Appendix
35
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Shared Hub: (A “Hub” refer to a shared hub.)
It is called a Multiport Repeater in IEEE802.3u. It doesn’t have functions such as filtering and switching.
Frames input to one port are repeated to all the other ports.
The following figure illustrates the data flow when data is sent from Station A to Station B if a shared hub is
used.
c
Data is sent from Station A to Shared Hub First Port.
d
In the Shared Hub, data received from the first port is repeated to the other ports.
e
Data is sent from the Shared Hub 4th Port to Station B.
1
2
3
4
5
6
7
8
E
E
E
E
E
E
E
E
c
d
e
Shared Hub
LAN Control LSI
RJ-45Connector
Station A
Station B
Station C
Station D
Figure A2.2 Operations of a Shared Hub
As shown in the figure above, C and D cannot communicate while A and B are communicating for a shared hub,
while C and D can communicate while A and B are communicating for a switching hub. When A and C send
data at the same time for the shared hub, a collision is detected.
The relations between communication modes and hub types are the following: For a switching hub, ports can be
full-duplex because data is temporarily stored in the buffer; for a shared hub, communication is half-duplex
since send and receive cannot be performed simultaneously, as shown in the figure above.
