Wed May 23 18:28:21 EDT 2012
Got a USB sniffer
First thing I see with the beagle is that there is traffic that is
not just the device visible on the line. Does a HUB send stuff to all
ports without being smart about where the devices are?
From  it seems that hubs just forward to all ports:
"During normal transmission, hubs are essentially transparent: data
received from its upstream port is broadcast to all devices attached
to its downstream ports; data received from a downstream port is
generally forwarded to the upstream port only."
and only for insertion there's a brief communication with host to
perform the reset signalling:
"Hubs are not transparent when dealing with changes in the status of
downstream ports, such as insertion or removal of devices. In
particular, if a downstream port of a hub changes status, this
change is dealt with in an interaction between the host and this
hub; the hubs between them act as transparent in this case."