SAP ONLINE BACKUP WITH RMAN

i need to configure policy for online incremental backup and according to Admin Guide NBU for SAP UNIX that can only possible with RMAN script sap_rman_backup. but i am confussed because for commands mentioned in this scripts that seems offline backups so please help me out how can i configure Online Backup with RMAN....... with out RMAN backups are currently running.

NBU 7.1 windows 2008

SAP on suse linux

commands in sap_rman_backup

"
if [ $SAP_FULL -eq 1 ]; then
    CMD_LINE="$SAP_ENV brbackup -d rman_util -t offline -m full -c"
elif [ $SAP_CINC -eq 1 ]; then
    CMD_LINE="$SAP_ENV brbackup -d rman_util -t offline -m incr -c"
fi"