At the beginning of the 1990s, GSM, the Global System for Mobile Communications triggered an unprecedented change in the way people communicate with each other. While earlier analog wireless systems were used by only a few people, GSM is used by over 5 billion subscribers worldwide in 2014. This has mostly been achieved by the steady improvements in all areas of telecommunication technology and the resulting steady price reductions for both infrastructure equipment and mobile devices.
This chapter discusses the architecture of this system, which also forms the basis for the packet-switched extension called General Packet Radio Service (GPRS), discussed in Chapter 2, for the Universal Mobile Telecommunications System (UMTS), which is described in Chapter 3 and Long-Term Evolution (LTE), which is discussed in Chapter 4.
While the first designs of GSM date back to the middle of the 1980s, GSM is still the most widely used wireless technology worldwide and it is not expected to change any time soon. Despite its age and the evolution toward UMTS and LTE, GSM itself continues to be developed. As shown in this chapter, GSM has been enhanced with many new features in recent years.
Therefore, many operators continue to invest in their GSM networks in addition to their UMTS and LTE activities to introduce new functionality and to lower their operational cost. In addition, it should be mentioned at this point that the industry has standardized on a new solution for voice telephony for LTE that has only little in common with GSM anymore.
Although standardization is complete, efforts to roll out the new system are significant, and at the time of writing, there were only few voice-over LTE systems to be found in practice. Current LTE-capable devices thus continue using GSM and UMTS networks for voice telephony with a fallback mechanism.