5G-NR

Talk about MCG /SCG and Split Bearers For EN-DC three bearer types exist those are 1.        MCG Bearer 2.        SCG Bearer 3.        Split Bearer In ENDC , Network can configure either E-utran PDCP or NR PDCP for MCG bearer whereas NR PDCP is must for SCG bearer and Split bearer Data Flow : MCG Bearer Using NR PDCP User plane data flow from the NR PDCP to LTE RlC Via MenB MCG Bearer using E-utran PDCP User plane data flow from the E-utran PDCP to LTE RlC Via MenB SCG bearer SCG bearer always Uses NR PDCP , and the data flow is from NR -PDCP to NR-RLC and NR-MAC via Senb Split Bearer Split bearer also Uses NR PDCP and the data flow is from NR-PDCP to LTE-RLC & NR-RLC For ex:  DRB -5 -LCID-4 (LTE-RLC ) and LCID-5(NR-RLC) NR PDCP can be created using R15 IE's i.e NR radio bearer config information -NRRadioBearerConfig will allow to configure DRB'

Talk about Dual connectivity In a Simple words Dual connectivity means UE can get resources from two different enodeB's that is Master Enodeb and Secondary Enodeb . Sometime back in Rel12 of 3GPP has introduced this Dual connectivity concept but for NR deployment dual connectivity plays major role . In NR , E-Utran NR dual connectivity (EN-DC) will have two nodes 1.       First one is Master Enb i.e. Enb (LTE) and 2.       second one is Secondary Enb i.e. gNB (NR) So , First UE will connect to one Enb that acts as Master Enb and the other one will act as Secondary Enb . For EN-DC , UE will connect to LTE (i.e Menb ) and later UE will get an access to Senb via SCG addition procedure . For EN-DC 3GPP specifies three different types of bearer i.e. (MCG,SCG,SPLIT).  For more details about Multi Rat dual connectivity you can refer spec 37.340