Study of Steering Protection Switch in Case of Unidirectional Link Failure in RPR

According to IEEE 802.17 standards, the TP frames which transfer the failure information can only indicate the span failure instead of each link failure. It leads resilient packet ring (RPR) treats all link failures as bidirectional. That means if one ringlet fails, the other in the same span will also be disabled. This operation will not impact the performance of wrapping protection switch for its intrinsic protection mechanism. But it will deteriorate the performance of steering protection switch in case of unidirectional link failure. In our paper, an improved steering protection switch scheme is proposed to overcome this shortcoming. It utilizes three reserved bits in extended control field to transfer more failure information in TP frame. With the help of the information, a special routing table defined in the proposed scheme for transmission is built and maintained at each station. By using the routing table each station can utilize the un-failed link to choose optimal transmit path. Our analysis shows this will save about 17% of the additional consumed link bandwidth than the original steering protection in case of unidirectional link failure. By analysis and simulation we show that the proposed steering protection switch can significantly increase the throughput of the network, lighten the congestion and decrease the traffic delay when unidirectional link failure occurs