The full name of GSM is: Global System for Mobile Communications. Chinese is the global mobile communication system, commonly known as "Global Passage". It is a mobile communication technology standard originating in Europe and is the second generation of mobile communication technology. Its development purpose is to make it available all over the world. A mobile phone network standard can be used together to allow users to use a mobile phone to travel around the world. China introduced this technology standard in the early 1990s. Until now, it has been using cellular analog mobile technology, which is the first generation of GSM technology (in December 31, 2001, China closed its analog mobile network). At present, China Mobile and China Unicom each have a GSM network, which is the world's largest mobile communications network. The GSM system includes several GSM 900:900MHz, GSM1800:1800MHz and GSM-1900:1900MHz frequency bands. The GSM system has several important features: good anti-theft copying capability, large network capacity, rich mobile phone number resources, clear calls, strong stability, and less interference, sensitive information, fewer dead calls, and low power consumption of mobile phones. At present, the two major GSM systems in China are GSM 900 and GSM 1800. Since different frequencies are used, the applicable mobile phones are also different. However, at present, most mobile phones are basically dual-band mobile phones and are free to switch between these two bands. In addition to GSM900 and GSM1800, GSM1900 is also commonly used in European countries. The mobile phone is a tri-band mobile phone. In China, with the further development of the mobile phone market, tri-band mobile phones have also emerged, and mobile phones that can be switched freely within the three frequency bands of GSM900, GSM1800, and GSM1900 have truly enabled a mobile phone to travel around the world. In the early days, the development of GSM900 was earlier and used more often, whereas the development of GSM1800 was later. In terms of physical characteristics, the former has a lower frequency spectrum, a longer wavelength, and a poorer penetrating power, but the transmission distance is relatively long, and the mobile phone has a relatively high transmission power and consumes a large amount of power, so the standby time is shorter; High, short wavelength, good penetration, but the transmission distance is short, the mobile phone's transmission power is small, standby time is correspondingly longer.