Network Support and the SLA

A Service Level Agreement will normally define the type and quality of support that your business will have for its IT network.

Your service level agreement is fundamental to the type of support agreement you will receive. The Service Level Agreement is normally scoped to give your business the IT platform availability it needs at the minimum cost.

Availability is defined as uptime in terms of minutes/hours per annum. There are a total of 6360 hours in a normal year. A leap year consists of 6384 hours. An availability of 99% means that you can expect to have a total outage of 63 hours in any one year. That is to say that the probability of your network being up and working is 0.99. This can be made up of any combination of outages with the proviso that the outages do not total more than the 63 hours.

The table below also provides details of the figures for 99.9% availability, 99.99% availability, 99.999% availability and full availability on an annual basis. The overall time of a year is on a moving window basis of 365 days or 366 days in a leap year. The actual times for a leap year may differ slightly in terms of minutes but the principle for calculating the availability is the same.

AvailabilityTime Available Time Unavailable MTTR
99%6296.4 hours 63.6 hoursBetween 2 and 4 hrs.
99.9%6353.64 hours 6.36 hoursBetween 2 and 4 hrs.
99.99%6359.36 hours 0.636 hoursNot Specified
99.999%6359.93 hours 0.636 hoursNot Specified
100%6360 hours 0 hoursNot Specified

Table showing relationship between availability and outage time

A second important set of metrics of the Service Level Agreement is the Mean Time Between Failures (MTBF) and the Mean Time To Return to service (MTTR). This is normally specified in hours and for a non-redundant system with an availability of 99% the MTBF may be 720 hours and the MTTR may be between 2 and 4 hours.

Taking a step back from these availability figures it is possible to set some expectations of the kind of service can be provided by your IT platform. An availability of 99% means you may have 15 outages of 4 hours each every rolling year. Say 1 outage per month each lasting 4 hours. An availability of 99.9% means you may have 3 outages per year of 2 hours each. Availability requirements of 99,99% and 99.999% effectively means that you are planning to have no outages of your IT platform on an annual basis.

Having set these expectations it is now possible to set a few parameters for your IT system in terms of hardware and design. These figures are based on what is required to meet the expectations given in the previous paragraph. A network offering 99% availability could be a network without any redundancy other than perhaps database redundancy. Faults would be cleared by a technician on a callout basis and the fault would take between 2 and 4 hours to repair.

A network designed to offer 99.99% availability may be a network with a significant amount of redundancy including a redundant internet connection and a no break power supply. Again, faults would be cleared by a technician on a callout basis and the fault would take between 2 and 4 hours to repair.

Networks designed for both 99.99% availability and 99.999% availability are unlikely to be networks supported by an SME. These networks are designed for large corporate customers or banks or networks where an outage cannot be tolerated and are likely to be cost prohibitive for an SME. These networks will have their own dedicated support teams available on a 24 by 7 basis.

The Brite Web has the knowledge and experience to provide a support package and design parameters for your IT network. Find out more about how The Brite Web can support and help your company by sending an enquiry via our enquiry page on the link below.

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