With Wi-Fi, cellular and satellite access networks, there is a growing fraction of the Internet traffic which is carried over radio waves. Although a detailed understanding of all the technology behind radio transmission is outside the scope of most networking courses for computer scientists, it is useful to have some basics understanding of the principles behind the transmission of radio signals.

An important point to remember is that the radio spectrum is a finite resources which is mainly managed by countries and international organizations. The radio spectrum is divided in bands that are used for specific purposes. A small fraction of the spectrum can be used by anyone. These are the ISM radio bands. These bands were allocated for Industrial, Scientific and Medical applications which do not require a specific license to be used. Since there is no license, each of these applications must be able to share the radio spectrum with other applications without breaking them. For example, microwave ovens operate in the 2.4GHz band and need to coexist with Wi-Fi or Bluetooth.

Besides the ISM bands, the radio spectrum is very crowded. A recent blog post provides a nice summary of different ways of visualizing the radio spectrum with various examples from different countries.

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