Explanation
According to the 5G SIB Messages, SIB1 is the only mandatory SI message that must be read on a 5G network. SIB1 contains essential information for accessing the network, such as cell identity, cell barring, and scheduling information for other SI messages. SIB2, SIB3, and SIB4 are optional SI messages that provide additional information such as radio resource configuration, intra-frequency cell reselection, and neighboring cell information.