EM4510-20GSFP+ module offers two additional 10G SFP+ slots for further optical network expansion on the ECS4510-28T or ECS4510-28F models. This increases total number of 10G optical ports of these switches to four. The two 10G SFP+ ports can be loaded with any SFP+ 10G transceiver and they are unrestricted (open) SFP slots.