Handover Cancel Acknowledge is the AMF-to-source-NG-RAN message used in the Handover Cancellation procedure to confirm that an ongoing handover was cancelled.
What is Handover Cancel Acknowledge in simple terms?
Handover Cancel Acknowledge is the AMF-to-source-NG-RAN message used in the Handover Cancellation procedure to confirm that an ongoing handover was cancelled.
Confirms that the AMF processed Handover Cancel and that the ongoing handover is no longer treated as active on the cancelled branch.
Why this message matters
Handover Cancel Acknowledge is the AMF telling the source NG-RAN that the requested handover cancellation is complete.
Where this message appears in the call flow
Successful completion of Handover Cancellation
Confirmation branch: after processing Handover Cancel, the AMF returns Handover Cancel Acknowledge to the source side.
Call flow position: After the source NG-RAN requested cancellation of an ongoing handover with Handover Cancel, the AMF returns the successful response.
Typical state: The handover is no longer treated as ongoing, and the source side has explicit AMF confirmation that the cancellation branch completed.
Preconditions:
An ongoing handover existed and Handover Cancel was sent by the source NG-RAN.
The AMF accepted and processed cancellation of the ongoing handover.
The identity pair in the acknowledge still matches the cancelled handover context.
Next likely message: No success-side continuation of the cancelled branch; the source now treats the cancellation as confirmed
The AMF confirms cancellation
Confirmation branch: after processing Handover Cancel, the AMF returns Handover Cancel Acknowledge to the source side.
Request and acknowledge pairing
Paired branch: the source requests cancellation, and the AMF confirms that the ongoing handover was cancelled.
Minimal acknowledge structure
Minimal branch: the acknowledge confirms cancellation without repeating Cause because the reason already appeared in Handover Cancel.
Domain: UE mobility management and cancellation-confirmation signaling
Signaling bearer: UE-associated NGAP signaling
Logical channel: SCTP carried NGAP successfulOutcome from AMF to source NG-RAN in the Handover Cancellation procedure
Transport / encapsulation: NGAP over SCTP/IP between AMF and source NG-RAN
Security context: The message is sent on the same UE-associated handover context used for the cancellation branch. Its role is confirmation of cancellation rather than failure reporting or mobility-success reporting.
Message Structure Overview
Handover Cancel Acknowledge is the AMF-to-source confirmation that the ongoing handover was cancelled.
The message is intentionally minimal because the cancellation reason was already carried in Handover Cancel.
Its payload is only the message identity plus AMF UE NGAP ID and RAN UE NGAP ID.
Operationally, it closes the cancellation branch cleanly and tells the source not to treat the handover as ongoing anymore.
The acknowledge is not a failure message and not a handover-success message.
Decode Handover Cancel Acknowledge by matching AMF UE NGAP ID and RAN UE NGAP ID to the earlier Handover Cancel. There is no Cause IE here because the cancellation reason belongs to the request, not to the confirmation.
5G NGAP - Handover Cancel Acknowledge - Example Dump
Treat this as a teaching example based on the spec structure, not as a captured trace.
The message is intentionally short because it only confirms cancellation rather than restating the reason.
Read it as the successful response paired with the earlier Handover Cancel request.
Important Information Elements
IE
Required
Description
Message Type
Yes
Identifies the NGAP PDU as Handover Cancel Acknowledge.
AMF UE NGAP ID
Yes
Mandatory AMF-side UE identifier used to match the acknowledge to the correct cancelled handover context.
RAN UE NGAP ID
Yes
Mandatory source-side UE identifier used by the source NG-RAN to associate the acknowledge with the correct handover context.
Detailed field explanation
Message Type
Identifies the NGAP PDU as Handover Cancel Acknowledge.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
AMF UE NGAP ID
Mandatory AMF-side UE identifier used to match the acknowledge to the correct cancelled handover context.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
RAN UE NGAP ID
Mandatory source-side UE identifier used by the source NG-RAN to associate the acknowledge with the correct handover context.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
What to check in logs and traces
Confirm Handover Cancel Acknowledge follows Handover Cancel for the same identity pair.
Verify direction is AMF to source NG-RAN.
Match AMF UE NGAP ID and RAN UE NGAP ID to the original cancellation request.
Do not expect a Cause IE in the acknowledge.
Keep this message distinct from Handover Success and from target-side messages like Handover Notify.
Common Issues and Troubleshooting
Engineers expect the acknowledge to repeat the cancellation reason.
Likely cause: The request carried Cause, but the response is only a confirmation.
What to inspect: Check Handover Cancel for the reason and Handover Cancel Acknowledge only for identity correlation and successful closure.
Next step: Use the request to analyze why the branch was cancelled and the acknowledge to prove the AMF accepted it.
The trace is misread as a mobility-success outcome.
Likely cause: The word acknowledge may be confused with other positive handover outcomes.
What to inspect: Check the preceding message. If the branch started with Handover Cancel, the acknowledge confirms cancellation, not handover success.
Next step: Keep cancellation-confirmation semantics separate from success-completion semantics such as Handover Success.
Multiple overlapping handovers make it hard to tell which cancellation was acknowledged.
Likely cause: Identity correlation may be incomplete.
What to inspect: Match both AMF UE NGAP ID and RAN UE NGAP ID against the original Handover Cancel.
Next step: Rebuild the request-response pair using the identity pair before drawing conclusions.
LTE / 5G / Variant Comparison
Compared with Handover Cancel
Handover Cancel is the source-side request carrying Cause. Handover Cancel Acknowledge is the AMF confirmation that the ongoing handover was cancelled.
Compared with Handover Success
Handover Success is an AMF-to-source notification that target access succeeded in DAPS handover. Handover Cancel Acknowledge confirms a cancelled branch, not a successful one.
Why the acknowledge has no Cause
The cancellation reason was already provided by Handover Cancel, so the acknowledge only needs to confirm the result and identify the UE context.
FAQ
What is Handover Cancel Acknowledge in 5G NGAP?
It is the AMF-to-source-NG-RAN message that confirms an ongoing handover was cancelled after Handover Cancel.
Who sends Handover Cancel Acknowledge?
The AMF sends Handover Cancel Acknowledge to the source NG-RAN node.
What is the response to Handover Cancel?
The response is Handover Cancel Acknowledge.
What does Handover Cancel Acknowledge confirm?
It confirms that the ongoing handover was cancelled.
Does Handover Cancel Acknowledge contain a Cause IE?
No. Cause is carried in Handover Cancel, while the acknowledge only confirms the outcome.
What is the difference between Handover Cancel and Handover Cancel Acknowledge?
Handover Cancel requests cancellation and carries Cause. Handover Cancel Acknowledge confirms that the cancellation took effect.
What UE identifiers are mandatory in Handover Cancel Acknowledge?
AMF UE NGAP ID and RAN UE NGAP ID are both mandatory.
How is this message different from Handover Success?
Handover Success is an AMF-to-source success notification for DAPS handover target access, while Handover Cancel Acknowledge confirms a cancelled handover branch.
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.
