Dual modular redundant
Encyclopedia
A machine which is Dual Modular Redundant has duplicated elements which work in parallel to provide one form of redundancy
. A typical example is a complex computer system which has duplicated nodes, so that should one node fail, another is ready to carry on its work. For instance: the Submarine Command System SMCS
used on submarines of the Royal Navy
employs duplicated central computing nodes, interconnected by a duplicated LAN.
A lockstep fault-tolerant machine uses replicated elements operating in parallel. At any time, all the replications of each element should be in the same state. The same inputs are provided to each replication, and the same outputs are expected. The outputs of the replications are compared using a voting circuit. A machine with two replications of each element is termed dual modular redundant (DMR). The voting circuit can then only detect a mismatch and recovery relies on other methods. Examples include 1ESS switch
. A machine with three replications of each element is termed triple modular redundant
(TMR). The voting circuit can determine which replication is in error when a two-to-one vote is observed. In this case, the voting circuit can output the correct result, and discard the erroneous version. After this, the internal state of the erroneous replication is assumed to be different from that of the other two, and the voting circuit can switch to a DMR mode. This model can be applied to any larger number of replications.
Redundancy (engineering)
In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
. A typical example is a complex computer system which has duplicated nodes, so that should one node fail, another is ready to carry on its work. For instance: the Submarine Command System SMCS
SMCS
SMCS, the Submarine Command System, was first created for the Royal Navy of the United Kingdom's Vanguard class submarines as a tactical information system and a torpedo weapon control system...
used on submarines of the Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
employs duplicated central computing nodes, interconnected by a duplicated LAN.
A lockstep fault-tolerant machine uses replicated elements operating in parallel. At any time, all the replications of each element should be in the same state. The same inputs are provided to each replication, and the same outputs are expected. The outputs of the replications are compared using a voting circuit. A machine with two replications of each element is termed dual modular redundant (DMR). The voting circuit can then only detect a mismatch and recovery relies on other methods. Examples include 1ESS switch
1ESS switch
The Number One Electronic Switching System, the first large-scale Stored Program Control telephone exchange or Electronic Switching System in the Bell System, was introduced in Succasunna, New Jersey, in May 1965. The switching fabric was composed of reed matrixes controlled by wire spring relays...
. A machine with three replications of each element is termed triple modular redundant
Triple modular redundancy
In computing, triple modular redundancy is a fault tolerant form of N-modular redundancy, in which three systems perform a process and that result is processed by a voting system to produce a single output. If any one of the three systems fails, the other two systems can correct and mask the...
(TMR). The voting circuit can determine which replication is in error when a two-to-one vote is observed. In this case, the voting circuit can output the correct result, and discard the erroneous version. After this, the internal state of the erroneous replication is assumed to be different from that of the other two, and the voting circuit can switch to a DMR mode. This model can be applied to any larger number of replications.