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A mobile communications network consists of several protocol stacks and layers designed to exchange information between the adjacent layers or between two peer network elements either directly or transparently through another network element. The general working model of a protocol layer consists of various services it offers to its higher layer or services it expects from the layer below it. The protocol layer working model also consists of collections of signaling procedures and functions. These functions are the building blocks of a particular protocol layer to transfer information accurately and error‐free as expected by the peer layer. This working model of a protocol layer is illustrated graphically in Figure 3.17 where a protocol layer N provides services to the layer N + 1 and also uses the services from the layer N − 1.

Example 3.11 describes the LTE/E‐UTRAN RLC layer with respect to its working principle.

Figure 3.17 Illustration: A working model of protocol layer.