X1 (Lawful Interception X1 Interface (ETSI TS 103 221-1))

Also known as: LI X1, X1 interface, ETSI TS 103 221-1

X1 is the ETSI-defined administration interface between a Law Enforcement Monitoring Facility (via the ADMF) and the Point of Interception (POI) inside a telecom network. It carries provisioning of intercept warrants — target identifiers, time bounds and delivery destinations — using an HTTPS/JSON schema defined in ETSI TS 103 221-1, and is strictly segregated from user traffic.

Categories: Radio Access NetworkThreats and AttacksProtocols and Standards

X1 in context

The radio access network is where mobile devices attach to the operator's infrastructure. Attacks in this layer include IMSI catching, rogue base stations and downgrade attacks; defenses rest on mutual authentication, integrity-protected signaling and Open RAN supply-chain hygiene.

Telecom threats range from opportunistic SMS phishing and SIM swap to nation-state grade location tracking. The common thread is that most attacks exploit the inherited trust model of legacy signaling protocols.

To place X1 in the wider telecom-security picture, review ETSI, Incident Response, Modulation, OT, RTSP and Telnet — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

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.