A network structure in which the nodes are laid out in a physical ring topology, or closed loop configuration, and are interconnected by two optical fibers, with one fiber transmitting in one direction and the other in the other direction. Such a configuration is highly resilient, not only because there is a redundant physical ring, but also because the counter-rotating transmission ensures that any node can communicate with any other node in one direction or the other in the event of the failure of only a single node or link. Fiber Distributed Data Interface (FDDI), Resilient Packet Ring (RPR), Synchronous Digital Hierarchy (SDH), and Synchronous Optical Network (SONET) all specify dual counter-rotating ring configurations. See also FDDI, ring topology, RPR, SDH, and SONET.