The Mean Time Between Failures (MTBF) and Mean Time to Repair (MTTR) are used to evaluate system reliability.
The MTBF refers to the average amount of time (usually expressed in hours) a component or a device works without any failure. A larger MTBF value indicates higher reliability.
The MTTR refers to the average amount of time that a component or a device takes to recover from a failure. MTTR also involves device management and customer service and is an important specification for device maintenance.
MTTR = Fault detection time + Hardware replacement time + System initialization time + Link recovery time + Route convergence time + Forwarding recovery time
A smaller MTTR value indicates higher reliability.