Researches On The Dynamic Control And Management Of Quality Of Service For ATM Networks

Asynchronous Transfer Mode (ATM) networks are proved to be advantageous over other forms of communication networks in providing Quality of Service (QoS) guarantees for a variety of traffic types. Based on such a consensus that Q0S guarantees are of the most importance in communication networks, academic and industrial circles have being developed a large number of researches in this field for more than ten years, with some methods into practical use. Up to now, ITU-T and ATM Forum have published corresponding standards and recommendations related to QoS in ATM scenarios, resulting in the establishment of the basic QoS framework. Being considered as implementation aspects in general, however, buffer management, cell discarding on a connection basis and cell scheduling are not documented. Since all these three issues play key roles in the dynamic QoS control, they continuously receive much attention and investigation. On the other hand, while the Operation And Maintenance(OAM) function in ATM Layer has been defined in the ITU-T抯 recommendation, 1.6 10, it is still imperfect and worthy to be improved, even with some necessary functions not considered at all. In view of these reasons, the dynamic QoS control of ATM networks is studied in depth in this dissertation. As a consequence, a series of new design ideas and mechanisms are proposed in order to overcome shortcomings and improve performance of existing schemes designed for buffer management, cell discarding, cell scheduling, and ATM Layer OAM functions. Analysis results show that these proposed methods are good in performance, simple in structure and implementation, and thus suitable for high-speed network environments like ATM. This dissertation consists of the following seven chapters. Chapter One introduces the basic concept of QoS, explains the present status and problems in buffer management, cell discarding, cell scheduling and OAM functions, and hence makes the research background clear. Finally, it presents detailed research contents carried out and main contributions. Based on such a new idea that the memory allocation on-demand is supported by means of the modularized structure, a novel buffer management scheme, called 揳dditional buffer assignment on-demand,?is proposed in Chapter Two. After the concept of 揳dditional buffer? and the principle of its assignment on-demand are explained, two queuing models corresponding to the proposed scheme, M/D/1/K(+K) and ~NMMBP(2)/D/l/K(+K), are constructed and closed expressions of cell loss probabilities of both systems are also derived. By theory and simulation, performance analysis of cell loss probabilities are finally presented. iv ABSTRACT In order to reduce the amount of wasted network resources due to cell discarding, a new cell discarding strategy, called the 搈inimum forwarding-intensity?strategy, is proposed in Chapter Three. With the definition of the 揷ell forwarding-intensity?given, the main points of the proposed strategy are explained. Moreover, closed formulas of the network resource utilization and cell loss probability are theoretically derived respectively, and simulation analyses of these two performance aspects are also carried out. Improvement of fairness associated with the above strategy is studied in Chapter Four. As a result, a fuzzy model for cell discarding based on the 揻orwarding-intensity?notion is proposed. With fundamentals of fuzzy sets reviewed, a new kind of fuzzy sets referred to as 搒ymmetric fuzz...