Abstract: A bi-directional network medium monitor including a tap apparatus connected inserted in a network media, e.g. Fiber Optic (FX) and Twisted Pair (TX), comprising a transceiver and a clock recovery element for each medium and medium monitor connection, and a bi-directional serial data multiplexer which directs the medium data while in the serial data format. Also, the medium monitor may interrupt medium data transfer in either medium direction and insert its data for diagnostic or other network purposes. Thus, the apparatus according to the present invention is operable to monitor a network at the maximum data rates currently used while providing no significantly network data delay.