In NSA mobility management several steps are followed once Ue goes from one SgNB (Secondary gNodeb) to another one, through the MeNB (Master eNodeb)
- First we have initial NSA access which is the same as LTE access.
- Then eNodeB delivers event B1 measurement configuration for NR SgNB addition.
- After this  eNodeB chooses whether Option3 or Option3X is used. (Option 3x is the mostly preferred by operators)
Below reminder of the main important procedure during a mobility management:
- SgNB addition: The eNodeB periodically adds an SgNB based on service volumes for a UE after an initial access, incoming handover, incoming reestablishment, or initial addition
- SgNB change: where we have an intra-frequency handover between gNodeBs
- SgNB release: The UE moves out of the gNodeB coverage area, event A2 is reported
- MeNB handover without SgNB change: Intra-/inter-frequency handover within a gNodeB or between gNodeBs based on event A3 or event A4
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