Atif,
9 times out of 10 it is NOT netbackup that is slow.
Oracle's RMAN is a very slow an clunky way to backup Oracle.
Oracle will be even slower ot tape if it's on a Sh*ty slow box or network.
Look at your systems.
How is it configured?
All NIC's and HBA's configured correctly, Kernel set correctly, do you have memory sufficiant enough to run your master?
JD