Reality Check On Five-Nines
by Gary Audin
Posted: 07/09/2002
Abstract:
While everyone in telecom has been using the term "five-nines" for decades, I'm willing to bet that few actually know what 99.999 percent really means, and even fewer know if it's really necessary. Of course, we all know that five-nines relates to reliability, and expectations are high— dialtone is expected at all times. Way back when AT&T's #1ESS switch was being developed, the development team's goal was to have less than one day of outage in 40 years. Obviously no one kept one in service long enough to find out if that target was actually met, but the 1Es cranked along pretty predictably.
Does telecom still need its gold-standard availability metric? Maybe not.
(Note: Since this article is already available in full-text format at the BCR web site, we're linking to that site.)
http://www.webtorials.com/main/resource/papers/BCR/paper32.htm