QoS Assurance Mechanism Based On IMS Architecture

Quality of Service (QoS) has become one of the key issues in NGN. Along with the rapid growing usage of the multimedia services, the added requirements of the quality can not be fulfilled by the traditional "best effort", which is subject to unpredictable delays and loss. Although many organizations, such as ITU, 3GPP, 3GPP2 and IETF, have been doing some research on it, QoS in NGN still needs further improvement.As the core architecture of NGN defined by 3GPP, QoS guarantee mechanism in IMS is policy-based, which depends on frequent signaling interactions between PCRF and PCEF to realize the control of service flow. However, when these essential interactions are in progress, they may cause serious time delay, especially when there is something wrong with their connection.To address this limitation, at the beginning, this thesis gives a brief introduction of the fundamental knowledge of IMS, Furthermore, basic concepts of QoS and its guarantee mechanism are presented. Then , IntServ, DiffServ, MPLS and policy-based QoS controlling model are introduced, we constructs the DiffServ simulationmodel with different queuing algorithms, the different characteristics of queuing algorithms are validated and compared through the network simulating. QoS guarantee mechanism in IMS and signaling procedure of Gx, Rx interface are discussed in detail,And to discuss the limitations of PCRF.Finally, Local PCRF model is proposed to reduce the unnecessary interactions between PCRF and PCEF. As for this model, at first, configuration and content in the cache are explained. Then, there are some discussions concerning the update of the decisions. At last, this thesis brings forward a mathematical model for the cache and related brief mathematical analysis.Theory and simulation results show that, Local PCRF model can remarkably decrease the time delay of IP-CAN session set-up and therefore can improve the QoS. Besides, due to the fault tolerance, it can also contribute to the stability of the system in some sense.