- allg. Erklärung
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http://www.howtogeek.com/192732/android-usb-connections-explained-mtp-ptp-and-usb-mass-storage/

 MTP stands for “Media Transfer Protocol.” When Android uses this protocol, it appears to the computer as a “media device”.
 PTP stands for “Picture Transfer Protocol”. When Android uses this protocol, it appears to the computer as a digital camera.
 MTP is actually based on PTP, but adds more features, or “extensions".
 If you have an older Android device, you may be forced to use USB mass storage. On a modern Android device, you have a choice between MTP and PTP — you should use MTP unless you have software that only supports PTP.

- UBUNTU USB ModeSwitch
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http://wiki.ubuntuusers.de/USB_ModeSwitch