IMS (IP Multimedia Subsystem)

The IP Multimedia Subsystem is the 3GPP architecture for delivering SIP-based voice, video, messaging, and presence over packet networks. It comprises the P/I/S-CSCF call control elements, the HSS for subscription data, MGCF and MGW for PSTN interworking, and IBCF/TrGW at the interconnect edge. IMS is the foundation of VoLTE, VoWiFi, VoNR, and RCS, and inherits the full SIP threat landscape, registration hijacking, fraud, eavesdropping, and DoS, alongside mobile-specific risks such as IMSI handling.

Categories: Radio Access NetworkCore NetworkSignaling

IMS 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 IMS in the wider telecom-security picture, review CSCF, Mobile Network, TEID, GSM, Interconnection and LTE: each entry cross-references back to this page so you can walk the topic in either direction.

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