网络视频监控系统中的目录服务设计

文章设计了一种基于C++类的网络视频监控系统的目录服务,系统采用类似于DNS的目录服务,将所有逻辑节点、物理节点都统一编码,集中存储到本地数据库中,实现了网络视频终端、客户监控端、管理平台、视频数据文件等信息的管理和访问。通过实际应用证明了该目录服务能较好的满足网络视频监控的需要。     

IP anycast point-to-(any) point communication

The Internet supports three communication paradigms. The first, unicast, is the point-to-point flow of packets between a single source (client) and destination (server) host. Web browsing and file Me transfer are unicast applications. The next, multicast, is the point-to-multipoint flow of packets between a single source host and one or more destination hosts. Broadcast-style videoconferencing, for example, employs IP multicast. Anycast is the point-to-point flow of packets between a single client and the "nearest" destination server identified by an anycast address. The idea behind anycast is that a client wants to send packets to any one of several possible servers offering a particular service or application but does not really care which one. Any number of servers can be assigned a single anycast address within an anycast group. A client sends packets to an anycast server by placing the anycast address in the packet header. Routers then attempt to deliver the packet to a server with the matching anycast address     

OmniCon: a Mobile IP‐based vertical handoff system for wireless LAN and GPRS links

Wi‐Fi based hotspots offer mobile users broadband wireless Internet connectivity in public work spaces and corporate/university campuses. Despite the aggressive deployment of these hotspots in recent years, high‐speed wireless Internet access remains restricted to small geographical areas due to the limited physical coverage of wireless LANs. On the other hand, despite their lower throughput, cellular networks have a significantly wider coverage and are thus much more available. Recognizing that 2.5G or 3G cellular networks can effectively complement wireless LANs, we set out to develop a vertical handoff system that allows mobile users to seamlessly fall back to such cellular networks as the general packet radio service (GPRS) or 3G whenever wireless LAN connectivity is not available. The resulting handoff mechanism allows a network connection of a mobile node to operate over multiple wireless access networks in a way that is transparent to end user applications. In this paper, we present the design, implementation, and evaluation of a fully operational vertical handoff system, called OmniCon, which enables mobile nodes to automatically switch between wireless LAN and GPRS, based on wireless LAN availability, by introducing a simple extension to the existing Mobile IP implementation. We discuss the design issues in the proposed vertical handoff system for heterogeneous networks, including connection setup problems due to network address translation, and the disparity in link characteristics between wireless LANs and GPRS. A detailed performance evaluation study of the OmniCon prototype demonstrates its ability to migrate active network connections between these two wireless technologies with low handoff latency and close to zero packet loss. Copyright © 2006 John Wiley & Sons, Ltd.     

延时受限的选播QoS路由算法的设计与仿真

选播是一种新型的网络服务,它使用户通过一个选播地址就能访问到该地址所表示的一组服务器中对用户来说“最近”的一个。在实时性要求较高的业务传输过程中,保证信息传输延时尽可能小是非常重要的。该文研究延时受限的选播路由问题,提出了一种改进的遗传算法以求解该问题。仿真实验结果表明,该算法是有效和切实可行的。     

使用特殊复合距离的选播路由算法

选播成员都是等价的服务器,服务数据的服务质量比作为请求的选播数据报更为重要．使用特殊复合距离的选播路由算法(ASCD)使用跳数、逆向传输延迟、逆向可用带宽以及服务器负载合成的距离来选择路径．不同于其他算法,ASCD使用度量在路径逆向上的值,即从选播数据报目标节点(服务器)到选播数据报源节点(客户)方向,而不是常规从选播数据报的源节点到目的节点方向．ASCD定位的路径和选播成员使选播数据报请求的服务数据能够得到更多路径资源．ASCD还能够在一定程度上平衡服务器负载．     

一种带时延约束的选播路由算法

选播是一种新型的网络服务，它使用户通过一个选播地址就能访问到该地址所表示的一组服务器中对用户来说“最近”的一个。在实时性要求较高的业务传输过程中，保证信息传榆时延尽可能小是非常重要的。本文研究时延受限的选播路由问题，提出一种时延受限的选播路由（DCAR）算法，生成一棵以时延为度量且代价最小的选播生成树。仿真实验结果表明了该算法的正确性和高效性。 [     

IPv6任播及其安全性分析

任播作为一种网络服务模式越来越受到关注，原因是它能够选择对于客户来说最优的一个（最好是一个）服务器。对任播技术的最初研究集中在网络层，在网络层路由器自动完成选路，而应用层任播通过客户的参与带来了更多的灵活性。本文分别对两种任播技术进行了论述，重点介绍如何在应用层找到最优服务器，并对任播的安全性问题进行了分析。     

A cost-efficient method for streaming stored content in a guaranteed QoS Internet

Quality-of-service techniques allow network providers to differentiate the services they offer to their customers. This differentiation makes it possible to consider charging new quality transport services based on network resource usage. In a content streaming framework, consumers pay for content and network access. Similarly, content providers pay to reserve transport service resources to deliver high-quality content. Therefore, content providers need new cost-efficient methods that optimize network resource reservations. Our paper proposes a new method that ensures data availability on the client side while optimizing network resource reservation when servers deliver stored content with semi-elastic unicast flows. The method uses network resource reservation to guarantee the delivery rate when stored data is below a minimum threshold in the client memory. When occupancy reaches a maximum threshold, the transmission changes to the classic best-effort service, which is not charged based on usage but at a flat rate. The proper design of these thresholds optimizes transmission cost. We validate our analytical method using the ns-2 simulator. We also present a new approach for improving this method when the best-effort delivery rate from the server to the client presents higher variability. Finally, we analyse the case of several homogeneous clients that simultaneously require resource reservation from the server. To avoid resource reservation rejection in the server, bandwidth must be suitably allocated among the clients. To evaluate this more complex case, we also perform some simulations and implement the associated prototype to validate the simulations. The qualitative simulation results reveal optimum working areas in which usage-cost reduction efficiency of the method is significant and extra signalling is minimum.     

吸收协议-一个选播路由协议

选播是一种很有用的通信模式．由于在复制服务器、移动IP等多个应用领域的需求．使越来越多的人关注怎样更好的实现选播．提出了一个选播路由协议一吸收协议．协议在提供最小端到端延迟路由前提下支持多路路由．以平衡网络流量．改善网络链路利用率．协议通过从选播成员开始的吸收过程．使网络中每个节点都有一条或者多条到选播地址的路由指向到该节点端到端延迟最小的选播成员．吸收协议原理简单，开销小．易于实现．不依赖其他路由协议．修改、升级不会影响其他路由协议．     

Anycast--IP的又一通信模式

Anycast是一种新型的网络服务,是IPv6的一个新特性．与unicast和multicast一样,它是IP的一种通信模式．Anycast给用户的期望是通过一个anycast地址就能访问到该地址所表示的一组服务器中对用户来说距离最近的一个．Anycast的应用空间非常广阔．但是,它的实现还面临着许多问题．现在,anycast研究者的注意力主要集中在路由协议、无状态服务问题、组管理协议、局域网通信、地址结构、安全问题、QoS保证以及可扩展性等方面．有些方面已经取得了一些进展．但是,仍然有许多研究工作有待进一步开展．关于anycast的一些协议和标准正在讨论之中,但仍然没有达成共识．作为下一代Internet新兴的服务方式,anycast为我们展开了广阔的探索空间．     

IP Mobility Issues for a Mobile Tele-Robotic System-NEPWAK

The network-centric applied research team (N-CART) is continuing its work on an ambitious project known as the network-enabled powered wheelchair adaptor kit (NEPWAK). It introduces techniques for modifying and using powered wheelchairs as mobile platforms enabling communication and remote control. The wheelchair is equipped with a laptop computer, a CCD camera and a wireless network interface card (NIC) for 802.11b Internet access. The laptop acts as a server allowing network clients to gain access through a custom control interface on the chair. The remote controlling client receives a video and audio feed from the chair and sends control signals for maneuvering. While traveling, the chair is able to change its network association from one access point (AP) to another within the same subnet-the process is known as handoff. However, there is no inter-network handoff mechanism presently available in IP networks. This restricts the mobility of the wheelchair to within the coverage area of the subnet APs. This paper shows that the Internet engineering task force's (IETF) network layer mobility protocol-Mobile IP suffers from large handoff latencies that can hinder communication between the client and the wheelchair during handoff. Mobile IP alone is not a sufficient solution for a mobile telebotic system such as NEPWAK. An interesting solution to the handoff latency problem comes from the Fast-handover protocol described in Section 4.4 with simulation results in Section 6.2.     

DISCWorld: an environment for service-based matacomputing

We describe our DISCWorld system for wide-area, high-performance metacomputing in which we adopt a high-level, service-based approach. Users’ client programs request combinations of services from a set of server nodes which communicate at a peer-based level. DISCWorld is a constrained metacomputing system, running only the service operations its participating resource administrators have chosen to provide and advertise, and provides a common integration environment for clients to access these services and developers to make them available. We discuss our software architecture and experiences building DISCWorld using Java and CORBA components, and the associated research issues for metacomputing that we are addressing.     

Context-aware handoff middleware for transparent service continuity in wireless networks

Advances in wireless networking and content delivery are enabling new challenging provisioning scenarios where a growing number of users access continuous services, e.g., audio/video streaming, while moving among different points of attachment to the Internet, possibly with different connectivity technologies, e.g., Wi-Fi, Bluetooth, and cellular 3G. That calls for novel middlewares capable of dynamically personalizing service provisioning to the characteristics of client environments, in particular to discontinuities in wireless resource availability due to handoffs. The paper proposes a novel middleware solution, called Mobile agent-based Ubiquitous multimedia Middleware (MUM), that performs effective and context-aware handoff management to transparently avoid service interruptions during both horizontal and vertical handoffs. MUM exploits the full visibility of wireless connections available and their handoff implementations (handoff awareness), of service quality requirements and handoff-related quality degradations (QoS awareness), and of network topology and local resource availability (location awareness); that visibility enables MUM to provide original solutions for handoff prediction, multimedia continuity via adaptive data buffering/pre-fetching, and proactive re-addressing/rebinding.     

基于社会网络特征的云服务副本放置策略

为提高云环境下业务流程的执行效率,提出一种云服务副本放置策略。该策略基于社会网络分析的思想,挖掘出云服务社区中服务网络的连通性、中心化等社会网络特征,从而确定服务网络中处于枢纽位置的中心服务节点。通过分析中心服务节点和其前驱节点的逻辑序列关系,结合服务节点所在物理机的负载情况,确定中心服务节点的副本的宿主物理机并进行预放置。实验结果表明,该策略可以减少云环境中的业务流程因异地服务的交互造成的时间消耗,均衡节点负载,提高业务流程的执行效率。     

TEASE: A novel Tunnel-based sEcure Authentication SchemE to support smooth handoff in IEEE 802.11 wireless networks

With the growing popularity of WiFi-based devices, WiFi-based wireless networks have received a great deal of interest in the wireless networks community. However, due to the limited transmission range of WiFi-based networks, mobile users have to switch their associated access points constantly to maintain continuing communications during their movement. The process of switching access points is called handoff. Handoff management is a key service in mobile networks, because providing seamless roaming in wireless networks is mandatory for supporting real-time applications in a mobile environment, such as VoIP, online games, and eConference. Security is another important issue in network communications, and to prevent possible attacks, authentication is required during the handoff process to guarantee the reliability of mobile clients and access points. In this paper, we propose a novel authentication scheme to achieve a smooth handoff in WiFi-based networks, which we refer to as TEASE. A tunnel is introduced to forward data packets between the new access point and the original reliable access point. The processing of a complete secure authentication and the transmitting of data between mobile terminals and their correspondence nodes can go on simultaneously. The security of handoff is achieved without increasing overhead to authentication servers, and handoff latency can be minimized to support seamless roaming. Simulation results show that our proposed scheme reduces significantly the communication interruption time and generates low packet loss ratio, and our method is suitable to be used for secure handoff in real-time applications.     

一种改进的网络选播路由算法

选播是一种新型网络服务,被IPv6规定为一种标准通信模型。用户通过一个选播地址就能访问到该地址所表示的一组服务器中离用户“最近”的一个。随着越来越多的网络应用需要选播服务支持,选播路由成为重要的研究课题。该文对选播服务和已有选播算法进行了分析,基于遗传算法思想将双种群策略引入到选播QoS路由。仿真实验表明,新算法能有效地提高网络搜索的速度,增加获得最优路径的概率,大大改善网络的服务质量。     

Context-aware middleware for resource management in the wireless Internet

The provisioning of Web services over the wireless Internet introduces novel challenging issues for service design and implementation: from user/terminal mobility during service execution, to wide heterogeneity of portable access devices and unpredictable modifications in accessible resources. In this scenario, there are frequent provision-time changes in the context, defined as the logical set of accessible resources depending on client location, access terminal capabilities, and system/service management policies. The development of context-dependent services requires novel middlewares with full context visibility. We propose a middleware for context-aware resource management, called CARMEN, capable of supporting the automatic reconfiguration of wireless Internet services in response to context changes without any intervention on the service logic. CARMEN determines the context on the basis of metadata, which include declarative management policies and profiles for user preferences, terminal capabilities, and resource characteristics. In addition, CARMEN exploits the mobile agent technology to implement mobile middleware components that follow the provision-time movement of clients to support locally their customized service access. The proposed middleware shows how metadata and mobile agents can favor component reusability and automatic service reconfiguration, by reducing the development/ deployment complexity.     

蓝鲸分布式文件系统的物理资源管理模型

蓝鲸分布式文件系统可以管理数百个存储节点，向上千个应用服务器提供远程文件访问服务，提供超大规模的系统容量。其物理资源管理模型能有效地管理分布的存储资源，形成统一的地址空间，动态分配各种资源，缩短查找和跟踪路径。此模型为整个蓝鲸分布式文件系统提供了统一的资源管理机制，是文件系统并发访问的基础。     

基于IPv6选播路由协议的负载平衡研究

为了提高网络服务的质量,在Internet上经常采用复制的方法产生一组镜像服务器。选播是在单个发送者与一组接收者中任意一个主机之间的数据通信,选播服务可以改善网络负载分布和简化网络应用;根据路径的距离,发往某选播地址的数据包被路由到拥有该地址且最近的镜像服务器;然而,最近的镜像服务器不一定是最佳的镜像服务器。负载平衡是一种通过充分利用所提供的冗余多链路进行业务量分配的模式。基于IPv6选播路由协议,文章提出了一个新的协议模型,通过TCP连接总数确定选播地址对应的最佳服务器,有效地解决由当前选播路由协议确定的最近服务器产生网络拥塞时如何改善路由策略问题,从而实现负载平衡并提高网络的传输性能。     

A buffered-bandwidth approach for supporting real-time video streaming over cellular networks

In this paper, we study the admission and bandwidth allocation problems in real-time video streaming in a cellular network. Admission control in a cellular network is a complex issue due to the mobility of the clients, and the additional workload imposed by incoming clients could exceed the network capacity of a cell and seriously degrade the quality of services provided to the resident clients. To minimize the number of forced terminations of real-time video playback, we incorporate the notion of buffered bandwidth in the admission test for handoff client. Using this approach, we can balance the video workload among adjacent cells to minimize the impact of overloading as the result of handoff operations. We also examine techniques to maintain fairness in services especially under overload situations even though the requested videos from various types of clients could generate very different workload. Simulation experiments confirm the effectiveness of our approach compared to widely used schemes.