allocate auxiliary channel

 Dear all,I want to allocate auxiliary to 4 channel. My command:

allocate auxiliary channel ch1 type disk;

allocate auxiliary channel ch2 type disk;

allocate auxiliary channel ch3 type disk;

allocate auxiliary channel ch4 type disk;

But when it execute (duplicate database) It just has one channel and no andy error appear. 

Starting restore at 19/08/2013 03:46:49

allocated channel: ORA_AUX_DISK_1

channel ORA_AUX_DISK_1: SID=1308 device type=DISK

I just show one channel. 

how to assign more on channel in this case? and what happen with it?

Thanks

DuyPM