Research On Admission Control Mechanisms In Web Clusters

Increasing number of internet users, diversity of service content and variability of user access lead overload to popular sites and important site,or even cause the failure of services. How to improve the Quality of Services(QoS) of Web cluster becomes an urgent to resolve. Admission Control Mechanism and Load Balance Mechanism ,which are regard as important means to ease system pressure and load balance, becomes one of the important research topics to improve the quality of service.The research focuses on how to improve the quality of service. The paper put forward a new quality control mechanism, based on session introducing Admission Control Mechanism in application layer. With window sliding strategy,making effect prediction of systmen resource utilization of TCP connection.In back-end server ,the paper introduces M/M/N queue model,adopting the priority property of real-time system queue task scheduling model,according to priority property,value and request URL,updating dispatch the queue request,to realize local accessibility. Theoretical analysis and simulation results show that the new mechanism improve session completion rate under different load and shortens arverage delay time.Modern network applications, such as E-commerce, most of them are designed as a multi-tier application model. The paper introduces the concept of multi-ties cluster architecture,and contribute a Self-adaptive Overload Control (SAOC) mechanism based on the multi-ties structure, which does not require any prior information on the incoming traffic or manual configuration of key parameters.The mechanism differentiate the traffic load into Normal Mode and Flash Crowd Management Mode,according to analyze the relationship between the observed response time (RT) and the rate of arrived sessions to count the limit value timely to achieve automatic conversion of the two traffic mode. SAOC mechanism dynamic adjusts the rate of admitted sessions in accordance with response time of each ties of back-end servers,to achieve self-configure parameters, self-optimize the resource utilization ,and self-prevent system overload.The experiment simulation proves that SAOC mechanism guarantees ensure service level agreements, reduces the user response time and maximize the utilization of system resources.