This paper proposes a cluster-based peer-to-peer system, called PeerCluster, for sharing data over the Internet. In PeerCluster, all participant computers are grouped into various interest clusters, each of which contains computers that have the same interests. The intuition behind the system design is that by logically grouping users interested in similar topics together, we can improve query efficiency. To efficiently route and broadcast messages across/within interest clusters, a hypercube topology is employed. In addition, to ensure that the structure of the interest clusters is not altered by arbitrary node insertions/deletions, we have devised corresponding JOIN and LEAVE protocols. The complexities of these protocols are analyzed. Moreover, we augment PeerCluster with a system recovery mechanism to make it robust against unpredictable computer/network failures. Using an event-driven simulation, we evaluate the performance of our approach by varying several system parameters. The experimental results show that PeerCluster outperforms previous approaches in terms of query efficiency, while still providing the desired functionality of keyword-based search.

Web caching and Web prefetching are two important techniques used to reduce the noticeable response time perceived by users. Note that by integrating Web caching and Web prefetching, these two techniques can complement each other since the Web caching technique exploits the temporal locality, whereas Web prefetching technique utilizes the spatial locality of Web objects. However, without circumspect design, the integration of these two techniques might cause significant performance degradation to each other. In view of this, we propose in this paper an innovative cache replacement algorithm, which not only considers the caching effect in the Web environment, but also evaluates the prefetching rules provided by various prefetching schemes. Specifically, we formulate a normalized profit function to evaluate the profit from caching an object (i.e., either a nonimplied object or an implied object according to some prefetching rule). Based on the normalized profit function devised, we devise an innovative Web cache replacement algorithm, referred to as Algorithm IWCP (standing for the Integration of Web Caching and Prefetching). Using an event-driven simulation, we evaluate the performance of Algorithm IWCP under several circumstances. The experimental results show that Algorithm IWCP consistently outperforms the companion schemes in various performance metrics.

In recent years, Internet telephony or voice-over IP is attracting an increasing amount of attention for the reason that it has the potential to significantly reduce the cost of long-distance voice communication. To provide the interoperability between different manufacturers and vendors, ITU-T is actively drawing up the standard for the Internet telephony as ITU-T Recommendation H.323. While H.323 is continuously revised, there are, however, still many important issues needed to be further discussed. In particular, the bandwidth management, address translation, and intelligent call signaling/routing, which are the major functions of an H.323 gatekeeper, have not yet been fully addressed. In view of this, we develop in this paper an H.323 gatekeeper prototype which fully complies with the H.323 recommendation, and explicitly illustrate the usefulness of this prototype by devising two improved call-routing methods to deal with the load-balancing problem among the gatekeepers. As a matter of fact, the existing call-routing method used in the current version of the H.323 is very primitive and will cause the loads of the gatekeepers unbalanced. Using the gatekeeper prototype devised, two improved call-routing methods are proposed based on Multiple-Registration with Multicasted Location Request (MRML) and Multiple-Registration with Hierarchical Database (MRHD). To evaluate the performance improvement by these two load-balancing methods, we design an event-driven simulator and conduct some experiments on it. We focus on two performance metrics, call-blocking rate and channel utilization , which are both sensitive to the load distribution. The experimental results show that the call-blocking ratio and channel utilization are optimized with the proposed load-balancing methods. It is also observed from our empirical results that the call-blocking ratio is more sensitive to the traffic load whereas the channel utilization is more sensitive to the duration of a call.

Recent technology advances in mobile networking have ushered in a new era of personal communication. Users can ubiquitously access the Internet via many emerging mobile appliances, such as portable notebooks, personal digital assistants (PDAs), and WAP-enabled cellular phones. While the transcoding proxy is attracting an increasing amount of attention in this environment, it is noted that new caching strategies are required for these transcoding proxies. We propose an efficient cache replacement algorithm for transcoding proxies. Specifically, we formulate a generalized profit function to evaluate the profit from caching each version of an object. This generalized profit function explicitly considers several new emerging factors in the transcoding proxy and the aggregate effect of caching multiple versions of the same object. It is noted that the aggregate effect is not simply the sum of the costs of caching individual versions of an object, but rather, depends on the transcoding relationship among these versions. The notion of a weighted transcoding graph is devised to evaluate the corresponding aggregate effect efficiently. Utilizing the generalized profit function and the weighted transcoding graph, we propose, in this paper, an innovative cache replacement algorithm for transcoding proxies. In addition, an effective data structure is designed to facilitate the management of the multiple versions of different objects cached in the transcoding proxy. Using an event-driven simulation, it is shown that the algorithm proposed consistently outperforms companion schemes in terms of the delay saving ratios and cache hit ratios.

Web caching and Web prefetching are two important techniques to reduce the noticeable response time perceived by users. Note that by integrating Web caching and Web prefetching, these two techniques can complement each other since Web caching technique exploits the temporal locality whereas Web prefetching technique utilizes the spatial locality of Web objects. However, without circumspect design, the integration of these two techniques might cause significant performance degradation to each other. In view of this, we propose in this paper an innovative cache replacement algorithm, which not only considers the caching effect in the Web environment but also evaluates the prefetching rules provided by various prefetching schemes. Specifically, we formulate a normalized profit function to evaluate the profit from caching an object (i.e., either a non-implied object or an implied object according to some prefetching rule). Based on the normalized profit function devised, we devise an innovative Web cache replacement algorithm, referred to as algorithm IWCP (standing for the Integration of Web Caching and Prefetching). Using an event-driven simulation, we evaluate the performance of algorithm IWCP under several circumstances. The experimental results show that algorithm IWCP consistently outperforms the companion schemes in various performance metrics.

This paper explores the aggregate effect when caching multiple versions of the same Web object in the transcoding proxy. Explicitly, the aggregate profit from caching multiple versions of an object is not simply the sum of the profits from caching individual versions, but rather, depends on the transcoding relationships among them. Hence, to evaluate the profit from caching each version of an object efficiently, we devise the notion of a weighted transcoding graph and formulate a generalized profit function which explicitly considers the aggregate effect and several new emerging factors in the transcoding proxy. Based on the weighted transcoding graph and the generalized profit function, an innovative cache replacement algorithm for transcoding proxies is proposed in this paper. Experimental results show that the algorithm proposed consistently outperforms companion schemes in terms of the delay saving ratios and cache hit ratios.

In this paper we explore a new model of mining general temporal association rules from large databases where the exhibition periods of the items are allowed to be different from one to another. Note that in this new model, the downward closure property which all prior Apriori-based algorithms relied upon to attain good efficiency is no longer valid. As a result, how to efficiently generate candidate itemsets form large databases has become the major challenge. To address this issue, we develop an efficient algorithm, referred to as algorithm SPF (standing for Segmented Progressive Filter) in this paper The basic idea behind SPF is to first segment the database into sub-databases in such a way that items in each sub-database will have either the common starting time or the common ending time. Then, for each sub-database, SPF progressively filters candidate 2-itemsets with cumulative filtering thresholds either forward or backward in time. This feature allows SPF of adopting the scan reduction technique by generating all candidate k-itemsets (k>2) from candidate 2-itemsets directly. The experimental results show that algorithm SPF significantly outperforms other schemes which are extended from prior methods in terms of the execution time and scalability.

Internet telephony is recently attracting an increasing amount of attention for the reason that it has the potential to significantly reduce the cost of long distance voice communication. To provide the interoperability between different manufacturers and vendors, ITU-T is actively drawing up the standard for the Internet telephony as ITU-T Rec. H.323. While the H.323 is continuously revised, there are, however, still many important issues needed to be further discussed. In particular, the bandwidth management, address translation, and intelligent call signaling/routing which are the major functions of an H.323 gatekeeper have not yet been fully addressed. In view of this, we develop in this paper an H.323 gatekeeper prototype which fully complies with the H.323 recommendation, and explicitly illustrate the usefulness of this prototype by devising two new methods to deal with the load balancing problem among the gatekeepers. Using the gatekeeper devised, one method for load balancing is based on Multiple-Registration with Multicasted LRQ and the other is based on Multiple-Registration with Hierarchical Database. It is noted that the gatekeeper prototype we devised is very versatile and can be easily extended to incorporate various features for further experiments.