The following clauses describe the functions supported in Xn interface.
These functions allow for managing of signalling associations between NG-RAN nodes, surveying the Xn interface and recovering from errors.
This function allows for the initial setup of an Xn interface between two NG-RAN nodes, including exchange of application level data.
This function allows the reporting of general error situations on application level.
This function allows an NG-RAN node to inform a second NG-RAN node that it has recovered from an abnormal failure and that either all or some of the contexts (except the application level data) related to the first node and stored in the second shall be deleted, and the associated resources released.
This function allows two NG-RAN nodes to update application level data at any time.
This function allows two NG-RAN nodes to remove the respective Xn interface.
This function allows the exchange of information between source and target NG-RAN nodes in order to initiate the handover of a certain UE to the target.
This function allows informing an already prepared target NG-RAN node that a prepared handover will not take place. It allows releasing the resources allocated during a preparation.
The Retrieve UE context function is used for a NG-RAN node to retrieve UE context from another one.
The RAN paging function allows a NG-RAN node to initiate the paging for a UE in the inactive state.
The data forwarding control function allows establishing and releasing transport bearers between source and target NG-RAN nodes for data forwarding.
This function allows informing a source NG-RAN node that the UE has successfully accessed a target NG-RAN node.
This function allows informing a source NG-RAN node that resources reserved for candidate target cell(s) during a conditional handover preparation are about to be released by the target NG-RAN node.
The dual connectivity function enables usage of additional resources in a secondary node in the NG-RAN.
This function enables decreasing energy consumption by indication of cell activation/deactivation over the Xn interface.
This function enables coordination of cell resource usage between two NG-RAN nodes.
This function enables the NG-RAN node to report Secondary RAT usage data information in case of MR-DC with 5GC, either with a dedicated procedure or by including Secondary RAT usage data information in other messages.
The Trace function provides means to control trace sessions for a UE over Xn interface.
This function allows exchanging resource status and traffic load information between NG-RAN nodes, such that the NG-RAN node can control the traffic load appropriately.
This function allows two NG-RAN nodes to exchange information in order to support self-optimization functionality.
This function is used to deliver F1-C traffic between the M-NG-RAN node and the S-NG-RAN node serving a dual-connected IAB-node, where the F1-C traffic is either received from the IAB-node or sent to the IAB-node.
This function allows the exchange of information between the F1-terminating IAB-donor-CU and the non-F1-terminating IAB-donor-CU of a boundary IAB-node, for the purpose of managing the migration of the boundary and descendant IAB-node traffic between the topologies managed by the two IAB-donor-CUs.
This function is used to exchange information between the F1-terminating IAB-donor-CU and the non-F1-terminating IAB-donor-CU of a boundary IAB-node in order to support resource multiplexing between the IAB-MT and the IAB-DU of the boundary IAB-node.
This function supports small data transmission sessions in RRC_INACTIVE both with and without anchor relocation, in case the UE is served by a new NG-RAN node.
The Partial UE Context Transfer function is used for the last serving NG-RAN node to provide part of the UE Context to the receiving gNB.
The QMC function provides means to support the mobility of QMC sessions over the Xn interface.
This function is used to support the management of MBS Sessions, including the addition of MBS related information in interface management and mobility procedures, and the support of RAN Multicast paging.
The data transfer function allows the transfer of data between NG-RAN nodes to support dual connectivity or mobility operation.
The flow control function enables a NG-RAN node receiving user plane data from a second NG-RAN node to provide feedback information associated with the data flow.
The assistance information function enables a NG-RAN node receiving user plane data from a second NG-RAN node to provide assistance information to the second node (e.g. related to radio conditions).
The fast retransmission function provides coordination between PDCP-hosting node and corresponding node in case of outage in one of the nodes, to enables the node in good RF conditions to handle data previously forwarded to the node in outage.