Loop-back functions direct transfer through the MAU. The Jabber detect. It removes equipment from the network whenever it continuously transmits for periods significantly longer than required for a maximum-length packet, indicating a possible problem with the NIC. Signal quality error test. The signal quality error test detects silent failures in the circuitry. Link integrity functions detects breaks in the wire pairs. Both Signal quality error test and Link integrity functions assist in fault isolation. Two modes of operation: Normal mode: The MAU functions as a direct connection between the baseband medium and the DTE. Data output from the DTE is output to the coaxial trunk medium and all data on the coaxial trunk medium is input to the DTE. This mode is the "normal" mode of operation for the intended message traffic between stations. Monitor mode or Isolated mode: The MAU functions as a receive-only connection between the baseband medium and the DTE. Data output from the DTE is suppressed and only data on the coaxial trunk medium is input to the DTE. This mode is for observing message traffic. MAU functional specifications: Transmit function The ability to transmit serial data bit streams on the baseband medium from the local DTE entity and to one or more remote DTE entities on the same network. Receive function The ability to receive serial data bit streams over the baseband medium. Collision Presence function The ability to detect the presence of two or more stations concurrent transmissions. Monitor function (Optional) The ability to inhibit the normal transmit data stream to the medium at the same time the normal receive function and collision presence function remain operational. Jabber function The ability to automatically interrupt the transmit function and inhibit an abnormally long output data stream. It removes equipment from the network whenever it continuously transmits for periods significantly longer than required for a maximum-length packet, indicating a possible problem with the NIC. MAU in this context is not to be confused with a Media Access Unit, which shares the same acronym. References Ethernet Computer connectors