FS.21 (Interconnect Signalling Security Recommendations)

In telecom networks, GSMA FS.21 consolidates interconnect signaling security recommendations across SS7, Diameter, and GTP for mobile operators, complementing FS.07, FS.11, FS.19, and FS.20 with cross-protocol guidance.

Categories: Core NetworkSignalingRoaming and Interconnect

FS.21 in context

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.

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 FS.21 in the wider telecom-security picture, review FS.07, MSSP, Defense in Depth, GTP-U Smuggling, Lateral Movement (Telecom) and FASG.

Related terms

Related topic hubs

  • Signaling Firewall Unified SS7/Diameter/GTP/SMS signaling firewall framework.
  • SS7 Firewall GSMA FS.11 category 1/2/3 SS7 message screening at the STP edge.
  • Diameter Firewall GSMA FS.19 screening at the Diameter Edge Agent on S6a/S9/S13.
  • GTP Firewall GSMA FS.20 GTP-C/GTP-U screening on GRX/IPX borders.

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