I think this should be dependent on you XDR mode. You can set the XDR mode for 2 XDR units or 1. If it is configured for 2, you have only 16 port B returns for each racks. Otherwise 48 
I think this should be dependent on you XDR mode. You can set the XDR mode for 2 XDR units or 1. If it is configured for 2, you have only 16 port B returns for each racks. Otherwise 48
