Replicated client-server execution to overcome unpredictability in mobile environment

Abstract

this paper examines the fundamental limitation of adaptation based methods in the presence of unpredictability and instability in wireless network bandwidth, server loads, and usage patterns. We argue that existing adaptation based methods may fail to produce good application response time given such unpredictability and instability, because they require somehow accurate prediction on resource conditions and usage patterns in order to perform effectively. We have designed and implemented a new, simple yet powerful, replicated client-server model which overcomes this fundamental problem of unpredictability and instability. The basic idea behind replicated client-server model is simple -application execution is replicated on both client and server, and the faster result is returned to the user. It provides the benefit of faster response time at the cost of computational overhead in replicating executions on both client and server. L INTRODUCTION A Pplication response time is one of the key parameters that affect interactive user experience in Internet-based applications. In this paper, we would like to make a case for a new replicated client-server model that could achieve good application response time in the presence of unpredictable wireless network bandwidth, server loads, and usage patterns in mobile computing environment. The basic idea behind the replicated client-server model is simple -replicate, whenever possible, computation on both the mobile client device and remote server, and bring the faster result to the user. Although this model is simple, it works well to achieve good application response time in mobile and distributed computing environments, where unpredictability and instability in wireless network bandwidth, server loads, and usage patterns can occur frequently.Unpredictability and instability in resource conditions and usage patterns are known to be fundamental limitations for adaptation based methods. In general, adaptation methods make use of feedback-prediction-adjustment loop. If future resource conditions or usage patterns cannot be accurately predicted based on feedbacks, adaptation will fail -consider the example of optimizing application response time, inaccurate prediction on network bandwidth or server loads would produce misplacements of application components on mobile client device and server.