title: What's different in USB class when the devices are modem?
body: <p>Every USB device has to come under some USB device class definition based on the device driver will get use on the Linux system.. that part i understood.</p>
  
  <p>but I can't understand something. For example, mostly all USB modem come under communication device class.. I have one 3G USB modem and one 3G USB dongle (e.g.,tata photon), both come under the same communication class but 3G USB modem uses CDC-ACM driver and 3G dongle uses serial converter driver(USB-Serial). What makes these devices differs?</p>
  
  <p>Can anyone explain this?</p>