5G NR Handover Types | Inter gNB handover,intra-NR RAN handover
This page describes 5G NR Handover Types. It covers 5G Inter gNB handover and 5G intra RAN handover (C-Plane Handling). This is as per specifications published from 3GPP with document reference 3GPP TS 38.300.
Introduction: There are two types of 5G NR handovers viz. network controlled and UE controlled. Network controlled handover is applied to 5G NR UEs in RRC_CONNECTED mode. This network controlled handover is categorized into following two sub types viz. Cell level and beam level.
• Explicit RRC signalling are required to be triggered in cell level mobility or handover.
i.e. handover. Following messages are exchanged for this inter-gNB handover type.
• The other subtype beam level mobility i.e. handover does not require explicit RRC signalling to be triggered. It is handled by lower layers. Moreover RRC is not required to know which beam is being used at a given point in time.
5G NR Inter gNB handover
The figure-1 depicts 5G Inter gNB handover type.
➨The source gNB initiates handover and issues a Handover Request over the Xn interface.
➨The target gNB performs admission control and provides the RRC configuration as part of the Handover Acknowledgement.
➨The source gNB provides the RRC configuration to the UE in the Handover Command. The Handover Command message includes at least cell ID and all information required to access the target cell so that the UE can access the target cell without reading system information. For some cases, the information required for contention based and contention free random access can be included in the Handover Command message. The access information to the target cell may include beam specific information, if any.
➨The UE moves the RRC connection to the target gNB and replies the Handover Complete.
5G NR intra RAN handover (C-Plane Handling)
The figure-2 depicts 5G intra-NR RAN handover (C-Plane Handling) where neither the AMF nor the UPF changes. U-Plane Handling handover is under development.
The intra-NR RAN handover procedure is shown in the figure-2 without involvement of 5GC (5G Core Network). Messages are directly exchanged between the gNBs. The release of the resources at the source gNB during the handover completion phase is triggered by the target gNB.
Reference: 3GPP TS 38.300 section 9 for 5G NR handover types
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