Concerning the concentrator

All the lengths of cable share the same home base, a concentrator, which is either a hub or a switch (routers have switches built in, so if you're using your router as a concentrator, you have a switch). Each cable run goes from the concentrator to a computer (or from a computer to the concentrator, depending on how you like to envision it).

At each end of a length of cable is a connector called an RJ-45 connector. One connector attaches to the concentrator, and the other connector attaches to the NIC in a computer.

When you purchase a concentrator, you have a choice between buying a hub or a switch. The difference between them is the way they send data to computers - the switch takes a more intelligent approach. When data is transmitted across the network, the ID of the target (receiving) computer is identified within the data packet. A hub ignores the computer ID and sends the data to all the computers on the network. The computers check the computer ID, and the computer that's supposed to receive the data accepts it; the other computers ignore it. However, the hub has to split up the bandwidth to send the data to all the computers, so the transmission speed to each individual computer is reduced. A switch notices which computer ID is the target of the data transmission and sends the data only to that computer, using all the available bandwidth for the transmission.

Warning One of the ports on a hub or a switch may differ from the others, although it looks the same. That port is an uplink port, and you don't use it to connect a computer to the hub. Instead, this port has a special use (see the section "Curing Your Network's Growing Pains," later in this tutorial). Look for an icon or label to identify the uplink port, or read the documentation that came with the hub so that you know which port to avoid.

The network arrangement shown in Figure below is called a star topology, although I'm not sure how that name was developed. Personally, I think the resemblance to a star is a little obscure. Perhaps wheel spokes is a more accurate description - which would explain the use of the word hub (as in the hub of a wheel).