SS7signaling

SS7 signaling, or Signaling System No. 7, is a family of telecommunication signaling protocols used to set up, manage, and tear down telephone calls and to provide number translation, roaming, and other services in PSTN and mobile networks. It operates as an out-of-band signaling system separate from the voice channels, enabling fast and reliable control information exchange between network elements.

The core network consists of signaling points such as Signal Transfer Points (STP), Service Switching Points (SSP) at switching centers, and Service Control Points (SCP) that host databases. The protocol stack includes the Message Transfer Part (MTP) levels 1–3 for signaling transport, ISUP for call control signaling, SCCP for routing and global title translations, and TCAP for database and transaction-based interactions. Mobile networks also rely on parts such as MAP for subscriber data and roaming, along with related applications.

SS7 enables functions such as establishing and releasing calls, number translation, roaming and handoff coordination, toll-free services, Intelligent Network services, and prepaid billing interfaces. It underpins inter-exchange signaling across PSTN and is used by both fixed and mobile networks, including interconnects between operators.

Security and evolution: SS7 has known vulnerabilities that can reveal subscriber location or enable intercepts; operators mitigate with perimeter controls, filtering, and firewalling. Modern trends include carrying SS7 signaling over IP using SIGTRAN protocols (M2PA, M3UA, SUA) to provide reliability on IP networks, and a gradual migration toward Diameter and IP-based signaling in 4G/5G.