Performance analysis of three multi-radio access control policies in heterogeneous wireless networks

Access control policy in wireless networks has a significant impact on QoS satisfaction and resource utilization efficiency. The design of access control policy in heterogeneous wireless networks （HWNs） becomes more challenging especially for the heterogeneous multiple access protocols of each radio network. In this paper, a Markov model is proposed to analyze the performance of three access control policies for HWNs. The first policy is the optimal radio access technology （O-RAT） selection, where the incoming traffic always tries to access one network with the maximum service rate before admission. The second policy intends to allocate the same data to all networks. And the traffic will leave the system if it is accomplished first by one of these networks, which is formulated as the aggregated multi-radio access （A-MRA） technology. The third policy is named the parallel multi-radio access （P-MRA） transmission, in which the incoming traffic is split into different networks. The traffic is served with the sum of the service rates provided by overall networks. Numerical and simulate results show the effectiveness of our analytical framework and the performance gain of the three access control policies. As illustrated with some representative results, the P-MRA policy shows superior performance gain to the other two policies independent on the specific parameters of the different multiple access protocols due to the multiplexing gain.     

HAT： an efficient buffer management method for flash-based hybrid storage systems

Flash solid-state drives （SSDs） provide much faster access to data compared with traditional hard disk drives （HDDs）. The current price and performance of SSD suggest it can be adopted as a data buffer between main memory and HDD, and buffer management policy in such hybrid systems has attracted more and more interest from research community recently. In this paper, we propose a novel approach to manage the buffer in flash-based hybrid storage systems, named hotness aware hit （HAT）. HAT exploits a page reference queue to record the access history as well as the status of accessed pages, i.e., hot, warm, and cold. Additionally, the page reference queue is further split into hot and warm regions which correspond to the memory and flash in general. The HAT approach updates the page status and deals with the page migration in the memory hierarchy according to the current page status and hit position in the page reference queue. Compared with the existing hybrid storage approaches, the proposed HAT can manage the memory and flash cache layers more effectively. Our empirical evaluation on benchmark traces demonstrates the superiority of the proposed strategy against the state-of-the-art competitors.     

A hybrid distributed-centralized conflict resolution approach for multi-aircraft based on cooperative co-evolutionary

Conflict resolution （CR） plays a crucial role in safe air traffic management （ATM）. In this paper, we propose a new hybrid distributed-centralized tactical CR approach based on cooperative co-evolutionary named the CCDG （cooperative co-evolutionary with dynamic grouping） strategy to overcome the drawbacks of the current two types of approaches, the totally centralized approach and distributed approach. Firstly, aircraft are divided into several sub-groups based on their interdependence. Besides, a dynamic grouping strategy is proposed to group the aircraft to better deal with the tight coupling among them. The sub-groups are adjusted dynamically as new conflicts appear after each iteration. Secondly, a fast genetic algorithm （GA） is used by each sub-group to optimize the paths of the aircraft simultaneously. Thirdly, the aircraft＇s optimal paths are obtained through cooperation among different sub-groups based on cooperative co-evolutionary （CC）. An experimental study on two illustrative scenarios is conducted to compare the CCDG method with some other existing approaches and it is shown that CCDG which can get the optimal solution effectively and efficiently in near real time, outperforms most of the existing approaches including Stratway, the fast GA, a general evolutionary path planner, as well as three well-known cooperative co-evolution algorithms.     

Towards Effective Integrated Access Control Lists in Internet Networks

ACLs （access control lists） represent a traditional way in filtering packets in routers. In modern complex enterprise networks that provide a vast array of services, there is an ever increasing need for verifying the integrity of ACLs to detect any potential security holes and improve the network performance. This paper concerns the integrity of routers＇ ACLs in large enterprise networks. We first investigate the integrity of the ACLs of two touters by describing a bottom-up approach for detecting redundancies in ACLs of two routers. We then extend our study to multiple touters and provide a heuristic algorithm for detecting redundant ACLs in multiple touters. We validate the practicality of ouralgorithm through real-life and synthetic router ACL groups of large networks. Performance results show that our heuristic algorithm do not only improve the performance by reducing the number of comparisons overhead, but also helps in discovering potential security holes that can not be discovered by considering the ACLs of each router individually.     

Dynamically reconfigurable radio-over-fiber network with medium access control protocol to provide network access to train passengers

An innovative dynamically reconfgurable radio-over-fber(RoF)network equipped with an intelligent medium access control(MAC)protocol is proposed to provide broadband access to train passengers in railway high-speed mobile applications.The proposed RoF network architecture is based on a reconfgurable control station and remote access unit(RAU)that is equipped with a fxed flter and tunable flter.The proposed hybrid frequency-division multiplexing/time division multiple access(FDM/TDMA)based MAC protocol realizes failure detection/recovery and dynamic wavelength allocation to remote access units.Simulation result shows that with the proposed MAC protocol,the control station can detect failures and recover and dynamic wavelength allocation can increase the wavelength resource utilization to maintain network performance.     

Managing behavioral academic self-esteem using FuzzyXteem

Behavioral academic self-esteem （BASE） has been used with children of preschool, elementary, and junior high school classes, both individually and in groups. In this study, BASE is used to estimate the factor structures and determine the levels of academic self-esteem of the student. The current practice of the existing system using BASE scale may be scored by hand or by computer based on the rigid crisp values to represent rating number one through five. Since BASE requires the ability for estimating the factor structure and also the ability to explain how the conclusion is derived, therefore artificial intelligent techniques that are required to perform BASE must be able to perform estimation and provide reasoning. For this purpose, fuzzy logic and expert system have been integrated in a web-based environment to demonstrate the use of hybrid system on BASE factor structure and levels of academic self-esteem. For each BASE factor, the sub score is provided based on the classifications of academic self-esteem and their respective ranges. In FuzzyXteem, users in particular teachers, counselors, or parent are allowed to measure students＇ self-esteem at early age using real time computation. FuzzyXteem facilitates user by automatically evaluating BASE factors and helps the user diagnoses their students＇ levels of academic self-esteem in 3 ratings： low, moderate and high. It is also able to provide explanation and describe how the conclusion can be derived. The system has been successfully tested by the counselors and conforms to the BASE factor rating scale and sub-scores. FuzzyXteem can be used as an aid to decision making in improving a person＇s self esteem, and indirectly increases an individual for productivity. The same system functions can be applied to business organization for managing and improving the organizations performance.     

Service for consistency management of replicas in data grid

Today, grid technology has evolved to the point where it is no longer a theory but a proven practice. It represents a viable direction for corporations to explore grid computing as an answer to their business needs within tight financial constraints. In general, grids enable the efficient sharing and management of computing resources for the purpose of performing large complex tasks. Data grid provides the data management features to enable data access, synchronization, and distribution of a grid. The main aim here is to ensure a efficient access and quality data, to improve the availability, and be able to continue delivering acceptable services. In such systems, these advantages are not yielded by means others than replication mechanisms. The effective use the replication technique involves several problems, in relation with the problem of the coherence maintenance of replicas. Our contribution consists new service for the consistency management in the data grid. This service combines between pessimistic and optimistic approaches, taking into account benefits of both approaches, to find a compromise between performance and quality. In addition, our service has been extended by a mechanism placement of replicas based on economics model.     

Usage control mechanism for securing the multi-organizational grid

Security is a fundamental but challenging issue in the dynamic and multi-organizational computational grid. Focusing on the closed system, traditional access control model considered static authorization decisions based on pre-assigned permissions. To facilitate collaborations and interoperations across the grid, we propose a usage control mechanism for computational grid. Our mechanism is based on the usage control model. By leveraging continuous usage control on grid services and monitoring the status and behaviors of the subjects involved in the collaborations, our mechanism improves collaboration＇s security. Furthermore, our mechanism enables richer and finer-grained control over authorizations on resources and services involved in collaborations and interoperations than that of traditional access control mechanisms. Our mechanism can contribute to maintain the security and interests of the service providers in the grid environment.     

Efficiency of hybrid index structures—Theoretical analysis and a practical application

Hybrid index structures support access to heterogeneous data types in multiple columns. Several experiments confirm the improved efficiency of these hybrid access structures. Yet, very little is known about the worst case time and space complexity of them. This paper aims to close this gap by introducing a theoretical framework supporting the analysis of hybrid index structures. This framework then is used to derive the constraints for an access structure which is both time and space efficient. An access structure based on a B+-Tree augmented with bit lists representing sets of terms from texts is the outcome of the analysis which is then validated experimentally together with a hybrid R-Tree variant to show a logarithmic search time complexity.     

Utility-optimal random access control in wireless multi-hop networks with queuing constraints

In this paper, a model of network utility maximization （NUM） is presented for random access control in multi-hop wireless networks. Different from the classical NUM framework, our model considers the queueing stability. We propose a distributed iterative prices and link probabilities adaption algorithm by using dual decomposition techniques, which only requires limited message passing, but converges to the global optimum of the total network utility. Numerical results and simulation comparison validate our conclusion.     

On the Comparison Analysis of Two 4G-WiMAX Base Stations in an Urban Sub-Saharan African Environment

A growth in the demand for WBA （wireless broadband access） technology has been seen in Ghana in the last few years.. The reason for this growth can be attributed to the emergence of the use of multimedia applications, demands for ubiquitous high-speed Intemet connectivity, the massive growth in the wireless and mobile communications sector and the deregulation in the telecommunications industry. WiMAX, which is a WBA technology, is currently being deployed in the 2,500-2,690 MHz band to help serve the ever increasing needs of broadband internet subscribers in the country. This paper presents simulation results and field trial measurements for two BS （base stations） in a newly deployed 4G-WiMAX network in a typical dense urban Sub-Saharan African environment. We have used a model which uses the interference to noise ratio （n） parameter to obtain the coverage range of these two BS under evaluation. The simulated cell range for site 1 is 4.90 km and that for site 2 is 3.19 kin. The final coverage simulation and the field measurements results have also been presented.     

Optimal resource allocation for transmission diversity in multi-radio access networks： a coevolutionary genetic algorithm approach

The next generation wireless communication systems aim at supporting enhanced diversified network access and data transmission abilities via the cooperative integration and unified management of various radio access technologies(RATs).The resource allocation is the core component leading the network system and mobile terminals to the service robustness and performance maximization.In this paper,a numeric optimization model for optimizing terminals’transmission power and allocated RAT bandwidth for maximizing system capacity is proposed with the focal consideration of the multi-radio transmission diversity for parallel transmission through multiple links from diferent RATs,and diferent terminal characteristics on RAT supports.Also,we design a centralized and periodic scheduling algorithm including an improved coevolutionary genetic algorithm for efciently solving the optimization problem.Simulation results demonstrate that our propose algorithm can distinctly enhance the system performance and improve the computational efciency.     

Robust first two rounds access driven cache timing attack on AES

The memory cache data access time uncertainty and resource multi-process sharing mechanism provide a new covert channel to leak process secret information. The AES software implementation uses many table lookup operations to access cache, and these lookup indices have close relationship with the secret key. According to 128-bit AES, we propose a new robust first two rounds access driven cache timing attack. We use a spy process to gather cache access patterns of AES process, thus get the table lookup indices during one AES encryption, combine certain analysis methods, finally recover 128-bit full AES key. With counter to current belief, our experiments show that, only through the first round attack, 350 samples are enough to recover full AES key. After we extend the attack to the second round, 80 samples are enough to recover full AES key.     

基于闪存的混合存储系统缓冲区管理算法

由于基于闪存的混合存储系统充分利用了闪存的高速随机读和磁盘的快速顺序写的特性,近年来已经成为了数据库管理系统的二级存储层的高效存储模式,但其I/O访问开销是一个继续提高存储性能的瓶颈.为了降低混合存储系统的I/O访问开销,提出了一种自适应缓冲区管理算法DLSB.该算法根据数据页的逻辑代价和物理代价进行自适应的数据域选择;并在选择的数据域中,比较闪存队列和磁盘队列容量的实际值与理想值来确定数据页的置换,达到了提高I/O访问效率的目的.实验结果表明,该算法有效且可行,显著降低了混合存储系统的I/O访问开销.     

Single versus hybrid time horizons for open access scheduling

Difficulty in scheduling short-notice appointments due to schedules booked with routine check-ups are prevalent in outpatient clinics, especially in primary care clinics, which lead to more patient no-shows, lower patient satisfaction, and higher healthcare costs. Open access scheduling was introduced to overcome these problems by reserving enough appointment slots for short-notice scheduling. The appointments scheduled in the slots reserved for short-notice are called open appointments. Typically, the current open access scheduling policy has a single time horizon for open appointments. In this paper, we propose a hybrid open access policy adopting two time horizons for open appointments, and we investigate when more than one time horizon for open appointments is justified. Our analytical results show that the optimized hybrid open access policy is never worse than the optimized current single time horizon open access policy in terms of the expectation and the variance of the number of patients consulted. In nearly 75% of the representative scenarios motivated by primary care clinics, the hybrid open access policy slightly improves the performance of open access scheduling. Moreover, for a clinic with strong positive correlation between demands for fixed and open appointments, the proposed hybrid open access policy can considerably reduce the variance of the number of patients consulted.     

基于ESCA系统的层次化显式访存机制研究

针对高性能混合计算系统中的存储墙问题,在分析其计算模式特点及传统访存机制局限性的基础上,提出适用于混合计算系统的层次化显式存储访问机制,并基于ESCA多核处理器系统进行实现和评测。实验结果显示,针对核心应用程序DGEMM,延迟隐藏能够占据整体运行时间的56%,并获得1.5倍的加速比,能弥补计算与存储访问间的速度差异,提高系统计算效率。     

A Reverse Auction Framework for Hybrid Access in Femtocell Network

In the two-tier macro-femto heterogeneous network, hybrid access is regarded as the most ideal access control approach to mitigating macro-femto cross-tier interference and enhancing overall network performance. However, the implementation of hybrid access is hindered by a lack of incentive market mechanism to motivate private femtocell owners to offer access permissions to macro users. In this paper, we propose a reverse auction framework for access permission transaction between a macrocell operator and multiple femtocell owners to promote hybrid access. Our goal is to maximize social welfare while guaranteeing the truthfulness of the auction. Since the coverage of multiple femtocells may overlap, we partition each cell to adjust the granularity of access permission availability. We first propose a Vickery-Clarke-Grove (VCG)-based mechanism, which costs the least among all auction mechanisms that produce maximum social welfare. As the VCG mechanism is too time-consuming, we propose two alternative truthful mechanisms, namely, generalized second-price and suboptimal mechanism. We further extend the auction framework to the scenario where femtocell owners have heterogeneous valuations for access permissions in different locations.     

Privacy preservation of electronic health records with adversarial attacks identification in hybrid cloud

An increasing trend in healthcare organizations to outsource EHRs’ data to the cloud highlights new challenges regarding the privacy of given individuals. Healthcare organizations outsource their EHRs data in a hybrid cloud that elevates the problem of security and privacy in terms of EHRs’ access to an unlimited number of recipients in a hybrid cloud environment. In this paper, we investigated the need for a privacy-preserving access control model for the hybrid cloud. A comprehensive and exploratory analysis of privacy-preserving solutions with the help of taxonomy for cloud-based EHRs is described in this work. We have formally identified the existence of internal access control and external privacy disclosures in outsourcing system architecture for hybrid cloud. Then, we proposed a privacy-preserving XACML based access control model (PPX-AC) that supports fine-grained access control with the multipurpose utilization of EHRs alongside state-of-the-art privacy mechanism. Our proposed approach invalidates the identified security and privacy attacks. We have formally verified the proposed privacy-preserving XACML based access control model (PPX-AC) with the invalidation of identified privacy attacks using High-Level Petri Nets (HLPN). Moreover, property verification of the proposed model in SMT-lib and Z3 solver and implementation of the model proves its effectiveness in terms of privacy-aware EHRs access and multipurpose usage.     

Partial indexing for nonuniform data distributions in relationalDBMS's

It is well known that the effectiveness of relational database systems is greatly dependent on the efficiency of the data access strategies. For this reason, much work has been devoted to the development of new access techniques, supported by adequate access structures such as the B⁺trees. The effectiveness of the B ⁺tree also depends on the data distribution characteristics; in particular, poor performance results when the data show strong key value distribution unbalancing. The aim of this paper is to present the partial index: a new access structure that is useful in such cases of unbalancing, as an alternative to the B⁺tree unclustered indexes. The access structures are built in the physical design phase, and at execution (or compilation) time, the optimizer chooses the most efficient access path. Thus, integration of the partial indexing technique in the design and in the optimization process are also described     

混合RBAC-DTE策略的多角色管理

混合的基于角色访问控制-域型增强（RBAC-DTE）访问控制模型因其不同层次的保护机制近年来颇受关注,但是尚未见到公开的文献讨论混合RBAC-DTE策略中的多角色管理问题．因此,从特权层面和访问许可权层面上,提出了一种角色划分粒度比域划分粒度粗的角色和域的划分方法,并引入域的静态继承关系．这种混合RBAC-DTE策略的多角色管理方法解决了不同域的进程共享访问许可权集、控制策略代码尺寸的问题,特别是它可以充分支持极小特权原则．