What is a SLA (Service Level Agreement)?

Guillaume Barre (UK)
10 Dec 2022

Article updated 27/12/22

The Service Level Agreement (SLA) is a part of the service contract between an IT service provider and its customer that defines the expected level of service and the associated guarantees. It is therefore an element that should not be overlooked when choosing a managed service offer or simple IT maintenance.

Offering very high levels of service is part of the added value expected when outsourcing an IT service. Wifirst, operator of professional WiFi networks, obviously includes an SLA to define the collaboration with its customers and implements substantial measures to meet its commitments.

The origin of Service Level Agreements

The SLA was born in the world of network service providers to evaluate their service by measuring its quality and performance. It has now spread to almost all technical solutions, from software to IT infrastructures. It is also at the heart of managed service offerings.

The Service Level Agreement defines the client's expectations and the service provider's commitments to meet them. This makes it possible to establish a clear relationship between the client and the service provider, with the expected service levels being contractualised in two forms:

  • expected performance targets
  • time taken by the technical teams to resolve incidents

The main components of a SLA

Scope of services covered

Although it may seem obvious, the scope of the service covered must be defined if the other components of the SLA are to be meaningful. It defines the functional framework for service guarantees.

Example: Wifirst provides SLAs on the network infrastructure but cannot be held responsible if an incident occurs to the overall power supply of a building.

Guaranteed Service Range (GSR)

The GSR defines the time frame for service availability and therefore for the assumption of guarantees. Together with the scope of the service covered, it is the starting point for any good SLA.

Example: Wifirst's GSR is generally 24 hours a day, 7 days a week.

Service Availability Rate

The Service Availability Rate is calculated annually. It measures the relationship between the service uptime and the guaranteed service range. To be credible, the availability rate must be defined in accordance with the Recovery Time Guarantee (see below).

For a 24/7 GSR, an availability rate of 99% indicates a maximum unavailability of 87 hours per year.

Example: Wifirst ensures an availability rate of 99.5% on its customers' network infrastructures.

Guaranteed Response Time (GRT)

The GRT sets out the service provider's response time following an incident. Although it is regularly used in SLAs, it does not provide the customer with any real security as to the actual time taken to bring the installation back into service.

Example: For obvious service quality reasons, Wifirst has chosen to commit to a GTR rather than a GTI, offering a clearer vision for the client.

Guaranteed Recovery Time (GTR)

The GTR is the maximum time the service provider has to restore the IT service after a technical incident. It can vary according to the type of incident. It is possible to imagine a longer GTR for a minor malfunction, whereas a total unavailability of the service will require a minimum GTR. Note that this can be expressed in working or non-working hours.

Example: Wifirst generally commits to a 4h or 8h GTR for critical incidents on its managed WiFi infrastructure.

Points to watch for on SLAs

Being realistic in the choice of SLAs is essential when engaging with an IT or network service provider. It is important to ensure that the SLAs chosen are consistent with the criticality of the service. In addition, there must be a link between the availability rate and the guaranteed recovery time to be acceptable.

Always opt for achievable SLAs rather than promises of service commitments that cannot be met. It should be noted that very high SLAs will inevitably have an impact on the cost of the solution. Keeping commitments to very high availability implies a great deal of effort on the part of the IT service provider.