The Research On The Construct Model And Relative Key Techniques Of QoS-based Distributed Web Services

Web service, widely considered as the future trend of grid in the next generation of Internet, takes up more than 70% of communication traffic and goes into its boom period. One of the major challenges Web service evolution faces, which is also a fundamental technology for the next generation networks, is how to build a well-defined architecture model and implement effective QoS control mechanisms and policies, so to fulfill increasing users' demand and moreover, to provide varied services and guarantee high performance for different users.The paper, focused on 2 research objects consisting of the LAN Web server clusters and the Grid Web service, carries on an intensive study about Web service architecture model, Web QoS control policies and, algorithms. At first, a Web cluster differentiate service model based on QoS-aware is put forward aiming at the Web server clusters. And then on such a basis a series of solution policies and algorithms is brought up with the guideline of system load balancing, differentiate service, integral self-similar access transaction characteristics and high availability. The policy suggests that QoS optimization at the beginning is taken on some aspect, and then gradually incorporated with the QoS guidelines mentioned above in the following solution, at last brought down on the maximal of system total payoff ratio as well as each QoS guidelines. Given the incomplete structure model of Grid Web service,a multi-level multi-tier architecture model for Web service is held out with the enhancement of QoS features in the capability of load balancing support in the lower part of the protocol. To sum up, Major research contributions are as follows:(1) A differentiate service architecture model over Web cluster is put forward to take a better effect on the solution to the shortcoming of differentiate service detachment in the front-back end over previous Web cluster system. On such a basis, the admission control policy for differentiate service based on the transaction is applied in the model. The experiment result and theory analysis reveal that the system stability is effectively guaranteed in the case of system over-loading and a better service quality is allocated to the high-priority task. it is better than the ones based on the session.(2) A admission control algorithm combined with the self-similar access characteristics over networks is brought forward. It is likely capable of overcoming the defect of self-similar request with the adjustment to the multiple factor regarding the consideration into the request access characteristics and load condition as well as optimizing the multi-dimension objective in the Web cluster system. The experiments result provesthe availability of the algorithm that can fit the self-similar access characteristics over networks as well as the schedule optimization in multi-dimension QoS.(3) A QoS control algorithm of resource optimization is set forth with the essence of multi-dimension QoS objective control. According to different service demands different resources, a heuristic algorithm (LBBA for shore) that makes full use of system resources also balances system load is raised. The experiment proves that the algorithm can take a apparent decline in the computation complexity in the resource optimization allocation to fulfill the requirement of real-time scheduling. Given the foundation, a dual minimal balance differentiate service scheduling algorithm (DMBA for shore) of resource optimization is further brought up in the combination of multi-dimension resource QoS optimization and differentiate service as well.(4) A QoS scheduling policy based on the inaccurate state aiming at the inaccuracy of the Web cluster system status is held forth. It makes a modeling of system inaccurate status via probability analysis in the purpose of maximizing the value ratio implemented by system with the total consideration into the differentiate service as well as other QoS guidelines. The simulation shows that the algorithm is likely to overcome the inaccuracy of system status and is better than EDF counterpart in the performance. Also taking account the self-similar access transaction flow and differentiate service directing towards the high availability, a error-tolerated scheduling algorithm is held out with the guarantee of high availability for high priority task.(5) A Grid Web service structure model over WAN is proposed. On a basis of the OGSA framework, it separates the logic frame of Web service resource from physical resource structure. And it carries on the searching and locating for Web service resource via the Web service naming system(WSNS for short)in the form of hierarchy organization and maintaining for Web service resource by the area autonomy system (AAS for short). Then it makes an improvement on the structure model. On a basis of the maintaining the advantage of original structure, a resource organization tree (WSROT for short) is appended with the support of good characteristic for QoS guarantee. In conclusion, it is a much better organization structure model over the current Computational Grid.