- GSM - Global System for Mobile Communications - developed in Europe and later used by AT&T (2nd generation)
- Added SIM - subscriber identity module: subscriber identification number, network subscriber is authorized, encryption keys. The SIM roams, not the device.
- Transmissions are encrypted (APMS was plain). But conversation in the land line is clear
- GSM designed to support data and image services, data rates up to 9.6 kbps supported.
- GSM entities: Subscriber, base transceiver, base station controllers, mobile services switching center (MSSC).
- The homelocation register database (HLR) keeps permanent and temporary location information -- Important temporary information: the location the subscriber is in VLR - visitor location register database.
- GSM spectral allocation 25 MHz base transmission (935-960MHz) and 25 MHZ for mobile transmission (890-915 MHz).
- GSM uses a combination of FDMA and TDMA in each frequency of 200kHz which provides 124 full-duplex channels - traffic and control. Traffic carries digitized voice or data.
- GSM uses FDM and divides the spectrum in 124 channels, then split each in eight parts (slots) using TDM. A slot carriers 156 bits. Eight slots form a frame. Twenty-six frames form a multiframe. Due to its complexity the GSM reuse factor is as low as 3.
- Each 3kHz voice channel is digitized and compressed to a 13-kbps digital signal. The channel data rate (without going in details of its calculation) is 270.8 kbps.