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

The mobile core is where subscriber sessions, mobility and policy live. 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. Core exposure is the difference between a single-subscriber leak and a fleet-wide breach.

To place GSM in the wider telecom-security picture, review Base Station (BS), LTE, Mobile Network, GPRS, Diameter and AMPS.

Related terms

Related topic hubs

  • Signaling Firewall Unified SS7/Diameter/GTP/SMS signaling firewall framework.
  • Diameter Attacks S6a IDR/PUR/CLR abuse, subscriber tracking, LTE signaling attacks.
  • SS7 Security SS7/MAP/CAP/SCCP attacks and defenses across 2G/3G interconnect.
  • SS7 Firewall GSMA FS.11 category 1/2/3 SS7 message screening at the STP edge.

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