Network availability is determined by the fault-free operating time of the network, related to a specific time interval. It is the time that a network is fully operational. It is expressed as a percentage and monitored to ensure that the service
to be provided is available to the end users. Network availability is determined through performance monitoring. Performance monitoring can be proactive or reactive. That is, even when the network is no longer available.
Themeasured uptime is an important key performance indicator (KPI) for the network service provider
, who can derive the quality of service from the measured values. The availability of the network is given as a percentage of time and is measured over a certain period of time. It is calculated by dividing the uptime by the total time, which is the uptime plus the downtime. Measured downtime includes all times when the network system is down, such as for maintenance, unplanned outages, and system startup, and ranges from basic availability to high availability. For the latter, the downtime is about 5 minutes per year.