eCSFB performs CS call setup while the UE still camp on LTE. after the UE redirect to legacy CS domain, the UE can start CS communication immediately.
About CSFB read here.
For further details i suggest you suggest you 3GPP TS 23.272 - CSFB in EPS
In LTE all operators use CSFB, my question is if they start using VoLTE then what would they gain or simply why operators use CSFB in place of VoLTE?
What will the first process after csfb call completion cell reselectin or TAU procedure?
How UE latch to the UTRAN in CSFB?Say UE connected to LTE and when UE wants to make an call then it has to move to UTRAN, in this scenario how UE leaves LTE and connects to 3G/2G. can anyone explain in detail with call-flow.
Assuming one case when UE was in LTE network and data transmission was ongoing. Due to incoming voice call, UE leaves LTE network and moves to legacy network to finish voice call. I want to know what will happen with ongoing data session in LTE network. Does the LTE network deletes UE context ? Does the LTE network buffers UE data coming in downlink direction ? Or UE establishes voice as well as data session is legacy network and he continues voice and data services (less through due to legacy network speed) in case UE and legacy network both support DTM (Dual transmission mode) ?
