Collision avoiding system and protocol for a two path multiple access

Abstract

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 one signal from the first path and for writing another signal on the first path. The one signal is read from the first path by an arrangement which electrically precedes the arrangement for writing the other signal on the first path. A similar read arrangement is electrically preceding a write arrangement on the second path. If the station has a packet to transmit, it can overwrite a busy control field of the one signal packet on either path. Having read the one signal on 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 through a busy control field. The packets flow down the path to a destination station. Eventually all packets will be transmitted and the busy control field may be detected at an end station for indicating the event that all packets have been transmitted. The end station on one path acts as the head station on the other oppositely directed path. Hence, responsive to detecting that all packets have been transmitted, the head station on the other path may transmit an end cycle packet, 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.