Protocols BroadNet answer

What is SS7?

Last reviewed July 22, 20261 min readReviewed by BroadNet engineering

Quick answer

SS7 (Signalling System No. 7) is the ITU-T-defined control-plane signalling system that 2G and 3G mobile networks use for call setup, mobility management, and SMS routing. Its layered stack — MTP, SCCP, TCAP, and MAP — carries the SendRoutingInfoForSM and MT-ForwardSM operations that deliver every cross-operator SMS to a handset. On 4G and 5G, Diameter and HTTP/2 signalling take over, but SS7 still underpins the majority of SMS delivered today.

Plain-language definitionVendor-neutralReviewed July 22, 2026

The long answer

Everything worth knowing, nothing that isn't.

§01

The SS7 stack, layer by layer

MTP (Message Transfer Part) is the transport; SCCP (Signalling Connection Control Part) adds global-title routing; TCAP (Transaction Capabilities) handles dialogues; and MAP (Mobile Application Part) is the mobile application layer that actually carries SMS and location operations. Over IP, SS7 rides on SIGTRAN. See /answers/ss7-map-explained and /answers/what-is-sigtran.

§02

Why SS7 is a security concern

SS7 was designed for a small, trusted club of state telcos, so peers largely trust each other with no per-message authentication. That trust is abused for location tracking and SMS interception — most notoriously via SendRoutingInfoForSM harvesting. GSMA FS.07 and FS.11 define the signalling-firewall controls that close these holes; BroadNet operates one at /operators/ss7-firewall.

BNWritten by the BroadNet engineering team·Operating carrier-grade messaging since 2003, headquartered in Dubai·Editorial standards

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