title: Differentiate multiple USB devices having same Vendor and Product ID
body: <p>I am writing an application which allows a Linux machine to connect to internet over usb modem. I have multiple usb modems having same vendor and product ID; I cannot differentiate them using <code>lsusb</code> which gives vendor and product ID. Also giving IDs according to their usb ports does not solve my problem either, because I want to be able to use usb modems in whichever port I want.<br>
  Is there a unique identifier which I can use to differentiate my usb devices?</p>