There are 3 ttyUSB (interface 0, 2 and 3) devices files created by the GobiSerial driver on Linux.
What is the purpose each of these device files?
/: Bus 06.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 5000M
|__ Port 1: Dev 2, If 0, Class=Vendor Specific Class, Driver=GobiSerial, 5000M
|__ Port 1: Dev 2, If 2, Class=Vendor Specific Class, Driver=GobiSerial, 5000M
|__ Port 1: Dev 2, If 3, Class=Vendor Specific Class, Driver=GobiSerial, 5000M
|__ Port 1: Dev 2, If 8, Class=Vendor Specific Class, Driver=GobiNet, 5000M
They enumerate incrementally unless a process is holding open a file descriptor with the path the driver wants. In that case it skips that number. For example if you reset the device while you have ttyUSB2 open, there will be a hole between ttyUSB1 and ttyUSB3. All the tty nodes after USB2 will be shifted up by one.