GSM (Global System for Mobile Communications)

The Global System for Mobile Communications is the 1991 ETSI/3GPP 2G digital cellular standard that became the dominant mobile technology of the 1990s and 2000s, defining the architecture (BTS/BSC/MSC/HLR), the SS7 interconnect model, and SMS. GSM uses A5/1, A5/2, and A5/3 air-interface ciphers, all of which have known weaknesses (A5/2 fully broken, A5/1 practical for well-resourced attackers), and lacks mutual authentication. Most operators are sunsetting GSM in favour of LTE and 5G.

Categories: Radio Access NetworkCore NetworkSignaling

GSM in context

The radio access network is where mobile devices attach to the operator's infrastructure. Attacks in this layer include IMSI catching, rogue base stations and downgrade attacks; defenses rest on mutual authentication, integrity-protected signaling and Open RAN supply-chain hygiene.

The mobile core carries subscriber sessions, mobility and policy. In 4G it is the EPC (MME, HSS, S/PGW); in 5G it is the Service-Based Architecture with AMF, SMF, UPF, AUSF, UDM and the NRF.

To place GSM in the wider telecom-security picture, review 5G SA, AMF, Base Station (BS), Capacity Planning, CAPEX and CSCF — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

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Browse the full TelcoSec Glossary, the Ultimate Guide to Mobile Network Security, or the P1 Arsenal of telecom-security tools.