| ＝OSI Model and Transmission Path＝ |
| A．OSI 7-Layer Model |
| B．Signals and Network Media |
| C．Data Link Layer |
| D．Bridges and Repeaters |
| E．ARP and ARP tables |
| F．Topologies and Access Methods |
 Related Items |
| D-1 HUBs |
| D-2 Repeaters |
| D-3 Bridges and Switches |
| D-4 Connection form of HUBs |
| ・ Exercise |
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D-4 Connection form of HUBs
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When there is lack of the entry points of a hub because of the increase of computers to be connected to a network, it is possible to increase the number of ports by connecting the hub to another one. There are the following cascading connection and stacking connection as this method.
D-4-1 Cascading connection
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Cascading connection increases the number of terminals which can be connected to a network by connecting communication devices which are relay points such as hubs. It is also called multi-stage connection.
The following figure shows the connection form of hubs.
| Figure D-4-1 Cascading connection using a straight cable |
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When connecting hubs A and B using cascading connection, the MDI port (normal port) of hub A and the MDI-X port (also called cascade port or uplink port) of hub B are connected using a straight cable. The above figure shows two-stage connection, but three-stage or four-stage connection is also possible. A hub with 10 ports can connect up to 10 terminals, but up to 18 terminals (except the ports for cascading connection) can be connected by the cascading connection of two hubs with 10 ports.
In this case, there is a disadvantage that the more the number of hubs, the larger is the delay. The maximum number of cascading connections is defined according to the standard, like 4 stages with 10BASE-T and 2 stages with 100BASE-T.
To connect hubs without MDI-X ports, a cross cable is used as shown in the following figure.
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Figure D-4-2 Cascading connection using a cross cable
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D-4-2 Stacking connection
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Stacking connection increases the number of ports by connecting hubs with the unique bus and cable. Because the hubs connected in this method can be recognized as one hub, the restriction of the number of connections in the case of cascading connection is eased. There is a disadvantage that an exclusive hub (stackable hub) and stack cable to connect hubs are needed because the stacking connection with straight or cross cables is impossible.
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Figure D-4-3 Stacking connection
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