Wrapback reconfiguration mechanism of a counter‐rotating dual token ring

Abstract

In the distributed‐control ring LAN (local area networks), a reconfiguration control is required to cope with the independent asynchronous failure detection in the stations. This paper proposes a wrapback reconfiguration mechanism in the dual‐token ring LAN with a parallel dual structure of distributed‐control token‐ring LAN. Here, the ring is wrapped back automatically by the distributed‐control of the stations when a fault is detected in the communication function in the physical layer or MAC (medium access control) layer. Each station connected by the dual ring determines its operation based only on the state of the two input links. When an abnormality is detected in a link, a failure‐detecting beacon is transmitted and the failure domain is located by the reception priority competition control, where the transmission is stopped by receiving the beacon. The stations adjacent to the failure domain artificially generate a fault in the output link paired to the failure link, so that the station to wrap back the ring at both sides of the failure link‐pair can be located by the same procedure as for the localization of the failure domain. In parallel to the ring wrapback, the active monitor is established, which is needed in the initialization of the ring. Each station discriminates between the current link and standby link, and the ring wrapback by the failure of the standby link is avoided. Applying the international standard (IEEE 802.5) to the token‐ring LAN, the failure recovery time is evaluated. The effectiveness of the proposed reconfiguration mechanism has already been verified by an experiment using the actual equipment.