6 Xn interface procedures

38.4203GPPNG-RANRelease 16TSXn general aspects and principles

6.1 General

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:

– Reset

– 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.