16.12.5.5 System Information

The in-coverage L2 U2N Remote UE is allowed to acquire any necessary SIB(s) over Uu interface irrespective of its PC5 connection to L2 U2N Relay UE.

The intermediate L2 U2N Relay UE acquires the SIB(s) requested from the child UE(s) or the SIB(s) of its own concerned. If the intermediate L2 U2N Relay UE is in the same cell of the last L2 U2N Relay UE, it is allowed to acquire any necessary SIB(s) over Uu interface irrespective of its PC5 connection to L2 U2N Relay UE.

The L2 U2N Remote UE or intermediate L2 U2N Relay UE can also receive the system information from the parent UE after PC5 connection establishment with L2 U2N Relay UE.

The L2 U2N Remote UE in RRC_CONNECTED can use the on-demand SIB framework as specified in TS 38.331 [12] to request the SIB(s) via L2 U2N Relay UE. The L2 U2N Remote UE in RRC_IDLE or RRC_INACTIVE can inform L2 parent UE of its requested SIB type(s) via PC5-RRC message. Then, the L2 U2N Relay UE in single-hop, the last L2 U2N Relay UE or the intermediate L2 U2N Relay UE triggers on-demand SI/SIB acquisition procedure as specified in TS 38.331 [12] according to its own RRC state (if needed) and sends the acquired SI(s)/SIB(s) to L2 child UE via PC5-RRC message.

Any SIB that the RRC_IDLE or RRC_INACTIVE L2 U2N Remote UE has a requirement to use (e.g., for relay purpose) can be requested by the L2 U2N Remote UE (from the L2 U2N Relay UE or the network). For SIBs that have been requested by the L2 U2N Remote UE from the L2 U2N Relay UE, the L2 U2N Relay UE forwards them again in case of any update for requested SIB(s). In case of RRC_CONNECTED L2 U2N Remote UE(s), it is the responsibility of the network to send updated SIB(s) to L2 U2N Remote UE(s) when they are updated. The L2 U2N Remote UE de-configures SI request with L2 U2N Relay UE when entering into RRC_CONNECTED state.

For SIB1 forwarding, for L2 U2N Remote UE, both request-based delivery (i.e., SIB1 request by the U2N Remote UE) and unsolicited forwarding are supported by L2 U2N Relay UE, of which the usage is left to L2 U2N Relay UE implementation. If SIB1 changes, for L2 U2N Remote UE in RRC_IDLE or RRC_INACTIVE, the L2 U2N Relay UE always forwards SIB1.

For the L2 U2N Remote UE in RRC_IDLE or RRC_INACTIVE, the short message over Uu interface is not forwarded by the L2 U2N Relay UE to the L2 U2N Remote UE. The L2 U2N Relay UE can forward PWS SIBs to its connected L2 U2N Remote UE(s).

RAN sharing is supported for L2 U2N Relay UE. In particular, the L2 U2N Relay UE may forward, via discovery message, cell access related information before the establishment of a PC5-RRC connection.