5G • Services
EPS Fallback
Voice EPS Fallback Procedure
Handover mechanism redirecting voice calls from 5G Standalone to 4G LTE when 5G voice is unavailable.
Technical Explanation
During early 5G SA rollouts where VoNR is not yet deployed across all base stations, EPS Fallback provides voice continuity. When a voice call is initiated, the gNodeB detects 5QI 1 QoS flow establishment and triggers immediate inter-RAT handover or redirection to 4G LTE over the N26 interface.
Key Functions
- Redirects voice calls from 5G SA to legacy 4G LTE VoLTE infrastructure
- Triggered automatically upon 5QI 1 voice bearer setup in non-VoNR zones
- Guarantees reliable call completion during transition to full VoNR coverage
Specifications
3GPP TS 23.501, TS 23.502
Interfaces
N26Uu
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