Xn Handover

• Initialy transmission in both UL and DL directions is done via source gNB.
• The UE sends measurement report to inform the gNB that signal from other cell is better than the one in the current cell.
• After report reception the source gNB takes a decision to trigger handover procedure towards target gNB.
• The target gNB starts to prepare resources to serve this UE and when ready acknowledges this to source gNB.
• The source gNB sends handover command message with information about target cell.
• At the same time the source gNB suspends the data transmission and starts forwarding data to target gNB.
• The UE needs to perform random access procedure towards the target cell.
• After successful random access procedure the UE confirms the handover towards target gNB.
• Target gNB starts the DL data transmission and informs the CN about completed handover.
• Data tunnels from Core Network are switched to target gNB.
• The target gNB informs source one that it may release UE resources.