Layered system

In telecommunication, a layered system is a system in which components are grouped, i.e. , layered, in a hierarchical arrangement, such that lower layers provide functions and services that support the functions and services of higher layers.

Note: Systems of ever-increasing complexity and capability can be built by adding or changing the layers to improve overall system capability while using the components that are still in place.

Source: from Federal Standard 1037C