Abstract: A redundant local area network uses two cables over which duplicate information is transmitted in parallel in the form of identical message frames. Each receiver on the network includes a circuit which evaluates the signals from the two cables and selects one of the signals to be processed. This circuit determines the length of the message frames received on each cable for a given transmission and indicates which cable, if any, carried the longer frame. The signal from the cable that carried the longer frame is then selected as the output of the receiver. Additional circuitry is provided to prevent two short frames on one cable from being considered as one long frame. An apparatus is provided to look at the historical reliability of the signals on the cables so that if one cable has had a significantly better performance than the other, a single poor transmission on the one cable will not cause the historically poorer cable to be selected until such time as the poorer cable has redeemed itself.

Abstract: A communications network is comprised of two or more stations which share mastership of the network by passing a token between them. While a station holds the token it may send low or high priority messages. It may also inform other stations of its intent to exit the network and it may solicit for new stations wanting to enter the network. The token is passed from station-to-station in accordance with a predetermined time schedule which insures each station fair access to the network while insuring that messages are conveyed between stations within a predetermined worst case time delay.