Patent ID: 7188206

Claim:
A Universal Serial Bus (USB) system comprising: a group of USB hubs, comprising at least one USB hub, wherein each USB hub comprises: an upstream port; and a plurality of downstream ports; wherein the group of USB hubs is installed in the same layer in the USB system, and the group of USB hubs comprises a first number of downstream ports in total; a USB compound device comprising: an upstream port for connecting a first downstream port among the first number of downstream ports of the group of USB hubs; a second number of USB devices, wherein the second number is not greater than the first number; and a control unit capable of setting states of the second number of USB devices, wherein a state of each USB device of the second number of USB devices is set to an on state in turn according to a predetermined rule, and when a state of one USB device of the second number of USB devices is set to the on state and the USB device is not assigned an address, the USB device is capable of setting its address according to an address assigning packet received from the upstream port of the USB compound device; wherein among the first number of downstream ports of the group of USB hubs, there are a third number of downstream ports prior to the first downstream port, in which the third number is not less than the second number minus one; and a fourth number of USB dummy devices connecting to a fourth number of downstream ports among the first number of downstream ports of the group of USB hubs, in which the fourth number of downstream ports are subsequent to the first downstream port, wherein each USB dummy device is capable of providing a connection event to a USB hub when connecting to a downstream port of the USB hub, in which the fourth number is the second number minus one.