Protocols for mobile phones
Two basic protocols are used to connect cellular phone calls: GSM and CDMA. Within these different frequencies and branches are used, however the basics of the two systems is the same. In addition to these two systems has been recently introduced a new system called RUIM, which is a hybrid CDMA and GSM.
GSM / TDMA
The protocol most popular to make and receive phone calls on cellular networks is GSM. This system is used by European cellular networks and is used in the U.S. by Sprint, AT & T and T-Mobile. GSM stands for Global System for Communications Mobile (part of the communication is involved).It consists of four different frequencies: 850 MHz, 900 MHz, 1.8 GHz and 1.9 GHz. The system in the United States is based on 1.9 GHz and 850 MHz, while the European system uses 1.Ghz and 900 Mhz. The GSM coverage is available to about 80 percent of the world population. It uses a small card to call from a card SIM (for its acronym in English) to track individual phones, allowing you to change from one phone to another by changing the card SIM. The GSM is actually based on an older technology called TDMA. While other technologies such as UMTS and EDGE have been added to the GSM networks, these technologies are not used for telephony. Instead, they are used for data transmission.
Some people are confused when referring to CDMA because they know that GSM is based on TDMA. TDMA stands for division multiple access, while multiple access CDMA means code division. The two systems are actually based on an earlier technology called FDMA (for its acronym in English), which is no longer used for cell phones. CDMA was created in 1993 and deployed in 1998 for the first time. It is commonly used in the United States by Verizon Wireless and is available in some 35 countries. The system does not use SIM cards, instead, relies on the phone itself to be uniquely identified. It is considered safer than the previous TDMA / GSM technology.
Although technically not a new protocol , RUIM is essentially an effort to bridge the gap between CDMA and GSM / TDMA. It makes use of a card special SIM that plugs into a phone thst GSM / TDMA also able to connect to CDMA networks, which allows as many connectivity options for telephony.