<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2007) (Learn how and when to remove this template message) </Td> </Tr> <P> A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring . Data travels from node to node, with each node along the way handling every packet . </P> <P> Rings can be unidirectional, with all traffic travelling either clockwise or anticlockwise around the ring, or bidirectional (as in SONET / SDH). Because a unidirectional ring topology provides only one pathway between any two nodes, unidirectional ring networks may be disrupted by the failure of a single link . A node failure or cable break might isolate every node attached to the ring . In response, some ring networks add a "counter-rotating ring" (C - Ring) to form a redundant topology: in the event of a break, data are wrapped back onto the complementary ring before reaching the end of the cable, maintaining a path to every node along the resulting C - Ring . Such "dual ring" networks include Spatial Reuse Protocol, Fiber Distributed Data Interface (FDDI), and Resilient Packet Ring . 802.5 networks - also known as IBM token ring networks - avoid the weakness of a ring topology altogether: they actually use a star topology at the physical layer and a media access unit (MAU) to imitate a ring at the datalink layer . </P> <P> Some SONET / SDH rings have two sets of bidirectional links between nodes . This allows maintenance or failures at multiple points of the ring usually without loss of the primary traffic on the outer ring by switching the traffic onto the inner ring past the failure points . </P>

A fiber break in the link between the two nodes