This cable is used between the top and bottom units of a stack of 3Com Switch 5500G-EI switches, so as to add resiliency to the 3Com eight-high XRN Stacking.Each Switch 5500G has two built-in XRN Stacking ports at the rear of the unit. For non-resilient stacking, a 3Com Switch 5500G Stacking Cable goes from the first stacking port of one switch to the second stacking port of the next switch, in and out, switch to switch, down the stack. This Resilient Stacking Cable then completes the stacking loop by connecting the top switch's available stacking port to the bottom switch's available stacking port.