In 5G, there are in general two operational modes, the tight interworking mode and standalone mode. In the tight interworking mode, a 5G NR eNodeB should work together with a LTE eNodeB, e.g. via dual connectivity or carrier aggregation. The LTE eNodeB will work as an anchor eNodeB for the 5G NR eNodeB. In a standalone mode, the 5G NR eNodeB could work independent from the assistance of the LTE eNodeB.

In 3GPP document R2-162965, “RAN interworking between NR and LTE”, 3GPP TSG-RAN WG2 Meeting #93bis, Dubrovnik, Croatia, 11-15 Apr. 2016, a protocol architecture of 5G user and control planes are presented. In this architecture, control signaling of NR RAN (Radio Access Network) is transferred via LTE data bearer, which could re-use existing LTE procedures with minimized modifications.

In 3GPP document R2-162753, “Tight integration of the New Radio interface (NR) and LTE: Control Plane design”, 3GPP TSG-RAN WG2 #93bis, Dubrovnik, Croatia, 11-15 Apr. 2016, a dual RRC is proposed in which two separate RRC entities, e.g. LTE eNodeB and NR eNodeB, can generate RRC messages to the UE. Control-plane diversity can be provided by means of PDCP (Packet Data Convergence Protocol) level split and combining. Local configuration of lower layers is possible. The coordination of RRM (Radio Resource Management) functions between NR and LTE RATs may be required.