Читать книгу Networking All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 40

A repeater is a layer-1 device that is designed to circumvent the maximum length limitation of twisted-pair network cables. A repeater contains two RJ45 ports, which are connected internally by an amplifier. Electrical signals received on either of the two ports are boosted by the amplifier and sent through the other port. Thus, the cables on both ends of the repeater can be up to 100 meters. The repeater effectively doubles the reach of the cable.

A hub is a repeater with more than two ports. For example, a hub may have four or eight ports. These ports can each connect to another device on the network such as a client computer, a server, or a printer. A port on a hub can also connect to another hub, so that (for example) an eight-port hub can connect to seven computers and another eight-port hub, which can connect to seven more computers. In this way, two eight-port hubs can connect 14 computers to each other.

There are two very important things to know about hubs.

The second most important thing to know about hubs is that an electrical signal received on any of the hub’s ports is amplified and repeated on all the other ports in the hub. So, in an eight-port hub, any electrical signals received on port 1 are amplified and then sent out on ports 2 through 8. Any devices that are connected to ports 2 through 8 see the signals that were received on port 1. The same is true for signals received on any of the other ports; for example, any signals received on port 4 will be amplified and repeated on ports 1 through 3 as well as ports 5 through 8.

That’s the second most important thing to know. The first most important thing to know about hubs is that they’re almost never used anymore. That’s because simply repeating all incoming signals on all ports is an incredibly bad idea, for reasons that will become apparent later in this chapter and in Chapter 3 of this minibook. If your network still has hubs, you should seriously consider replacing them with switches, which are described in the next section and further explained in the next chapter.