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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 travel from node to node, with each node along the way handling every packet. 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.〔Bradley Mitchell "Network Topologies" (), About.com Guide, retrieved May 24, 2010〕 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. 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. ==Advantages== *Very orderly network where every device has access to the token and the opportunity to transmit *Performs better than a bus topology under heavy network load *Does not require a central node to manage the connectivity between the computers *Due to the point to point line configuration of devices with a device on either side (each device is connected to its immediate neighbor), it is quite easy to install and reconfigure since adding or removing a device requires moving just two connections. *Point to point line configuration makes it easy to identify and isolate faults. *Reconfiguration for line faults of bidirectional rings can be very fast, as switching happens at a high level, and thus the traffic does not require individual rerouting 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ring network」の詳細全文を読む スポンサード リンク
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