Increased system redundancy can benefit the network if traffic needs to be redirected during an emergency, construction/refurbishment, collision, or other disruptive event. In many systems important to safety, such as electrical and hydraulic systems in aircraft, some parts of the control system may be triple, formally referred to as triple modular redundancy (TMR). An error in one component can be rejected by the other two. In a triple redundant system, the system consists of three sub-components, all three of which must fail before the system fails. Since each rarely fails, and subcomponents are expected to fail independently of each other, the probability of failure of all three components is considered to be extremely low; often outweighed by other risk factors such as human error. Reservation may also be known by the terms "majority voting systems" or "voting logic". This article discusses the main aspects of system redundancy, analyzes the reasons and factors for the use of backup equipment, and studies the role of a fault-tolerant system.