S1 Application Protocol

S1AP 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 S1AP in the wider telecom-security picture, review NGAP, RANAP, Diameter, IPsec, IMS-AKA and N2.

Related terms

• NGAP
• RANAP
• Diameter
• IPsec
• IMS-AKA
• N2
• Man-in-the-Middle (MITM)
• SC

Related topic hubs

• LTE Security Training Training on 4G/LTE core, Diameter, NAS and RRC security.
• NAS Security Non-Access Stratum security, integrity and ciphering algorithms.
• Diameter Security 4G/LTE Diameter threats across IPX/roaming and DEA defenses.
• Diameter Attacks S6a IDR/PUR/CLR abuse, subscriber tracking, LTE signaling attacks.

More from the TelcoSec Glossary

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