Network redundancy models ensure reliability by providing alternative communication paths. There are various redundancy protocols for a wide range of applications. An important feature of redundancy is the recovery time. Generally speaking, open standards tend to have a longer recovery time than proprietary standards. Open standards: STP, RSTP, MSTP, MRP serve a variety of topologies. The recovery time ranges from a few seconds to a few minutes Proprietary standards: O-Ring, O-Chain, Turbo-Ring and Turbo-Chain offer ring redundancy or line redundancy. The recovery time is between 20 and 40 milliseconds