38.4203GPPNG-RANRelease 16TSXn general aspects and principles
The Xn interface supports procedures over the control plane (Xn-C) and user plane (Xn-U).
6.2 Control plane protocol procedures
6.2.1 Mobility management procedures
The mobility management procedures are used to manage the UE mobility in Connected or RRC_Inactive modes:
– Handover Preparation
– Handover Cancel
– SN Status Transfer
– Retrieve UE Context
– RAN Paging
– Xn-U Address Indication
– UE Context Release
– Handover Success Indication
– Conditional Handover Cancel
6.2.2 Dual Connectivity procedures
The dual connectivity procedures are used to add, modify and releases resources for the operation of Dual Connectivity:
– S-NG-RAN-node Addition Preparation
– S-NG-RAN-node Reconfiguration Completion
– M-NG-RAN-node initiated S-NG-RAN-node Modification Preparation
– S-NG-RAN-node initiated S-NG-RAN-node Modification
– M-NG-RAN-node initiated S-NG-RAN-node Release
– S-NG-RAN-node initiated S-NG-RAN-node Release
– S-NG-RAN-node Counter Check
– RRC Transfer
– Notification Control Indication
– Activity Notification
– Secondary RAT Data Usage Report
6.2.3 Global procedures
The global procedures are used to exchange configuration level data between two NG-RAN nodes, or to remove Xn connectivity between two NG-RAN nodes in a controlled manner:
– Xn Setup
– NG-RAN-node Configuration Update
– Xn Removal
6.2.4 Interface Management procedures
The interface management procedures are used to align resources between two NG-RAN nodes in the event of failures, and to report detected protocol errors:
– Error Indication
6.2.5 Energy saving procedures
– Cell Activation procedure: enables an NG-RAN node to request the activation of a previously deactivated cell hosted in another NG-RAN node.
6.2.6 Resource coordination procedures
– E-UTRA – NR Cell Resource Coordination procedure: enables an ng-eNB and a gNB to interact for resource coordination purposes.
6.2.7 UE Tracing procedures
The following procedures are used to trace the UE:
– Trace Start procedure
– Deactivate Trace procedure
6.2.8 Load management procedures
The load management procedures are used by NG-RAN nodes to indicate resource status, overload and traffic load to each other.
– Resource Status Reporting Initiation
– Resource Status Reporting
6.2.9 Data exchange for self-optimisation procedures
The data exchange for self-optimisation procedures are used to transfer failure and mobility related information among NG-RAN nodes to enable self-optimisation
– Failure Indication
– Handover report
– Mobility Settings Change
– Access and Mobility Indication
6.3 User plane protocol procedures
The user plane protocol procedures are used to exchange user plane information between Xn-U protocol peers:
– Transfer of Downlink User Data procedure: enables the node hosting the NR PDCP entity to provide user plane information to the corresponding node.
– Downlink Data Delivery Status procedure: enables the corresponding node to provide feedback to the node hosting the NR PDCP entity.
– Transfer of Assistance Information: enables the corresponding node to provide assistance information to the node hosting the NR PDCP entity.
– Transfer of PDU Session Information procedure: enables an NG-RAN node to provide user plane information associated with the forwarding of data towards a peer NG-RAN node, when using PDU session tunnels.