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These three layers are referred to as the session, presentation, and application layers, respectively. In practice their details are not encountered as much from the network perspective as they are by the inner workings of a specific application, which is why they are not going to be described in the same level of detail as the lower levels of the stack are in this chapter. As the functions at these layers are often handled within a single application at a single endpoint, the protocols at each of these upper layers as well as the interfaces between them tend to be less distinct than those at the lower layers where interoperation between endpoints from many sources is needed for the network to function.

As further degrees of interoperation between the network and the processing resources of the data centre both at the infrastructure edge and at the regional or national scale are used to support next generation use cases, the functions of these three upper layers of the OSI model will be increasingly used to provide that underlying network and data centre infrastructure with intelligence about the specific characteristics of the application in use, which will then be used to make nuanced decisions about how infrastructure resources can be allocated and used for optimal cost and user experience.