This paper presents the summary of a method proposal for designing Quality of Services Models in Networks. The proposal consists of several steps where Real System is defined and specified with the hypothesis and the problem which will be solved by the model; then, the model is defined, taking it into account as a real system abstraction, and ends with the implementation and simulation of the model. In the second part of the paper the design of a Quality of Service model for Next Generation Networking is presented as study case, showing in a synthetic way many of the obtained results.