Reconfigurable collision avoiding system, station and protocol for a two path multiple access digital communications system

摘要

In order to control the transfer of packets of information among a plurality of stations, e.g., digital computers, the instant communications system, station and protocol contemplate first and second oppositely directed signal paths. At least two stations are coupled to both the first and the second signal paths. A station includes arrangements for reading (and writing) signals from (and on) each of the two paths. Signals are read from either path by an arrangement which electrically precedes the arrangement for writing signals on the path. If the station has a packet to transmit, it can overwrite a busy control field of a packet on either path. Also having read a packet signal from the path, a logical interpretation may be made within the station as to whether the path is busy or is not busy. If the path is not busy, the packet may be written on the path by overwriting any signal thereon. If the path is busy, the station may defer the writing until the path is detected as not busy e.g. by reading a busy control field of another packet. Here the two paths are coupled to form two ring structures so the packets flow down the path to a destination station. Eventually all packets will be transmitted and the busy control field loops around to a station which is designated as a control station. The control station, responsive to detecting that all packets have been transmitted on one of the paths, may transmit a start cycle packet on the one path, responsive to which event a new cycle may be started by initializing each station on the one path and by permitting each initialized station to transmit. In the event of an electrical open, the system, station and protocol are adapted to reconfigure the system so that the station electrically preceding the open functions as an end station while the station electrically succeeding the open functions as a head station.