N2 Handover Cancel Call Flow

This section describes the N2 Handover cancel call flow.

The source NG-RAN sends Handover Cancel Request to the source AMF, prior to sending the Handover command to UE. It sends this request when it observes the following:

  • Timer expiry

  • Internal failure within the source NG-RAN

  • UE return to source cell

Handover Cancel Request releases the handover reserved resources in the target system.

N2 Handover Cancel Call Flow
N2 Handover Cancel Call Flow Description

Step

Description

1

The S-gNB (source gNB) sends the Handover Cancel to the S-AMF (source AMF).

2

S-AMF sends the Namf_Comm_ReleaseReq to the T-AMF (target AMF).

3, 4

T-AMF sends the UE Context Release Command to the T-gNB (target gNB) and receives the UE Context Release Complete.

5

T-AMF sends the Relocation Cancel Indication (Nsmf_Update_Req) to the SMF.

6

SMFsends Nsmf_update_Rsp to T-AMF.

7

S-AMF receives Namf_Comm_ReleaseRsp from the T-AMF.

8

S-AMF sends Handover Cancel ACK to the S-gNB.