A ring topology is a topology for a Local Area Network (LAN) in which every device has exactly two neighbours for communication purposes.
Typically, all messages travel through a ring in the same direction. A failure in any cable or device breaks the loop and will take down the entire segment. Another disadvantage of the ring is that if any device is added to or removed from the ring, the ring is broken and the segment fails.
In wide area networks (WAN) and meteropolitan area networks (MAN), a ring topology is used to as the topology for the backbone (sometimes called a city ring) to connect the customers. In that case the ring is used in both directions to have two distinctive paths to the public switch.