USB connection to BeagleBone Black drops
The BeagleBone Black consumes ~300mA at idle, with minimal if any peripherals connected. Under load, it will require more. If your USB connection only provides 100mA as you have stated, the connection drops are painfully obvious. The BBB is starving. Any time it attempts to pull more current, it will brown-out, stop drawing power, reset, and rinse lather repeat.

You need a stronger power supply, or a powered usb hub if your computer's usb port is not up to snuff. It should be providing 500mA at least. Even that may be borderline (5V @ .5A = 2.5W).


  What power peripherals are required/desirable?
  There are several ways to power a Beagle. The option exists to feed the on-board regulators through either the 5V barrel connector input or USB input. When powered up over USB, the regulators are somewhat limited in what they can supply the system. Power over USB is sufficient as long as the software and system running perform some management to keep it under the USB current limit threshold. For simplicity and maximum capability, powering over the 5V barrel connector is typically recommended.
  The power adapter is required to provide 5V over a 5.5mm outer diameter and 2.1mm inner diameter barrel connector (a barrel connector length of 9.5mm is more than sufficient). The recommended supply current is at least 1.2A (or 6W), but at least 2A (or 10W) is recommended if you are going to connect up anything over the USB. The actual power consumption will vary greatly with changes on the USB load.