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 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.

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.

To place SRI in the wider telecom-security picture, review IAMF, MSC, OTP Bypass Attacks, SMS, SMSC and VoLTE — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

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