S-CSCF (Serving Call Session Control Function)

Also known as: Serving CSCF, Serving Call Session Control Function

S-CSCF is the central SIP registrar and session controller in the IMS. It authenticates users during IMS-AKA registration using authentication vectors fetched from the HSS over Cx, applies initial Filter Criteria to trigger Application Servers over the ISC interface, and routes originating and terminating SIP sessions. Compromise or misconfiguration of the S-CSCF can enable identity spoofing, service abuse, and lawful interception evasion.

Categories: SignalingInternet and Routing

S-CSCF in context

Signaling protocols carry the control-plane messages that set up calls, register subscribers and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA as top-tier telecom risk.

Telecom networks depend on Internet-style routing (BGP, DNS, MPLS) for interconnect. Route hijacks and DNS abuse can degrade or intercept signaling, which is why RPKI and DNSSEC are now standard hardening for carrier networks.

To place S-CSCF in the wider telecom-security picture, review Exposure Mapping, ISDN, MUX, Trunk, P-CSCF and MGCF — 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.