SRI (Send Routing Information)

Send Routing Information is the MAP operation a gateway MSC uses to query the HLR for the routing number of a mobile subscriber being called. The variant SRI-for-SM does the same for SMS delivery. Both expose subscriber location and reachability information, and are a primary tool used in SS7 location-tracking attacks. SRI is filtered as a Category 2 operation by SS7 firewalls, and SMS Home Routing specifically intercepts SRI-for-SM to hide subscribers from foreign SMSCs.

Categories: Core NetworkSignalingIdentity and Subscriber

SRI 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 SRI in the wider telecom-security picture, review SMSC, MSC, SMS, Signaling Screening, SMS Home Routing and SS7.

Related terms

Related topic hubs

  • SS7 Firewall GSMA FS.11 category 1/2/3 SS7 message screening at the STP edge.
  • Signaling Firewall Unified SS7/Diameter/GTP/SMS signaling firewall framework.
  • SMS Firewall SMS spam, phishing, A2P bypass and MAP-layer SMS filtering.
  • SS7 Security SS7/MAP/CAP/SCCP attacks and defenses across 2G/3G interconnect.

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