Advantage of redundant networks
The advantage of redundant networks lies in the increased reliability for all participants. Whereas in unmanaged networks, due to the strict star topology, a network switch can only be reached via exactly one single path and therefore any failure of any switch on the way to the subscriber immediately leaves the subscriber "in the dark", in ring networks there are two paths to each switch and thus to each subscriber: "around to the left" or "around to the right". In the case of even higher demands on fail-safety, where the ring master is also designed redundantly as a "single point of failure", the network connection from the sender to the receiver can also be designed twice across the entire network. This requires two network ports at each of the terminals, both of which are connected to switches, which in turn are each part of a ring network. Maximum redundancy through dual homing plus double ring.
Technically, a network ring is managed by a selected switch, the ring master. By default, the ring master internally connects the primary path ("left-hand side") and blocks the secondary or backup path ("right-hand side"). If a switch on the left-hand path fails, the ring master releases the backup path and the data packets reach their right-hand destination. For the reorganisation of the topology and the learning of the new paths, there are own standardised protocols such as the Spanning Tree Protocol (STP), which historically was soon replaced by the more efficient Rapid Spanning Tree Protocol (RSTP). But even this protocol, with recovery times in the order of 100 milliseconds, is still far too slow for industrial environments. For this reason, manufacturers developed their own proprietary ring protocols and achieve recovery times of 10-30msec under names such as Superring, Hiperring and the like. Similar fast times are also achieved with the widely supported Media Redundancy Protocol (MRP).
Areas of application
Redundant networks are mainly used in scenarios where a network failure of only 1 second or even less is critical. This applies, for example, in factory automation (bottle filling, robot movement, etc.) or in process automation (tank filling, mixture production, gas production) or also in power generation (substations, power distribution). The additional costs and the increased management effort will have already paid for themselves with the first "emergency", in which a network fault was silently intercepted by network redundancy.