Probably the oldest and most investigated random network model has been introduced by Erd ˝os and Renyi (ER) [8,9], who were the rst to study the statistical aspects of random graphs by probabilistic methods. In the model we start with N vertices and no bonds (see Fig. 1a). With probability pER, we connect each pair of vertices with a line (bond or edge), generating a random network. The greatest discovery of ER was that many properties of these graphs appear quite suddenly, at a threshold value of pER(N).