Keqiu Li

Optimal methods for coordinated enroute web caching for tree networks

Web caching is an important technology for improving the scalability of Web services. One of the key problems in coordinated enroute Web caching is to compute the locations for storing copies of an object among the enroute caches so that some specified objectives are achieved. In this article, we address this problem for tree networks, and formulate it as a maximization problem. We consider this problem for both unconstrained and constrained cases. The constrained case includes constraints on the cost gain per node and on the number of object copies to be placed. We present dynamic programming-based solutions to this problem for different cases and theoretically show that the solutions are either optimal or convergent to optimal solutions. We derive efficient algorithms that produce these solutions. Based on our mathematical model, we also present a solution to coordinated enroute Web caching for autonomous systems as a natural extension of the solution for tree networks. We implement our algorithms and evaluate our model on different performance metrics through extensive simulation experiments. The implementation results show that our methods outperform the existing algorithms of either coordinated enroute Web caching for linear topology or object placement (replacement) at individual nodes only.

Multimedia Object Placement for Transparent Data Replication

Transparent data replication is a promising technique for improving the system performance of a large distributed network. Transcoding is an important technology which adapts the same multimedia object to diverse mobile appliances; thus, users requests for a specified version of a multimedia object could be served by a more detailed version cached according to transcoding. Therefore, it is particularly of theoretical and practical necessity to determine the proper version to be cached at each node such that the specified objective is achieved. In this paper, we address the problem of multimedia object placement for transparent data replication. The performance objective is to minimize the total access cost by considering both transmission cost and transcoding cost. We present optimal solutions for different cases for this problem. The performance of the proposed solutions is evaluated with a set of carefully designed simulation experiments for various performance metrics over a wide range of system parameters. The simulation results show that our solution consistently and significantly outperforms comparison solutions in terms of all the performance metrics considered

Optimal placement of Web proxies for tree networks

Placement of Web proxy servers is an important avenue to save network bandwidth, alleviate server load, and reduce latency experienced by users. The general problem of Web proxy placement is to compute the optimal locations for placing k Web proxies in a network such that the objective concerned is minimized or maximized. We address this problem for tree networks and propose a novel mathematical model for it. In our model, we consider maximizing the overall access gain as our objective and formulate this problem as an optimization problem. The optimal placement is obtained using a computationally efficient dynamic programming-based algorithm. Applying our mathematical model, we also present a solution to Web proxy placement for autonomous systems (ASes), as a natural extension of the solution for tree networks. Our algorithms have been implemented. The simulation results show that our model significantly outperforms the random placement model.

Cache Replacement for Transcoding Proxy Caching

In this paper, we address the problem of cache replacement for transcoding proxy caching. First, an efficient cache replacement algorithm is proposed. Our algorithm considers both the aggregate effect of caching multiple versions of the same multimedia object and cache consistency. Second, a complexity analysis is presented to show the efficiency of our algorithm. Finally, some preliminary simulation experiments are conducted to compare the performance of our algorithm with some existing algorithms. The results show that our algorithm outperforms others in terms of the various performance metrics.

An effective cache replacement algorithm in transcoding-enabled proxies

In this paper, we address the problem of cache replacement for transcoding proxy caching. Transcoding proxy is a proxy that has the functionality of transcoding a multimedia object into an appropriate format or resolution for each client. We first propose an effective cache replacement algorithm for transcoding proxy. In general, when a new object is to be cached, cache replacement algorithms evict some of the cached objects with the least profit to accommodate the new object. Our algorithm takes into account of the inter-relationships among different versions of the same multimedia object, and selects the versions to replace according to their aggregate profit which usually differs from simple summation of their individual profits as assumed in the existing algorithms. It also considers cache consistency, which is not considered in the existing algorithms. We then present a complexity analysis to show the efficiency of our algorithm. Finally, we give extensive simulation results to compare the performance of our algorithm with some existing algorithms. The results show that our algorithm outperforms others in terms of various performance metrics.

Two Cache Replacement Algorithms Based on Association Rules and Markov Models

In this paper, two cache replacement algorithms are presented. One is based on association rules, in which we extend the LRU replacement algorithm by making it sensible to Web access models extracted from Web log data using Web mining techniques. The other one is based on Markov models, in which we improve the LRU replacement algorithm by applying Markov models.

A Survey of Cache/Proxy for Transparent Data Replication

Web caching is an important technology for reduc- ing Internet access latency, alleviating network traf- fic, and spreading server load. An important issue that affects the performance of web caching is caching architecture, in which several caches are usually fed- erated for making caches cooperate on a large scale and effectively increase the cache population. Trans- parent data replication is such a caching architec- ture, which has shown to be easy to manage and have good system scalability. In this paper, we present an survey of state-of-the-art techniques of cache/proxy placement for transparent data replication.

The Cache Replacement Problem for Multimedia Object Caching

Multimedia object caching, by which the same multimedia object can be adapted to diverse mobile appliances through the technique of transcoding, is an important technology for improving the scalability of Web services, especially in the environment of mobile networks. The performance of multimedia object caching mainly depends on how the objects are selected to be removed for a new object (multimedia object replacement) and where the different versions of a multimedia object are placed (multimedia object placement). In this paper, we address the problem of cache replacement for multimedia object caching. We first propose an optimal solution for this problem. The performance objective is to minimize the total access cost by considering both transmission cost and transcoding cost. The performance of the proposed solution is evaluated with a set of carefully designed simulation experiments for various performance metrics over a wide range of system parameters. The simulation results show that our solution consistently and significantly outperforms comparison solutions in terms of all the performance metrics considered.

Cache Design for Transcoding Proxy Caching

As audio and video applications have proliferated on the Internet, transcoding proxy caching is attracting an increasing amount of attention, especially in the environment of mobile appliances. Since cache replacement and consistency algorithms are two factors that play a central role in the functionality of transcoding proxy caching, it is of particular practical necessity to involve them into transcoding cache design. In this paper, we propose an original cache maintenance algorithm, which integrates both cache replacement and consistence algorithms. Our algorithm also explicitly reveals the new emerging factors in the transcoding proxy. Specifically, we formulate a generalized cost saving function to evaluate the profit of caching a multimedia object. Our algorithm evicts the objects based on the generalized cost saving to fetch each object into the cache. Consequently, the objects with less generalized cost saving are to be removed from the cache. On the other hand, our algorithm also considers the validation and write rates of the objects, which is of considerable importance for a cache maintenance algorithm. Finally, we evaluate our algorithm on different performance metrics through extensive simulation experiments. The implementation results show that our algorithm outperforms comparison algorithms in terms of the performance metrics considered.

Placement solutions for multiple versions of a multimedia object

Transcoding is an important technology which adapts the same multimedia object to diverse mobile appliances; thus, users requests for a specified version of a multimedia object could be served by a more detailed version cached according to transcoding. Therefore, it is of particularly theoretical and practical necessity to determine the proper versions to be cached at a node such that the specified objective is achieved. In this paper, we address the problem of multimedia object placement. The performance objective is to minimize the total access cost by considering both transmission cost and transcoding cost. We present an optimal dynamic programming-based solution for this problem. The performance of the proposed solutions is evaluated with a set of carefully designed simulation experiments for various performance metrics over a wide range of system parameters. The simulation results show that our solution consistently and significantly outperforms comparison solutions in terms of all the performance metrics considered.