On the right side of FIG. 13, a NR cell is tightly integrated in a LTE cell via NextGen Core. The LTE eNodeB and the NR eNodeB communicate with the NextGen Core, wherein the LTE eNodeB performs control plane CP and user plane UP communication with the NextGen Core and the NR eNodeB performs only user plane UP communication with the NextGen Core. The LTE eNodeB and the NR eNodeB can perform control plane CP and user plane UP communication with each other.
Hence, in all three scenarios, there exists one C-plane connection between the core network CN and the RAN. U-plane data UP is routed to the RAN directly through the CN on a bearer basis (line marked with UP in FIG. 13). Alternatively, the U-plane data can be included in the same bearer as the control plane data CP at the RAN, wherein the bearer is split accordingly (see line CP+UP between the eNodeBs).
