The Catalyst 3900 is now enhanced with a four-port copper and a four-port fiber expansion module, which can be inserted into one of the two available Catalyst 3900 expansion slots. With these modules, a single Catalyst 3900 can support up to 28 Token Ring ports. Up to eight units can be stacked using the optional stack port module and the Catalyst Matrix switch, for a total configuration of 224 Token Ring ports