5G NGAP - AMF Configuration Update Acknowledge

Message Fact Sheet

What is AMF Configuration Update Acknowledge in simple terms?

AMF Configuration Update Acknowledge is the NG-RAN-to-AMF successful-outcome message used to confirm that the NG-RAN successfully updated configuration data received in AMF Configuration Update for an NG-C interface instance.

Confirms that the NG-RAN accepted and applied the AMF-driven configuration refresh on the successful branch of the AMF Configuration Update procedure and, when relevant, reports per-association TNL setup success or failure back to the AMF.

Why this message matters

AMF Configuration Update Acknowledge is the NG-RAN telling the AMF that the requested node-level configuration refresh succeeded, and it can also report which requested TNL associations were set up successfully or failed.

Where this message appears in the call flow

Successful confirmation of AMF-driven configuration refresh

Call flow position: The NG-C interface instance already exists, the AMF has sent updated configuration data, and the NG-RAN has successfully applied the accepted configuration changes.

Typical state: The procedure is on the successful branch and the NG-RAN is ready to confirm completion back to the AMF.

Preconditions:

• AMF Configuration Update reached the NG-RAN successfully.
• The NG-RAN accepted the included node-level changes.
• The procedure remains non-UE-associated and does not disturb existing UE-related contexts.

Next likely message: Normal NGAP operation continues with synchronized AMF and NG-RAN configuration

TNL association setup outcome reporting

Call flow position: The AMF Configuration Update included AMF TNL Association to Add List, so the NG-RAN attempted to establish one or more requested control-plane TNL associations before sending the successful outcome.

Typical state: The NG-RAN has per-association results to report rather than only a binary success indication.

Preconditions:

• AMF TNL Association to Add List was present in the request.
• The NG-RAN attempted setup using the signalled address information.
• If the AMF address omitted a port number, the NG-RAN assumed SCTP port 38412.

Next likely message: The acknowledge reports AMF TNL Association Setup List and or AMF TNL Association Failed to Setup List

Success branch versus failure branch

Call flow position: The NG-RAN chooses AMF Configuration Update Acknowledge instead of AMF Configuration Update Failure because the update was accepted and processed successfully.

Typical state: The configuration refresh ends with acceptance rather than rejection and retry handling.

Preconditions:

• The update content did not trigger rejection.
• No Cause-based failure reporting or Time to Wait backoff is needed.

Next likely message: Configuration remains synchronized until a later interface-management change

Call flow position

Previous message(s): AMF Configuration Update, NG-C interface instance already established

Next message(s): Normal NGAP procedures using synchronized configuration, Later AMF Configuration Update if another AMF-side change occurs, AMF Configuration Update Failure as the alternative unsuccessful outcome

Message direction and transport

Security context: AMF Configuration Update Acknowledge does not create, release, or modify UE-specific security context. It is a node-level successful-outcome message, and the parent procedure does not affect existing UE-related contexts.

Message Structure Overview

• AMF Configuration Update Acknowledge is a non-UE-associated successfulOutcome in the Interface Management family.
• The sender is the NG-RAN node and the receiver is the AMF on the N2 or NG-C interface.
• The message confirms successful processing of AMF-driven configuration changes for one NG-C interface instance.
• Unlike a truly empty acknowledge, this message can return AMF TNL Association Setup List, AMF TNL Association Failed to Setup List, and optional Criticality Diagnostics.
• If an IE was omitted in the earlier AMF Configuration Update request, the corresponding stored configuration remains unchanged at the NG-RAN.
• If the request carried full replacement lists such as Served GUAMI List or PLMN Support List, successful acknowledgment implies the NG-RAN is now operating with the overwritten values.

ASN.1 for 5G NGAP - AMF Configuration Update Acknowledge

AMFConfigurationUpdateAcknowledge ::= SEQUENCE {
  protocolIEs ProtocolIE-Container { {AMFConfigurationUpdateAcknowledge-IEs} },
  ...
}

AMFConfigurationUpdateAcknowledge-IEs NGAP-PROTOCOL-IES ::= {
  { ID id-AMFTNLAssociationSetupList           CRITICALITY reject TYPE AMFTNLAssociationSetupList           PRESENCE optional } |
  { ID id-AMFTNLAssociationFailedToSetupList   CRITICALITY ignore TYPE AMFTNLAssociationFailedToSetupList   PRESENCE optional } |
  { ID id-CriticalityDiagnostics               CRITICALITY ignore TYPE CriticalityDiagnostics               PRESENCE optional },
  ...
}

AMFTNLAssociationSetupList ::= SEQUENCE (SIZE (1..maxnoofTNLAssociations)) OF AMFTNLAssociationSetupItem

AMFTNLAssociationSetupItem ::= SEQUENCE {
  aMFTNLAssociationAddress CPTransportLayerInformation,
  ...
}

How to read this ASN.1

This successfulOutcome is richer than a simple empty ACK. Its main operational value comes from the optional per-association TNL setup result lists, especially when the AMF asked the NG-RAN to add new control-plane TNL associations.

5G NGAP - AMF Configuration Update Acknowledge - Example Dump

NGAP-PDU
  initiatingMessage
    procedureCode: id-AMFConfigurationUpdate
    criticality: reject
    value: AMFConfigurationUpdate
      protocolIEs:
        - id: id-ExtendedAMFName
          value:
            amf-name-utf8: "Core-AMF-West-1"
        - id: id-ServedGUAMIList
          value:
            - guami:
                plmn-id: 00101
                amf-region-id: 0x22
                amf-set-id: 0x104
                amf-pointer: 0x31
        - id: id-AMFTNLAssociationToAddList
          value:
            - amf-tnl-association-address:
                endpoint-ip-address: 10.10.10.20
              tnl-association-usage: both
              tnl-address-weight-factor: 20

NGAP-PDU
  successfulOutcome
    procedureCode: id-AMFConfigurationUpdate
    criticality: reject
    value: AMFConfigurationUpdateAcknowledge
      protocolIEs:
        - id: id-AMFTNLAssociationSetupList
          value:
            - amf-tnl-association-address:
                endpoint-ip-address: 10.10.10.20
                port-number: 38412
        - id: id-AMFTNLAssociationFailedToSetupList
          value:
            - amf-tnl-association-address:
                endpoint-ip-address: 10.10.10.21
                port-number: 38412
        - id: id-CriticalityDiagnostics
          value:
            procedureCode: id-AMFConfigurationUpdate
            triggeringMessage: initiatingMessage

NGAP-PDU
  unsuccessfulOutcome
    procedureCode: id-AMFConfigurationUpdate
    criticality: reject
    value: AMFConfigurationUpdateFailure
      protocolIEs:
        - id: id-Cause
          value:
            misc: unspecified

How to read this dump

• Treat this as a teaching example based on the spec structure, not as a captured network trace.
• The acknowledge can be more than a plain success flag because it may also report detailed TNL association setup outcomes.
• If the AMF TNL association address in the request omits a port number, the NG-RAN assumes SCTP port 38412 when attempting setup.
• Read the acknowledge together with the earlier AMF Configuration Update to understand which configuration blocks were actually changed and which omitted blocks stayed unchanged.

Important Information Elements

Detailed field explanation

What to check in logs and traces

• Confirm the acknowledge follows a valid AMF Configuration Update on the same non-UE-associated interface path.
• Check which request IEs were present, because any omitted IE in the update means the corresponding configuration remained unchanged.
• If AMF TNL Association to Add List was present, verify that each requested association appears in either AMF TNL Association Setup List or AMF TNL Association Failed to Setup List.
• Validate port handling carefully when the AMF transport-layer address omitted a port number, because the NG-RAN should assume SCTP port 38412.
• For Served GUAMI List and PLMN Support List, confirm the NG-RAN treated included lists as full overwrites rather than incremental additions.
• If Criticality Diagnostics is present, decode it alongside the initiating AMF Configuration Update to understand any reporting context.

Common Issues and Troubleshooting

LTE / 5G / Variant Comparison

FAQ

Related message pages

Related Procedures

Related Tools

• 3GPP Decoder
• NR ARFCN Calculator
• NR GSCN Calculator

Use This Reference in Practice

Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.