Читать книгу NG-RAN and 5G-NR - Frédéric Launay - Страница 24

The mobile is in the RRC_INACTIVE state for the NG-RAN and in the CM_CONNECTED state for the 5G core network. The mobile context is always stored on the node where the mobile was connected.

The mobile can move in the RAN Notification Area (RNA) without notifying the NG-RAN nodes. An RNA zone comprises one or several cells located in the same TAI zone.

In the case of mobile terminating data, the UPF transfers the packet to the last NG-RAN node on which the mobile had established a radio connection. The NG-RAN node broadcasts a paging request over the air interface and transmits (through the Xn interface) a paging order to neighboring NG-RAN nodes that are configured on the same RNA area. If the paging request fails (the mobile is not reachable), then the NG-RAN node informs the AMF.

If the mobile establishes a radio connection with an NG-RAN node other than the last serving node, then the new NG-RAN node initiates a procedure to retrieve the context of the mobile UE from the old serving node. In the case where the request fails, the NG-RAN node triggers a new RRC connection.