第三代移动通信系统与无线局域网互联互通研究

阐述了第三代移动通信系统与无线局域网互联互通的背景、体系结构、关键机制以及应用场景等,特别是对网络选择、认证、鉴权、计费、数据路由等关键机制进行了深入研究并给出了相应的解决方案及两种不同应用场景下的网络架构组成。     

T-MPLS与MPLS网络互通模型的分析与研究

分析了T-MPLS技术的演进过程,介绍了T-MPLS的功能体系结构,并详细分析了T-MPLS网络和MPLS网络的互通模型,根据对等模式和层叠模式,在不同的网络配置场景的基础上讨论了在互通过程中出现的问题,研究了这些问题出现的背景及原因,针对这些问题提出了相应的解决方法.     

A hierarchical distributed control model for coordinating intelligent systems

This paper describes a hierarchical distributed control (HDC) model for coordinating cooperative problem-solving among intelligent systems. The model was implemented using SOCIAL^TM, an innovative object-oriented tool for integrating heterogeneous, distributed software systems. SOCIAL embeds applications in “wrapper” objects called Agents, which supply predefined capabilities for distributed communication, control, data specification and translation. The HDC model is realized in SOCIAL as a “Manager” Agent that coordinates interactions among application Agents. The HDC-Manager indexes the capabilities of application Agents; routes request messages to suitable server Agents; and stores results in a commonly accessible “bulletin board.” This centralized control model is illustrated in a fault-diagnosis application for launch operations support of the Space Shuttle fleet at the NASA Kennedy Space Center.     

T-MPLS层网络和以太网间基于PW的互通模型

目前的发展趋势表明,T-MPLS(传送多协议标签交换)将逐渐成为一种新的传送机制.文章介绍了端到端PW(伪线)模型,分析了T-MPLS网络的信号封装机制,提出了基于PW的T-MPLS层网络与以太网互通模型.在此基础上文章结合T-MPLS信号封装机制,详细讨论了基于PW的以太网互通模型.     

Monitoring distributed systems

It is suggested that a functional model of monitoring in terms of the generation, processing, dissemination, and presentation of information can help determine the facilities needed to design and construct distributed systems. Implementation issues are also discussed, with attention given to the intrusiveness of monitoring systems and object-based implementation. It is concluded that generic monitoring services are important tools for managing distributed systems and for debugging during system development. Monitoring services may also be needed as part of the application itself, such as in process control and factory automation     

面向分布式系统访问控制的信任度量化模型

通过引入社会学中信任的研究成果,定义了分布式系统访问控制中信任的具体语义、基本特性与上下文相关属性.针对信任的主观性、模糊性与不确定性,采用模糊数学与概率论相结合的方法,给出了信任的数学定义,建立了包括信任综合评价与信任计算的信任度量化模型.该模型综合了访问控制背景下信任相关的各种因素,符合推荐信任的衰减与增强规律.     

A novel congestion control model for interworking AAA in heterogeneous networks

In the 3rd generation partnership project (3GPP) and wireless local area network (WLAN) interworking networks, 3GPP authentication, authorization, accounting (AAA) server located in 3GPP core network will be responsible for the AAA request from WLAN access network (AN). However, centralized AAA deployment is bound to give rise to the single point failure, resulting in system congestion. In order to solve this problem, this paper presents a novel congestion control model for AAA. In addition, through analyzing the model, the conclusion can be drawn that the average congestion rate of extensible authentication protocol (EAP) user request is related with factors, such as the arrival rate of EAP request, the number of EAP re-authentication, and the system buffer queue length. Finally, the simulation results show that EAP request arrival rate is directly proportional to the congestion rate, and when the number of EAP re-authentication and system buffer queue length are fixed, the number of corresponding user authentication vectors should be directly proportional to the EAP request arrival rate, so as to ensure the average congestion rate of EAP request is less than 0.005.     

Research of P2P overlay in heteromerous network

Most of the existing overlays are designed for only one network. This paper analyses the characteristic of heteromerous network and proposes a tree structure overlay for it. We classify the nodes into two types: common node and hybrid node. We design new routing table and new algorithms for node (especially for hybrid node) joining, leaving and searching. The simulation result shows that the overlay is well suit for heteromerous network. The algorithm is convergent in large-scale situation.     

Indirect closed-loop systems identification of distributed systems

In many cases it is impossible to remove the feedback during systems identification as it will make the system unstable. This paper presents an identification method for spatially interconnected distributed systems with identical subsystems operating in closed-loop feedback control. The proposed method takes into consideration the boundary conditions. The approach provides parameters estimate with minimum bias for unstable plant models when there is additive colored noise in output data. This yields consistent parameters estimate and, compared with other techniques to identify such systems under similar situations, takes far less time. The method is illustrated for two-dimensional systems (one for time and one for space), but is equally applicable for systems having more dimensions in space. The proposed technique is for general two-dimensional systems which may be causal, semi-causal (spatially interconnected systems) or non-causal. The effectiveness of the approach is demonstrated with a simulation example.     

分布式系统中的安全问题

信息安全在计算机系统中,尤其在分布式系统中是至关重要的。介绍了分布式计算机系统中信息安全的保障措施,着重介绍了几种常见的信息加密、解密技术的工作原理及其实现方法。     

A programming model and system infrastructure for real-timesynchronization in distributed multimedia systems

One of the major requirements of distributed multimedia applications is the need to maintain often complex, real-time synchronization constraints. More specifically, it is necessary to be able to manage arbitrary intra- and inter-media synchronization across activities in the distributed environment. Furthermore, it is important that such developments are integrated into emerging object-oriented standards for distributed computing. This paper presents an object-oriented programming model and associated implementation to meet these requirements. The main concepts behind the proposed approach are, firstly, the use of reactive objects for real-time control and synchronization and, secondly, quality of service controlled bindings for predictable communication between objects. The flexibility of the approach is demonstrated by three contrasting examples of real-time synchronization. The implementation extends the real-time capabilities of the Chorus micro-kernel by introducing the concepts of rtports, rthandlers and quality of service controlled connections. The paper demonstrates how reactive objects and bindings are realized on this infrastructure     

Computer networks and distributed systems

Computer Networks and Distributed Systems, along with Multiprocessor Systems, comprise the class of computer systems known as Multiple Instruction Multiple Data (MIMD). We distinguish Multi-processor Systems, which are not covered in this review, from the other members of MIMD, by the degree of autonomy of the computing elements and the means of communication between them. A system where the processors communicate by using shared memory or where there is a master-slave relationship among the processors is neither a network nor a Distributed System. This paper identifies, analyzes and classifies various aspects of distributed systems.     

Adaptation in distributed multimedia systems

The real-time requirements of continuous media call for careful resource management in distributed multimedia systems. In complex and mobile systems, however, effective resource reservation becomes almost impossible. Recent research suggests adaptive applications as a complementary solution. This article reviews heterogeneous networks and the rationale behind adaptation, gives implementation examples, and discusses some outstanding research issues     

Voting mechanisms in distributed systems

It is shown how voting mechanisms can be exploited to improve the reliability of decisions in a distributed system. A model of decision making in which several processors (nodes) are assigned to work independently on various aspects of a problem and each returns a binary answer to a coordinator node is assumed. The coordinator combines the answers, using a voting mechanism to arrive at a final answer. Two issues are addressed: (1) if the reliability of each node is known, then by assigning suitable votes to the various nodes it is possible to maximize the probability of a correct decision by the coordinator; and (2) if a cost vs. reliability function for each node is known, then it is possible to determine a best operating point for each node so as to minimize the total cost of the computation. Algorithms for minimizing the cost were designed and tested, and conditions under which savings can be realized were identified     

Security aspects of 3G-WLAN interworking

Third-generation cellular systems will provide wide coverage and nearly universal roaming, but will not realistically live up to the bit rate expectations placed on them. On the other hand, WLAN systems already offer bit rates surpassing those of 3G systems, but are often found lacking with respect to roaming and mobility support. In short, WLAN systems are great for hot spot coverage, while 3G systems provide global coverage and the necessary network and management infrastructure to cater for security, roaming, and charging requirements. The focus of the article is on security aspects of 3GPP-WLAN interworking.     

The distributed simulation of multiagent systems

Agent based systems are increasingly being applied in a wide range of areas including telecommunications, business process modeling, computer games, control of mobile robots, and military simulations. Such systems are typically extremely complex and it is often useful to be able to simulate an agent based system to learn more about its behavior or investigate the implications of alternative architectures. The authors discuss the application of distributed discrete event simulation techniques to the simulation of multiagent systems. We identify the efficient distribution of the agents' environment as a key problem in the simulation of agent based systems and present an approach to the decomposition of the environment that facilitates load balancing     

Load balancing in heterogenous distributed systems

In most distributed systems, the work generated at a node is processed there; little sharing of computational resources is provided. In such systems it is possible for some nodes to be heavily loaded while others are lightly loaded, resulting in poor overall system performance. The purpose of load balancing is to improve performance by redistributing the workload among the nodes.In this paper four load balancing techniques are studied by simulations. The study is limited to a class of techniques where the jobs are lined up in a generic queue and sent to a central job dispatcher which allocates the job to a particular processor based upon the following criteria: nondeterministic routing, response time, system time and throughout.We propose an algorithm that reduces the computational complexity of algorithms ensuring minimum system time.     

Multimedia service interworking over heterogeneous networkingenvironments

This article discusses technical issues related to delivery of multimedia services, such as video-on-demand, over heterogeneous networking environments. In particular, it describes the design and implementation of an experimental system for multimedia service interworking between a DAVIC (Digital Audio Visual Council) domain and an Internet domain. The system, called MIDDLEMEN (middlemen for multimedia environment), consists of the broker and the interworking unit, which work together to provide multimedia services across different types of networks in a seamless manner. The broker acts as a guide to multimedia services, and complements servers or clients that are not equipped with full functionality. The broker also controls the resources in MIDDLEMEN. The interworking unit performs various translation functions under the control of the broker, including stream transport protocol conversion, traffic monitoring and bit-rate control, service gateway conversion, and stream control conversion. Current implementation supports the delivery of a DAVIC-compliant VOD service from an ATM network to an IP network