99 %
Acceptable for ordinary WiFi connection
Never used when designing stable radio links
99.9 %
Can be used for links where other factors decrease the total Availability significantly e.g. unstable electricity supply
99.95 %
Sometime used by ISPs for services with very low Service Level Requirements
Unlicensed bands can meet such requirements
99.98 %
Standard level of Reliability
Often used for less demanding last-mile links
Very often combined with ACM function, which allows maintenance of availability during signal drops on the cost of reduced data-speed due to atmospheric or other issues (customer experiences link operation without interruptions; only capacity may fluctuate)
99.99 %
The most common used for microwave links design
Suitable for last-mile links requiring reasonable quality
If applied to backbone links, it is recommended to use ACM function or other mechanism to retain reliability
99.995 %
Used for backbone links with guaranteed capacity
Licensed bands offer these levels of reliability
99.999 %
Typical reliability level for high availability applications
Used on backbone links
Licensed band is a must
Typically used over shorter distances due to cost implications
99.9999 %
Used on backbone links
Licensed band is a must
Typically used over shorter distances due to cost implications
Alternative expressions of Availability:
| Availability | 99% | 99.9% | 99.95% | 99.98% | 99.99% | 99.995% | 99.998% | 99.999% |
| Amount of “nines” | 2 | 3 | – | – | 4 | – | – | 5 |
| Unavailability during a year | 88 hours | 8.8 hours | 4.4 hours | 105 mins | 53 mins | 26 mins | 10 mins | 5.2 mins |