Performance optimization problem in speculative prefetching

Speculative prefetching has been proposed to improve the response time of network access. Previous studies in speculative prefetching focus on building and evaluating access models for the purpose of access prediction. This paper investigates a complementary area which has been largely ignored, that of performance modeling. We analyze the performance of a prefetcher that has uncertain knowledge about future accesses. Our performance metric is the improvement in access time, for which we derive a formula in terms of resource parameters (time available and time required for prefetehing) and speculative parameters (probabilities for next access). We develop a prefetch algorithm to maximize the improvement in access time. The algorithm is based on finding the best solution to a stretch knapsack problem, using theoretically proven apparatus to reduce the search space. An integration between speculative prefetching and caching is also investigated.

Resource-aware speculative prefetching in wireless networks

Mobile users connected to wireless networks expect performance comparable to those on wired networks for interactive multimedia applications. Satisfying Quality of Service (QoS) requirements for such applications in wireless networks is a challenging problem due to limitations of low bandwidth, high error rate and frequent disconnections of wireless channels. In addition, wireless networks suffer from varying bandwidth. In this paper we investigate object prefetching during times of connectedness and bandwidth availability to enhance user perceived connectedness. This paper presents an access model that is suitable for multimedia access in wireless networks. Access modelling for the purpose of predicting future accesses in the context of speculative prefetching has received much attention in the literature. The model recognizes that a web page, instead of just a single file, is typically a compound of several files. When it comes to making prefetch decisions, most previous studies in speculative prefetching resort to simple heuristics, such as prefetching an item with access probabilities larger than a manually tuned threshold. This paper takes a different approach. Specifically, it models the performance of the prefetcher, taking into account access predictions and resource parameters, and develops a prefetch policy based on a theoretical analysis of the model. Since the analysis considers cache as one of the resource parameters, the resulting policy integrates prefetch and cache replacement decisions. The paper investigates the effect of prefetching on network load. In order to make effective use of available resources and maximize access improvement, it is beneficial to prefetch all items with access probabilities exceeding certain threshold.

Performance modelling of speculative prefetching for compound requests in low bandwidth networks

To improve the accuracy of access prediction, a prefetcher for web browsing should recognize the fact that a web page is a compound. By this term we mean that a user request for a single web page may require the retrieval of several multimedia items. Our prediction algorithm builds an access graph that captures the dynamics of web navigation rather than merely attaching probabilities to hypertext structure. When it comes to making prefetch decisions, most previous studies in speculative prefetching resort to simple heuristics, such as prefetching an item with access probabilities larger than a manually tuned threshold. The paper takes a different approach. Specifically, it models the performance of the prefetcher and develops a prefetch policy based on a theoretical analysis of the model. In the analysis, we derive a formula for the expected improvement in access time when prefetch is performed in anticipation for a compound request. We then develop an algorithm that integrates prefetch and cache replacement decisions so as to maximize this improvement. We present experimental results to demonstrate the effectiveness of compound-based prefetching in low bandwidth networks.

A performance model of speculative prefetching in distributed information systems

Previous studies in speculative prefetching focus on building and evaluating access models for the purpose of access prediction. This paper investigates a complementary area which has been largely ignored, that of performance modelling. We use improvement in access time as the performance metric, for which we derive a formula in terms of resource parameters (time available and time required for prefetching) and speculative parameters (probabilities for next access). The performance maximization problem is expressed as a stretch knapsack problem. We develop an algorithm to maximize the improvement in access time by solving the stretch knapsack problem, using theoretically proven apparatus to reduce the search space. Integration between speculative prefetching and caching is also investigated, albeit under the assumption of equal item sizes.

Effect of speculative prefetching on network load in distributed systems

Previous studies in speculative prefetching focus on building and evaluating access models for the purpose of access prediction. This paper on the other hand investigates the performance of speculative prefetching. When prefetching is performed speculatively, there is bound to be an increase in the network load. Furthermore, the prefetched items must compete for space with existing cache occupants. These two factors-increased load and eviction of potentially useful cache entries-are considered in the analysis. We obtain the following conclusion: to maximise the improvement in access time, prefetch exclusively all items with access probabilities exceeding a certain threshold.

Investigation of a prefetch model for low bandwidth networks

We investigate speculative prefetching under a model in which prefetching is neither aborted nor preempted by demand fetch but instead gets equal priority in network bandwidth utilisation. We argue that the non-abortive assumption is appropriate for wireless networks where bandwidth is low and latency is high, and the non-preemptive assumption is appropriate for Internet where prioritization is not always possible. This paper assumes the existence of an access model to provide some knowledge about future accesses and investigates analytically the performance of a prefetcher that utilises this knowledge. In mobile computing, because resources are severely constrained, performance prediction is as important as access prediction. For uniform retrieval time, we derive a theoretical limit of improvement in access time due to prefetching. This leads to the formulation of an optimal algorithrn for prefetching one access ahead. For non-uniform retrieval time, two different types of prefetching of multiple documents, namely mainline and branch prefetch, are evaluated against prefetch of single document. In mainline prefetch, the most probable sequence of future accesses is prefetched. In branch prefetch, a set of different alternatives for future accesses is prefetched. Under some conditions, mainline prefetch may give slight improvement in user-perceived access time over single prefetch with nominal extra retrieval cost, where retrieval cost is defined as the expected network time wasted in non-useful prefetch. Branch prefetch performs better than mainline prefetch but incurs more retrieval cost.

Speculative fictions for understanding global change environments: two thought experiments

The purpose of a thought experiment, as the term was used by quantum and relativity physicists in the early part of the twentieth century, was not prediction (as is the goal of classical experimental science), but more defensible representations of present ‘realities’. Speculative fictions, from Mary Shelley's Frankenstein to the Star Wars cinema saga, can be read as sociotechnical thought experiments that produce alternative representations of present circumstances and uncertainties, and anticipate and critique possible futures. In this essay I demonstrate how two examples of popular speculative fictions, Frank Herbert's Dune (1965) and Ursula Le Guin's The Telling (2000), function as thought experiments that problematise global transitions in their respective eras. I argue that critical readings of such stories can help us to anticipate, critique, and respond constructively to social and cultural changes and change environments within nation-states that constitute, and are constituted by, global change processes and their effects.

On the extent of speculative activity in the Indian stock market during badla and post-badla period

The authors test the existence of speculative activity in the Indian stock market during badla and post-badla period. They further investigate whether speculative activity migrated to single stocks futures market after banning of badla system. In both the tests it is found that there is no evidence of strong speculative activity in the Indian market. The research raises some questions on the regulators decision of banning badla system and sheds some light on the future decisions with respect to single stock futures market.

Changing times in research? A speculative analysis of refereed contributions to distance education journal from 1980 to 2003

The paper observes a number of possible changes impacting on the field of distance education research and suggests that these are likely to have lead to an increasing interest in research on computer-based instructional design and delivery, and a concomitant decrease in interest in other areas of distance education research. A fairly simple analysis of contributions to Distance Education since 1980 bears out the suggestion. Some opportunities and some threats to distance education as a field are discussed as a consequence of the analysis.

Democracy, global transitions, and education : using speculative fictions as thought experiments in anticipatory critical inquiry

The purpose of a thought experiment, as the term was used by quantum and relativity physicists in the early part of the twentieth century, was not prediction (as is the goal of classical experimental science), but more defensible representations of present 'realities'. Indeed, one of the best-known examples of a thought experiment ('Schrodinger's cat') demonstrates the impossibility of prediction at the quantum level. Speculative fictions, from Mary Shelley's Frankenstein to the Star Wars saga, can be read as socio-technical thought experiments that can help us to apprehend and comprehend present 'realities' and uncertainties, and to anticipate and critique possible futures. In this paper I will demonstrate how two examples of popular speculative fictions, Frank Herbert's Dune (1965) and Ursula Le Guin's The Telling (2000), can be read as thought experiments that describe problematic aspects of contemporary social and cultural transformations. I will argue that critical and deconstructive readings of these novels can help us to produce anticipatory critiques of possible ways in which democratic institutions are being transformed by globalisation. I will conclude by considering the implications of such anticipatory critiques for generating questions, problems and issues in educational inquiry and for choosing appropriate methodologies for investigating them.

Efficient web browsing with perfect anonymity using page prefetching

Anonymous web browsing is a hot topic with many potential applications for privacy reasons. The current dominant strategy to achieve anonymity is packet padding with dummy packets as cover traffic. However, this method introduces extra bandwidth cost and extra delay. Therefore, it is not practical for anonymous web browsing applications. In order to solve this problem, we propose to use the predicted web pages that users are going to access as the cover traffic rather than dummy packets. Moreover, we defined anonymity level as a metric to measure anonymity degrees, and established a mathematical model for anonymity systems, and transformed the anonymous communication problem into an optimization problem. As a result, users can find tradeoffs among anonymity level and cost. With the proposed model, we can describe and compare our proposal and the previous schemas in a theoretical style. The preliminary experiments on the real data set showed the huge potential of the proposed strategy in terms of resource saving.

Australia, Asia and cultural anxiety : inaugural AHA Anniversary Public Lecture, given at the Grand Hotel, Mildura on 29 September (2003).

My theme tonight is the recurrent idea that Australia could be expected to have an Asian future. From the 1880s there developed a speculative literature around the notion that Asia ('generic Asia' as I prefer to call it) would exert an increasing influence, possibly a determining influence, on the development and settlement of the Australian continent. There is a certain pathos about this story of a young, newly formed community on the threshold of nationhood finding Asia blocking its path. Would the ensuing contest be the making of white Australia; would the young nation define its national purpose and assert its right to exist or would it succumb to a force more powerful? Would white Australia become nothing more than a faint historical memory, a failed experiment in the complex and uncertain business of nation building? In short, would white Australia fail?

International sentencing law: in search of a justification and coherent framework

An international sentencing jurisprudence is emerging from the decisions by the International Criminal Tribunal for the Former Yugoslavia (ICTY or the Yugoslav tribunal) and the International Criminal Tribunal for Rwanda (ICTR or the Rwanda tribunal) (collectively, 'the tribunals'). This article examines international sentencing law and practice and discusses the justification for the practice. International sentencing law has several objectives. The main goals are reconciliation, deterrence, retribution and rehabilitation. The sentencing inquiry is marked by a high degree of discretion and has resulted in sentencers developing a large amount of aggravating and mitigating considerations, such as being in a position of authority, remorse and good character. It is argued that the current international sentencing approach is flawed - fundamentally so. Most of the stated goals of international sentencing in the form of reconciliation, retribution and rehabilitation are either highly speculative or misguided. The only justification for the practice is general deterrence. This is, however, significantly undermined by the selective and infrequent enforcement of crimes within the jurisdiction of such tribunals. The stated aggravated and mitigating considerations are not valid given that they are not justified by reference to the stated aims of sentencing and only serve to undermine the search for a penalty which is commensurate the serious of the offence. This article suggests a coherent framework for international sentencing policy and practice.