Please explain me about the Non-DRX and DRX handling in the RRC layer of LTE protocol stack.
What exactly would you like to know about them?
How to handle the non-drx paging in RRC idle and connected mode perspectives?
Especially will u clarify the Non-DRX /DRX handling when RRC idle state is cell selection or cell reselection or plmn selection process?
Basically, DRX (discontinuous reception) allows the UE to ignore the downlink on a known (calculated) schedule, primarily to save battery life. DRX in idle state is used mostly for paging; cell selection and reselection are independent functions. In connected state, there's no need to page the UE; however, connected mode DRX may be used to allow the UE to not scan the PDCCH every millisecond, again primarily for battery life.
Addition to what Don says above, any UE that supports ETWS, CMAS (or KPAS etc.) warning / notification system, shall monitor its paging occasion also in RRC connected mode. This is because the notification about the warning message broadcast is included in the paging messages. If a notification is received from the paging message, the UE shall immediately start to acquire SIB1 and see which SIB's (SIB10-11 for ETWS, SIB12 for ETWS/KPAS etc.) are scheduled.
So on the network side, does the eNB "spam" the EWTS message? or does it take the time to calculate the subframes in which it expects there to be UEs listening based on UEs that have recently connected?
The network does not know which mobiles are camping on the cell. Remember that within a tracking area any UE can be camping on any cell without the network knowing the exact cell each UE in idle mode is actually camping in.
Therefore, in case an ETWS or CMAS notification needs to be passed on, I believe the network has to send paging messages in _every_ paging occasion used in the cell to let (possible) UE's know there's an ETWS or CMAS notification being broadcast.