In this book, a detailed analysis of Optical Burst Switched (OBS) networks is presented. Three different parameters are used to study different Quality of Service (QoS) techniques. Number of wavelengths, wavelength conversion capability and number of slots per burst are used to evaluate the blocking probability and Burst Loss Rate of Just-In-Time-with-Wavelength Conversion. We depended on the theory of Markov chain to find product form analytical solution of complex stochastic problems. The QoS for slotted optical burst comparison between three parameters has been shown in this book. Chapter 2 presents the background of the topics relevant to the subject of the book such as optical network evolution, OCS, OPS and OBS. Chapter 3 casts the developed models to analyze QoS by using the BLR of an OBS. Chapter 4 shows the analytical results of the QoS models developed in Chapter 3 and gives a comparison between the studied schemes to give a good analysis and discussion of the proposed models. Chapter 5 summarizes the conclusions and suggests some recommended points for future work in the same scope of book. The book is terminated by a list of references and an Arabic summary.