ARC-1883ix controller firmware default enables the ROC edfb function. This will low the performance when ROC edfb=enable and Expander edfb (dhpm) =disable. From firmware version 1.52 date: 2014-10-28 or later, ARC-1883ix has added the ROC "End Devices Frame Buffering" function in the Advanced Configuration. You should set the ROC "End Devices Frame Buffering" option=disable if you connect less devices on the ARC-1883ix.