Components of a pluggable I/O interface include a host board Pluggable Transceiver (PT) connector; a cage or guide rail, which provides EMI containment and guidance for the mating plug; and a mating plug, which may be in the form of a pluggable transceiver or direct attach cable assembly.  A transceiver requires a mating cable assembly.  Accessories include heatsinks, lightpipes, dust plugs, and EMI plugs.  This illustration shows a QSFP application.