Comment 101 for bug 952080

For full-speed devices, a disconnect is detected when the D+ data line drops to 0 volts for an extended period. For low-speed devices, a disconnect is detected when the D- data line drops to 0 V for an extended period. High-speed devices revert to full-speed signalling when they are suspended. For high-speed devices that aren't suspended, a disconnect is detected when the signal echoes from the end of the cable change phase (or something like that; I'm not clear on the details).

Detection is the same for OHCI, UHCI, and EHCI. The only difference is in the device's speed (and the fact that neither OHCI nor UHCI supports high speed, whereas EHCI doesn't support low speed or full speed). Hubs work the same way.