In EPC-based NSA networking, if a UE supports both LTE and New Radio (NR) non-Standalone(NSA), it can connects that to Dual connectivity (DC) to both an LTE eNodeb and NR gNodeb, and use resources provided by these base stations for data transmission.
Data can be split between the two base stations. Dual connectivity can be implented using the aggregation of up to five component carriers (CCs) on the eNodeb side and the aggreagation of up to two CCs on the gNodeb side.
The main option used in 5G NSA is the option 3x where the LTE eNodeb is the master eNodeb (MeNB) and the NR gNodeb is the secondary gNodeb (SgNB).
The user plane data can be split by the eNodeb or gNodeb
In Option 3x, the gNodeb is the data split anchor.
- The gNodeb distributes the user-plane data to the enNodeb and itself, and the bearer is called the secondary cell group (SCG) split bearer.
- The Data is split at the PDCP layer of the SgNB to the RLC layer of the MeNB and the RLC layer of the SgNB, and then aggregated at the PDCP layer of the UE Side
What are MeNB, SgNB, MCG and SCG ?
The Master eNodeb (MeNb) of an NSA DC UE is the LTE eNodeb that serves the cell on which the UE is currently camping. In this version, only an LTE eNodeb can be configured as an Menb
The secondary gNodeb (SgNB) of and NSA DC UE is the NR gNobde condigured for the UE Through an RRC message sent by MeNB. In this version, only an NR gNobde can be configured as an SgNB.
The master cell group (MCG) of an NSA DC UE is an LTE cell group configured on the LTE ide
The secondary cell group (SCG) of an NSA DC UE is the NR Cell group configured on the NR Side