The Nine nines of reliability often quoted is for the availability of a complete distributed system, including maintenance downtime. A typical single Ericsson

The Nine nines of reliability often quoted is for the availability of a complete distributed system, including maintenance downtime. A typical single Ericsson AXD 301 switch had a target of 5 nines of reliability without network redundancy, which is 5mins/year, including planned outages. see http://www.erlang.se/publications/Ulf_Wiger.pdf http://www.erlang.se/publications/Ulf_Wiger.pdf One of the advantages of these switches was that they could manage 95% throughput at 150% load (Throughput then drops linearly to 40% at 1000% sustained load), which is also extremely useful, although not mentioned often.