Proxy agent based replication control model for wireless internet

Mobile computing allows users to request critical information and receive swift responses at any places, but mobile users could suffer from unreliable and ill-timed services due to the characteristics of wireless media. One way that reduces possibility of the unsatisfactory services is data replication. Data replication, however, inevitably induces the overhead of maintaining replica consistency which requires more expensive synchronization mechanism. We propose a new replicated data management scheme in distributed mobile environment. In order to alleviate negative impact of synchronization message overhead in fault-prone mobile environment, we devise a new replication control scheme called proxy quorum consensus (PQC). PQC minimizes the message overhead by coordinating quorum access activities by means of proxy mediated voting (PMV) which exploits reliable proxy hosts instead of unreliable mobile hosts in voting process. We also propose a simulation model to show the performance of PQC. Based on the results of the performance evaluation, we conclude that PQC scheme outperforms the traditional schemes.     

移动代理系统安全问题研究

该文对当前移动代理系统的安全问题作了较全面的分析,并针对恶意代理和恶意主机问题,分别提出了移动代理安全传输协议和三层保护方案。     

Algorithms for validating E-tickets in mobile computing environment

E-tickets issued online can be used by different vendors to provide services such as discount coupons for E-shopping, or an entrance for a football game. One major issue associated with E-tickets is the problem of validation, which becomes more severe in a mobile environment due to mobility of a mobile host (MH) and frequent failure/disconnection of validation servers known as mobile support stations (MSSs). Some additional problems include the identification of duplicate submissions of an E-ticket by a MH. Thus, this paper proposes two protocols using the Flat and Hierarchical schemes for E-ticket processing and validation in a mobile environment that guarantee at least and at most once property (each E-ticket is validated at least and at most once). The protocols have been validated and compared through complexity analysis and experiments.     

Synchronization and handoff management schemes for wireless multimedia systems

This paper presents handoff management schemes for synchronization algorithms for wireless multimedia systems. The synchronization and handoff management schemes allow mobile hosts to receive time-dependant multimedia streams without delivery interruption while moving from one cell to another. They also maintain the correct ordering of the media components, through the execution of the wireless multimedia application by a means of timestamped messages passed among mobile hosts, base stations and servers. The timestamp values are used to compute the delay for each multimedia unit for each server. Furthermore, the proposed schemes always search for a quasi-receiver among the base stations with which the mobile hosts can communicate to synchronize multimedia units. We discuss the algorithms and present a set of simulation experiments that evaluate the performance of our schemes, using message complexity and buffer usage at each frame arrival time. Our results indicate that our schemes exhibit no underflow or overflow within the bounded delivery time.     

移动IPv6移动性能的改进

主要问题是移动IPv6协议中移动主机移动性能的改进。通过对现有方案的研究和分析，提出了一种新的多层次移动IPv6方案。新方案中采用了新的方法计算主机的移动速度以便移动主机选择合适的MAP，同时还提出了新的缓存机制来减少转交过程中数据包的丢失。还利用了NS2对新方案进行了模拟仿真。新方案可以适应移动主机的快速移动，并能够减少绑定更新报文和数据包的丢失。     

The Bengal Database Replication System

Mobile computers often suffer from limited connectivity, or even complete lack of network access. Moreover, in wireless networks some machines are often more accessible to mobile computers than others are. Ideally, nomadic users want the same quality and speed of database access as when they are well connected to the network. Replicated databases meet this need by allowing each mobile machine to carry its own copy of key data. But existing replicated systems are not well suited for all nomadic scenarios. Certain important mobile computing situations require optimistic peer-oriented database replication. The Bengal Database Replication System has these characteristics and was designed to operate in difficult nomadic conditions. This paper presents the design assumptions of the system, describes its architecture, presents performance data on its operation, and discusses future enhancements for the system. The paper also contrasts the system to other replicated databases, concentrating on their suitability for nomadic computing. The Bengal technology can play an important role in the development of highly scalable, highly available, fault-tolerant database systems.     

Efficient task replication and management for adaptive fault tolerance in Mobile Grid environments

Fault tolerant Grid computing is of vital importance as the Grid and Mobile computing worlds converge to the Mobile Grid computing paradigm. We present an efficient scheme based on task replication, which utilizes the Weibull reliability function for the Grid resources so as to estimate the number of replicas that are going to be scheduled in order to guarantee a specific fault tolerance level for the Grid environment. The additional workload that is produced by the replication is handled by a resource management scheme which is based on the knapsack formulation and which aims to maximize the utilization and profit of the Grid infrastructure. The proposed model has been evaluated through simulation and has shown its efficiency for being used in a middleware approach in future mobile Grid environments.     

一种基于移动计算环境的因果日志卷回恢复算法

由于移动节点的不可靠和无线网络连接的脆弱性,研究移动计算系统容错机制具有重要意义.对可以跨区移动、随时可以与网络断开的自治性很强的移动节点来说,异步的卷回恢复是一种重要的容错手段.现有的移动计算环境下的卷回恢复算法都无法完全实现一致的异步卷回恢复.基于因果消息日志,提出一种新的移动计算环境的卷回恢复算法:通过先行图来记录节点间的消息依赖关系,将异步检查点、基于发送方的暂存消息日志和先行图全部在移动支持站上存储和处理,为移动节点提供一种透明的容错服务,完全消除依赖关系在移动节点之间造成的影响.用形式化的方法证明了系统的一致性.仿真结果表明,在卷回开销达到最低的同时,也显著降低了无错运行时的通信和存储开销.     

基于移动数据库复制技术的同步模型研究

移动复制是提高移动数据库系统性能的一项关键技术.提出一种以事务结果集为同步粒度的同步机制,并且以此建立了一种新的移动复制数据库系统模型-事务结果集传递(TLRSP)移动复制模型.     

MASHED: Security and privacy-aware mutual authentication scheme for heterogeneous and distributed mobile cloud computing services

ABSTRACT

Rapid development in mobile devices and cloud computing technologies has increased the number of mobile services from different vendors on the cloud platform. However, users of these services are facing different security and access control challenges due to the nonexistence of security solutions capable of providing secure access to these services, which are from different vendors, using a single key. An effective security solution for heterogeneous Mobile Cloud Computing (MCC) services should be able to guarantee confidentiality and integrity through single key-based authentication scheme. Meanwhile, a few of the existing authentication schemes for MCC services require different keys to access different services from different vendors on a cloud platform, thus increases complexity and overhead incurred through generation and storage of different keys for different services.

In this paper, an efficient mutual authentication scheme for accessing heterogeneous MCC services is proposed. The proposed scheme combines the user’s voice signature with cryptography operations to evolve efficient mutual authentication scheme devoid of key escrow problem and allows authorized users to use single key to access the heterogeneous MCC services at a reduced cost.     

一种新的基于移动IP外地代理分层结构的注册方案

为了在移动网络中运用IP协议,因特网工程任务组(IETF)制定了MobileIP协议。移动IP技术给人们带来极大便利的同时,也造成了许多安全隐患。本文提出一种基于移动IP外地代理分层结构的注册方案,该方案对现有外地代理分层结构的注册方案加以改进,使得移动IP快速切换能力得以提高,减少了注册时延,并提高了移动节点注册过程的安全性。     

REDMAN: An optimistic replication middleware for read-only resources in dense MANETs

The spread of wireless portable devices is pushing towards service provisioning over dense Mobile Ad hoc NETworks (MANETs), i.e., limited spatial regions, such as shopping malls and airports, where a high number of mobile peers can autonomously cooperate without a statically deployed network infrastructure. The paper proposes the REDMAN middleware to manage, retrieve, and disseminate replicas of data/service components to cooperating nodes in a dense MANET. The guideline is to exploit high node population to enable optimistic lightweight resource replication capable of tolerating node exits/failures. REDMAN adopts original approximated solutions, specifically designed for dense MANET, that have demonstrated good scalability and limited overhead for dense MANET configuration (node identification and manager election), for replica distribution/retrieval, and for lazily consistent replica degree maintenance.     

基于区块链的边缘移动群智感知声誉更新方案

移动群智感知利用移动用户的智能终端设备以低成本获取大量感知数据,而恶意用户可能上传虚假数据以获取奖励。声誉管理是一种有效的解决办法,但是基于云服务器的移动群智感知系统存在高延迟、单点故障和隐私泄露问题。针对这些问题,结合区块链和边缘计算构建基于区块链的边缘移动群智感知系统,提出一种感知数据隐私保护的声誉更新方案,采用轻量级的隐私保护方法聚合感知数据,根据数据质量和历史任务表现更新声誉。该方案可有效抵抗恶意用户、降低时延,避免单点故障和保护数据隐私。仿真实验证明了所提方案的可行性和高效性,理论分析证明了系统的安全性。     

在移动计算环境中基于移动代理的缓存失效方案

1 引言缓存技术是分布式计算环境中的重要技术,它可以改善系统的整体性能(如查询响应时间、吞吐量等),而移动计算的网络环境是一种特殊的分布式环境,与传统的分布式系统相比,它具有鲜明的特点:移动性、断接性、带宽多样性、可伸缩性、弱可靠性、网络通信的非对称性、电源能力局限性等等。这些特点使得缓存技术在移动计算环境中尤为重要。因为缓存能有效减少带宽需求,并能节省移动计算机的能耗。     

Fast Directional Handoff and lightweight retransmission protocol for enhancing multimedia quality in indoor WLANs

More and more mobile devices such as smartphones are being used with IEEE 802.11 wireless LANs (WLANs or Wi-Fi). However, mobile users are still experiencing poor service quality on the move due to the large handoff delay and packet loss problem. In order to reduce the delay, a new handoff scheme using the geomagnetic sensor embedded in mobile devices is proposed in this paper. The proposed scheme predicts the movement direction of a Mobile Station (MS) from the currently associated Access Point (AP) and performs active scanning with a reduced number of channels. In terms of the packet loss, a lightweight retransmission protocol is also proposed to minimize lost packets on Wi-Fi without producing a lot of acknowledgement packets. The proposed approaches are implemented on Android smartphones, and their performance is evaluated in a real indoor WLAN environment. The evaluation results demonstrate that the proposed schemes maintain seamless quality for real-time video even in an environment with frequent handoffs. Note that the proposed schemes are a client-only solution and do not require modification of the existing APs, which renders them very practical.     

Mobile IP与MPLS集成的研究

MPLS技术结合了三层转发的灵活和二层交换的高速,为骨干网络解决方案提供了高速的IP转发能力和极大的可扩展性。MobileIP为用户提供了移动处理的功能。论文介绍了MobileIP与MPLS结合的几种形式,详细研究了在移动节点handoff时,集成方案的处理过程。分析了各种现有的结合方式中的一些缺陷,提出了相应的解决方案。最后简要介绍了MobileIPv6与MPLS集成的方案,并说明这两种技术集成的优势。     

Voting as the optimal static pessimistic scheme for managingreplicated data

This paper investigates the problem of finding an optimal static pessimistic replica control scheme. It has been widely accepted that coteries (proposed by Garcia-Molina and Barbara) provide the most general framework for such schemes. We demonstrate that voting schemes, a very small subset of static pessimistic schemes, are optimal for fully connected networks with negligible link failure rates, as well as for Ethernet systems. We also show that voting is not optimal for somewhat more general systems. We propose a modification of the algorithm of Z. Tong and R.Y. Kain (1988) for computing optimal voting in operation independent case, so that it runs in linear (rather than exponential) time. Finally, we propose the first efficient algorithm for computing the optimal vote assignment and appropriate thresholds for fully connected networks when relative frequencies of read and write operations are known. We also extend this result to Ethernet systems     

Mutable checkpoints: a new checkpointing approach for mobilecomputing systems

Mobile computing raises many new issues such as lack of stable storage, low bandwidth of wireless channel, high mobility, and limited battery life. These new issues make traditional checkpointing algorithms unsuitable. Coordinated checkpointing is an attractive approach for transparently adding fault tolerance to distributed applications since it avoids domino effects and minimizes the stable storage requirement. However, it suffers from high overhead associated with the checkpointing process in mobile computing systems. Two approaches have been used to reduce the overhead: First is to minimize the number of synchronization messages and the number of checkpoints; the other is to make the checkpointing process nonblocking. These two approaches were orthogonal previously until the Prakash-Singhal algorithm combined them. However, we found that this algorithm may result in an inconsistency in some situations and we proved that there does not exist a nonblocking algorithm which forces only a minimum number of processes to take their checkpoints. In this paper; we introduce the concept of “mutable checkpoint,” which is neither a tentative checkpoint nor a permanent checkpoint, to design efficient checkpointing algorithms for mobile computing systems. Mutable checkpoints can be saved anywhere, e.g., the main memory or local disk of MHs. In this way, taking a mutable checkpoint avoids the overhead of transferring large amounts of data to the stable storage at MSSs over the wireless network. We present techniques to minimize the number of mutable checkpoints. Simulation results show that the overhead of taking mutable checkpoints is negligible. Based on mutable checkpoints, our nonblocking algorithm avoids the avalanche effect and forces only a minimum number of processes to take their checkpoints on the stable storage     

温和一致性代理复制机制MCARM

提出了一种新的复制机制：温和一致性代理复制机制（MCARM）。MCARM采用了主节点的复制管理器与辅助节点的MSS-Agent协调工作的架构，吸取严格一致性协议和弱一致性协议的优势，又避开其局限性和复杂性，更好地适应移动计算环境的要求，并能与缓存失效策略CISBMA协同工作，较好满足了移动应用的需求。     

A generic energy optimization framework for heterogeneous platforms using scaling models

Mobile platforms are becoming highly heterogeneous by combining a powerful multiprocessor system-on-a-chip (MpSoC) with numerous other resources, including display, memory, power management IC, battery and wireless modems into a compact package. Furthermore, the MpSoC itself is a heterogeneous resource that integrates many processing elements such as CPU cores, GPU, video, image, and audio processors. Platform energy consumption and responsiveness are two major considerations for mobile systems, since they determine the battery life and user satisfaction, respectively. As a result, energy minimization approaches targeting mobile computing need to consider the platform at various levels of granularity. In this paper, we first present power consumption, response time, and energy consumption models for mobile platforms. Using these models, we optimize the energy consumption of baseline platforms under power, response time, and thermal constraints with and without introducing new resources. Finally, we validate the proposed framework through experiments on Qualcomm’s Snapdragon 800 Mobile Development Platforms.