5G XnAP Messages – Complete Xn Interface Message List & Procedures
XnAP, or Xn Application Protocol, is the control-plane protocol used on the Xn-C interface between NG-RAN nodes such as gNBs and ng-eNBs. Defined in 3GPP TS 38.423, XnAP supports inter-node setup, Xn handover, target-side resource preparation, SN status transfer, UE context release, paging coordination, RAN configuration transfer, and other mobility-related coordination between neighbouring RAN nodes.
Use this page to search or browse 5G XnAP messages by procedure category. Each message page explains the message direction, trigger, call-flow role, key Information Elements, and practical troubleshooting notes.
Based on 3GPP TS 38.423
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Xn Interface Management Messages
Non-UE-associated messages used to establish, reset, update, and manage the Xn interface between neighbouring NG-RAN nodes.
Xn Setup Request
Starts Xn interface setup and advertises node identity and served cells.
Xn Setup Response
Accepts Xn setup and returns peer configuration context.
Xn Setup Failure
Rejects Xn setup with cause and optional retry handling.
Coming soonXn Reset
Requests reset of Xn interface or UE-associated contexts.
Coming soonXn Reset Acknowledge
Confirms Xn reset handling.
Coming soonXn Configuration Update
Updates Xn peer configuration and served-cell information.
Coming soonXn Configuration Update Acknowledge
Confirms successful Xn configuration update.
Coming soonXn Configuration Update Failure
Rejects Xn configuration update with cause.
Coming soonError Indication
Reports protocol errors or invalid XnAP procedure handling.
Coming soonHandover Preparation Messages
UE-associated messages used when the source NG-RAN prepares target-side resources over Xn before handover execution.
Handover Request
Requests target-side handover resource preparation.
Handover Request Acknowledge
Confirms target-side handover preparation.
Handover Preparation Failure
Reports failed target-side handover preparation.
Coming soonHandover Execution / Cleanup Messages
Messages used after handover preparation for cleanup, cancellation, and release of old UE resources.
UE Context Release
Informs the peer that old UE resources may be released.
Handover Cancel
Cancels an ongoing Xn handover preparation.
Coming soonHandover Cancel Acknowledge
Confirms cancellation of an Xn handover.
Coming soonStatus Transfer Messages
Messages used to transfer PDCP sequence number and HFN status between source and target nodes during handover or context transfer.
UE Context Management Messages
Messages used for UE context transfer, retrieval, release, and inter-node UE context coordination.
Retrieve UE Context Request
Requests retrieval of UE context from a peer node.
Coming soonRetrieve UE Context Response
Returns requested UE context information.
Coming soonRetrieve UE Context Failure
Reports failed UE context retrieval.
Coming soonUE Context Release
Informs the peer that old UE resources may be released.
UE Context Release Request
Requests release of UE context at the peer node.
Coming soonUE Context Release Complete
Confirms UE context release completion.
Coming soonPaging Messages
Messages used for paging coordination between NG-RAN nodes.
RAN Paging
Coordinates RAN paging between neighbouring nodes.
Coming soonRAN Paging Request
Requests peer-side RAN paging handling.
Coming soonMulticast Group Paging
Coordinates multicast group paging for MBS-related service.
Coming soonRAN Configuration Transfer Messages
Messages used to transfer RAN configuration or inter-node configuration information over Xn.
Uplink RAN Configuration Transfer
Transfers RAN configuration information in the uplink direction.
Coming soonDownlink RAN Configuration Transfer
Transfers RAN configuration information in the downlink direction.
Coming soonMobility / Dual Connectivity Messages
Messages used for dual connectivity, secondary node procedures, conditional handover, and mobility-related inter-node coordination.
S-NG-RAN Node Addition Request
Requests secondary NG-RAN node addition for dual connectivity.
Coming soonS-NG-RAN Node Addition Request Acknowledge
Accepts secondary NG-RAN node addition.
Coming soonS-NG-RAN Node Addition Request Reject
Rejects secondary NG-RAN node addition.
Coming soonS-NG-RAN Node Modification Request
Requests secondary NG-RAN node modification.
Coming soonS-NG-RAN Node Modification Request Acknowledge
Accepts secondary NG-RAN node modification.
Coming soonS-NG-RAN Node Modification Request Reject
Rejects secondary NG-RAN node modification.
Coming soonS-NG-RAN Node Release Request
Requests release of secondary NG-RAN node resources.
Coming soonS-NG-RAN Node Release Confirm
Confirms secondary NG-RAN node release.
Coming soonConditional Handover Cancel
Cancels a conditional handover branch.
Coming soonConditional Handover Cancel Acknowledge
Confirms conditional handover cancellation.
Coming soonError Handling Messages
Messages used to report protocol errors or unsuccessful XnAP procedure handling.
Error Indication
Reports protocol errors or invalid XnAP procedure handling.
Coming soonHandover Preparation Failure
Reports failed target-side handover preparation.
Coming soonXn Setup Failure
Rejects Xn setup with cause and optional retry handling.
Coming soonXn Configuration Update Failure
Rejects Xn configuration update with cause.
Coming soonAdvanced / Release-Specific Messages
Additional XnAP messages used for release-specific features, MBS, positioning support, inter-node coordination, or advanced mobility.
Most Used XnAP Messages
Common XnAP Procedure Flows
Xn Setup Flow
Xn Setup Request -> Xn Setup Response / Xn Setup Failure
Xn Handover Preparation Flow
Handover Request -> Handover Request Acknowledge / Handover Preparation Failure
Status Transfer Flow
SN Status Transfer
Handover Cleanup Flow
UE Context Release
Xn Reset Flow
Xn Reset -> Xn Reset Acknowledge
Xn Configuration Update Flow
Xn Configuration Update -> Acknowledge / Failure
FAQ
What is XnAP in 5G?
XnAP is the Xn Application Protocol used between NG-RAN nodes over the Xn-C interface.
Which interface uses XnAP?
XnAP is used on the Xn-C control-plane interface between neighbouring NG-RAN nodes such as gNBs and ng-eNBs.
Which 3GPP specification defines XnAP?
XnAP is defined in 3GPP TS 38.423.
What is the difference between XnAP and NGAP?
NGAP runs between NG-RAN and AMF over N2, while XnAP runs between neighbouring NG-RAN nodes.
What is XnAP used for during handover?
XnAP is used for Xn handover, target resource preparation, status transfer, and context cleanup.
What are the most important XnAP messages?
Common XnAP messages include Xn Setup Request, Xn Setup Response, Handover Request, Handover Request Acknowledge, SN Status Transfer, UE Context Release, Xn Reset, and Error Indication.
What is SN Status Transfer in XnAP?
SN Status Transfer carries PDCP status information from source to target during handover.
What is UE Context Release in XnAP?
UE Context Release tells the peer node that old UE resources may be released.
References
- 3GPP TS 38.423 – NG-RAN; Xn Application Protocol (XnAP)
- 3GPP TS 38.401 – NG-RAN architecture description
- 3GPP TS 38.300 – NR and NG-RAN overall description
- 3GPP TS 38.331 – NR RRC protocol specification