Julian Chesterfield’s research while affiliated with University of Cambridge and other places

In this paper we focus on the problems of maintaining ad hoc network connectivity in the presence of node mobility whilst providing globally efficient and robust routing. The common approach among existing wireless ad hoc routing solutions is to establish a global optimal path between a source and a destination. We argue that establishing a globally optimal path is both unreliable and unsustainable as the network diameter, traffic volume and number of nodes all increase in the presence of moderate node mobility. To address this we propose landmark guided forwarding (LGF), a protocol that provides a hybrid solution of topological and geographical routing algorithms. We demonstrate that LGF is adaptive to unstable connectivity and scalable to large networks. Our results indicate therefore that landmark guided forwarding converges much faster, scales better and adapts well within a dynamic wireless ad hoc environment in comparison to existing solutions.

Recently, there has been an increasing interest in wireless broadcast systems as a means to enable scalable content delivery to large numbers of mobile users. However, gracefully providing efficient reconciliation of different versions of a file over such broadcast channels still remains a challenge. Such systems often lack a feedback channel and consequently updates cannot be easily tailored to a specific user. Moreover, given the potentially large number of possible versions of a file, it is impractical to send a tailored update for each particular user.In this paper we consider the problem of efficiently updating files in such wireless broadcast channels. To this extent, we present DeltaCast, a system that combines hierarchical hashes and erasure codes to minimise the amount of battery power and the amount of time needed to synchronise each mobile device. Based on our experimental results, we show that DeltaCast is able to efficiently identify the missing portions of a file and quickly updated each client.

Abstract In recent years, research in wireless Ad Hoc routing seems to be moving towards the approach of position based forwarding. Amongst proposed algorithms, Greedy Perimeter Stateless Routing has gained recognition for guaranteed delivery with modest network overheads. Although this addresses the scaling limitations with topological routing, it has limited tolerance for position inaccuracy or stale state reported by a location service. Several researchers have demonstrated that the

Wireless wide area networks (WWANs) are becoming ubiquitous across most geographic regions, enabling simultaneous coverage from multiple providers. WWAN channels exhibit both uncorrelated and correlated behaviour on a variety of levels. In this paper we examine the statistical properties of WWAN links, and illustrate the benefits in heterogeneity that can be exploited to improve statistical throughput and multimedia quality. Our results are based on real network measurements. We describe the design and implementation of a high quality multimedia streaming application that implements WWAN streaming optimisations utilising unequal error protection coding techniques, and we evaluate the performance over an operational WWAN network.

Abstract Wireless Ad Hoc network routing presents some extremely challenging research problems, trying to optimize parameters such as energy conservation vs connectivity and global optimization vs routing overhead scalability. In this paper we focus on the problems of maintaining network connectivity in the presence of node mobility whilst providing globally ecien t and robust routing. The common,approach among existing wireless Ad Hoc routing solutions is to establish a global optimal path between a source and a destination. We argue that establishing a globally optimal

We present a comparative performance study of a wide selection of optimization techniques to enhance application performance in the context of wide-area wireless networks (WWANs). Unlike in traditional wired and wireless IP-based networks, applications running over WWAN cellular environments are significantly affected by the vagaries of the cellular wireless medium. Prior research has proposed and analyzed optimizations at individual layers of the protocol stack. In contrast, we introduce the first detailed experiment-based evaluation and comparison of all such optimization techniques in a commercial WWAN testbed. This paper, therefore, summarizes our experience in implementing and deploying an infrastructure to improve WWAN performance.The goals of this paper are: (1) to perform an accurate benchmark of application performance over such commercially deployed WWAN environments, (2) to implement and characterize the impact of various optimization techniques across different layers of the protocol stack, and (3) to quantify their interdependencies in realistic scenarios. Additionally, we also discuss measurement pitfalls that we experienced and provide guidelines that may be useful for future experimentation in WWAN environments.

This paper explores the extension of a model for the operation of an ad hoc mobile network to more general providerless networks, such as peer-to-peer systems. The model incorporates incentives for users to act as transit nodes on multi-hop paths and to be rewarded with their own ability to send traffic. The paper explores some of the trust questions that arise in this problem space and conjectures that the very structure of a peer organisation may have some hidden benefits for trust re-enforcement, that have not been previously explored (to our knowledge).

We introduce MAR, a commuter mobile access router infrastructure that exploits wireless diversity (e.g. channel diversity, network diversity, and technology diversity) to provide improved data performance for wireless data users. Our system design stems from the observation that rather than choosing a single wireless service provider (e.g. Sprint, AT&T, BT, Vodafone), a single technology (e.g. GPRS, UMTS, CDMA, 802.11), or a single wireless channel, users can obtain significant benefits by using the multiplicity of choices available. MAR is a wireless multi-homed device that can be placed in moving vehicles (e.g. car, bus, train) to enable high-speed data access. MAR dynamically instantiates new channels based on traffic demand, aggregates the bandwidth and dynamically shifts load from poor quality to better quality channels. MAR, thus, provides a faster, more stable, and reliable communication channel to mobile users.We have implemented and tested the MAR system in our testbed which spans the networks of three different cellular providers. Through our experiments we have performed a detailed evaluation to quantify the benefits of MAR for different protocols and applications. For example, even in highly mobile environments, MAR, on average, improves the end-user experience of web-browsing and streaming applications by a factor of 2.8 and 4.4 respectively. Our results show that significant benefits can be obtained by exploiting the diversity in coverage offered by many cellular operators, different technology networks (e.g. GPRS, CDMA), and diverse wireless channels.

We present measurement approaches to evaluate performance optimizations, employed at different layers of the protocol stack, to enhance application performance over wide-area wireless networks (WWANs). Applications running over WWAN cellular environments (e.g web browsing) are significantly affected by the vagaries of the cellular wireless links. Much of the prior research has focussed on variety of isolated performance optimizations and their measurements over wired and wireless environments. In this paper we introduce experiment-based measurement approaches to benchmark application performance using optimizations performed at individual layers of the protocol stack. These measurement initiatives are aimed at: (1) performing an accurate benchmark of application performance over commercially deployed WWAN environments, (2) characterizing the impact of a wide selection of optimization techniques applied at different layers of the protocol stack, and (3) quantifying the interdependencies between the different optimization techniques and providing measurement initiatives for future experimentation to obtain consistent and repeatable application benchmarks in WWAN environments.

We introduce MAR, a commuter mobile access router infrastructure that exploits wireless diversity (e.g. channel diversity, network diversity, and technology diversity) to provide improved data performance for wireless data users. Our system design stems from the observation that rather than choosing a single wireless service provider (e.g. Sprint, AT&T, BT, Vodafone), a single technology (e.g. GPRS, UMTS, CDMA, 802.11), or a single wireless channel, users can obtain signi cant bene ts by using the multiplicity of choices available to the user. MAR is a wireless multi-homed device that can be placed in moving vehicles (e.g. car, bus, train) to enable high-speed data access. MAR dynamically instantiates new channels based on trac demand, aggregates the bandwidth and dynamically shifts load from poor quality channels to better quality ones, thus, providing a faster, more stable, and reliable communication channel to mobile users.