5G (NR) RAN Learning - Path Request in Handover (5)

The purpose of the PATH SWITCH REQUEST process is to establish a UE-related signaling connection with the 5GC and, if applicable, request that the downlink termination point of the NG-U transport bearer be switched to a new termination point. 3GPP defines the relevant processes of 5G in TS38.413 after enabling IAB, slicing, positioning and ranging technologies as follows;

I. IAB Authorization Processing

• If the PATH SWITCH REQUEST ACKNOWLEDGE message contains the IAB Authorization IE, the NG-RAN node (if supported) shall store the received IAB authorization information in the UE context and use it as specified in TS 38.401.

• If the PATH SWITCH REQUEST ACKNOWLEDGE message contains the Mobile IAB Authorization IE, the NG-RAN node (if supported) shall store the received Mobile IAB authorization status in the UE context of the Mobile IAB-MT. If the Mobile IAB Authorization IE of the Mobile IAB-MT is set to "Unauthorized," the NG-RAN node (if supported) shall ensure that the Mobile IAB node does not serve any UE.

II. NSSAI and Ranging and Positioning

• If the "Partially Allowed NSSAI" IE is included in the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message, the NG-RAN node (if supported) shall infer the partially allowed network slice for the UE from it, store and replace any previously received "Partially Allowed NSSAI," and use it as specified in TS 23.501.

• If the "Ranging and Sidetrack Location Service Information" IE is included in the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message, the NG-RAN node (if supported) shall update the UE's ranging and sidetrack location service information accordingly. If the "Ranging and Sidetrack Positioning Authorization" IE in the Ranging and Sidetrack Positioning Service Information IE is set to "Unauthorized," the NG-RAN node (if supported) should take steps to ensure that the UE no longer has access to ranging and sidetrack positioning services.

III. RRC Inactive Transition Report Procedure

• If the RRC Inactive Transition Report Request IE is included in the Path Switch Request Acknowledgement message and is set to "Single RRC Connection Status Report," and the UE is in the RRC_CONNECTED state, the NG-RAN node (if supported) should send an RRC Inactive Transition Report message to the AMF to report the UE's RRC status.

• If the RRC Inactive Transition Report Request IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message and is set to "Single RRC Connection Status Report", and the UE is in RRC_INACTIVE state, the NG-RAN node shall (if supported) send an RRC Inactive Transition Report message to the AMF, and a subsequent RRC Inactive Transition Report message upon RRC state transition to RRC_CONNECTED.

• If the RRC Inactive Transition Report Request IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message and is set to "Subsequent State Transition Report", the NG-RAN node shall (if supported) send an RRC INACTIVE TRANSITION REPORT message to the AMF to report the UE's RRC status, and a subsequent RRC INACTIVE TRANSITION REPORT message to report the UE's RRC status upon the UE entering or leaving RRC_INACTIVE state.

IV. PDU Session Resource Notification Procedure

• If the Path Switch Request Acknowledge Transfer IE of the PATH SWITCH REQUEST ACKNOWLEDGE message contains QoS-related parameters (e.g., CN Packet Delay Budget Downlink IE or CN Packet Delay Budget Uplink IE), but the NG-RAN node is unable to successfully accept the parameters, the NG-RAN node shall continue to use the old values ​​(if any) received from the source NG-RAN node. If supported, the NG-RAN node shall notify the AMF by sending a PDU SESSION RESOURCE NOTIFY message.