The phrase "Ethernet over USB" can refer to several different ways in which the Ethernet standard for computer networking can interact with Universal Serial Bus (USB) technology commonly used to attach accessories and peripherals to computers and consumer electronics. Often the term describes USB dongles that plug into a computer and provide an external Ethernet networking port. It may also describe a technique that allows USB cables to serve as the physical medium for small Ethernet protocol-based networks.
Ethernet and USB are both connectivity technologies widely used in computers and consumer electronics since the late 1990s. Each technology consists of a physical medium that connects multiple computers or devices and a protocol that sets rules for how messages are sent and received over the physical connectors. Ethernet is used almost exclusively for wired networking, while USB connects computers with peripherals and other devices such as cameras, external hard disks, and portable media players. The two standards generally do not interact, but as the term Ethernet over USB implies, there are situations where they can be used together.
In many cases, Ethernet over USB refers to external devices or dongles that plug into a USB port to provide a computer or other device with an Ethernet port. These dongles work just like any other Ethernet port, except that they connect to a computer through an external medium. They may be used on computers that have a damaged network card, smaller laptops that forego Ethernet in favor of wireless connectivity, or consumer electronics devices that lack built-in networking hardware. Many Ethernet over USB dongles are "plug-and-play," meaning users do not have to install additional driver software in order to use the device.
Ethernet over USB can also have a more literal meaning, thus referring to the use of the Ethernet protocol over physical USB cables and connectors. This can allow two devices to be networked quickly by using cables that most computer users own. It is also a useful way to provide a wired network connection to a device that lacks an Ethernet port such as a Personal Digital Assistant (PDA). In both cases, one computer may act as a bridge, thereby forwarding data from this USB mini-network to a more standard network port. Since this is not a standard use of either technology, special software generally needs to be installed on both computers or devices networked in this fashion.