10.16 Support of inter-system handover involving EN-DC or MR-DC with 5GC

37.3403GPPMulti-connectivityNROverall descriptionRelease 17Stage 2TS

10.16.1 General

Inter-system handover is specified in TS 23.501 [11] and TS 23.502 [20]. Data forwarding for inter-system handover is specified in TS 38.300 [3] and clause 8.4.

Inter-system Inter-Master node handover with/without SN change is not supported in this version of the protocol (e.g. no transition from EN-DC to NGEN-DC or NR-DC).

Inter-system HO from NR to E-UTRA with EN-DC configuration is supported in this version of the specification. N26 based inter-system HO will be executed between source RAN and gNB.

Inter-system HO from E-UTRA connected to 5GC to E-UTRA with EN-DC configuration is not supported. Inter-system HO from E-UTRA with EPC to MR-DC with 5GC is not supported.

Inter-system handover with source gNB and the target en-gNB or the source en-gNB and the target gNB being realised within the same network entity is supported in this version of the specification as described in clause 10.16.2 and clause 10.16.3.

10.16.2 Inter-system handover from EPS to 5GS with the Secondary Node used as target

Inter-system handover from EPS to 5GS with the Secondary Node used as target refers to a deployment scenario where the source en-gNB and the target gNB are realised within the same network entity.

Figure 10.16.2-1: Inter-system handover from EPS to 5GS with the Secondary Node used as target

– Step 1: The (source) eNB, performing EN-DC with the (source) en-gNB triggers handover preparation including the SgNB UE X2AP ID within the Source NG-RAN to Target NG-RAN Transparent Container.

– Step 2: The target gNB infers from the received SgNB UE X2AP ID in the Handover Request message that direct data forwarding can be performed in a node-internal way.

– Step 3: DL UP data is forwarded in a node-internal way for the SN terminated bearers.

– Step 4: After the end marker has arrived from the SGW, the (target) gNB processes UP data from the UPF.

10.16.3 Inter-system handover from 5GS to EPS with the Source Node used as target Secondary Node

Inter-system handover from 5GS to EPS with the Source Node used as target Secondary Node refers to a deployment scenario where the source gNB and the target en-gNB are realised within the same network entity.

Figure 10.16.3-1: Inter-system handover from 5GS to EPS with the Source Node used as target Secondary Node

1. The (source) gNB triggers handover preparation phase including in the Source eNB to Target eNB Transparent Container the Source NG-RAN node ID and the RAN UE NGAP ID.

2. The target eNB receives the Source NG-RAN node ID and the RAN UE NGAP ID in the Source eNB to Target eNB Transparent Container.

3.-4. The X2AP SgNB Addition procedure is performed towards the (target) en-gNB indicated in the Source NG-RAN node ID received in step 2. The eNB includes the RAN UE NGAP ID received in step 2 in the X2 SgNB Addition Request message.

5.-8. Handover proceeds.

9. DL UP data is forwarded in a node-internal way for the SN terminated bearers.