For more information regarding traffic classes please check OBAS Online help on PCC > Service Director > Service Level Manager > Traffic Classes screen or the corresponding article in OBAS Provider's Guide.
If date/time of <to> tag matches exactly <to> date/time of any record imported before, new import will overwrite traffic usage for that time stamp. In other cases newly imported traffic is added to the total traffic amount for the date.
It is possible to import negative traffic to correct previous import if needed. It works only if traffic usage for the date is not zero.