5G EPS Fallback – 5G to 4G Handover

A Network Operator providing 5G NR and 4G LTE service, but it may not be possible to have 5G coverage everywhere and at some point when 5G coverage or service not available to 5G system (5GS) may attempt to fallback the RAT to 4G Evolved Packet System (4G-EPS) . EPS Fallback can be defined as the mobility procedure where network trigger the procedure for UE to change Radio Access from 5G to 4G.

We can see following fiugre showing the mobility profile for a UE performing mobility 5G to 4G, 4G to 4G and 4G to 5G. Here we can see the gNB and eNB are co-located and gNB is operating on higher frequency band with lower coverage footprint and eNB operating on lower frequency band with larger coverage footprint.

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In case 5G TAC is not defined in 4G MME, will EPS fallback and return to NR work?