Embodiments of a Next Generation Node-B (gNB) and methods of communication are generally described herein. The gNB may be configurable to operate as a source gNB. The gNB may be configured with logical nodes including a gNB central unit (gNB-CU) and a gNB distributed unit (gNB-DU). The gNB-CU may comprise a gNB-CU control plane (gNB-CU-CP) for control-plane functionality, and a gNB-CU user plane (gNB-CU-UP) for user-plane functionality. When a handover of a User Equipment (UE) from the source gNB to a target gNB is performed, the gNB may transfer, from the gNB-DU to the gNB-CU-UP, a downlink data delivery status (DDDS) message to indicate that the gNB-CU-UP is to stop transfer, to the gNB-DU, of downlink data intended for the UE.