Service Level Agreements (SLAs) often state a commitment to up-time as a percentage. For example, "The Network Operations Center (NOC) agrees to provide network services seven days a week, 24 hours a day, with a commitment to 97% uptime each week." This level of commitment provides for over five hours of down-time each week. What might cause the down-time? Do you think this commitment is sufficient for a Network Operations center? Can you think of some types of customer who might require 100% up-time?