before = earlier, i got that… but if something has changed between “before” and “now”, it means there is a cause. Since the MS is the only one deciding to come back from 2G to 3G, based on 2G parameters provided by the 2G network, then:
1- either your 2G parameters are wrong
2- or, the 2G system is not sending those parameters properly
3- or, the MS are not interpreting the parameters properly
There is counter in the 3G network that is counting how many 2G to 3G reselections are done within a specific period of time. You could see how it evolved over time ?
If you upgraded your 2G network, ensure that the way FDD and Scrambling codes to be measured are well defined after the upgrade.
1/ Which ALU release are you using ?
2/ Collect your 2G to 3G reselection attempts and successes counters (from 3G network, not 2G), and compare those amouns before vs after
3/ Check this 2G3G reselection success rate (attempt / succes) between before and after.
If succes rate degrades, then the core network might be involved (refusing to give access to some specific MS)