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Layers in the internet? These layers refer to a division of network functionality. They aren't actual physical things inside a computer or network, but rather think of them as tools used by developers and computer scientists to help us understand how protocols interact with one another.
A layer is a group of protocols that all serve a similar function. For example since UDP and TCP do the same kind of job in two different ways, they would be in the same layer. Think of these layers as a means of categorising protocols, of making them easier to think about and work with.