A UE in RRC_CONNECTED may initiate the re-establishment procedure to continue the RRC connection when a failure condition occurs (e.g. radio link failure, reconfiguration failure, integrity check failure…).
The following figure describes the re-establishment procedure started by the UE:
The UE re-establishes the connection, providing the UE Identity (PCI+C-RNTI) to the gNB where the trigger for the re-establishment occurred.
If the UE Context is not locally available, the gNB, requests the last serving gNB to provide UE Context data.
The last serving gNB provides UE context data.
The gNB continues the re-establishment of the RRC connection. The message is sent on SRB1.
The gNB may perform the reconfiguration to re-establish SRB2 and DRBs when the re-establishment procedure is ongoing.
If loss of user data buffered in the last serving gNB shall be prevented, the gNB provides forwarding addresses, and the last serving gNB provides the SN status to the gNB.
The gNB performs path switch.
The gNB triggers the release of the UE resources at the last serving gNB.
The IAB-MT in SA mode follows the same re-establishment procedure as described for the UE. After the backhaul has been established, the re-establishment procedure of the IAB-MT is part of the intra-CU backhaul RLF recovery procedure for IAB-nodes defined in TS 38.401
. Modifications to the configuration of BAP sublayer and higher protocol layers above the BAP sublayer are described in TS 38.401