In the last years hybrid optical networking is a topic of increasing interest for graceful migration to future high capacity integrated service networks.A new hybrid network architecture is proposed to harmonize different transport technologies and to support a suitable set of services: ''3-Level Integrated Hybrid Optical Network'' (3LIHON).The aim of this thesis is to study the performance of 3LIHON focusing on examining the Quality of Service (QoS) in the output part of the node.In particular we study the performance for Statistically Multiplexed (SM) traffic.In Chapter 1 we present the motivation of our study and the current work.We give the problem definition and define the goal of the thesis.Chapter 2 shows concepts and architecture of 3LIHON. Firstly we introduce the reference classes used and the Quality of Service (QoS) requirement.Furthermore we give a complete description of 3LIHON architecture describing transport services, architecture in detail, input and output part of the node.Finally we describe the advantages of 3LIHON network.To simulate the 3LIHON architecture we use a programming language called Simula and a context class for discrete event simulation called DEMOS.In Chapter 3 firstly we describe the simulation model implemented, moreover we give a code description.We show the sources characterization and the packets characterization for all type of traffic that 3LIHON is able to handle: Guaranteed Service Transport (GST) traffic, Statistically Multiplexed (SM) Real Time (RT) traffic and Statistically Multiplexed (SM) Best Effort (BE) traffic.The code used in this work is available in Appendix C.In Chapter 4 firstly we present the simulation scenario and then the obtained results.To evaluate the accuracy's level of our results we use a 95% confidence interval and more theoretical details about that are given in Appendix A.We consider three study cases and for each of them we analyze in details the Packet Loss Probability (PLP) of Statistically Multiplexed Real Time (SM/RT) packets, the Packet Loss Probability (PLP) of Statistically Multiplexed Best Effort (SM/BE) packets and the delay of Statistically Multiplexed Best Effort (SM/BE) packets in the Best Effort queue. Some additional results used to obtain the study case called Series Two in Chapter 2 are shown in Appendix B.In Chapter 5 are presented some conclusions of this work and in Chapter 6 we show some hints that can be the sparkle for further works.