P-CSCF Discovery (Proxy-CSCF Discovery)

P-CSCF discovery is the procedure by which a VoLTE/VoNR UE learns the IP address(es) of its serving Proxy-CSCF: via DHCP options 120/135 (RFC 3319/3361), PCO in EPS/5GS attach (TS 29.061/29.503), or via home-domain DNS NAPTR/SRV lookup. The selected P-CSCF becomes the SIP entry point and IMS-AKA anchor for the subscriber.

Categories: Radio Access NetworkSignalingThreats and Attacks

P-CSCF Discovery 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.

Signaling protocols carry the control-plane instructions that set up calls, register subscribers, hand over sessions 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 FS.11 / FS.19 / FS.20 as a top-tier telecom risk.

To place P-CSCF Discovery in the wider telecom-security picture, review Bidding-Down Attack, Lawful Interception Abuse Risk, Lawful Interception Architecture, Revenue Assurance, Telecom Penetration Testing and Chain of Custody.

Related terms

Equipment

IMS core (CSCF, TAS, MRF, MGCF, BGCF)

Articles in the P1 mobile network security guide

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