The main ring used in the Fiber Distributed Data Interface (FDDI), which uses a dual ring topology. The primary ring is the only ring used unless it has a fault, in which case the network reconfigures itself to use the secondary ring with the data traveling in the opposite direction. The dual ring configuration provides FDDI with fault tolerance.
Run the FDDI primary ring and secondary ring along different physical paths to make the network more redundant. An accident or disaster affecting one of the rings will not affect the other.