| Global Systems for Mobile Communication (GSM) | | | | information between the antenna tower and the |
| is the main technology used by the international | | | | phone. |
| digital wireless systems and cell phones; however, | | | | The architecture used by GSM consists of three |
| GMS is used only by a small percentage of cell | | | | main component, a mobile station, a base station |
| phone carriers in the United States. GSM is | | | | subsystem, and a network subsystem. These |
| interesting in that it uses a modified and far more | | | | components work in tandem to allow a cell phone |
| efficient version of TDMA (Time Division Multiple | | | | user to travel seamlessly without interruption of |
| Access). GSM keeps the idea of timeslots on | | | | service, while offering the flexibility of having any |
| frequency channels, but corrects several major | | | | GSM cell phone device used permanently or |
| shortcomings. Since the GSM timeslots are smaller | | | | temporarily by any user. Utilizing the three |
| than TDMA, they hold less data but allow for data | | | | separate components of the GSM network, this |
| rates starting at 300 bits per second. Thus, a call | | | | type of communication is truly portable. A cell |
| can use as many times slots as necessary up to | | | | phone user can place an identification card called |
| a limit of 13 kilobits per second. When a call is | | | | Subscriber Identity Module (SIM) in the wireless |
| inactive (silence) or can be compressed more, | | | | device, and the device will take on the personal |
| fewer timeslots are used. To facilitate filling in | | | | configurations and information of that user. This |
| gaps left by unused timeslots, calls do frequency | | | | includes telephone numbers, home system, and |
| hopping in GSM. This means that calls will jump | | | | billing information. Although the United States has |
| between channels and timeslots to maximize the | | | | migrated towards CDMA and TDMA as the |
| system's usage. A control channel is used to | | | | premier mode of wireless communications, a large |
| communicate the frequency hopping and other | | | | part of the world uses GSM. |