Cisco offers a variety of connectivity, expansion and upgrade modules and cards to accommodate the customer specific needs. Cisco's components are easily and inexpensively upgradeable as customer requirements change.Cisco offers its four-port fiber expansion module, which can be inserted into 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.