Distribution automation systems are used to automate the distribution grid, i.e., the medium and low voltage parts of the electricity grid. Remote Terminal Units (RTUs) play a central role in distribution automation by performing two main kinds of functions: collecting measurements from field devices and sending commands to control breakers and switches. RTUs communicate measurements, alarms, changes in registers, and other status information to the central systems. In this document the scope is restricted to RTUs placed in secondary substations that transform medium voltage into low voltage.