
<s>
Dual-speed	O
hubs	B-Protocol
internally	O
consist	O
of	O
two	O
hubs	B-Protocol
with	O
a	O
bridge	O
between	O
them	O
.	O
</s>
<s>
Since	O
every	O
packet	O
is	O
repeated	O
on	O
every	O
other	O
port	B-Protocol
,	O
packet	O
collisions	O
affect	O
the	O
entire	O
network	O
,	O
limiting	O
its	O
overall	O
capacity	O
.	O
</s>
<s>
A	O
network	O
hub	B-Protocol
is	O
an	O
unsophisticated	O
device	O
in	O
comparison	O
with	O
a	O
switch	B-Protocol
.	O
</s>
<s>
As	O
a	O
multiport	B-Protocol
repeater	I-Protocol
it	O
works	O
by	O
repeating	O
transmissions	O
received	O
from	O
one	O
of	O
its	O
ports	O
to	O
all	O
other	O
ports	O
.	O
</s>
<s>
It	O
is	O
aware	O
of	O
physical	B-Application
layer	I-Application
packets	O
,	O
that	O
is	O
it	O
can	O
detect	O
their	O
start	O
(	O
preamble	O
)	O
,	O
an	O
idle	O
line	O
(	O
interpacket	B-Protocol
gap	I-Protocol
)	O
and	O
sense	O
a	O
collision	O
which	O
it	O
also	O
propagates	O
by	O
sending	O
a	O
jam	O
signal	O
.	O
</s>
<s>
A	O
hub	B-Protocol
cannot	O
further	O
examine	O
or	O
manage	O
any	O
of	O
the	O
traffic	O
that	O
comes	O
through	O
it	O
.	O
</s>
<s>
A	O
hub	B-Protocol
has	O
no	O
memory	O
to	O
store	O
data	O
and	O
can	O
handle	O
only	O
one	O
transmission	O
at	O
a	O
time	O
.	O
</s>
<s>
Therefore	O
,	O
hubs	B-Protocol
can	O
only	O
run	O
in	O
half	O
duplex	O
mode	O
.	O
</s>
<s>
Due	O
to	O
a	O
larger	O
collision	B-Protocol
domain	I-Protocol
,	O
packet	O
collisions	O
are	O
more	O
likely	O
in	O
networks	O
connected	O
using	O
hubs	B-Protocol
than	O
in	O
networks	O
connected	O
using	O
more	O
sophisticated	O
devices	O
.	O
</s>
<s>
The	O
need	O
for	O
hosts	O
to	O
be	O
able	O
to	O
detect	O
collisions	O
limits	O
the	O
number	O
of	O
hubs	B-Protocol
and	O
the	O
total	O
size	O
of	O
a	O
network	O
built	O
using	O
hubs	B-Protocol
(	O
a	O
network	O
built	O
using	O
switches	O
does	O
not	O
have	O
these	O
limitations	O
)	O
.	O
</s>
<s>
For	O
10Mbit/s	O
networks	O
built	O
using	O
repeater	B-Protocol
hubs	I-Protocol
,	O
the	O
5-4-3	B-Protocol
rule	I-Protocol
must	O
be	O
followed	O
:	O
up	O
to	O
five	O
segments	O
(	O
four	O
hubs	B-Protocol
)	O
are	O
allowed	O
between	O
any	O
two	O
end	O
stations	O
.	O
</s>
<s>
For	O
10BASE-T	B-Protocol
networks	O
,	O
up	O
to	O
five	O
segments	O
and	O
four	O
repeaters	O
are	O
allowed	O
between	O
any	O
two	O
hosts	O
.	O
</s>
<s>
For	O
100Mbit/s	O
networks	O
,	O
the	O
limit	O
is	O
reduced	O
to	O
3	O
segments	O
(	O
2	O
Class	O
II	O
hubs	B-Protocol
)	O
between	O
any	O
two	O
end	O
stations	O
,	O
and	O
even	O
that	O
is	O
only	O
allowed	O
if	O
the	O
hubs	B-Protocol
are	O
of	O
Class	O
II	O
.	O
</s>
<s>
Some	O
hubs	B-Protocol
have	O
manufacturer-specific	O
stack	O
ports	O
allowing	O
them	O
to	O
be	O
combined	O
in	O
a	O
way	O
that	O
allows	O
more	O
hubs	B-Protocol
than	O
simple	O
chaining	O
through	O
Ethernet	O
cables	O
,	O
but	O
even	O
so	O
,	O
a	O
large	O
Fast	B-Protocol
Ethernet	I-Protocol
network	O
is	O
likely	O
to	O
require	O
switches	O
to	O
avoid	O
the	O
chaining	O
limits	O
of	O
hubs	B-Protocol
.	O
</s>
<s>
Most	O
hubs	B-Protocol
detect	O
typical	O
problems	O
,	O
such	O
as	O
excessive	O
collisions	O
and	O
jabbering	O
on	O
individual	O
ports	O
,	O
and	O
partition	O
the	O
port	B-Protocol
,	O
disconnecting	O
it	O
from	O
the	O
shared	O
medium	O
.	O
</s>
<s>
Thus	O
,	O
hub-based	O
twisted-pair	B-Protocol
Ethernet	I-Protocol
is	O
generally	O
more	O
robust	O
than	O
coaxial	O
cable-based	O
Ethernet	O
(	O
e.g.	O
</s>
<s>
10BASE2	O
)	O
,	O
where	O
a	O
misbehaving	O
device	O
can	O
adversely	O
affect	O
the	O
entire	O
collision	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
Even	O
if	O
not	O
partitioned	O
automatically	O
,	O
a	O
hub	B-Protocol
simplifies	O
troubleshooting	O
because	O
hubs	B-Protocol
remove	O
the	O
need	O
to	O
troubleshoot	O
faults	O
on	O
a	O
long	O
cable	O
with	O
multiple	O
taps	O
;	O
status	O
lights	O
on	O
the	O
hub	B-Protocol
can	O
indicate	O
the	O
possible	O
problem	O
source	O
or	O
,	O
as	O
a	O
last	O
resort	O
,	O
devices	O
can	O
be	O
disconnected	O
from	O
a	O
hub	B-Protocol
one	O
at	O
a	O
time	O
much	O
more	O
easily	O
than	O
from	O
a	O
coaxial	O
cable	O
.	O
</s>
<s>
In	O
the	O
early	O
days	O
of	O
Fast	B-Protocol
Ethernet	I-Protocol
,	O
Ethernet	B-Protocol
switches	I-Protocol
were	O
relatively	O
expensive	O
devices	O
.	O
</s>
<s>
Hubs	B-Protocol
suffered	O
from	O
the	O
problem	O
that	O
if	O
there	O
were	O
any	O
10BASE-T	B-Protocol
devices	O
connected	O
then	O
the	O
whole	O
network	O
needed	O
to	O
run	O
at	O
10Mbit/s	O
.	O
</s>
<s>
Therefore	O
,	O
a	O
compromise	O
between	O
a	O
hub	B-Protocol
and	O
a	O
switch	B-Protocol
was	O
developed	O
,	O
known	O
as	O
a	O
dual-speed	O
hub	B-Protocol
.	O
</s>
<s>
These	O
devices	O
make	O
use	O
of	O
an	O
internal	O
two-port	O
switch	B-Protocol
,	O
bridging	B-Protocol
the	O
10Mbit/s	O
and	O
100Mbit/s	O
segments	O
.	O
</s>
<s>
When	O
a	O
network	B-Device
device	I-Device
becomes	O
active	O
on	O
any	O
of	O
the	O
physical	O
ports	O
,	O
the	O
device	O
attaches	O
it	O
to	O
either	O
the	O
10Mbit/s	O
segment	O
or	O
the	O
100Mbit/s	O
segment	O
,	O
as	O
appropriate	O
.	O
</s>
<s>
This	O
obviated	O
the	O
need	O
for	O
an	O
all-or-nothing	O
migration	O
to	O
Fast	B-Protocol
Ethernet	I-Protocol
networks	O
.	O
</s>
<s>
These	O
devices	O
are	O
considered	O
hubs	B-Protocol
because	O
the	O
traffic	O
between	O
devices	O
connected	O
at	O
the	O
same	O
speed	O
is	O
not	O
switched	O
.	O
</s>
<s>
100Mbit/s	O
hubs	B-Protocol
and	O
repeaters	O
come	O
in	O
two	O
different	O
classes	O
:	O
Class	O
I	O
delay	O
the	O
signal	O
for	O
a	O
maximum	O
of	O
140	O
bit	O
times	O
.	O
</s>
<s>
This	O
delay	O
allows	O
for	O
translation/recoding	O
between	O
100BASE-TX	B-Protocol
,	O
100BASE-FX	O
and	O
100BASE-T4	O
.	O
</s>
<s>
Class	O
II	O
hubs	B-Protocol
delay	O
the	O
signal	O
for	O
a	O
maximum	O
of	O
92	O
bit	O
times	O
.	O
</s>
<s>
This	O
shorter	O
delay	O
allows	O
the	O
installation	O
of	O
two	O
hubs	B-Protocol
in	O
a	O
single	O
collision	B-Protocol
domain	I-Protocol
.	O
</s>
<s>
Repeater	B-Protocol
hubs	I-Protocol
are	O
defined	O
in	O
the	O
standards	O
for	O
Gigabit	O
Ethernet	O
but	O
commercial	O
products	O
have	O
failed	O
to	O
appear	O
due	O
to	O
the	O
industry	O
's	O
transition	O
to	O
switching	O
.	O
</s>
<s>
Historically	O
,	O
the	O
main	O
reason	O
for	O
purchasing	O
hubs	B-Protocol
rather	O
than	O
switches	O
was	O
their	O
price	O
.	O
</s>
<s>
By	O
the	O
early	O
2000s	O
,	O
there	O
was	O
little	O
price	O
difference	O
between	O
a	O
hub	B-Protocol
and	O
a	O
low-end	O
switch	B-Protocol
.	O
</s>
<s>
Hubs	B-Protocol
can	O
still	O
be	O
useful	O
in	O
special	O
circumstances	O
:	O
</s>
<s>
For	O
inserting	O
a	O
protocol	B-Protocol
analyzer	I-Protocol
into	O
a	O
network	O
connection	O
,	O
a	O
hub	B-Protocol
is	O
an	O
alternative	O
to	O
a	O
network	B-Device
tap	I-Device
or	O
port	B-Protocol
mirroring	I-Protocol
.	O
</s>
<s>
A	O
hub	B-Protocol
with	O
both	O
10BASE-T	B-Protocol
ports	O
and	O
a	O
10BASE2	O
port	B-Protocol
can	O
be	O
used	O
to	O
connect	O
a	O
10BASE2	O
segment	O
to	O
a	O
modern	O
Ethernet-over-twisted-pair	B-Protocol
network	O
.	O
</s>
<s>
A	O
hub	B-Protocol
with	O
both	O
10BASE-T	B-Protocol
ports	O
and	O
an	O
AUI	B-Protocol
port	I-Protocol
can	O
be	O
used	O
to	O
connect	O
a	O
10BASE5	O
segment	O
to	O
a	O
modern	O
network	O
.	O
</s>
<s>
As	O
hubs	B-Protocol
have	O
lower	O
latency	O
and	O
jitter	O
compared	O
to	O
switches	O
–	O
as	O
long	O
as	O
there	O
are	O
no	O
collisions	O
–	O
,	O
they	O
may	O
be	O
better	O
suited	O
for	O
real-time	B-Protocol
networks	I-Protocol
,	O
e.g.	O
</s>
<s>
Ethernet	B-Protocol
Powerlink	I-Protocol
.	O
</s>
