An efficient and easily deployable QoS-based routing scheme for online Internet multicasting

With the advent of multimedia applications, the support of online multicasting with quality of service guarantees has gained considerable attention in the field of communication networks and distributed systems. Online multicasting requires the support of online join and leave operations. In this paper, a new Simple and Efficient Low-cost Delay-bounded Online Multicasting (SELDOM) heuristic is proposed. SELDOM is particularly tailored to networks in which group membership changes frequently. SELDOM supports two modes of operations: non-rearrangeable and rearrangeable. The scheme handles join requests dynamically by determining the least-cost path which satisfies the required delay-bounds to which the new group member is to be attached. To handle a leave request, the scheme seeks to limit the number of rearrangements required in order to reduce the disturbance such a request may cause to current group members. The worst case time complexity of SELDOM is O(n²). An important research contribution of this work shows that if any non-rearrangeable multicast heuristic uses a path other than the least-delay path to add a node to the multicast tree, then the resulting multicast tree can have cycles or nodes with two incoming paths. A simulation-based comparison between non-rearrangeable and rearrangeable online multicast trees is also presented.     

Threshold configuration and routing optimization for PCN-based resilient admission control

Pre-Congestion Notification (PCN) in IP networks uses packet metering and marking within a PCN domain to notify its egress nodes whether link-specific admissible or supportable rate thresholds have been exceeded by high-priority traffic. Based on this information simple admission control and flow termination is implemented. The latter is a new flow control function and useful in case of overload through high priority traffic which can occur in spite of admission control, e.g., when traffic is rerouted in failure cases. Resilient admission control admits only so much traffic that admitted traffic can be rerouted without causing congestion on backup paths in case of a likely failures, e.g., single link failures.We propose algorithms to configure the link-specific PCN rate thresholds such that resources are utilized efficiently and fairly by competing traffic aggregates while meeting resilience constraints. This is done for the single and dual marking PCN architecture whereby the single marking case is more demanding since it requires that the supportable rate is a fixed multiple of the admissible rate on all links within a single PCN domain. Furthermore, we derive objective functions to optimize the underlying routing system for both cases. Our performance results for various network types show that the dual marking PCN architecture leads to significantly better resource efficiency than the single marking PCN architecture.     

Dynamic transaction routing in distributed database systems

The authors investigate dynamic transaction routing strategies for locally distributed database systems in which the database is partitioned and distributed among multiple transaction-processing systems, and the incoming transactions are routed by a common front-end processor. If a transaction issues a database request referencing a nonlocal database partition, the request has to be shipped to the system owing the referenced partition for processing. Various dynamic strategies are studied. Their performance is compared with that of the optimal static strategy. A class of dynamic transaction routing strategies which take into account routing history and minimize the estimated response time of incoming transactions is proposed; they are found to provide a substantial improvement over the optimal static strategy. The robustness of the strategies is further studied through sensitivity analysis over various transaction loads, communication overheads, and database reference distributions     

Transaction processing in mobile, heterogeneous database systems

As technological advances are made in software and hardware, the feasibility of accessing information "any time, anywhere" is becoming a reality. Furthermore, the diversity and amount of information available to a given user is increasing at a rapid rate. In a mobile computing environment, a potentially large number of users may simultaneously access the global data; therefore, there is a need to provide a means to allow concurrent management of transactions. Current multidatabase concurrency control schemes do not address the limited bandwidth and frequent disconnection associated with wireless networks. This paper proposes a new hierarchical concurrency control algorithm. The proposed concurrency control algorithm, v-lock, uses global locking tables created with semantic information contained within the hierarchy. The locking tables are used to serialize global transactions, detect and remove global deadlocks. Additionally, data replication, at the mobile unit, is used to limit the effects of the restrictions imposed by a mobile environment. The replicated data provides additional availability in case of a weak connection or disconnection. Current research has concentrated on page and file-based caching or replication schemes to address the availability and consistency issues in a mobile environment. In a mobile, multidatabase environment, local autonomy restrictions prevent the use of a page or file-based data replication scheme. This paper proposes a new data replication scheme to address the limited bandwidth and local autonomy restrictions. Queries and the associated data are cached at the mobile unit as a complete object. Consistency is maintained by using a parity-based invalidation scheme. A simple prefetching scheme is used in conjunction with caching to further improve the effectiveness of the proposed scheme. Finally, a simulator was developed to evaluate the performance of the proposed algorithms. The simulation results are presented and discussed.     

Transaction management in distributed heterogeneous database management systems

Current distributed, heterogeneous database management systems (DBMSs) address the issue of distributed transaction management (DTM) in two different ways: some systems rely solely on unmodified local transaction managers (LTMs), thereby helping preserve local DBMS autonomy, but limit functionality (e.g. allow only unsynchronized retrievals, preclude distributed updates, etc.); others maintain full functionality but require the (re)design of the LTMs to enforce homogeneous DTM across all heterogeneous DBMSs, thereby giving up most of the local DBMS autonomy.

The goal of the work presented here is to establish the minimum set of modifications to LTMs that allow synchronized retrievals and distributed updates (whenever semantic conflicts can be resolved), and will continue to maintain a high degree of local DBMS autonomy. The problems of: (1) distribution of responsibility between DTM and LTMs, (2) concatenation of functionally-equivalent LTM mechanisms, and (3) providing compensation mechanisms for functionally-limited LTMs are introduced. Solutions to the above problems are shown to exist. However, the interconnection of autonomous, heterogeneous DBMSs is significantly more difficult than anticipated, despite communication standardization and current optimism.     

Damage assessment and repair in attack resilient distributed database systems

Preventive measures sometimes fail to defect malicious attacks. With attacks on data-intensive applications becoming an ever more serious threat, intrusion tolerant database systems are a significant concern. The main objective of such systems is to detect attacks, and to assess and repair the damage in a timely manner. This paper focuses on efficient damage assessment and repair in distributed database systems. The complexity caused by data partition, distributed transaction processing, and failures makes intrusion recovery much more challenging than in centralized database systems. This paper identifies the key challenges and presents an efficient algorithm for distributed damage assessment and repair.     

求解QoS组播路由问题的满意优化方法*

通过分析目前QoS路由优化的一些关键问题,提出一种基于满意优化原理的QoS路由多目标满意优化求解模型,使之更适合解决QoS路由优化问题.仿真结果表明,该算法能极大地缩短路由求解时间,具有很强的适用性和灵活性.     

Signature caching in parallel object database systems

In many application areas, the access pattern is navigational and a large fraction of the accesses are perfect match accesses/queries on one or more words in text strings in the objects. One example of such an application area is XML data stored in object database systems. Such systems will frequently store large amounts of data, and in order to provide the necessary computing power and data bandwidth, a parallel system based on a shared-nothing architecture can be necessary. In this paper, we describe how the signature cache approach can significantly reduce the average object access cost in parallel object database systems.     

Data placement in shared-nothing parallel database systems

Data placement in shared-nothing database systems has been studied extensively in the past and various placement algorithms have been proposed. However, there is no consensus on the most efficient data placement algorithm and placement is still performed manually by a database administrator with periodic reorganization to correct mistakes. This paper presents the first comprehensive simulation study of data placement issues in a shared-nothing system. The results show that current hardware technology trends have significantly changed the performance tradeoffs considered in past studies. A simplistic data placement strategy based on the new results is developed and shown to perform well for a variety of workloads. Edited by M. Adiba. Received May 11, 1993 / Accepted April 24, 1996 November 1, 1995     

Anomaly detection and resilient control of networked control system with multi-hop routing

With the wide application of networked control systems, how to deal with data injection attacks and maintain the stability of control systems including wireless multi-hop networks is a problem that the researchers and technological workers must consider and solve. Based on the construction of a control system including wireless multi-hop networks, the data transmission mode between routing nodes and the stability condition of the control system are given. Considering the existence of data injection attacks to routing nodes, a real-time detection method for anomaly behaviours is presented on the basis of chi-square goodness-of-fit test. In the case of data injection actions taking place, a strategy of switching paths in turn is used to execute the control task. The strategy is satisfied with the resilient stability of the control system. The simulation results show that the detection method can detect the data injection actions in real time, and the control strategy can restore control variables to proper values when the data injection actions exist. These methods have certain application prospects and popularisation values.     

基于机群架构的并行数据库实现技术研究

在总结了现有并行数据库实现模型的基础上,基于"半重写变换"模型[1]实现了一个并行数据库系统的原型.通过对数据划分/重划分、并行选择、并行排序、并行连接等关键操作的实验分析,指出了.半重写变换"模型存在的缺陷,并提出了一种混合式的改进模型.从理论上说,在机群架构下实现并行数据库系统,这种混合模型较单一模型更有优势.     

不确定奇异时滞系统的时滞相关型鲁棒∞弹性控制

讨论了不确定奇异时滞系统的时滞相关型鲁棒弹性控制器设计问题.在一个关于标称奇异时滞系统的新的时滞相关型稳定性判据的基础上给出了一种新的有界实引理(BRL:bounded real lemma);基于此给出了时滞相关型鲁棒弹性控制器存在的充分性条件,最后通过数值算例说明本文结果的有效性.     

Technologies of parallel database systems for hierarchical multiprocessor environments

For the multiprocessor systems of the hierarchical-architecture relational databases, a new approach to data layout and load balancing was proposed. Described was a database multiprocessor model enabling simulation and examination of arbitrary multiprocessor hierarchical configurations in the context of the on-line transaction processing applications. An important subclass of the symmetrical multiprocessor hierarchies was considered, and a new data layout strategy based on the method of partial mirroring was proposed for them. The disk space used to replicate the data was evaluated analytically. For the symmetrical hierarchies having certain regularity, theorems estimating the laboriousness of replica formation were proved. An efficient method of load balancing on the basis of the partial mirroring technique was proposed. The methods described are oriented to the clusters and Grid-systems.     

Divergence control for distributed database systems

This paper presents distributed divergence control algorithms for epsilon serializability for both homogeneous and heterogeneous distributed databases. Epsilon serializability allows for more concurrency by permitting non-serializable interleavings of database operations among epsilon transactions. We first present a strict 2-phase locking divergence control algorithm and an optimistic divergence control algorithm for a homogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction are the same. In such an environment, the total inconsistency of a distributed epsilon transaction is simply the sum of those of all its sub-transactions. We then describe a divergence control algorithm for a heterogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction may not be the same and the total inconsistency of a distributed epsilon transaction may be greater than the sum of those of all its sub-transactions. As a result, in addition to executing a local divergence control algorithm in each site to maintain the local inconsistency, a global mechanism is needed to take into account the additional inconsistency Recommended by: Meichum Hsu     

并行计算机群的节能调控

针对并行计算机群空闲费电的问题,提出了一种利用作业排队调度系统（OpenPBS）来调控并行计算机群的方案。采用脚本文件控制的方法,实现了计算节点的自动开、关机功能,达到了任务计算和节约电能的动态平衡。     

嵌入式控制结点群上的一种通信方案设计

为解决现行RS485组网方式限制了通信节点数及网络扩展的问题,基于RS485总线提出了一种嵌入式控制结点群的组网方式及控制协议。通过在主控器与叶子节点间加入中继器,将485总线支持的节点数扩展到2.7万个,建立一对多控制的嵌入式结点集群。针对该网络特点,对Modbus协议进行扩展,增加了中继层规约。与传统单纯增加物理地址长度的方式不同,新扩展协议采用局部寻址方式,打破了Modbus地址长度对子节点数的限制,并引入节点扫描和差错反馈机制,从而实现了主控器对各网络节点的可靠控制;同时,控制协议保持了原Modbus协议的简单性,还具有易移植、可扩展的特点,便于在单片机上实现。在采用扩展协议时,一层中继器的引入导致周转延迟增加10.36%,而两层中继器则将延迟率增加了69.9%,并使总延迟较原始Modbus系统增加2.4倍左右,但实际中采用的两层中继系统将平均延迟控制在了70 ms以下。结果表明,该方案在牺牲一定系统实时性能的前提下,实现了嵌入式节点的集群化管理。     

Concurrency control in database systems

Ideas that are used in the design, development, and performance of concurrency control mechanisms have been summarized. The locking, time-stamp, optimistic-based mechanisms are included. The ideas of validation in the optimistic approach are presented in some detail. The degree of concurrency and classes of serializability for various algorithms have been presented. Questions that relate arrival rate of transactions with degree of concurrency and performance have been briefly presented. Finally, several useful ideas for increasing concurrency have been summarized. They include flexible transactions, adaptability, prewrites, multidimensional time stamps, and relaxation of two-phase locking     

A Transactional Asynchronous Replication Scheme for Mobile Database Systems

In mobile database systems,mobility of users has a significant impact on data replication.As a result,the various replica control protocols that exist today in traditional distributed and multidatabase environments are no longer suitable To solve this problem,a new mobile database replication scheme,the Transaction-Level Result-Set Propagation(TLRSP)model,is put forward in this paper,The conflict dectction and resolution strategy based on TLRSP is discussed in detail,and the implementation algorithm is proposed,In order to compare the performance of the TLRSP model with that of other mobile replication schemes,we have developed a detailde simulation model.Experimantal results show that the TLRSP model provides an effcient support for replicated mobile database systems by reducing reprocessing overhead and maintaining database consistency.     

A novel dynamic load balancing scheme for parallel systems

Adaptive mesh refinement (AMR) is a type of multiscale algorithm that achieves high resolution in localized regions of dynamic, multidimensional numerical simulations. One of the key issues related to AMR is dynamic load balancing (DLB), which allows large-scale adaptive applications to run efficiently on parallel systems. In this paper, we present an efficient DLB scheme for structured AMR (SAMR) applications. This scheme interleaves a grid-splitting technique with direct grid movements (e.g., direct movement from an overloaded processor to an underloaded processor), for which the objective is to efficiently redistribute workload among all the processors so as to reduce the parallel execution time. The potential benefits of our DLB scheme are examined by incorporating our techniques into a SAMR cosmology application, the ENZO code. Experiments show that by using our scheme, the parallel execution time can be reduced by up to 57% and the quality of load balancing can be improved by a factor of six, as compared to the original DLB scheme used in ENZO.