US Patent 9497025 Ethernet interface module

An Ethernet interface module comprises a duplex port operable to transfer frames between said Ethernet network and a device and a path coupling a receive portion of the duplex port to a transmit portion of said first full duplex port. A queue is disposed in said first path. Evaluation apparatus is coupled to the queue and determines whether a received frame is addressed to said Ethernet interface module and whether a frame type field contains a frame type. The Ethernet interface module is operable in a first mode such that every said received frame is echoed back out the full duplex port; and is operable in a second mode such that each received frame that meets predetermined evaluation criteria is echoed back out the duplex port and those received frames that do not meet the predetermined evaluation criteria are discarded.