CSFB (Circuit-Switched Fallback)

Circuit Switched Fallback is the 3GPP mechanism (TS 23.272) that lets a 4G-only LTE network deliver legacy circuit-switched voice by temporarily moving the device to 2G/3G for the call. CSFB has higher call-setup latency and lower throughput than VoLTE and is being retired as VoLTE/VoNR coverage matures; it also reintroduces the security exposure of GSM/UMTS for the duration of the call.

Categories: Radio Access NetworkProtocols and StandardsIoT

CSFB 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 security is written into standards from 3GPP, GSMA, ETSI, IETF and ITU-T. Understanding which body owns which specification, and how they interlock, is essential for both design and audit work.

To place CSFB in the wider telecom-security picture, review 5G, MTSI, 6G, Jitter, LEO and LTE-Advanced (LTE-A): each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

Related topic hubs

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.