Explain how a relatively unreliable system can provide a high level of availability.

Explain how a relatively unreliable system can provide a high level of availability.
Ans: A telephone exchange switch that routes phone calls is an example of a system where availability is more important than reliability. Users expect a dial tone when they pick up a phone, so the system has high availability requirements. If a system fault occurs while a connection is being set up, this is often quickly recoverable. Exchange switches can usually reset the system and retry the connection attempt. This can be done very quickly and phone users may not even notice that a failure has occurred. Furthermore, even if a call is interrupted, the consequences are usually not serious. Therefore, availability rather than reliability is the key dependability requirement for this type of system.