5G (NR) RAN Learning - Path Request in Handover (4)

The purpose of the handover path request process is to establish the relevant signaling connection between the terminal (UE) and the 5GC and, if applicable, request the downlink termination point of the NG-U transport bearer to be switched to a new termination point. For the handover of UE-related services in the PC5 interface in Sildlink, 3GPP defines it in TS38.413 as follows;

I. PC5 QoS Processing The path request in handover of the PC5 interface in Sildlink is defined as follows;

• If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message contains the PC5 QoS parameter IE, the NG-RAN node shall (if supported) use it as defined in TS 23.287.
• If the Path Switch Request Acknowledge (PATH SWITCH REQUEST ACKNOWLEDGE) message contains the A2X PC5 QoS parameter IE, the NG-RAN node shall (if supported) use it as defined in TS 23.256.
• If the Path Switch Request Acknowledge message includes the Alternate QoS Parameter Set List IE, the NG-RAN node shall (if supported) use it as specified in TS 23.502.

II. Path Request in CE-mode-B and User Plane CIoT Handover is defined as follows:

• If the Path Switch Request Acknowledge message includes the CE-mode-B Restriction IE, the Enhanced Coverage Restriction IE is not set to "restricted", and the Enhanced Coverage Restriction information stored in the UE context is not set to "restricted", the NG-RAN node shall (if supported) store this information in the UE context and use it as defined in TS 23.501.
• If the Path Switch Request Acknowledge message includes the UE User Plane CIoT Support Indicator IE, the NG-RAN node shall (if supported) store this information in the UE context and assume that the UE supports User Plane CIoT 5GS Optimization as specified in TS 23.501.
• If the Path Switch Request Acknowledge message includes the UE Radio Capability ID IE, the NG-RAN node shall (if supported) use it as specified in TS 23.501 and TS 23.502.

III. PDU Session Expected UE Activity and Path Request in MDT Handover are defined as follows:

• For each PDU Session, if the PATH SWITCH REQUEST ACKNOWLEDGE message includes the "PDU Session Expected UE Activity Behavior" IE, the NG-RAN node shall (if supported) process this information as specified in TS 23.501.
• If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the "Management-Based MDT PLMN List" IE, the NG-RAN node shall store it in the UE context and, if supported, use this list to allow subsequent selection of the UE for management-based MDT as defined in TS 32.422.
• If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the "Management-based MDT PLMN Modification List" IE, the NG-RAN node (if supported) shall use this list to overwrite any previously stored management-based MDT PLMN list information in the UE context and use the received information to allow subsequent selection of the UE for management-based MDT as defined in TS 32.422.
• If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the Time Synchronisation Assistance Information IE, the NG-RAN node (if supported) shall store this information in the UE context and use it as defined in TS 23.501.

IV. Path Request in 5G ProSe Handover is defined as follows:

• If the PATH SWITCH REQUEST ACKNOWLEDGE message includes the 5G ProSe Authorized IE, the NG-RAN node (if supported) shall update its ProSe authorization information for the UE accordingly.
• If the 5G ProSe Authorization Information (5G ProSe Authorized IE) contains one or more IEs set to "Unauthorized," the NG-RAN node (if supported) should take steps to ensure that the UE no longer has access to the associated 5G ProSe services. If the 5G ProSe PC5 QoS Parameters IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message, the NG-RAN node (if supported) should use it as defined in TS 23.304.
• If the Aerial UE Subscription Information IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message, the NG-RAN node (if supported) should store this information or overwrite any previously stored information in the UE context and use it as defined in TS 38.300.
• If the 5G ProSe UE PC5 Aggregate Maximum Bit Rate IE is included in the PATH SWITCH REQUEST ACKNOWLEDGE message, the NG-RAN node shall (if supported) perform the following actions:

1. Replace the previously provided 5G ProSe UE PC5 Aggregate Maximum Bit Rate (if available in the UE context) with the received value;
2. Use the received value for sidelink communications for the associated UE in the network scheduling mode for the 5G ProSe service.