Will users notice a downtime of 10.70 seconds? Certainly some users will, but for some applications, a downtime of 10.70 seconds every hour is tolerable. An uptime of 99.70 percent could mean that approximately every hour the network is down for 10.70 seconds. The downtime could be all at once, which could be a problem if it's not during a regularly scheduled maintenance window, or it could be spread out over the week. This uptime means 30 minutes of downtime during a week.

Consider an uptime of 99.70 percent again. Availability requirements should be specified as uptime per year, month, week, day, or hour. Not only should your customers specify a timeframe with percent uptime requirements, they should also specify a time unit. But a downtime of 30 minutes every Saturday evening for regularly scheduled maintenance might be fine. A downtime of 30 minutes in the middle of a working day is probably not acceptable. Go back to the example of 99.70 percent uptime, which equated to 30 minutes of downtime per week. It is also important to specify a timeframe with percent uptime requirements. Availability requirements should be specified with at least two digits following the decimal point. An uptime of 99.95 percent means the network is down 5 minutes per week, which may be acceptable, depending on the type of business. An uptime of 99.70 percent means the network is down 30 minutes per week, which is not acceptable to many customers. Consider the difference between an uptime of 99.70 percent and an uptime of 99.95 percent.

You should encourage your customers to specify availability requirements with precision.

Internet uptime fails often