Before turning to the definition of a USB network hub, let us find out what a network hub is. It is a device that enables more than one computer to connect to a network. It acts as a point of convergence allowing the transfer of data packets through the network. Generally, the function of a network hub is to duplicate data packets, which it receives from one port and make them available on other ports. A packet arriving at one port is made available on all the other ports so that it becomes available to all the devices connected to the network. It thus facilitates sharing of data between the devices that form a network.
A USB hub allows USB devices to connect to a single USB port on a host computer or another hub. How do USB hubs look? In some hubs, the USB ports are located close to each other. In this case, it becomes difficult to plug in devices on adjacent ports on the hub. In star-shaped USB hubs, this difficulty does not arise as the ports located on different arms of the star point in different directions. With more number of USB hubs connected to each other, the size of the network increases. The USB cable length is about 5 meters. It can be extended by using USB repeaters. Many USB hubs support a hub system of four ports while some come with seven port hub controllers.
How do these hubs draw power? They come in two varieties. They are either self-powered or powered by means of a bus. A self-powered hub draws power from an external power supply, thus being able to provide greater power to each of the ports. On the other hand, a bus-powered hub draws power from the USB interface of the host computer. A drawback of bus-powered USB hubs is that they provide the devices with less amount of power than what the devices actually need. A bus-powered USB network hub allocates a current of about 100-500 mA per port. If a network device requires more current than that provided by the hub, the operating system of the host computer indicates this condition to the user, on which the device may have to be provided with current from an external power supply.
How does a network host detect the attachment of a network device? Obviously, it does so with the help of the network hub. The hub detects the device being attached and reports it to the host machine. The host signals the hub to reset the port on which the device has been attached. And then begins the interaction between the host computer and the newly added network device.
The upstream and downstream ports of a USB network hub enable it to facilitate data transfer between network devices and the host computer. The hub is connected to the host by means of an upstream port while network devices are connected to the downstream ports of the hub. The data received from a downstream port is forwarded to the upstream port, thus allowing data from a network device to be received only by the host machine. On the other hand, the data received from the upstream port of the USB hub is forwarded to all its downstream ports, whereby it can be transmitted to all the network devices.
How does a USB hub handle network traffic? Does it tackle with high- and low-speed traffic in the same way? For network devices to operate on high speeds, all the hubs between the device and the host computer need to be capable of supporting high-speed traffic. Through a process known as transaction translation, low-speed traffic is separated from high-speed traffic on the network.
Look at the transparency in this entire process of communication. The USB hub is so loyal with the devices attached to it. It does not misuse the information obtained from any of the network devices by relaying it to other devices on the network. Moreover, it is impartial in broadcasting data it receives from the host, to all the devices on the network. Also, it is intelligent enough to deal with different types of communication in different ways. If only human beings could act like that.