USB uses four-wire cables, two of which are serial channels for data transfer and the other two of which provide power to Downstream devices. USB transfers data at full speed of 12 Mbps for high-speed peripherals that require high bandwidth;
For low-speed peripherals, USB transfers data at 1.5 Mbps. The USB bus automatically switches dynamically between the two transfer modes depending on the peripherals. USB is a token-based bus. Similar to Token Ring network or
FDDI Token-based bus. The USB host broadcasts a token that detects if the address on the bus matches the address in the token and responds by receiving or sending data to the host. USB is supported by suspend / resume operations
Manage USB bus power. The USB system uses a cascading star topology consisting of three basic components: the Host, the Hub, and the functional device.
The host, also referred to as the root, root, or root hub, is installed on the motherboard or as an adapter on a computer that contains the host controller and the root hub (-RootHub) that controls the data on the USB bus Control information
There is only one root hub per USB system, which is connected to the host controller.
A hub is a specific part of the USB fabric that provides a point called a port that connects the device to the USB bus while detecting the devices connected to the bus and providing power management for these devices,
Barrier detection and recovery. Hubs provide energy for the bus, as well as provide power for itself (power from the outside). Devices that provide their own energy can be plugged into a bus to provide energy to the hub, but the bus provides energy to the device
Can not be plugged into its own energy-providing hub or downstream ports that support more than four, and can not be connected to a bus-powered hub if it requires more than 100mA for an energy device.
The functional device is connected to the bus via the port. USB Hub can be used at the same time.
