NGAP Messages
The NG Application Protocol (NGAP) is the core signalling protocol used on the N2 interface between the NG-RAN (gNB) and the 5G Core (AMF). Defined in 3GPP TS 38.413, NGAP enables major control-plane procedures in 5G, including registration, mobility management, PDU session handling, handovers, paging, reset, and overload control.
This page provides a complete NGAP message reference, covering every message defined in the specification with detailed explanations, call flow context, message direction, and Information Element (IE) breakdowns. Whether you are troubleshooting network issues, analyzing logs, or learning 5G signalling, this guide helps you quickly understand how NGAP messages work in real deployments.
- Procedure context and call flow placement
- Message direction and triggering conditions
- Mandatory and optional IEs
- Practical interpretation for engineers and troubleshooting
Use this hub to explore all NGAP procedures from NG Setup and Handover to Configuration Updates, Reset, and Overload handling, and navigate to detailed message-level pages.
Start typing to search message names, slugs, categories, descriptions, and acronyms.
NAS Transport Messages
Initial UE Message, uplink/downlink NAS transport, NAS non-delivery, and reroute NAS handling.
Initial UE Message
Carries the first uplink NAS message from UE to AMF.
Downlink NAS Transport
Carries downlink NAS signalling from AMF to UE through NG-RAN.
Uplink NAS Transport
Carries uplink NAS signalling from UE to AMF through NG-RAN.
NAS Non Delivery Indication
Reports that a NAS message could not be delivered.
Reroute NAS Request
Requests rerouting of NAS signalling toward another AMF.
UE Context Management Messages
Initial context setup, UE context modification, release, suspend/resume, RRC inactive reporting, and connection establishment indication.
Initial Context Setup Request
Establishes the initial UE context at NG-RAN.
Initial Context Setup Response
Reports successful initial UE context setup.
Initial Context Setup Failure
Reports failed initial UE context setup.
UE Context Release Request
Requests release of a UE-associated NGAP context.
UE Context Release Command
Commands release of UE-associated NGAP resources.
UE Context Release Complete
Confirms UE context release completion.
UE Context Modification Request
Requests modification of established UE context.
UE Context Modification Response
Reports successful UE context modification.
UE Context Modification Failure
Reports failed UE context modification.
UE Context Suspend Request
Requests suspension of a UE context.
UE Context Suspend Response
Confirms successful UE context suspend handling.
UE Context Suspend Failure
Rejects UE context suspend request.
UE Context Resume Request
Requests resumption of a suspended UE context.
UE Context Resume Response
Confirms successful UE context resume.
UE Context Resume Failure
Rejects UE context resume request.
RRC Inactive Transition Report
Reports RRC inactive transition outcome.
Connection Establishment Indication
Indicates establishment of a UE-associated connection.
Mobility Management Messages
Handover preparation, handover resource allocation, path switch, RAN status transfer, and cancellation messages.
Handover Required
Starts handover preparation from source NG-RAN.
Handover Command
Commands source NG-RAN to execute handover after target preparation succeeds.
Handover Preparation Failure
Reports unsuccessful handover preparation.
Handover Request
Requests target-side handover resource allocation.
Handover Request Acknowledge
Confirms target-side handover resource allocation.
Handover Failure
Reports target-side handover resource allocation failure.
Handover Notify
Reports successful UE arrival at target NG-RAN after handover.
Handover Success
Notifies source NG-RAN of successful UE target access during DAPS handover.
Handover Cancel
Requests cancellation of an ongoing handover.
Handover Cancel Acknowledge
Confirms that an ongoing handover was cancelled.
Path Switch Request
Requests core user-plane path switch after handover.
Path Switch Request Acknowledge
Confirms successful core path switch and returns session outcomes.
Path Switch Request Failure
Reports failed core path switch and released PDU session resources.
Uplink RAN Status Transfer
Transfers source-side PDCP/RAN status information during handover.
Downlink RAN Status Transfer
Delivers RAN status transfer information to target NG-RAN.
PDU Session Management Messages
PDU session setup, modify, release, notify, and session-resource transfer messages.
PDU Session Resource Setup Request
Requests setup of PDU session resources.
PDU Session Resource Setup Response
Reports setup result for requested PDU session resources.
PDU Session Resource Modify Request
Requests modification of existing PDU session resources.
PDU Session Resource Modify Response
Reports successful and failed PDU session modification results.
PDU Session Resource Modify Indication
NG-RAN initiated modification indication for existing PDU session resources.
PDU Session Resource Modify Confirm
Confirms outcome of NG-RAN initiated PDU session modification.
PDU Session Resource Notify
Notifies AMF of PDU session resource status or release information.
PDU Session Resource Release Command
Commands release of PDU session resources.
PDU Session Resource Release Response
Confirms release of PDU session resources.
Paging Messages
Paging, RAN paging, multicast group paging, and paging-related NGAP messages.
Paging
Requests NG-RAN paging for a UE.
RAN Paging Request
Requests RAN paging handling.
Multicast Group Paging
Pages multicast group members for MBS-related service.
Coming soonInterface Management Messages
NG setup, reset, overload, AMF/RAN configuration updates, and AMF status.
NG Setup Request
Starts NG-C setup and advertises RAN-supported TAs, PLMNs, slices, and paging parameters.
NG Setup Response
Confirms successful NG setup and returns AMF served GUAMIs, PLMN support, and AMF capacity.
NG Setup Failure
Rejects NG setup with cause and optional retry timing.
RAN Configuration Update
Updates AMF-side view of RAN configuration such as supported TAs, slices, and TNL changes.
RAN Configuration Update Acknowledge
Confirms successful RAN configuration update processing.
RAN Configuration Update Failure
Rejects a RAN configuration update with cause and optional Time to Wait.
AMF Configuration Update
Updates NG-RAN-side AMF configuration such as GUAMI, PLMN support, capacity, and TNL associations.
AMF Configuration Update Acknowledge
Confirms successful AMF configuration update and may report TNL setup results.
AMF Configuration Update Failure
Rejects AMF configuration update with cause and optional Time to Wait.
NG Reset
Requests full or partial NG interface reset.
NG Reset Acknowledge
Confirms completion of requested NG reset actions.
Overload Start
Starts AMF overload control and instructs NG-RAN to reduce selected signalling traffic.
Overload Stop
Clears AMF overload state and resumes normal traffic handling.
AMF Status Indication
Indicates AMF status information to NG-RAN.
Coming soonError Indication
Reports NGAP protocol errors or unexpected message handling conditions.
Warning / PWS Messages
Write-replace warning, PWS cancel, restart, and failure indication messages.
Write Replace Warning Request
Requests start or replacement of public warning broadcast.
Write Replace Warning Response
Reports write-replace warning request result.
PWS Cancel Request
Requests cancellation of an active public warning broadcast.
PWS Cancel Response
Reports warning cancellation result.
PWS Restart Indication
Reports PWS restart information.
Coming soonPWS Failure Indication
Reports public warning system broadcast failure.
Coming soonUE Radio Capability Messages
Capability information, compatibility check, and capability ID mapping messages.
UE Radio Capability Info Indication
Reports UE radio capability information or capability ID context.
UE Radio Capability Check Request
Requests NG-RAN compatibility check for UE radio capability.
UE Radio Capability Check Response
Returns UE radio capability compatibility result.
UE Radio Capability ID Mapping Request
Requests mapping or resolution of a UE Radio Capability ID.
UE Radio Capability ID Mapping Response
Returns capability ID mapping result.
Trace & Location Reporting Messages
Trace start/deactivation, cell traffic trace, location reporting control, reports, and failure indications.
Trace Start
Requests NG-RAN to initiate a trace session for a UE.
Coming soonTrace Failure Indication
Reports trace session failure.
Coming soonDeactivate Trace
Requests NG-RAN to stop a trace session.
Coming soonCell Traffic Trace
Reports cell traffic trace information.
Coming soonLocation Reporting Control
Requests NG-RAN to report UE location under configured conditions.
Coming soonLocation Report
Reports UE location, area presence, or timestamp information.
Coming soonLocation Reporting Failure Indication
Reports location reporting failure.
Coming soonNRPPa / RIM / RAN Transfer Messages
NRPPa transport, RAN information management, and RAN configuration transfer messages.
Downlink UE Associated NRPPa Transport
Carries UE-associated NRPPa signalling downlink.
Coming soonUplink UE Associated NRPPa Transport
Carries UE-associated NRPPa signalling uplink.
Coming soonDownlink Non UE Associated NRPPa Transport
Carries non-UE-associated NRPPa signalling downlink.
Coming soonUplink Non UE Associated NRPPa Transport
Carries non-UE-associated NRPPa signalling uplink.
Coming soonUplink RAN Configuration Transfer
Transfers RAN configuration information uplink.
Coming soonDownlink RAN Configuration Transfer
Transfers RAN configuration information downlink.
Coming soonUplink RIM Information Transfer
Transfers RAN Information Management information uplink.
Coming soonDownlink RIM Information Transfer
Transfers RAN Information Management information downlink.
Coming soonAdvanced / Usage Reporting Messages
Advanced NGAP reporting messages such as secondary RAT data usage reporting.
Secondary RAT Data Usage Report
Reports secondary RAT data usage information.
Coming soonFAQ
What are NGAP messages?
NGAP messages are control-plane signalling messages exchanged between NG-RAN and AMF over the NG interface/N2.
Which 3GPP specification defines NGAP?
NGAP is defined in 3GPP TS 38.413.
What is the difference between UE-associated and non-UE-associated NGAP messages?
UE-associated messages relate to a specific UE context. Non-UE-associated messages manage interface-level procedures such as NG setup, reset, overload, configuration, warning, and some transport functions.
What is the difference between NGAP and NAS?
NGAP carries signalling between NG-RAN and AMF. NAS carries UE-to-core signalling and can be transported inside NGAP messages such as Initial UE Message, Uplink NAS Transport, and Downlink NAS Transport.
Why are NGAP messages grouped by procedure?
Grouping by procedure helps engineers scan related messages together, such as NAS transport, UE context, mobility, PDU session, paging, and interface management procedures.
References
- 3GPP TS 38.413 – NG-RAN; NG Application Protocol (NGAP)
- 3GPP TS 38.300 – NR and NG-RAN overall description
- 3GPP TS 23.502 – 5G system procedures