How are the data transmitted?

The data are transmitted using radio waves at a frequency of about 2,4 GHz at the nodes, where you can log is (the interlinks between nodes use a frequency of about 5 GHz). In fact there are several channels available (in Europe thirteen). However, these channels are partly overlapping. The 2,4 GHz band is a 'free' frequency, which implies that you do not need a license to use it. The only restriction is the maximum transmission power (100 mW maximum). This is very low (a thousand times less than eg. gsm or umts or the power that radio amateurs are using). This is one of the reasons that you need a 'line of sight' between sender and receiver.