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Collaboration, Voice & AV · Intermediate

Signaling System 7 (SS7)

The carrier-grade out-of-band signaling network used between PSTN switches for call setup, routing and number portability.

Definition

SS7 is a protocol suite (MTP, ISUP, SCCP, TCAP and others) that carries call control and database queries between telephone switches over dedicated signaling links. ISUP sets up and releases trunks between switches, and TCAP supports services such as toll-free lookup and local number portability. SS7 has known security weaknesses that allow location tracking and SMS interception because it trusts signaling partners.

Example

A long-distance call uses ISUP IAM, ACM and ANM messages to reserve and connect trunks between carrier switches.

Exam tip

SS7 is a carrier technology; enterprise systems normally see its effects through PRI or SIP trunks rather than configuring it directly.

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