N2 Handover with AMF Change Call Flow
This section describes the N2 Handover with AMF change call flow.
This call flow is similar to the N2 Handover without AMF change except the creation of the context on the new AMF and splitting up of the steps between the two nodes.

Step |
Description |
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1 |
The source gNB sends a HANDOVER REQUIRED message to the AMF. |
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2 |
The AMF analyses the target identifier and recognizes that it’s not a target it serves. The AMF selects a new AMF to serve the UE and sends it a CreateUE Context message.
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3 |
The target AMF receives the message and verifies that it can serve the UE. For each PDU session that must be handed over, the AMF sends a Modify SM Context message to the SMF. |
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4 |
The SMF does all the necessary procedures that are required to handle the UE in the new target and responds to the AMF. |
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5 |
The target AMF identifies the gNB that is going to handle the UE and sends a HANDOVER REQUEST to the gNB. |
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6 |
Once the necessary resources are allocated by the target gNB, the target gNB responds with a HANDOVER REQUEST ACK. |
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7 |
The AMF updates the SMF with the message transfer IE in the gNB. |
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8 |
The SMF responds to the requests in the AMF. |
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9 |
The target AMF responds to the source AMF and includes any Target to Source container in the response. This response also includes any PDU sessions that have failed to set up in the target AMF due to any condition. |
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10 |
The source AMF sends a HANDOVER COMMAND to the source gNB. |
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11 |
The handover completes in the UE and the target gNB sends a HANDOVER NOTIFY to the target AMF. |
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12 |
The target AMF indicates receipt of the HANDOVER NOTIFY to the source AMF. This causes the source AMF to start a timer the expiry of which leads to the release of resources in the source gNB. |
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13 |
The source AMF responds to the target. |
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14 |
The source AMF clears any PDU sessions that have failed to set up at the target. |
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15 |
The SMF responds to the release request in the source AMF. |
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16 |
The target AMF update the SMF on the completion of the handover. |
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17 |
The SMF acknowledges the message in the AMF. |
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18 |
When the timer expires for clearing of resources (or eventually when the UDM notifies the source that the registration for UECM isn’t valid), the source AMF releases resources both locally and at the gNB. The AMF releases the resources at the gNB by sending a UE CONTEXT RELEASE COMMAND. |
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19 |
The source gNB responds with a UE CONTEXT RELEASE COMPLETE message. |