Connected mode

5G NG-based (N2) handover

Handover whose preparation is signalled through the AMF over N2 instead of directly between gNBs.

Overview

In inter NG-RAN node N2 based handover the source gNB sends the N2 Handover Required message to the AMF, which asks the target gNB to prepare, and finally returns the Handover Command to the source. The UE-side behaviour is the same reconfiguration with sync as in Xn handover.

The core-network procedure, including preparation and execution phases, is in TS 23.502 clause 4.9.1.3.

Call flow

1
UEtoSource gNB
MeasurementReport
2
Source gNBtoAMF
HANDOVER REQUIRED (N2)
3
AMFtoTarget gNB
HANDOVER REQUEST (N2)
4
Target gNBtoAMF
HANDOVER REQUEST ACKNOWLEDGE
5
AMFtoSource gNB
HANDOVER COMMAND (N2)
6
Source gNBtoUE
RRCReconfiguration (reconfigurationWithSync)
The UE starts T304.
7
UEtoTarget gNB
Random access, then RRCReconfigurationComplete
8
Target gNBtoAMF
HANDOVER NOTIFY (N2)

Timers and parameters

Name	Where	Role
T304	UE	Same supervision as Xn-based handover.

Full parameter and timer lookup →

Specifications

Spec	What it covers
TS 23.502	Inter NG-RAN node N2 based handover.(see clause 4.9.1.3)
TS 38.300	Handover in RRC_CONNECTED.(see clause 9.2.3.2)
TS 38.331	T304 expiry (reconfiguration with sync failure).(see clause 5.3.5.8.3)

Failure behaviour in the specs

UE-side failure handling is the same as Xn handover: T304 expiry leads to RRC re-establishment with cause handoverFailure.

Symptom-based troubleshooting →

Connected mode

5G Xn-based handover

Inter-gNB handover prepared over the Xn interface, with an NG path switch toward the core.

Connected mode

Conditional handover (CHO)

The network pre-configures candidate target cells with execution conditions and the UE moves when a condition is met.

5GNTN