A hub-based Ethernet network still faces the principal liability of Ethernet: Performance degrades as traffic increases.
No computer can transmit unless the line is free. Furthermore, each network adapter must receive and process every frame placed on the Ethernet.
A smarter version of a hub, called a switch, was developed to address these problems with Ethernet.
In its most fundamental form, a switch looks very similar to the hub shown in Figure 9.2.
Each computer is attached to the switch through a single line. However, the switch is smarter about where it sends the data received through one of its ports.