5G System Learning - Downlink RAN ​​Configuration Transfer

1. The purpose of the RAN Downlink Configuration Transfer procedure is to transfer RAN configuration information from the AMF to the NG-RAN node; the configuration transfer procedure is shown in Figure 8.8.2.2-1 below and uses non-UE-associated signaling.

2. The Downlink RAN ​​Configuration Transfer procedure is initiated by the AMF sending a "Downlink RAN ​​Configuration Transfer" message to the NG-RAN. Here, the following steps are used:

• If the NG-RAN node receives a SON Information IE containing a SON Information Request IE in a SON Configuration Transfer IE or an EN-DC SON Configuration Transfer IE, it may transfer the requested information back to the NG-RAN node indicated in the Source RAN Node ID IE of the SON Configuration Transfer IE, or to the eNB indicated in the Source eNB-ID IE of the EN-DC SON Configuration Transfer IE, by initiating the Uplink RAN ​​Configuration Transfer procedure.
• If the NG-RAN node receives an Xn TNL Configuration Information IE containing an Xn Extended Transport Layer Address IE in the SON Configuration Transfer IE, it may use it as part of its ACL function configuration operation (if such ACL function is deployed).
• If the NG-RAN node receives a SON Information IE containing a SON Information Reply IE (including the Xn TNL Configuration Information IE as a reply to a previous request) in the SON Configuration Transport IE, it can use it to initiate Xn TNL establishment.
• If the IP-Sec Transport Layer Address IE is present and the GTP Transport Layer Address IE in the Xn Extended Transport Layer Address IE is not empty, GTP traffic will be transported within the IP-Sec tunnel, which terminates at the IP-Sec tunnel endpoint specified in the IP-Sec Transport Layer Address IE.
• If the IP-Sec Transport Layer Address IE is not present, GTP traffic will terminate at the endpoint specified by the address list in the Xn GTP Transport Layer Address IE in the Xn Extended Transport Layer Address IE.
• If the Xn GTP Transport Layer Address IE is empty and the IP-Sec Transport Layer Address IE is present, SCTP traffic will be transported within the IP-Sec tunnel, which terminates at the IP-Sec tunnel endpoint specified in the IP-Sec Transport Layer Address IE in the Xn Extended Transport Layer Address IE.
• If the Xn SCTP Transport Layer Address IE is present and the IP-Sec Transport Layer Address IE is also present, the associated SCTP traffic will be transported within the IP-Sec tunnel, which terminates at the IP-Sec tunnel endpoint specified in this IP-Sec Transport Layer Address IE, within the Xn Extended Transport Layer Address IE.
• If an NG-RAN node receives a SON Information IE containing a SON Information Report IE, it may use it as specified in TS 38.300.
• If an NG-RAN node receives an Inter-System SON Information IE containing an Inter-System SON Information Report IE, it may use it as specified in TS 38.300.
• If an NG-RAN node receives an Inter-System SON Information IE containing an Inter-System SON Information Request IE or an Inter-System SON Information Reply IE, it may use it as specified in TS 38.300.
• If the "Reporting System IE" in the Inter-System SON Information Request IE is set to "No Report", the "Downlink RAN ​​Configuration Transfer" message shall be ignored.
• If the NG-RAN node is configured to use one IPsec tunnel for all NG and Xn traffic (IPsec hub-and-spoke topology), traffic to the peer NG-RAN node SHOULD be routed through this IPsec tunnel and the IP-Sec Transport Layer Address IE SHOULD be ignored.