Analysis and Provision of QoS for Distributed Grid Applications

Grid computing provides the infrastructure necessary to access and use distributed resources as part of virtual organizations. When used in this way, Grid computing makes it possible for users to participate in collaborative and distributed applications such as tele-immersion, visualization, and computational simulation. Some of these applications operate in a collaborative mode, requiring data to be stored and delivered in a timely manner. This class of applications must adhere to stringent real-time constraints and Quality-of-Service (QoS) requirements. A QoS management approach is therefore required to orchestrate and guarantee the timely interaction between such applications and services. We discuss the design and a prototype implementation of a QoS system, and demonstrate how we enable Grid applications to become QoS compliant. We validate this approach through a case study of an image processing task derived from a nanoscale structures application.     

嵌入式自适应安全关键中间件设计方法研究

由于嵌入式安全关键系统自身的特点和应用环境的特殊性,导致了设计嵌入式安全关键应用比一般的嵌入式实时应用要困难得多。在分析传统嵌入式实时中间件技术应用于嵌入式安全关键系统不足的基础上,提出了一种新的自适应安全关键中间件(ASCM)的设计方法,并对相应的体系结构和关键技术进行了讨论。另外,针对嵌入式安全关键系统运行环境的特殊性,重点讨论了一种端到端的自适应服务质量(QoS)管理机制。     

Supporting configurability and real time in RTD channels

Network communication services that can be configured to customize functionality provide significant advantages over monolithic versions, but can be difficult to construct if the services must also provide real‐time guarantees on message delivery. This paper describes how practical issues related to the combination of configurability and real time have been addressed in real‐time dependable (RTD) channels, a communication abstraction that has been prototyped using the Cactus system. The architecture and implementation of RTD channels are described, including facilities for translating an application's quality of service requirements into configuration‐specific resource requirements, and an admission control architecture that uses system‐wide information to determine whether sufficient resources exist to create new channels. In addition, the results of experiments that demonstrate that the desired channel properties—including real‐time guarantees—are provided for various configurations are presented. Finally, practical problems and lessons learned from implementing RTD channels on the general‐purpose MK 7.3 Mach operating system are discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

一种基于服务质量的多媒体任务模型

实时调度算法研究一直是实时系统领域的热点和难点.近年来,发展快速的多媒体应用由于需要保证一定的服务质量而呈现实时需求.然而,多媒体应用的特点使得很难使用传统任务模型对其进行描述.本文提出了一种基于服务质量的多媒体任务模型,并给出了在该模型下计算系统QoS指标的算法.该模型将有助于多媒体实时系统的理论分析和调度算法研究.     

基于SOA的嵌入式安全关键中间件

由于嵌入式安全关键系统自身的特点和应用环境的特殊性,导致了设计分布式嵌入式安全关键应用比一般的嵌入式实时应用要困难得多。提出了一种新的基于SOA构架的自适应安全关键中间件,极大地简化了嵌入式安全关键系统应用的开发,并对相应的体系结构和关键技术进行了讨论。另外,针对嵌入式安全关键系统运行环境的特殊性,重点讨论了SOA构架中基于动态配置服务的端到端的自适应QoS管理机制和实时容错机制的设计和实现。     

An overview of the Real-Time CORBA specification

A growing class of real-time systems require end-to-end support for various quality-of-service (QoS) aspects, including bandwidth, latency, jitter and dependability. Applications include command and control, manufacturing process control, videoconferencing, large-scale distributed interactive simulation, and testbeam data acquisition. These systems require support for stringent QoS requirements. To meet this challenge, developers are turning to distributed object computing middleware, such as the Common Object Request Broker Architecture, an Object Management Group (OMG) industry standard. In complex real-time systems, DOC middleware resides between applications and the underlying operating systems, protocol stacks and hardware. CORBA helps decrease the cycle time and effort required to develop high-quality systems by composing applications using reusable software component services rather than building them entirely from scratch. The Real-Time CORBA specification includes features to manage CPU, network and memory resources. The authors describe the key Real-Time CORBA features that they feel are the most relevant to researchers and developers of distributed real-time and embedded systems     

CORBA实时性研究初探

ＣＯＲＢＡ是有关用于简化分布式应用与服务软件开发的对象请求中介的一个中间件标准。该文主要讨论了基于ＣＯＲＢＡ的对象请求中介的两个方面。首先,论述了常规ＣＯＲＢＡ实现中有关性能优化及服务质量上的缺陷;其次,阐述了实时应用对基于ＣＯＲＢＡ的对象请求中介的要求,并提供有关性能优化策略。     

基于中间件的QoS管理模型的研究与应用

随着多媒体处理技术和高速网络技术的发展,分布式多媒体应用得到长足发展,分布式多媒体中的实时音频、视频应用的一个关键问题就是多媒体的QoS管理和控制问题。该文提出了一种应用层的基于中间件的QoS管理模型,研究端系统的QoS和资源管理。该框架允许用户和应用对QoS管理策略和适应性调整策略进行应用级的定制。文章在资源管理中提出了通用资源接口及其具体实现方法。并从应用层的角度,结合国内外的研究成果,在网络层和操作系统之上提出通用接口应具备的功能,以及如何与QoS管理器协调工作,及其简单实现。     

基于IP网络的自适应QoS管理方案研究

目前实时音频、视频多媒体应用已经开始进入IP网络,但还有许多问题没有得到很好地解决,其中一个关键问题是多媒体服务的QoS问题、TCP／IP协议本身只提供一种“Best-effort”级别的服务,对QoS支持很少,“Best-effort”级别的服务往往会导致实时应用出现延迟抖动、分组丢失率高,从而极大的影响了实时应用的运行效果,因此必须研究可行的、高效的基于IP网络的QoS控制机制。IP网络QoS已成为分布式多媒体和网络通信的重要研究热点和难点课题。本文在IEＴＦ Intserv与Diffserv相结合的体系结构基础上,提出了一种适用于IP网络的自适应QoS管理框架,与Intserv或Diffserv模型不同的是,该QoS管理框架引入优先级节和自适应概念,QoS俦权处理采用基于多媒体优先级节的算法,在传输控制上采用了自适应QoS控制算法。它在应用层上完成,因此独立于底层网络协议。本文首先讨论了基本概念和函数,然后提出一种基于优先级节的自适应QoS管理框架和优先级调度流程。提出一种基于IP的自适应QoS协商机制,基本思想是基于RSVP（资源预留协议）。在提出QoS请求时进行QoS映射,然后启动适应性函数和资源管理函数进行协商,直到获得一组在当前资源状况下最佳的QoS指标。最后,本文还讨论了此方案的有效性并在自行开发的实验平台GUT上进行的QoS实验。实验表明应用该方法可以根据网络当前状态自适应地整多媒体实时应用的QoS需求。     

A protocol for deadlock-free dynamic reconfiguration in high-speedlocal area networks

High-speed local area networks (LANs) consist of a set of switches interconnected by point-to-point links, and hosts linked to those switches through a network interface card. High-speed LANs may change their topology due to switches being turned on/off, hot expansion, link remapping, and component failures. In these cases, a distributed reconfiguration protocol analyzes the topology, computes the new routing tables, and downloads them to the corresponding switches. Unfortunately, in most cases, user traffic is stopped during the reconfiguration process to avoid deadlock. These strategies are called static reconfiguration techniques. Although network reconfigurations are not frequent, static reconfiguration such as this may take hundreds of milliseconds to execute, thus degrading system availability significantly. Several distributed real-time applications have strict communication requirements; Distributed multimedia applications have similar, although less strict, quality of service (QoS) requirements. Both stopping packet transmission and discarding packets due to the reconfiguration process prevent the system from satisfying the above requirements. Therefore, in order to support hard real-time and distributed multimedia applications over a high-speed LAN, we need to avoid stopping user traffic and discarding packets when the topology changes. In this paper, we propose a new deadlock-free distributed reconfiguration protocol that is able to asynchronously update routing tables without stopping user traffic. This protocol is valid for any topology, including regular as well as irregular topologies. It is also valid for packet switching as well as for cut-through switching techniques and does not rely on the existence of virtual channels to work. Simulation results show that the behavior of our protocol is significantly better than for other protocols based on stopping user traffic     

QoS-aware service composition for distributed video surveillance

Quality of Service (QoS) is essential for the ubiquitous access of media services in real-time distributed video surveillance applications. To have ubiquitous access of desired media with emergency officials’ handheld devices, appropriate media transcoding services are required. Currently, it is challenging to select and compose these services for each of the devices to satisfy the desired QoS demand. To compose these media services so that video stream is available for target pervasive and smart devices, a composition algorithm is required. Thus, this paper presents a QoS-aware service composition algorithm to select the best composition for the target ubiquitous client so that it can optimally provide QoS to heterogeneous users. We have implemented a video surveillance prototype to demonstrate the performance of the proposed QoS-aware composition algorithm. Results from this prototype reveal that the approach is suitable for real-time video surveillance.     

A QoS model for collaboration through Distributed Virtual Environments

Today’s virtual environments are expected to be distributed to allow collaboration for common purposes. However, they must ensure a high level of Quality of Service (QoS) to the user, especially in an open context with unknown, a priori, man-in-the-loop event occurrence. This paper presents our Distributed Virtual Environment Collaboration Model (DVECOM) and its implementation which aims to provide an end-user QoS support for distributed virtual reality applications. This model aims to reconcile openness and real-time requirements for collaborative relationships using virtual environments. Real-time requirements ensure the logical synchronization between the displayed scenes of the same virtual world on a set of distributed machines. The DVECOM model is based partially upon COREMO concepts and further work done in the context of the Amusement European Esprit project.DVECOM integrates QoS provision and management. The major idea is to guarantee the consistency of scene rendering and the synchronization of the display from the user point of view. The other idea is to auto-adapt rendering in accordance with the retained strategy, ensuring best effort and least suffering virtual world rendering. Representation degradation is driven by the users’ choices and is assisted by the system. The receiver-side protocol is based upon end-user preferences, physical level capability information, as well as pertinence of notification to each client (contextual end-user information). The model should be able to guarantee logical consistency and synchronization of virtual world distributed displays, with the least rendering degradation possible. When available, such guarantees would make it possible to use DVE out of a closed, oversized, very restricted context for industrial collaborative applications with an expected QoS.     

ASCM:基于SOA的嵌入式安全关键中间件

由于嵌入式安全关键系统自身的特点和应用环境的特殊性,导致了设计分布式嵌入式安全关键应用比一般的嵌入式实时应用要困难得多。提出了一种新的基于SOA构架的自适应安全关键中间件,极大地简化了嵌入式安全关键系统应用的开发,并对相应的体系结构和关键技术进行了讨论。另外,针对嵌入式安全关键系统运行环境的特殊性,重点讨论了SOA构架中基于动态配置服务的端到端的自适应QoS管理机制和实时容错机制的设计和实现。     

Modelling and performance evaluation of the IEEE 802.11 DCF for real-time control

Popular wireless networks, such as IEEE 802.11/15/16, are not designed for real-time applications. Thus, supporting real-time quality of service (QoS) in wireless real-time control is challenging. This paper adopts the widely used IEEE 802.11, with the focus on its distributed coordination function (DCF), for soft-real-time control systems. The concept of the critical real-time traffic condition is introduced to characterize the marginal satisfaction of real-time requirements. Then, mathematical models are developed to describe the dynamics of DCF based real-time control networks with periodic traffic, a unique feature of control systems. Performance indices such as throughput and packet delay are evaluated using the developed models, particularly under the critical real-time traffic condition. Finally, the proposed modelling is applied to traffic rate control for cross-layer networked control system design.     

Semantic-based QoS management in cloud systems: Current status and future challenges

Cloud Computing and Service Oriented Architectures have seen a dramatic increase of the amount of applications, services, management platforms, data, etc. gaining momentum for the necessity of new complex methods and techniques to deal with the vast heterogeneity of data sources or services. In this sense Quality of Service (QoS) seeks for providing an intelligent environment of self-management components based on domain knowledge in which cloud components can be optimized easing the transition to an advanced governance environment. On the other hand, semantics and ontologies have emerged to afford a common and standard data model that eases the interoperability, integration and monitoring of knowledge-based systems. Taking into account the necessity of an interoperable and intelligent system to manage QoS in cloud-based systems and the emerging application of semantics in different domains, this paper reviews the main approaches for semantic-based QoS management as well as the principal methods, techniques and standards for processing and exploiting diverse data providing advanced real-time monitoring services. A semantic-based framework for QoS management is also outlined taking advantage of semantic technologies and distributed datastream processing techniques. Finally a discussion of existing efforts and challenges is also provided to suggest future directions.     

A trustworthy QoS-based collaborative filtering approach for web service discovery

Many network services which process a large quantity of data and knowledge are available in the distributed network environment, and provide applications to users based on Service-Oriented Architecture (SOA) and Web services technology. Therefore, a useful web service discovery approach for data and knowledge discovery process in the complex network environment is a very significant issue. Using the traditional keyword-based search method, users find it difficult to choose the best web services from those with similar functionalities. In addition, in an untrustworthy real world environment, the QoS-based service discovery approach cannot verify the correctness of the web services’ Quality of Service (QoS) values, since such values guaranteed by a service provider are different from the real ones. This work proposes a trustworthy two-phase web service discovery mechanism based on QoS and collaborative filtering, which discovers and recommends the needed web services effectively for users in the distributed environment, and also solves the problem of services with incorrect QoS information. In the experiment, the theoretical analysis and simulation experiment results show that the proposed method can accurately recommend the needed services to users, and improve the recommendation quality.     

Cloud computing system risk estimation and service selection approach based on cloud focus theory

The main cloud computing service providers usually provide cross-regional and services of Crossing Multi-Internet Data Centers that supported with selection strategy of service level agreement risk constraint. But the traditional quality of service (QoS)-aware Web service selection approach cannot ensure the real-time and the reliability of services selection. We proposed a cloud computing system risk assessment method based on cloud theory, and generated the five property clouds by collecting the risk value and four risk indicators from each virtual machine. The cloud backward generator integrated these five clouds into one cloud, according to the weight matrix. So the risk prediction value is transferred to the risk level quantification. Then we tested the Web service selection experiments by using risk assessment level as QoS mainly constraint and comparing with LRU and MAIS methods. The result showed that the success rate and efficiency of risk assessment with cloud focus theory Web services selection approaches are more quickly and efficient.

     

Model driven middleware: A new paradigm for developing distributed real-time and embedded systems

Distributed real-time and embedded (DRE) systems have become critical in domains such as avionics (e.g., flight mission computers), telecommunications (e.g., wireless phone services), tele-medicine (e.g., robotic surgery), and defense applications (e.g., total ship computing environments). These types of system are increasingly interconnected via wireless and wireline networks to form systems of systems. A challenging requirement for these DRE systems involves supporting a diverse set of quality of service (QoS) properties, such as predictable latency/jitter, throughput guarantees, scalability, 24x7 availability, dependability, and security that must be satisfied simultaneously in real-time. Although increasing portions of DRE systems are based on QoS-enabled commercial-off-the-shelf (COTS) hardware and software components, the complexity of managing long lifecycles (often ∼15-30 years) remains a key challenge for DRE developers and system integrators. For example, substantial time and effort is spent retrofitting DRE applications when the underlying COTS technology infrastructure changes.This paper provides two contributions that help improve the development, validation, and integration of DRE systems throughout their lifecycles. First, we illustrate the challenges in creating and deploying QoS-enabled component middleware-based DRE applications and describe our approach to resolving these challenges based on a new software paradigm called Model Driven Middleware (MDM), which combines model-based software development techniques with QoS-enabled component middleware to address key challenges faced by developers of DRE systems — particularly composition, integration, and assured QoS for end-to-end operations. Second, we describe the structure and functionality of CoSMIC (Component Synthesis using Model Integrated Computing), which is an MDM toolsuite that addresses key DRE application and middleware lifecycle challenges, including partitioning the components to use distributed resources effectively, validating software configurations, assuring multiple simultaneous QoS properties in real-time, and safeguarding against rapidly changing technology.     

GridVideo: A Practical Example of Nonscientific Application on the Grid

Starting from 1990s and until now, Grid computing has been mainly used in scientific laboratories. Only in the last few years it is evolving into a business-innovating technology that is driving commercial adoption. In this paper we describe GridVideo, a Grid-based multimedia application for the distributed tailoring and streaming of media files. The objective is to show, starting from a real experience, how Grid technologies can be used for the development of non-scientific applications. Relevant performance aspects are analyzed, regarding both user-oriented (in terms of responsiveness) and provider-oriented (in terms of system efficiency) requirements. Different multimedia data dissemination strategies have been analyzed and an innovative technique, based on the Fibonacci series, is proposed. To respond to the stringent Quality of Service (QoS) requirements, typical of soft real-time applications, a reservation-based architecture is presented. Such architecture is able to manage the Grid resource allocation, thus enabling the provisioning of advanced services with different QoS levels. Technical and practical problems encountered during the development are discussed and a thorough performance evaluation of the developed prototype is presented.     

Ad hoc网络中基于TDMA的定向发送和接收算法

近期研究结果表明利用有向天线实现定向发送和定向接收比用全向方式能显著提高系统吞吐量.为了支持多媒体和实时业务,在Ad hoc网络中提供服务质量(QoS)是一个关键部分.提出了一种利用有向天线且提供QoS支持适用于Ad hoc网络的分布式媒体接入控制(MAC)算法.仿真结果表明该算法与IEEE 802.11相比提高了系统吞吐量并降低了端-端延迟.