Understand USB suspended or unconnected mode
What is the standard for USB suspended mode and how is different from
a disconnected cable?

In connected state the bus conducts two actions:

Device side maintains 1.5k pull-up;
Host side sends periodic frame packets, 1ms (or 125 us) frames. (in LS mode these are simple pulses called &quot;keep alive&quot;)

If the pull-up (device side!) disappears just for 2.5 us, the host identifies this state as DISCONNECT. Since the host keeps 15 k pull-downs on both D+ and D-, cable disconnect causes the same condition - single-ended zero.
If the host stops the transmission of SOFs (Start of Frames or &quot;keepalive&quot;) for more than 3 ms, the device must recognize this as SUSPEND, and act accordingly by transitioning into low power state.
Therefore, to &quot;simulate&quot; SUSPEND state of the USB, you need to terminate bus &quot;activity&quot;. One way is to disconnect both D+ and D- wires on host side while maintaining the VBUS connection. Normal way, however, is to sent SUSPEND command from inside RPi to corresponding (selected) port, which will block all data transmission and create SUSPEND state (after 3 ms).