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The increasing importance of fast and reliable communication has resulted in the creation of certain communication rules, which nowadays, we call communication protocols. In this chapter, a historical overview of early protocol development and deployment is presented as a look-back to the evolution of communication protocols. Then we introduce the most important terms and notions of the protocol theory. To make it easier to understand these concepts, we use the INRES protocol as demonstration tool. In the next topic, we summarize the steps of the protocol engineering. At the end of the chapter, we give some guidelines for protocol classification.

The physical modelling is based on the solving of partial differential equations. Analytical solutions are only possible by extreme simplifications, for more accurate results numerical methods must be used. One way of the possible numerical solving is the discretization based upon mathematical considerations. Another way is when the discretization is based on physical considerations after Linvill's basic idea: the regional approximation. The advantages and difficulties of the regional approximation by using circuit models are mentioned.The process modelling is applied for the simulation of different processes of semiconductor structure fabrication, like diffusion, oxidation and ion implantation etc. This problem also leads to the solving of coupled partial differential equations, where the difficulties are due to the interactions between the diffusion transports of the dopants, to the vacancies, to the field strength of the ionized dopants, andin case of oxidationto the moving SiSiO, interface and to the change in the dimensions of the structure. Examples are given for the anomalous phosphorus diffusion and some new results are shown related to the ion implantation.

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