Designing of smart edge routers and shaping the self-similar traffic in optical switched networks arise recently a lot of interest. Here, we propose an analytical approach which we consider useful in modelling and dimensioning of buffers in the edge routers between electronic and optical networks. We study a single buffer where packets of various sizes, classified by the class of service and the destination, are stored to build an optical packet of a fixed size. We already studied this problem with the use of simulation model, remarking that self-similar traffic at the entrance of such a buffer remains self-similar when leaving it. Now we are building analytical model based on diffusion approximation. and our previous contributions to this approach, i.e. a method to solve transient diffusion models. The model is used to analyse the process of buffer filling and a a numerical example proves that this approach may give reasonable results in relatively short (compared to simulation, especially simulation of transient states) time.
