First of all, as you might know there are several tipes of HO according to their cause of origin: level,quality,distance, power budget etc. For each of them there are specific time period in BSC database called Handover averaging window. So for each of this tipe of HO the above mentioned values of level,quality,distance, power budget are measured first and if any of them exceeds the threshold specified for level,quality,distance, power budget then this tipe of HO is executed. To find out what are the averaging periods you must see the values of HOAVLEV,HOAVQUAL,HOAVDIST,HOAVPWRBin your database. Those parameter names are for the Siemens BSS.