Levels of Reliability Requirements

There are three requirement levels according to the objective of the implementation and the implementation itself. Table 1 lists three levels of reliability requirements.

**Table 1** Levels of reliability requirements
Level	Objective	Implementation
1	Fewer faults in the system software and hardware	Hardware: simplified circuit design, improved production technique, and reliability test Software: software reliability design and test
2	No impact on the system when a fault occurs	Device and link redundancy design, switchover policy, and switchover success rate
3	Rapid recovery from a fault that affects the system	Fault detection, diagnosis, isolation, and recovery

All three levels of reliability must be considered during different stages of building a network:

Level 1 when designing and producing network devices
Level 2 when designing network architectures
Level 3 when using reliability technologies during network deployment