Global System for Mobile communications is a 2G mobile network technology and currently the most popular globally, with a market share of more than 80 per cent. It is used by about 700 operators in 214 countries, covering 29 per cent of the global population. In GSM, voice signals are digitised, then compressed, and sent along with two similar data streams in different time slots but the same frequency spectrum (900 MHz or 1800 MHz). This indicates that it uses TDMA (Time Division Multiple Access) to send data. GSM networks also offer a degree of data encryption.