From the Canarie news mailing list.
I don't think I've ever experienced five 9's on any telco service, I have always assumed I must be the one customer experiencing down-time, and the aggregate was somehow five 9's. How is network reliability calculated to end up with five 9's? Pete. ---------- Forwarded message ---------- Date: Wed, 24 Apr 2002 10:08:18 -0400 (EDT) From: CAnet-3-NEWS@canarie.ca Subject: [news] The Myth of Five 9's Reliability For more information on this item please visit the CANARIE CA*net 3 Optical Internet program web site at http://www.canet3.net/news/news.html ------------------------------------------- [A good article on the truth about five 9's reliability. Some excerpts - BSA] http://www.bcr.com/forum Deep Six Five-Nines? For much of the 20th century, the U.S. enjoyed the best network money could buy; hands-down, it was the most modern, most ubiquitous and most reliable in the world. And one term--five-nines--came to symbolize the network's robustness, its high availability, its virtual indestructibility. When the goal of five-nines was set, the network was planned, designed and operated by a monopoly, which was guaranteed a return on whatever it invested. It was in the monopoly's interest to make the network as platinum-plated as possible. One of the key points is that "five-nines" has long been somewhat overrated. Five-nines is NOT an inherent capability of circuit-switched, TDM networks. It's a manmade concept, derived from a mathematical equation, which includes some things and leaves out others. It's critical to remember that when you run the performance numbers on ALL the items in a network--those that are included in the five-nines equation and those that aren't--you're probably going to wind up with a number less than 99.999 percent. A well-run network actually delivers something around 99.45 percent. The gap between the rhetoric of five-nines and actual network performance leads to the conclusion that five-nines may not be a realistic or even necessary goal.