The Myth of Five 9's Reliability (fwd)

Wed Apr 24 21:21:35 UTC 2002

This is the sort of thing that can be discussed forever, but here's an 
anecdote anyway:

At my previous employer, we hired a lot of people who had spent their 
entire careers either running or developing equipment for TDM voice 
networks. Their view of five nines for voice was that the network was "up" 
if the voice signaling infrastructure worked as designed -- not that you 
could actually get calls through the network. So, for example, if your long 
distance call could not be completed because bearer trunks were down, there 
wasn't enough capacity etc. etc. then the voice network was still "up" for 
five 9s calculation purposes even though you couldn't use it for its 
intended purpose.

How many times have you received the "All circuits are busy" message? Some 
would say that was the voice network failing to function -- the Bell-shaped 
heads said it was working as designed. They were clear that what mattered 
was the signaling integrity of the network, not the application of voice 
connectivity itself. So, if you can get dial tone but not place a call, 
that's five 9s reliability at work.

When applied randomly to the Internet, I suppose that means if you can dial 
into a RAS and establish a PPP/IPCP session, but the RAS' connection to the 
Internet is down, then the service is up :-)

Cheers,

Mathew

At 04:51 PM 4/24/2002 -0400, Art Houle wrote:

>How to calculate uptime and get 5 9s
>
>-do not include any outage less than 20 minutes.
>-only include down lines that are actually reported by customers.
>-when possible fix the line and report 'no trouble found'.
>-remember that your company is penalized by the FCC for bad ratings, so
>don't report any problems that you do not have to.
>
>On Wed, 24 Apr 2002, Pete Kruckenberg wrote:
>
> >
> > >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 at 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.
> >
>
>Art Houle                               e-mail:  houle at acns.fsu.edu.
>Academic Computing & Network Services   Voice:  850-644-2591
>Florida State University                   FAX:  850-644-8722

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