When a USB device has been removed from one of its ports, the hub automatically disables the port and provides an indication of device removal to the host. Then the host removes knowledge of the USB device from any host data structures. If the removed USB device is a hub, the removal process must be performed for all of the USB devices that were previously attached to the hub. If the removed USB device is a function, removal notifications are sent to interested host software. Only hubs have the ability to provide additional USB attachment points.
Functions provide additional capabilities to the host.
No text of specified style in document.-1 shows a typical hub. Hubs serve to simplify USB connectivity from the user s perspective and provide robustness at low cost and complexity. Attachment points are referred to as ports. Each hub converts a single attachment point into multiple attachment points. The architecture supports concatenation of multiple hubs.