What Does “Five Nines” Mean to You?

By: John Shepler

Five nines reliability. It's the standard often quoted for traditional telephone service and top network equipment vendors. But what does it really mean? Just how close to perfect is five nines anyway? Let’s take a look.


Reliability or Availability
The spoken term five-nines refers to the number 99.999%. This number is generally referred to as a reliability figure. Actually, what people call reliability is more correctly called "availability." It's not just how often a piece of equipment has a software crash or a power supply bursts into flames that is really important. It's how much of the time you actually get to use it. In other words, how much of the time is this particular device available. Availability includes how often it breaks and then how fast it gets put back into service. You also have to include how often it is out of service or unavailable due to routine maintenance.

An Example
Say your softswitch has a software glitch that only shows up under obscure combinations of events. When the glitch occurs once every six months, the software crashes and automatically reboots. That takes a minute. Does this switch have five nines uptime? Yes. Now if a power supply smokes once a year and it takes 20 minutes to fix it, that's not good enough for five nines even though the power supply failure occurs less frequently.

By the Numbers
Here are some handy numbers to give you perspective on the whole nines issue:

Five nines or 99.999% availability means 5 minutes, 15 seconds or less of downtime in a year.

Or, if you are really ambitious, shoot for six nines or 99.9999% availability, which allows 32 seconds or less downtime per year.

Otherwise, four nines or 99.99% availability allows 52 minutes, 36 seconds downtime per year.

Three nines or 99.9% availability allows 8 hours, 46 minutes downtime per year. This is often acceptable for many non-critical applications.

Two nines or 99% availability allows 3 days, 15 hours and 40 minutes downtime per year. That’s somewhat marginal for business.

One nine or 9% availability allows over 332 days of downtime per year. That's right. You're only up and running about a month out of the year on average.

Zero nines, of course, is totally useless. It's 100% downtime per year.

How do you get more nines?
Buy the best equipment that's the easiest to repair. Then add redundancy. Highly reliable systems often include multiple power supplies & processors, plus battery backup, diesel or natural gas generators for longer power outages than batteries can handle, multiple diverse communication lines and extras of whatever else is likely to fail. Buggy software that crashes all the time is going to hurt your reliability. If it goes down a lot and takes a long time to get back online your availability also be hurt.

Include Everything
One thing to be aware of is that the five nines criteria tends to apply to whatever the person quoting it says it applies to. PBX systems that meet five nines availability may only do so for the core system and might not include individual line cards and certainly not the phones themselves and their wiring. If it's REALLY important that you minimize downtime, you need to consider EVERYTHING that can fail and make sure it is backed up and/or very easy to fix.

On Cloud 9’s
Another option to consider seriously is to move all those hardware availability issues to the cloud. Cloud services aren’t perfect, either, but they often can provide higher service availability than you can afford locally. That’s because the cloud architecture is designed for considerable redundancy and fast failover when problems occur. If you do opt for the cloud, though, be sure you have highly reliable bandwidth connections to your provider. A 5 nines hosted PBX system isn’t all that available if you have a flakey internet connection from your facility to the cloud. A dedicated SIP Trunk or a set of redundant trunks is a much better solution.

Nines for Your Needs
How many nines do you need and what’s the cost for WAN or cloud availability? Get the best price vs performance options for your particular requirements now.

3 Mbps to 6 Mbps Bonded Internet Access

Business Internet access is critical to communicating with customers and perhaps taking and fulfilling orders. You want rock solid stability and decent bandwidth, but at a price that won’t break the bank. Here’s a look at how you can incrementally increase your Internet connection speed to match your business activity.

Not that long ago, you had a couple of choices for dedicated Internet access. You could get a T1 line at 1.5 Mbps or move up to a T3 line (DS3 bandwidth) at 45 Mbps. There really wasn’t anything in-between. Shared bandwidth services offer a larger range of choices, but shared bandwidth means variable performance and assurance of availability. You also have to contend with asymmetrical speed, where download line speed is 10x the upload line speed.

Dedicated Internet access, like T1 and T3, offers symmetrical bandwidth that is the same for both upload and download, a fixed line speed that doesn’t vary, and high availability with a Service Level Agreement (SLA). The one issue is cost, especially when you need more than what a T1 line can provide but not the full capacity of a T3 line.

Sometimes you can get what’s called a fractional line service. The service provider installs a full capacity line, but rate limits your bandwidth. The result is referred to a fractional T3 or fractional DS3 service. It saves some money over the full service level but isn’t that great of a deal on a per Mbps cost basis.

A better option today is to order bonded line service to increase your bandwidth. Bonding is an industry standard for connecting multiple lines of the same type to combine their bandwidths. For instance, you can bond two T1 lines together and get 3 Mbps instead of 1.5 Mbps. The view from your router is one larger bandwidth service rather than juggling two separate lines. That bonding process takes place within the Customer Premises Equipment (CPE) that is installed by the service provider.

Bonding is a great way to increase your bandwidth incrementally, but there are a couple of things to consider. First, you can’t just go out and buy a second T1 line from just anybody. You have to get your bonded lines from the same carrier. Remember that it is the service provider who does the bonding through equipment at both ends of the line.

Also, the cost goes up by the same increment as the bandwidth. In other words, two T1 lines cost twice as much as one T1 line. There is no economy of scale. That’s no big deal if you are happy with doubling your line speed and your cost versus have to pay 10x the price to move up to the next standard line speed increment of T3. However, this technique does get less attractive with the more lines that you bond in.

Yes, you can go beyond double bonded T1. Bond three T1 lines for 4.5 Mbps, four lines for 6 Mbps, 5 lines for 7.5 Mbps, 6 lines for 8 Mbps, 7 lines for 9.5 Mbps or 8 T1 lines to get 11 Mbps. By the time you get 8 T1 lines bonded, the cost may be approaching what you’d pay for 45 Mbps T3 and you’d have a lot higher line speed.

There is an alternate bonded line service that may give you more bandwidth for less money. This is Ethernet over Copper or EoC. Like bonded T1, EoC uses multiple wire pairs to transport the signal. Providers will bond 2, 4, 6 or 8 pair to increase the speed of Ethernet over Copper service. Unlike T1, EoC offers a much wider range of available bandwidth options. For the price of a T1 line, you can get 2 or 3 Mbps EoC. Other speed options include 5, 10, 15, 20, 25, 30, 35, 40 and 45 Mbps. Cost per Mbps actually decreases as you order higher bandwidth levels.

The one limitation of Ethernet over Copper is availability. It is a newer service and not all central offices are equipped to provide this line service. Also, EoC is highly distance sensitive. You need to be close to your CO to get the highest speeds. Otherwise you may top out at 10 or 15 Mbps. That’s still about the best you can do with bonded T1 and for considerably less cost.

Are you looking for a rock solid connection to the Internet to support your business activities. If so, check availability and pricing for bonded T1 and EoC dedicated Internet access options.