The hot-swappable Input/Output (I/O) cards provide excellent in-service expansion capabilities in convenient sets of 16 ports per I/O card for the HDX576, thus allowing re-configuration without interrupting signal processing. Each I/O card consists of one Transmit (T) and one Receive (R) optic per port. I/O Cards are available with LC-type fiber connectors and are assembled with Single-mode optics (SFP+). Each individual I/O Card lists the ports as 1 through 16. The Fan Tray module lists the port numbers (all numbering is bottom to top, left to right. A LED located at the top of each I/O card indicates when power is ON to that card.