Since the late 1980s, SLAs have been used by fixed telecommunications operators. Today, SLAs are so prevalent that large organizations have many different SLAs in the company itself. Two different units in an organization write an SLA, one being the customer and the other the service provider. This approach helps maintain the same quality of service across different units of the organization and across multiple locations in the organization. This internal SLA scripting also makes it possible to compare the quality of service between an internal department and an external service provider.  When applications are moved from dedicated hardware to the cloud, they must achieve the same or even more demanding service levels as traditional installations. SLAs for cloud services focus on data center characteristics and more recently include network features (see carrier cloud) to support end-to-end SLAs.  The underlying advantage of cloud computing is that of shared resources that are supported by the underlying nature of a shared infrastructure environment. Therefore, SLAs span the entire cloud and are offered by service providers as a service agreement and not a customer-based agreement. Measuring, monitoring, and reporting on cloud performance is based on the final UX or its ability to consume resources. The disadvantage of cloud computing compared to SLAs is the difficulty of determining the cause of service interruptions due to the complexity of the nature of the environment.
It is not uncommon for an Internet backbone service provider (or network service provider) to explicitly display its own SLA on its website.    The United States The Telecommunications Act of 1996 does not expressly require companies to have SAs, but it does provide a framework for companies in Sections 251 and 252.  For example, Section 252(c)(1) (“Obligation to Trade”) requires established local stock exchange operators (ILECs) to negotiate in good faith issues such as resale and access to rights of way. Service level agreements are also defined at different levels: A web service level agreement (WSLA) is a standard for tracking web services service level agreement compliance….