CSCF (Call Session Control Function)

The Call Session Control Function is the SIP-based control plane of the IMS network. It exists in three roles: the Proxy-CSCF, the first contact for the UE; the Interrogating-CSCF, which routes registrations to the correct Serving-CSCF; and the Serving-CSCF, which handles registration, authentication via the HSS over Diameter Cx, and call control. CSCFs anchor VoLTE, VoNR, and RCS services and are exposed to SIP abuse such as registration hijacking, toll fraud, and DoS.

Categories: Radio Access NetworkCore NetworkSignaling

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

Related terms

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