The premise of the vendors is that femtocells should require no radio planning. Since operators do not, by and large, know where any individual femtocell will be deployed, they cannot reconfigure their macro network to account for this. There is substantial research and trial work ongoing to reduce the impact of the femtocell on the outdoor macrocellular network. Since the signal levels are very low power and do not easily penetrate walls, little is radiated outside the premises where they are located. Some femtocells also “listen” to the external macrocellular network to pick a frequency which will cause minimum interference.