Hi Experts,
What is EPS fallback call in NR?
It is voice fallback.
Similar to fallback 4G to 3G.
Now we have fallback from 5G to 4G.
Ok, means without VoNR.
Is it redirection blind like CSFB?
When 5G Core not connected to IMS and UE need to perform voice call.
Yes kind of gNB release UE and provides 4G cell earfcn for fallback.
Is it for SA or ENDC as well used EPSFB?
It is for SA.
What happen if user initiate voice call during ENDC ongoing data call?
Does it release NR leg and go for VoLET call?
Why it need to release NR?
Let me tell one real example: I have One Plus 8 mobile which does not support VoNR but it support SA.
While doing data session UE can be connected to 5G SA but as soon as I need to make voice call, I need to move to legacy RAT.
And first legacy RAT it would go for LTE which is EPS.
Good example 
Depends on operator’s strategy.
Usually the vendors allow to choose between keeping the PSCELL or remove it once the QCI1 is setup.
I know Huawei also have a dynamic option, which, based on RF metrics, it will decide to remove the NR PSCELL.
Ok, means it is parameter controlled, so voice call can be set up at LTE leg without dropping NR leg for ENDC.
Correct.
Ericsson strongly recommends to tier down the NR leg, especially because they have several limitations related to keeping both without compromising the voice quality.
Samsung releases SgNb if qci-1 bearer set up.
Again add it once qci-1 releases.
What’s the rationale of it if there’s data transfer ongoing in NR leg?
Just trying to understand…
I guess issue is with UL power.
VoLTE uplink coverage reduces with NR uplink ongoing.
Network could release NR leg if avg (tx power higher than threshold for certain time) to ensure voice continuity on cell border only.
It’s purely configuration choice, you can keep, you can release.
Huawei would call it “advanced data call with crystal clear voice on extreme radio environments”.