The ring topology is a physical network topology with a self-contained cable ring. The transmission medium of the ring topology is connected to each network station. Access to the ring topology follows a deterministic access procedure with predictable delay times.
The physical ring topology is constructed so that each network station and node is connected to the ring with two cables: one for incoming signals and one for outgoing signals. Information is transmitted in a predetermined transmission direction. Typically, the transmission medium is accessed sequentially from station to station by means of a polling system from the central station or by a token. The buffering ranges from one bit to several data packets. The message passes all stations. There is usually a fixed station for control tasks, the monitor, in the case of the Token Ring it is the Token Ring monitor.
In ring topology, the failure of a computer or the ring interruption inevitably leads to the failure of the entire ring. In practice, ring interruptions caused by failed computers are bypassed by concentrators with bypass functions. Transmission medium interruptions are avoided by redundant transmission media over which data traffic is switched. Typical standardized networks in ring structure are the Token Ring( IEEE 802.5) and FDDI, which operates with a double ring.
Ring topologies are easy to expand, have a smaller number of lines than star topologies and a decentralizable protocol structure. Disadvantages arise in the event of line or station failure as well as in the duration of message transmission, which increases proportionally to the number of connected stations.