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Fixed Wireless Business

What SLAs (Wired and Wireless) Mean

If you're building SLAs, don't try to get away with the games the monopolies play.

[October 8, 2007]

On the ISP-Wireless list in September, GM wrote:

Our 146-mile backbone is built on protected Nortel RD-6s with spatial diversity. The uptime guarantee we have from our provider is 99.9995%. Try doing that on license exempt! We did, and it broke!

. . .

As you get larger, the *real deal* becomes how well any of the Linux-based systems scale to multi-thousand unit deployments. Take OSPF as an example. And the answer? No one seems to know, and if they do, they don't seem to be on this list talking about it.

[RY replied] "In doing a bit of arithmetic, 99.9995% uptime leaves only 2.628 minutes of downtime per year. Expecting this kind of uptime seems a bit unrealistic to me under ANY circumstances. Any technical glitch at all will result in more than that in downtime. Telcos claim 5 nines. I have personally yet to experience it anywhere."

[GG agreed] "I second that. Anyone who promises 99.999 uptime is reading the sales brochure to you."

Some recommended licensed wireless, which is available in Canada. GM wrote:

"Sounds silly but it's true. We are piggy-backing on an inter-telco SLA that reads 99.9997%. So far the guys have missed something like 5 packets in three years. They get a call if they drop a single packet on the long-haul telco backbone.

We have experienced about 1.5 hours in downtime from DS3-Ethernet converter failures, but that was not a radio problem. Amazing what you can do with protected radios in a 9 radio array (8 working plus the protection radio)!! Each radio is 3 x DS-3s for a total of just over a gigabit per 30 mile hop. Pretty cool stuff and it's been around for donkey's years. Makes the stuff we do seem pretty small by comparison. The long-haul guys laugh at our license exempt stuff, but at least it's good natured and they do understand it's a completely different market.

. . .

The reliability is simply stuffing compared even to our fibre feed. Lose at least 1 hour per year on that due to hardware failures."

DF complained about telco self-monitoring on SLAs.

It's also how the carrier ends up 'guaranteeing' it ... I've dealt with carriers that will guarantee five nines

• in a month-long period instead of across an entire year.
  
  
• only if you open a ticket on the issue.
  
  
• "scheduled maintenance" isn't calculated... you were warned, so it doesn't count (to them).
  
  
• how many times does their network monitoring system check a circuit/node before counting it down? And does it then consider the whole time it took to get to 'down', or just the time after it was judged 'down'?

So in the real world, once or twice a year now each of our carriers has a problem that causes a couple hours of downtime... but that's what BGP is for.

Responding to "that's what BGP is for", DF wrote:

Aye to that.

—End