With the immense popularity of the Web,the world is witnessing an unprecedented demand for data services. At the same time, the Internet is evolving towards an information super-highway that incorporates a wide mixture of existing and emerging communication technologies, including wireless, mobile, and hybrid networking. Taking advantage of these new technologies, we are proposing a hybrid scheme which effectively combines broadcast for massive data dissemination and unicast for individual data delivery. In this paper, we describe a technique that uses the broadcast medium for storage of frequently requested data, and an algorithm that continuously adapts the broadcast content to match the hot-spot of the database. We show that the hot-spot can be accurately obtained by monitoring the "broadcast misses" observed through direct requests. This is a departure from other broadcast-based systems which rely on efficient scheduling based on precompiled user profiles. We also show that the pro...

With the increasing popularity of portable wireless computers, mechanisms to efficiently transmit information to such clients are of significant interest. The environment under consideration is asymmetric in that the information server has much more bandwidth available, as compared to the clients. In such environments, often it is not possible (or not desirable) for the clients to send explicit requests to the server. It has been proposed that in such systems the server should broadcast the data periodically. One challenge in implementing this solution is to determine the schedule for broadcasting the data, such that the wait encountered by the clients is minimized. A broadcast schedule determines what is broadcast by the server and when. In this report, we present algorithms for determining broadcast schedules that minimize the wait time. Simulation results are presented to demonstrate that our algorithms perform well. Variations of our algorithms for environments subject to errors, and systems where different clients may listen to different number of broadcast channels are also considered.

Caching frequently accessed data items on the client side is an effective technique for improving performance in a mobile environment. Classical cache invalidation strategies are not suitable for mobile environments due to frequent disconnections and mobility of the clients. One attractive cache invalidation technique is based on invalidation reports (IRs). However, the IR-based cache invalidation solution has two major drawbacks, which have not been addressed in previous research. First, there is a long query latency associated with this solution since a client cannot answer the query until the next IR interval. Second, when the server updates a hot data item, all clients have to query the server and get the data from the server separately, which wastes a large amount of bandwidth. In this paper, we propose an IR-based cache invalidation algorithm, which can significantly reduce the query latency and efficiently utilize the broadcast bandwidth. Detailed analytical analysis and simulation experiments are carried out to evaluate the proposed methodology. Compared to previous IR-based schemes, our scheme can significantly improve the throughput and reduce the query latency, the number of uplink request, and the broadcast bandwidth requirements.

Recently, push-based delivery has attracted considerable attention as a means of disseminating information to large client populations in both wired and wireless settings. In this paper, we address the problem of ensuring the consistency and currency of client read-only transactions in the presence of updates. To this end, additional control information is broadcast. A suite of methods is proposed that vary in the complexity and volume of the control information transmitted and subsequently differ in response times, degrees of concurrency, and space and processing overheads. The proposed methods are combined with caching to improve query latency. The relative advantages of each method are demonstrated through both simulation results and qualitative arguments. Read-only transactions are processed locally at the client without contacting the server and thus the proposed approaches are scalable, i.e., their performance is independent of the number of clients.

: With the increasing acceptance of wireless technology, mechanisms to efficiently transmit information to wireless clients are of interest. The environment under consideration is asymmetric in that the information server has much more bandwidth available, as compared to the clients. It has been proposed that in such systems the server should broadcast the information periodically. A broadcast schedule determines what is broadcast by the server and when. This paper makes the simple, yet useful, observation that the problem of broadcast scheduling is related to the problem of fair queueing. Based on this observation, we present a log-time algorithm for scheduling broadcast, derived from an existing fair queueing algorithm. This algorithm significantly improves the time-complexity over previously proposed broadcast scheduling algorithms. Modification of this algorithm for transmissions that are subject to errors is considered. Also, for environments where different users may be listenin...

Recently, broadcasting has attracted considerable attention as a means of disseminating information to large client populations in both wired and wireless settings. In this paper, we exploit versions to increase the concurrency of client transactions in the presence of updates. We consider three alternative mediums for storing versions: (a) the air: older versions are broadcast along with current data, (b) the client's local cache: older versions are maintained in cache, and (c) a local database or warehouse at the client: part of the server's database is maintained at the client in the form of a multiversion materialized view. The proposed techniques are scalable in that they provide consistency without any direct communication from clients to the server. Performance results show that the overhead of maintaining versions can be kept low, while providing a considerable increase in concurrency.

AbstractÐRecent work has shown that invalidation report (IR)-based cache management is an attractive approach for mobile environments. However, the IR-based cache invalidation solution has some limitations, such as long query delay, low bandwidth utilization, and it is not suitable for applications where data change frequently. In this paper, we propose a proactive cache management scheme to address these issues. Instead of passively waiting, the clients intelligently prefetch the data that are most likely used in the future. Based on a novel prefetch-access ratio concept, the proposed scheme can dynamically optimize performance or power based on the available resources and the performance requirements. To deal with frequently updated data, different techniques (indexing and caching) are applied to handle different components of the data based on their update frequency. Detailed simulation experiments are carried out to evaluate the proposed methodology. Compared to previous schemes, our solution not only improves the cache hit ratio, the throughput, and the bandwidth utilization, but also reduces the query delay and the power consumption. Index TermsÐInvalidation report, power conservation, query latency, caching, mobile computing. æ 1

In this paper, we investigate efficient ways of broadcasting data to mobile users over multiple physical channels, which cannot be coalesced into a lesser number of high-bandwidth channels. We propose the use of MLMC (Multi-Level Multi-Channel ) Air-Cache which can provide mobile users with data based on their popularity factor. We provide a wide range of design considerations for the server which broadcasts over the MLMC cache. We also investigate some novel techniques for the mobile user to access data from the MLMC cache and show the advantages of designing the broadcast strategy in tandem with the access behavior of the mobile users . Finally, we provide experimental results to compare the techniques we introduce.

Mobile Ad-hoc Networks (MANET) is an emerging area of research. Most current work is centered on routing issues. This paper discusses the issues associated with data communication with MANET database systems. While data push and data pull methods have been previously addressed in mobile networks, the proposed methods do not handle the unique requirements associated with MANET. Unlike traditional mobile networks, all nodes within the MANET are mobile and battery powered. Existing wireless algorithms and protocols are insufficient primarily because they do not consider the mobility and power requirements of both clients and servers. This paper will present some of the critical tasks facing this research.

Abstract—Given a data set P,ak-means query returns k points in space (called centers), such that the average squared distance between each point in P and its nearest center is minimized. Since this problem is NP-hard, several approximate algorithms have been proposed and used in practice. In this paper, we study continuous k-means computation at a server that monitors a set of moving objects. Reevaluating k-means every time there is an object update imposes a heavy burden on the server (for computing the centers from scratch) and the clients (for continuously sending location updates). We overcome these problems with a novel approach that significantly reduces the computation and communication costs, while guaranteeing that the quality of the solution, with respect to the reevaluation approach, is bounded by a user-defined tolerance. The proposed method assigns each moving object a threshold (i.e., range) such that the object sends a location update only when it crosses the range boundary. First, we develop an efficient technique for maintaining the k-means. Then, we present mathematical formulas and algorithms for deriving the individual thresholds. Finally, we justify our performance claims with extensive experiments. Index Terms—k-Means, continuous monitoring, query processing. Ç