Frames (3)

If an I/O device detects no bus activity (no SOF packet) for 3 ms, it assumes that the PC has powered down and it enters automatically into a suspend state
An I/O device can send a remote wakeup signal to bring the PC out of its powered down state (a USB modem might want to wake up the PC when the phone rings)
The remote wake-up capability must be predeclared in the device configuration descriptor

If an I/O device detects no bus activity (no SOF packet) for 3 ms, it assumes that the PC has powered down and it enters automatically into a suspend state