As you may know that UE can access the network if it can receive some of the System Information (SI) from the Cell (Mandatory). So Let’s understand the main difference between SIBs in 4G and 5G NR.
🧧 Difference Number 1
LTE MIB, SIB1, and SIB2 are mandatory for the UE to access a cell and all system information is periodically transmitted by the network. However, for more energy saving in 5G, UE should, as a minimum, receive MIB and SIB1 or is called Minimum_SI and the other SIBs, The UE does not need to receive these SIBs before accessing the cell.
🧧 Difference Number 2
SIB5, SIB6, and SIB7 in LTE contain parameters for Cell_Reselection information, However, in 5G, their messages are responsible for Public Warning Systems (PWS) like Earthquake and Tsunami Warning System (ETWS) and Commercial Mobile Alert System (CMAS) Which were sent on SIB10, SIB11 and SIB12 in LTE (not in this figure).
🧧 Difference Number 3
There are not any messages (so far as per my knowledge) to make a cell reselection from 5G to 2G or 3G like the case in LTE.
Also, I think MIB, SIB1 and SIB2 functions are almost the same for 4G and 5G NR.
I hope this comparison to be clear and help RF engineers to make a good analysis for the Layer 3 messages ^^