This paper presents the design and implementation of an adaptive architecture to provide relative, absolute and hybrid service delay guarantees for different service classes on web servers under HTTP 1.1. The first contribution of this paper is the architecture based on feedback control loops that enforce delay guarantees for classes via dynamic connection scheduling and process reallocation. The second contribution is our use of feedback control theory to design the feedback loop with proven performance guarantees. In contrast with ad hoc approaches that often rely on laborious tuning and design iterations, our control theory approach enables us to systematically design an adaptive web server with established analytical methods. The design methodology includes using system identification to establish dynamic models for a web server, and using the Root Locus method to design feedback controllers to satisfy performance specifications. The adaptive architecture has been implemented by modifying an Apache web server. Experimental results demonstrate that our adaptive server provides robust delay guarantees even when workload varies significantly. Properties of our adaptive web server also include guaranteed stability, and satisfactory efficiency and accuracy in achieving desired delay or delay differentiation. 1.

The second generation of Web sites provides more complex services than those related to Web publishing. Many users already rely on the Web for up-to-date personal and business information and transactions. This success motivates the need to design and implement Web architectures being able to guarantee the service level agreement that will rule the relationship between users and Web service providers. As many components of the Web infrastructure are beyond the control of Web system administrators, they should augment satisfaction percentage of the assessed service levels by relying on two mechanisms that can be integrated: differentiated classes of services/users, Web systems with multi-node architectures. The focus of this paper is on this latter approach. We review systems where replicated Web services are provided by locally and geographically distributed Web architectures. We consider different categories of Web applications, and evaluate how static, dynamic and secure requests affect performance and quality of service of distributed Web sites.

Various real-time services, like webcasting, audio/videoconferencing and telemedicine, are being deployed over the Internet. This requires the network to provide the guarantee of the service being provided to the receiver. The needs of the application is specified in terms of the Quality of Service (QoS) metrics like desired bandwidth, response time, etc. End-to-end QoS can be provided most efficiently when each layer of the protocol stack translates the application provided requirement into layer specific requirement and satisfies the same. Network layer has a critical role to play in the QoS provision process. It provides the desired QoS by considering the QoS metrics in the path selection process. The focus of this paper is on the QoS routing algorithms and protocols for unicast and multicast in the IPv4 based Internet that constrains or optimizes an individual or combination of metrics. The desired features of a router supporting QoS have been discussed in detail. QoS routing leads to an increase

Service differentiation in web caching and content distribution will result in significant technical and economic efficiency gains, to the benefit of both content publishers and service providers. Through preferential storage allocation and coordinated transitioning of objects across priority queues, we demonstrate a QoS caching scheme that achieves quantifiable service differentiation with Httle efficiency overhead. We develop and empirically validate a model to quantify, predict, and compare the performance of traditional and servicedifferentiated caching schemes.

With the explosive growth of Web traffic, the load on a Web server becomes heavier, leading to the longer user-perceived latency. Website operators would like to employ service differentiation to offer better throughput and shorter user-perceived latency to some specific users. This paper presents an HTTP request scheduling algorithm deployed at the Website gateway to enable the Web quality of service without any modification to client or server software. A variation of the deficit round robin algorithm for packet scheduling and a window control mechanism are presented to decide the order and the releasing time of requests, respectively. The order is decided by the response size of the requests and the pre-defined service weights. The ratio of the service rate got by the service classes is determined by the weights, whereas the releasing time is decided by the service rate of the Web server. The evaluation shows the scheduling algorithm can provide service differentiation and improve server throughput and user-perceived latency. When the weight ratio 6:3:1 is assigned to three service classes, the QoS Website gateway makes them get 60%, 30%, and 10 % of the overall throughput as expected, regardless whatever page sizes. In addition, the throughput and the user-perceived latency of the class with the largest weight can be improved by up to 176 % and 69 % of the QoS-disabled values, respectively.