STP (Signal Transfer Point)

Also known as: Signalling Transfer Point, Signaling Transfer Point

The Signal Transfer Point is the packet switch of an SS7/SIGTRAN network, routing SS7 traffic at the MTP and SCCP layers. It relays traffic between signalling endpoints such as MSCs, HLRs and SMSCs rather than originating it. Sitting at the interconnect edge, the STP is where operators enforce SS7 message screening and GSMA FS.11 category filtering, which makes it the primary control point for signalling security.

Categories: SignalingRoaming and InterconnectSecurity Controls

STP in context

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.

Roaming and interconnect are where two operators, often with an IPX or GRX carrier in between, exchange signaling and user-plane traffic. Trust boundaries here are the primary attack surface for location tracking, SMS interception and fraud, which is why GSMA now mandates SEPP with PRINS on 5G interconnect.

To place STP in the wider telecom-security picture, review SS7, Signaling Firewall, Global Title Abuse, MAP, MSC and HLR.

Related terms

Equipment

STPs and signalling gateways (SS7/SIGTRAN)

Articles in the P1 mobile network security guide

Related topic hubs

  • SS7 Security SS7/MAP/CAP/SCCP attacks and defenses across 2G/3G interconnect.
  • 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.

More from the TelcoSec Glossary

Browse the full TelcoSec Glossary, the Ultimate Guide to Mobile Network Security, or the P1 Arsenal of telecom-security tools.