Proxies + Path Prediction: Improving Web Service Provision in Wireless–Mobile Communications

Mobile computing is considered of major importance to the computing industry for the forthcoming years due to the progress in the wireless communications area. A proxy-based architecture for accelerating Web browsing in wireless customer premises networks is presented. Proxy caches, maintained in base stations, are constantly relocated to follow the roaming user. A cache management scheme is proposed, which involves the relocation of full caches to the most probable cells but also percentages of the caches to less likely neighbors. Relocation is performed according to the output of a user movement prediction algorithm based on a learning automaton. The simulation of the scheme shows considerable benefits for the end user.     

Answering queries using cooperative semantic cache in mobile computing environments

In cooperative cache research domain, most of previous work engage in peer-to-peer systems and distributed systems, but do not involve applying cooperative semantic cache in mobile computing environments, which wireless communications disconnect at times and clients move frequently. In this paper, we extend the general semantic cache mechanism by enabling mobile clients to share their local semantic caches in a cooperative matter, and the process way and flow chart of the algorithm are described in detail. In addition, we discuss the methods used in cache consistence maintenance, which focus on confirm receiver of the periodic cache invalidation report and the process of validate client’s local cache. The experiment results indicate cooperative semantic cache mechanism could reduce query response time and increase cache hit ratio effectively.     

Intrusion Detection Techniques for Mobile Wireless Networks

The rapid proliferation of wireless networks and mobile computing applications has changed the landscape of network security. The traditional way of protecting networks with firewalls and encryption software is no longer sufficient and effective. We need to search for new architecture and mechanisms to protect the wireless networks and mobile computing application. In this paper, we examine the vulnerabilities of wireless networks and argue that we must include intrusion detection in the security architecture for mobile computing environment. We have developed such an architecture and evaluated a key mechanism in this architecture, anomaly detection for mobile ad-hoc network, through simulation experiments.     

移动网络中基于两级缓存的流媒体调度算法

提出一种适用于移动通信网的两级缓存流媒体系统结构2CMSA（two—level cache mobile streaming architecture），它突破了移动流媒体系统中终端缓存空间小、无线接入网带宽窄的局限；针对2CMSA结构设计了基于两级缓存的移动流媒体调度算法2CMSS（two—level cache based mobile streaming scheduling algorithm），建立数学模型分析了其性能；仿真实验证明，与原有的移动流媒体系统相比，使用2CMSS调度算法能够有效地节省网络传输开销，降低用户启动时延。     

Energy-Efficient Data Caching and Prefetching for Mobile Devices Based on Utility

In mobile computing environments, vital resources like battery power and wireless channel bandwidth impose significant challenges in ubiquitous information access. In this paper, we propose a novel energy and bandwidth efficient data caching mechanism, called GreedyDual Least Utility (GD-LU), that enhances dynamic data availability while maintaining consistency. The proposed utility-based caching mechanism considers several characteristics of mobile distributed systems, such as connection-disconnection, mobility handoff, data update and user request patterns to achieve significant energy savings in mobile devices. We develop an analytical model for energy consumption of mobile devices in a dynamic data environment. Based on the utility function derived from the analytical model, we propose algorithms for cache replacement and passive prefetching of data objects. Our comprehensive simulation experiments demonstrate that the proposed caching mechanism achieves more than 10% energy saving and near-optimal performance tradeoff between access latency and energy consumption. Huaping Shen received his M.S. and B.S. degrees in computer science from Fudan University, China, in 2001 and 1998, respectively. He is currently a Ph.D. student in the Department of Computer Science and Engineering at the University of Texas at Arlington. His research interests include data management in mobile networks, mobile computing, peer-to-peer networks, and pervasive computing. Mohan Kumar is an Associate Professor in Computer Science and Engineering at the University of Texas at Arlington. His current research interests are in pervasive computing, wireless networks and mobility, active networks, mobile agents, and distributed computing. Recently, he has developed or co-developed algorithms for active-network based routing and multicasting in wireless networks and caching prefetching in mobile distributed computing. He has published over 90 articles in refereed journals and conference proceedings and supervised Masters and doctoral theses in the areas of pervasive computing, caching/prefetching, active networks, wireless networks and mobility, and scheduling in distributed systems. Kumar is on the editorial board of The Computer Journal and he has guest edited special issues of several leading international journals including MONET and WINET issues and the IEEE Transactions on Computers. He is a co-founder of the IEEE International Conference on pervasive computing and communications (PerCom)—served as the program chair for PerCom 2003, and is the vice general chair for PerCom 2004. He has also served in the technical program committees of numerous international conferences/workshops. He is a senior member of the IEEE. Mohan Kumar obtained his PhD (1992) and MTech (1985) degrees from the Indian Institute of Science and the BE (1982) from Bangalore University in India. Prior to joining The University of Texas at Arlington in 2001, he held faculty positions at the Curtin University of Technology, Perth, Australia (1992–2000), The Indian Institute of Science (1986-1992), and Bangalore University (1985–1986). Dr. Sajal K. Das is currently a Professor of Computer Science and Engineering and also the Founding Director of the Center for Research in Wireless Mobility and Networking (CReWMaN) at the University of Texas at Arlington (UTA). Prior to 1999, he was a professor of Computer Science at the University of North Texas (UNT), Denton where he founded the Center for Research in Wireless Computing (CReW) in 1997, and also served as the Director of the Center for Research in Parallel and Distributed Computing (CRPDC) during 1995–97. Dr. Das is a recipient of the UNT Student Association’s Honor Professor Award in 1991 and 1997 for best teaching and scholarly research; UNT’s Developing Scholars Award in 1996 for outstanding research; UTA’s Outstanding Faculty Research Award in Computer Science in 2001 and 2003; and the UTA College of Engineering Research Excellence Award in 2003. An internationally-known computer scientist, he has visited numerous universities, research organizations, government and industry labs worldwide for collaborative research and invited seminar talks. He is also frequently invited as a keynote speaker at international conferences and symposia.Dr. Das’ current research interests include resource and mobility management in wireless networks, mobile and pervasive computing, wireless multimedia and QoS provisioning, sensor networks, mobile internet architectures and protocols, parallel processing, grid computing, performance modeling and simulation. He has published over 250 research papers in these areas, directed numerous industry and government funded projects, and holds four US patents in wireless mobile networks. He received the Best Paper Awards in the 5th Annual ACM International Conference on Mobile Computing and Networking (MobiCom’99), 16th International Conference on Information Networking (ICOIN-16), 3rd ACM International Workshop on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWiM 2000), and 11th ACM/IEEE International Workshop on Parallel and Distributed Simulation (PADS’97). Dr. Das serves on the Editorial Boards of IEEE Transactions on Mobile Computing, ACM/Kluwer Wireless Networks, Parallel Processing Letters, Journal of Parallel Algorithms and Applications. He served as General Chair of IEEE PerCom 2004, MASCOTS’02 ACM WoWMoM 2000-02; General Vice Chair of IEEE PerCom 2003, ACM MobiCom-2000 and IEEE HiPC 2000-01; Program Chair of IWDC 2002, WoWMoM 1998-99; TPC Vice Chair of ICPADS 2002; and as TPC member of numerous IEEE and ACM conferences. He is Vice Chair of the IEEE TCPP and TCCC Executive Committees and on the Advisory Boards of several cutting-edge companies.Dr. Sajal K. Das received B.S. degree in 1983 from Calcutta University, M.S. degree in 1984 from Indian Institute of Science, Bangalore, and Ph.D. degree in 1988 from the University of Central Florida, Orlando, all in Computer Science. Zhijun Wang received the M.S degree in Electrical Engineering from Pennsylvania State University, University Park, PA, 2001. He is working toward the Ph.D. degree in Computer Science and Engineering Department at the University of Texas at Arlington. His current research interests include data management in mobile networks and peer-to-peer networks, mobile computing and networking processors.This revised version was published online in August 2005 with a corrected cover date.     

一种基于GPRS网络的缓存一致性策略

提出了在GPRS网络中加入一个验证服务器VS维护无线移动环境下的缓存一致性的策略,利用GPRS骨干网中SGSN的有关移动终端的位置信息和用户访问的局域性,有针对性地只向在线终端发送所缓存数据的失效信息,有效地降低异步传输中的信息量。性能分析表明,该策略简化了维护缓存一致性的复杂性,使用很少的移动终端计算量,支持任意断开连接时间和一个PLMN网内的漫游。     

CCSim：基于Pin的CMPCache访问模拟器

随着芯片集成制造工艺的日益发展,拥有多级Cache的片上多处理器(CMP)已成为桌面应用和高端计算的主流平台.为了优化程序在CMP下运行性能,文中以Pin工具软件为基础,提出并设计了一个面向CMP体系架构的多级Cache访问模拟器——CCSim.该模拟器不仅可以模拟同构CMP下传统方式的Cache访问,而且还可以对CMP中最后一级共享Cache的竞争访问以及非传统方式的Barcelona式Cache访问模式进行模拟分析.     

Disconnected Processes, Mechanisms and Architecture for Mobile E-Business

With the tremendous advances in hand-held computing and communication capabilities, rapid proliferation of mobile devices, and decreasing device costs, we are seeing a growth in mobile e-business in various consumer and business markets. In this paper, we present a novel architecture and framework for end-to-end mobile e-business applications (e.g., point of sales). The architecture takes into consideration disconnection, application context, synchronization, transactions and failure recovery modes to provide mobile users with seamless and transparent access to business transactions and business-context specific data. In our architecture, we consider a novel business process design based on state-machines and event management to handle disconnection, resource limitations and failures. We designed, implemented and deployed a system for mobile e-business on clients (e.g., PDAs and PocketPCs) integrated with private exchanges and sell-side servers. The state-machine model with failure recovery mechanisms enables handling of one-to-many and many-to-one disconnections in large mobile e-business environments. The e-business framework on mobile clients is implemented based on J2ME, Webservices, and open XML standards. A detailed performance study of commerce transactions was done on different mobile client devices with diverse computing, memory and storage capabilities. We compare the performance of a purchasing application and the middleware on various devices such as PDAs and Laptops. We demonstrated that for small devices with limited capability the performance is reasonable. For devices with more computing capability, the response time is excellent.     

Adaptive wireless thin‐client model for mobile computing

The thin‐client computing model has the potential to significantly increase the performance of mobile computing environments. By delivering any application through a single, small‐footprint client (called a thin client) implemented on a mobile device, it is possible to optimize application performance without the need for building wireless application gateways. We thus present two significant contributions in the area of wireless thin‐client computing. Firstly, a mathematical performance model is derived for wireless thin‐client system. This model identifies factors that affect the performance of the system and supports derivation and analysis of adaptation strategies to maintain a user‐specified quality of service (QoS). Secondly, a proxy‐based adaptation framework is developed for wireless thin‐client systems, which dynamically optimizes performance of a wireless thin client via dynamically discovered context. This is implemented with rule‐based fuzzy logic that responds to variations in wireless link bandwidth and client processing power. Our fuzzy inference engine uses contextual data to dynamically optimize tradeoffs among different quality of service parameters offered to the end users. Additionally, our adaptation framework uses highly scalable wavelet‐based image coding to provide scalable QoS that can degrade gracefully. Our thin‐client adaptation framework shields the user from ill effects of highly variable wireless network quality and mobile device resources. This improves performance of active applications, in which the display changes frequently. Further, active application behaviour may produce high transmission latency for screen updates, which can adversely affect user perception of QoS, resulting in poor interactivity. We report measured adaptive performance under realistic mobile device and network conditions for several different clients and servers. Copyright © 2008 John Wiley & Sons, Ltd.     

Intelligent Handoff for Mobile Wireless Internet

This paper presents an intelligent mobility management scheme for Mobile Wireless InterNet – MWIN. MWIN is a wireless service networks wherein its core network consisting of Internet routers and its access network can be built from any Internet-capable radio network. Two major standards are currently available for MWIN, i.e., the mobile IP and wireless LAN. Mobile IP solves address mobility problem with the Internet protocol while wireless LAN provides a wireless Internet access in the local area. However, both schemes solve problems independently at different layers, thereby some additional problems occur, e.g., delayed handoff, packet loss, and inefficient routing. This paper identifies these new problems and performs analyses and some real measurements on the handoff within MWIN. Then, a new handoff architecture that extends the features of both mobile IP and wireless LAN handoff mechanism was proposed. This new architecture consists of mobile IP extensions and a modified wireless LAN handoff algorithm. The effect of this enhancement provides a linkage between different layers for preventing packet loss and reducing handoff latency. Finally, some optimization issues regarding network planning and routing are addressed.     

Piecewise Network Awareness Service for Wireless/Mobile Pervasive Computing

This paper presents a piecewise framework for network awareness service (NAS) for wireless/mobile pervasive computing. We investigate how piecewise consideration of wired and wireless elements of the framework architecture benefits service advertisement and discovery and network-awareness techniques. We also discuss scalability of the NAS framework with respect to platform computing capabilities. The framework is suitable for a wide range of computing devices, from powerful ones with multi-tasking operating systems (OS) to small ones with lightweight OS. Case studies applying the NAS framework to sensor monitoring in home networks and data streaming in pervasive multimedia computing are presented. The analytical results on the performance of the NAS framework in these case studies show that it has significant advantages over traditional network-awareness frameworks in terms of reducing wireless bandwidth consumption and saving battery energy of mobile devices.     

Improving reliable transport and handoff performance in cellular wireless networks

TCP is a reliable transport protocol tuned to perform well in traditional networks where congestion is the primary cause of packet loss. However, networks with wireless links and mobile hosts incur significant losses due to bit-errors and handoffs. This environment violates many of the assumptions made by TCP, causing degraded end-to-end performance. In this paper, we describe the additions and modifications to the standard Internet protocol stack (TCP/IP) to improve end-to-end reliable transport performance in mobile environments. The protocol changes are made to network-layer software at the base station and mobile host, and preserve the end-to-end semantics of TCP. One part of the modifications, called the snoop module, caches packets at the base station and performs local retransmissions across the wireless link to alleviate the problems caused by high bit-error rates. The second part is a routing protocol that enables low-latency handoff to occur with negligible data loss. We have implemented this new protocol stack on a wireless testbed. Our experiments show that this system is significantly more robust at dealing with unreliable wireless links than normal TCP; we have achieved throughput speedups of up to 20 times over regular TCP and handoff latencies over 10 times shorter than other mobile routing protocols.This work was supported by ARPA Contract J-FBI-93-153. This paper was in part presented at the ACM Mobile Computing and Networking Conference (Mobicom '95), Berkeley, California, 14–15 November 1995.     

Keep Your Data Safe and Available While Roaming

The possibility of accessing and/or receiving local or remote data anywhere and at anytime constitutes an important advantage in many business environments. However, when working with mobile devices, users face many problems, such as: (1) devise exposure problems – mobile devices are more vulnerable and fragile than stationary devices, because they can be easily stolen, lost or damaged, (2) media problems – wireless communications are often unstable, asymmetric and expensive, and (3) availability problems – mobile devices stay disconnected for long periods of time. To alleviate these problems, we present a service, Data Lockers, which offers to its users first, the possibility of keeping their data in a secure and safe space in a proxy, thus alleviating the device exposure problem. Next, data stored in a data locker are available even when the mobile device is disconnected, thus providing a solution to the availability problem. Finally, specific tasks are carried out at the fixed network on behalf of the mobile user, in this way relieving the media problem. The architecture of the Locker Rental Service is based on mobile agents. These agents, and the locker, stay always close to the location of the user, traveling to meet the user wherever the user moves, therefore, allowing users to use anywhere-anytime, ubiquitous persistent storage space located at the fixed network.     

Proactive content caching by exploiting transfer learning for mobile edge computing

To address the vast multimedia traffic volume and requirements of user quality of experience in the next‐generation mobile communication system (5G), it is imperative to develop efficient content caching strategy at mobile network edges, which is deemed as a key technique for 5G. Recent advances in edge/cloud computing and machine learning facilitate efficient content caching for 5G, where mobile edge computing can be exploited to reduce service latency by equipping computation and storage capacity at the edge network. In this paper, we propose a proactive caching mechanism named learning‐based cooperative caching (LECC) strategy based on mobile edge computing architecture to reduce transmission cost while improving user quality of experience for future mobile networks. In LECC, we exploit a transfer learning‐based approach for estimating content popularity and then formulate the proactive caching optimization model. As the optimization problem is NP‐hard, we resort to a greedy algorithm for solving the cache content placement problem. Performance evaluation reveals that LECC can apparently improve content cache hit rate and decrease content delivery latency and transmission cost in comparison with known existing caching strategies.     

Design and analysis of low-power cache using two-level filter scheme

Power consumption is an increasingly pressing problem in modern processor design. Since the on-chip caches usually consume a significant amount of power, it is one of the most attractive targets for power reduction. This paper presents a two-level filter scheme, which consists of the L1 and L2 filters, to reduce the power consumption of the on-chip cache. The main idea of the proposed scheme is motivated by the substantial unnecessary activities in conventional cache architecture. We use a single block buffer as the L1 filter to eliminate the unnecessary cache accesses. In the L2 filter, we then propose a new sentry-tag architecture to further filter out the unnecessary way activities in case of the L1 filter miss. We use SimpleScalar to simulate the SPEC2000 benchmarks and perform the HSPICE simulations to evaluate the proposed architecture. Experimental results show that the two-level filter scheme can effectively reduce the cache power consumption by eliminating most unnecessary cache activities, while the compromise of system performance is negligible. Compared to a conventional instruction cache (32 kB, two-way) implemented with only the L1 filter, the use of a two-level filter can result in roughly 30% reduction in total cache power consumption. Similarly, compared to a conventional data cache (32 kB, four-way) implemented with only the L1 filter, the total cache power reduction is approximately 46%.     

Challenges and Solutions to Adaptive Computing and Seamless Mobility over Heterogeneous Wireless Networks

Recent years have witnessed the rapid evolution of commercially available mobile computing environments. This has given rise to the presence of several viable, but non-interoperable wireless networking technologies – each targeting a niche mobility environment and providing a distinct quality of service. The lack of a uniform set of standards, the heterogeneity in the quality of service, and the diversity in the networking approaches makes it difficult for a mobile computing environment to provide seamless mobility across different wireless networks. Besides, inter-network mobility will typically be accompanied by a change in the quality of service. The application and the environment need to collaboratively adapt their communication and data management strategies in order to gracefully react to the dynamic operating conditions.This paper presents the important challenges in building a mobile computing environment which provides seamless mobility and adaptive computing over commercially available wireless networks. It suggests possible solutions to the challenges, and describes an ongoing research effort to build such a mobile computing environment.     

QoS Provisioning in Wireless/Mobile Multimedia Networks Using an Adaptive Framework

Recently there is a growing interest in the adaptive multimedia networking where the bandwidth of an ongoing multimedia call can be dynamically adjusted. In the wireless/mobile multimedia networks using the adaptive framework, the existing QoS provisioning focused on the call blocking probability and the forced termination probability should be modified. We, therefore, redefine a QoS parameter – the cell overload probability – from the viewpoint of the adaptive multimedia networking. Then, we propose a distributed call admission control (CAC) algorithm that guarantees the upper bound of the cell overload probability. Also, a bandwidth adaptation algorithm which seeks to minimize the cell overload probability is also presented. Simulation experiments are carried out to verify the performance of the proposed CAC algorithm. Furthermore, the performance of the adaptive wireless/mobile network is compared to that of the existing non-adaptive wireless/mobile networks. As a further step in QoS provisioning, we propose another QoS parameter, the degradation period ratio, and discuss analytically how the CAC algorithm guarantees the upper bound of the degradation period ratio.     

基于移动计算的智能家庭研究

在家庭网络、无线通讯、移动计算技术迅速发展的时代,伴随着信息家电的出现,智能家庭得到广泛的应用。但现有的智能家庭只能通过家庭内部设备提供相关服务,在远程控制方面技术尚未成熟并且不具有移动性,提出的是一种将智能家庭和移动计算相互融合的构想,即借助家庭网关和移动网络服务来实现智能家庭享受移动计算提供的优质服务。后期还要靠很多具体理论和实践工作来实现。     

The influence of processor architecture on the design and the results of WCET tools

The architecture of tools for the determination of worst case execution times (WCETs) as well as the precision of the results of WCET analyses strongly depend on the architecture of the employed processor. The cache replacement strategy influences the results of cache behavior prediction; out-of-order execution and control speculation introduce interferences between processor components, e.g., caches, pipelines, and branch prediction units. These interferences forbid modular designs of WCET tools, which would execute the subtasks of WCET analysis consecutively. Instead, complex integrated designs are needed, resulting in high demand for memory space and analysis time. We have implemented WCET tools for a series of increasingly complex processors: SuperSPARC, Motorola ColdFire 5307, and Motorola PowerPC 755. In this paper, we describe the designs of these tools, report our results and the lessons learned, and give some advice as to the predictability of processor architectures.