GSM-R is based on the cellular GSM technology, with further enhancements specific to the requirements of railroad operation, such as train control.
In general, GSM-R uses characteristics that are identical or similar to those of the GSM system, such as frequency spacing (200 kHz), modulation (Gaussian minimum shift keying, GMSK) and access type (TDMA, TDD/FDD). The frequencies of GSM-R are extended below the frequencies of the GSM-900 standard.
The general packet radio services (GPRS) for data communications up to 14.4 kbit/s is supported by GSM-R for data transport in the same way as with the regular GSM system. It serves customized applications such as automatic train control (ATC) and electronic train control system (ETCS) for remote or automatic control of train movements and monitoring as well as functional addressing (calling a user by an assigned function rather than by a fixed number) and location-dependent addressing.
Additional railway-specific characteristics include advanced speech call items (ASCI) such as voice group call service (VGCS) and voice broadcast service (VBS) to communicate to a group of handsets simultaneously. GSM-R mobile phones are similar to cellular mobile phones but are more robust. They also offer extended functionality and a different user interface to utilize the additional applications.