School of Specs 23.501v20.2.0

3GPP 23.501 v20.2.0 — the document's own text

5.35A.3.4 MBSR mobility

Taught in 26. Relays, satellites, femtos and shared networks (The 5G system architecture, in depth).

The mobility of MBSR between different IAB-donor gNBs is described in clause 8.23 of TS 38.401 [42].

If a MBSR operates without PDU sessions,

  • For N2 Handover, the NG-RAN triggers the N2 handover procedure for a dummy PDU session and includes the related dummy PDU session information in the Handover Required message, as specified in TS 38.413 [34] towards the AMF of the MBSR (IAB-UE). The AMF checks the UE context it stores for the MBSR (IAB-UE) and since it includes no PDU sessions, the AMF shall not forward the PDU Session information it receives in the Handover Required message to any SMF. The AMF shall then perform the handover procedures as specified in clause 4.9.1.3 of TS 23.502 [3] without involving any SMF and it includes in the Handover Request message towards the target NG-RAN the PDU session information received in the Handover Required message with an indication to cause the target NG-RAN to ignore the received PDU session information (No PDU Session Indication IE defined in TS 38.413 [34]). If the AMF is reallocated during the handover, the target AMF checks whether the UE context for the MBSR (IAB-UE) it receives from the source AMF includes any PDU sessions related information and if none is detected, it continues the handover without involving any SMF and it includes in the Handover Request message towards the target NG-RAN with an indication to cause the target NG-RAN to ignore the received PDU session information (No PDU Session Indication IE defined in TS 38.413 [34]).
  • For Xn Handover: the NG-RAN triggers the Xn handover procedure for a dummy PDU session and includes the related dummy PDU session information in the Path Switch Request message, as specified in TS 38.413 [34]. The AMF checks the UE context it stores for the MBSR (IAB-UE) and since it includes no PDU sessions, the AMF shall then perform the handover procedures as specified in clause 4.9.1.2 of TS 23.502 [3] without involving any SMF and it includes in the Path Switch Acknowledge towards the target NG-RAN dummy PDU session information. The NG-RAN ignores the received PDU session information from the AMF as it has no PDU sessions in the RAN UE context.