In GPRS/EGPRS, there is no handover : indeed the MS is in charge of deciding to perform a cell reselection or not. This is the default “NC0” mode.
A reselection is always a “bad” suprise for the BSS : the transfer is stopped until the MS eventually finished to reselect the new cell. Then only, after the MS gathered some sys-info messages, the transfer is resumed.
NACC/PSI add 2 main features to this “stupid” reselection :
1. the MS informs the BSS beforehand –> the BSS transmits the needed SI before the reselection
2. after reselection, the needed SI are transmitted ASAP, in order for the MS to be ready for resume.
I’m simplfying a lot because I don’t have all the details in memory. Do you need more info ?