Which type of network model describes the functions that must be completed at a particular layer, but does not specify exactly how each protocol should work?

The type of network model that describes the functions that must be completed at a particular layer, but does not specify exactly how each protocol should work is the OSI (Open Systems Interconnection) model. This model is a conceptual framework that standardizes the functions of a communication system into seven different categories, or layers. Each layer performs specific functions to support the layers above it and uses the layers below it. However, the OSI model does not dictate how these functions should be performed.