(By Black Box) Although Ethernet is usually thought of as having a star topology, it’s also possible to build an Ethernet network as a ring. This configuration has the advantage of providing a redundant pathway if a link goes down. A ring topology is often used in application such as traffic signals and surveillance, where long distances may make it difficult to run fiber in a star formation from a central switch and where downtime must be minimized.
The key to the ring topology is spanning tree protocol. One switch-in this case, the switch in the central office-is the root of the spanning tree. A node on the opposite side of the ring blocks on of the ports leading back to the root switch, creating a topology that functions like a long line of Ethernet switches. If a link breaks, the network reorganizes itself to relink all the switches. Although this convergence isn’t instantaneous, it takes only a few seconds to bring the network back. In the diagram below, Hardened Managed Ethernet Switches create a ring topology that operates at Gigabit speed to support traffic cameras at the interaction. Industrial Ethernet Serial Servers make the connection from the switch to the serial interface on the traffic signals, enabling central management of the lights across the Ethernet network.
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