X3 (LI) (Lawful Interception X3 Interface — Content of Communication)

Also known as: LI X3, X3 LI interface

X3 is the ETSI lawful-interception interface (TS 103 221-2) that carries Content of Communication (CC) — the actual voice, SMS payload, VoLTE/VoNR media or user-plane packets — from the POI/MF to the LEMF. Traffic is framed with correlation identifiers matching X2 IRI events and is protected in transit inside the LI network.

Categories: Threats and AttacksProtocols and StandardsRegulation and Compliance

X3 (LI) in context

Telecom threats range from opportunistic SMS phishing and SIM swap to nation-state grade location tracking and lawful-interception abuse. The common thread is that most attacks exploit the inherited trust model of legacy signaling. SS7 and Diameter were designed for a closed operator community that no longer exists.

Telecom security is written into standards from 3GPP, GSMA, ETSI, IETF and ITU-T. Understanding which body owns which specification, and how the specs interlock (for example 3GPP TS 33.501 with GSMA FS.34 for 5G SBA security), is essential for both design and audit work.

To place X3 (LI) in the wider telecom-security picture, review X2 (LI), ETSI TS 103 221, X1, IRI, CC (LI) and HI2.

Related terms

Equipment

Lawful interception systems (ADMF, mediation, HI1/2/3)

Articles in the P1 mobile network security guide

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