3GPP 38.300 v19.3.0 — the document's own text
4.9.3 Signalling procedures
Taught in 4. What NR actually is, in the shape its own document gives it (TSG RAN — the group that specifies the radio, overview).
RRC signalling is utilized to configure the NCR-MT to receive side control information from a gNB, which is used to control the amplify-and-forward function of the NCR-Fwd. If the side control configuration is removed, the NCR-Fwd ceases its amplifying-and-forwarding function.
MAC CE indications can be used to configure the backhaul link and the access link of the NCR-Fwd as specified in TS 38.321 [6].
When the NCR-MT is in RRC_CONNECTED state, the NCR-Fwd may amplify-and-forward RF signals based on the side control information received from the gNB. The NCR-MT does not support RRM measurements in RRC_CONNECTED.
When the NCR-MT transitions from RRC_CONNECTED state to RRC_INACTIVE state, the NCR-Fwd may continue to amplify-and-forward RF signals in accordance with the last side control information received from the gNB. When the NCR-MT is in RRC_INACTIVE state, the NCR-Fwd ceases to amplify-and-forward RF signals if no suitable cell is detected, or if the NCR-MT selects a different cell than the last serving cell on which side control configuration was received.
When an NCR-MT in RRC_INACTIVE state determines degradation of the NCR-Fwd backhaul link beam, then the NCR-Fwd should cease amplifying-and-forwarding RF signals, and the NCR-MT should attempt to resume its RRC connection (with cause value mo-Signalling). The criteria to evaluate backhaul beam degradation are left to the NCR-node implementation.
When the NCR-MT transitions from RRC_CONNECTED state to RRC_IDLE, the NCR-Fwd ceases any amplifying-and-forwarding of RF signals. How an NCR-MT transitions back from RRC_IDLE state to RRC_CONNECTED state is left to NCR-node or network implementation.
An NCR-MT can detect RLF on the control link as specified in TS 38.331 clause 5.3.10 [12]. When RLF is detected, the NCR-MT performs the RRC re-establishment procedure as specified in TS 38.331 [12]. During the RRC re-establishment procedure, the NCR-Fwd ceases to amplify-and-forward RF signals.
After successfully performing the RRC re-establishment procedure, the NCR-MT waits for the new side control configuration for the NCR-Fwd to resume the amplifying-and-forwarding of RF signals.
An NCR-MT can also perform Beam Failure Detection (BFD) and Beam Failure Recovery (BFR) as described in clause 9.2.8. Once the NCR-MT detects beam failure in the control link, the NCR-Fwd should cease amplifying-and-forwarding RF signals until BFR is completed.