Hubs are simple network devices, and their simplicity is reflected in their low cost. Small hubs with four or five ports (often referred to as workgroup hubs) cost less than $50; with the requisite cables, they provide everything needed to create a small network. Hubs with more ports are available for networks that require greater capacity. Figure 3.1 shows an example of a workgroup hub, and Figure 3.2 shows an example of the type of hub you might see on a corporate network.
Figure 3.1 A workgroup hub.
Figure 3.2 A high-capacity, or high-density, hub.
Computers connect to a hub via a length of twisted-pair cabling. In addition to ports for connecting computers, even an inexpensive hub generally has a port designated as an uplink port that enables the hub to be connected to another hub to create larger networks. The "Working with Hubs and Switches" section later in this chapter presents a detailed discussion of this feature.
Most hubs are referred to as either active or passive. Active regenerate a signal before forwarding it to all the ports on the device and requires a power supply. Small workgroup hubs normally use an external power adapter, but on larger units the power supply is built in. Passive hubs, which today are seen only on older networks, do not need power and they don’t regenerate the data signal.
Regeneration of the signal aside, the basic function of a hub is to take data from one of the connected devices and forward it to all the other ports on the hub. This method of operation is inefficient because, in most cases, the data is intended for only one of the connected devices. You can see a representation of how a hub works in Figure 3.3.
Figure 3.3 How a hub works.
Due to the inefficiencies of the hub system and the constantly increasing demand for more bandwidth, hubs are slowly but surely being replaced with switches. As you will see in the next section, switches offer distinct advantages over hubs.