Mac reconfiguration mechanism for a dual‐ring lan

Abstract

AbstractIn a reconfiguration mechanism for improving the RAS of a ring LAN, it is necessary to guarantee the proper functioning of communication functions up to the medium access control (MAC) layer. This paper proposes a reconfiguration mechanism for distributed‐control dual ring LANs which maximizes the size of the ring while maintaining MAC layer communication functions by automatic ring merging and wrapback. Each station bases its actions on the state of the two input links. When a link fails, the failed segment is isolated by ring wrap‐back and the ring operates in wrapback mode. When multiple failures occur, the ring is wrapped back further into a smaller ring or several rings until the MAC layer functions are recovered. On the other hand, when the MAC layer functions of the failed segment are recovered, wrapback is released and the failed segment is merged into the active ring. With this reconfiguration mechanism, the largest ring possible to maintain MAC layer functions is formed automatically regardless of failures, powering up or down, etc. This mechanism is represented using finite state machine (FSM) diagrams. The recovery times from multiple failures are evaluated using the specifications of the international LAN standard (ISO 8802‐5). This reconfiguration mechanism has been approved as the IEEE standard (recommended practice) for a dual‐ring reconfiguration mechanism, and its effectiveness has been proven by field trials.