Pipeline Publishing, Volume 3, Issue 11
This Month's Issue:
The Long Arm of Telecommunications Law
download article in pdf format
last page next page

Carrier Grade: The Myth and the Reality of Five Nines

back to cover

By Wedge Greene and Barbara Lancaster, LTC International

Carrier grade power

What is the hard fast requirement for Carrier-Grade? Is “five-nines” or 99.999% up or 0.99999 available a hard, fast requirement of telecommunications or is it the telecommunications equivalent of an Urban Myth? From a common sense perspective, the meaning of availability is clear, and given the essential nature of telecommunications, the necessity of five-nines is easily understood. But when you want to measure it, and hold someone accountable for delivering that availability, you must establish an operational definition for it. We asked a cross section of telecom and OSS experts if they knew the origin of five-nines and surprisingly some answered that in reality there was ‘no such thing.’ (We suspect that these folks skipped their Statistical Analysis classes, or perhaps meant to say that measuring five-nines is not sufficient to achieve Carrier Grade performance…) Wikipedia has a useful entry for “The myth of the nines” which supports the latter:

In information technology, the myth of the nines is the idea that standard measurements of availability can be misleading.”
[Wikipedia, http://en.wikipedia.org/wiki/

So we set out to track down just what carrier-grade is and where it comes from.

For the thirty years we have been in this industry, five-nines was the number one rule-of-thumb: the most basic underlying tenant of hardware construction, network design, and the expressed goal of every network system. It is the very heart of the operational war stories on which we were raised. For example, there is the case of telecom power requirements – the very foundation of the ‘set apart’ and ‘we are different’ basis of Point of Presence (POP – the local building where telecom switching equipment was placed) construction. Power loss was once identified as the single greatest threat to telecom network reliability as alternating circuit equipment was prone to costly service variations (telecom could not rely on cycle timing from a power utility) and unacceptable equipment failure rates. So DC rail-based power was mandated for telecom POP construction and every carrier-grade network element had to run off that DC power. For certain, it made power failovers remarkably straightforward with all those batteries. Even computing servers (where they were lightly scattered across voice POPs) had to have DC powered versions. Never mind that high voltage DC rail power can fry your personnel six ways from Sunday, once all POPs were powered by DC, the domestic

Is “five-nines” or 99.999% up or 0.99999 available a hard, fast requirement of telecommunications or is it the telecommunications equivalent of an Urban Myth?


photo here
network “failures attributable to power outages over the last n years (N being variable in the stories) could be counted on one hand.” And this is true, DC power in POPs is remarkably reliable, probably six-nines reliable considered, in full, as a redundant system. But the story of DC power and five-nines availability is an oral tradition handed down from those who taught us and to those we taught.

NOC Targets

Also it is very real that the yardstick standard for availability of networks to be delivered by the Network Operations Center was 99.999%. This was not a soft target. Performance reviews of NOC management were frequently based on hitting that target. Availability was the number one KPI for networks and NOCs were tasked with restoring any outages so that network availability would be maintained. But early on in the then-named Network Management Forum (now the TeleManagement Forum), participants of the newly formed SLA group (though it was not called SLA back in 1994) realized that each of them had different ways of computing that figure for availability. It took years to hammer this out to an agreement on what to count and how to calculate it. (For more details, see the current SLA Handbook Solution Suite Version 2.0) But in reality, every standards group, and even every industry, seems to have a different way of defining availability. What-to-count as an outage becomes “key”.

Wedge Greene has a personal experience with the traps lying in wait for those trying to measure and report on availability. Back in the early nineties when he was a signaling and routing specialist, but because he had software and systems experience, he was yanked out of his comfortable theoretical work and tasked with developing a system to

article page | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
last page back to top of page next page

© 2006, All information contained herein is the sole property of Pipeline Publishing, LLC. Pipeline Publishing LLC reserves all rights and privileges regarding
the use of this information. Any unauthorized use, such as copying, modifying, or reprinting, will be prosecuted under the fullest extent under the governing law.