Reliable overlay multicast trees for private Internet broadcasting with multiple sessions

With rapid advances of computing technologies and high speed networks, various high volume multimedia services have become popular in the Internet. Private Internet broadcasting is a typical way to support these services and overlay multicast technology is known to be a promising solution to support this method. In an overlay multicast network, members are dynamically joining or leaving their multicast group. To reduce frequent updates of multicast members and provide a reliable multicast route, overlay multicast trees are investigated. The problem is formulated as a binary integer programming which maximizes the minimum link reliability for all multicast sessions. Tabu search heuristic is developed with repeated intensification and diversification. Robust computational result is obtained that is comparable to the optimal solution and applicable in real time.     

组播视频会议环境下的H.323接入网关的设计与实现

H.323[1]会议系统是基于单播的视频会议系统,多点会议通过多点控制单元(MultipointControlUnit,MCU[1])来进行。IP网络上另一类会议系统是基于组播(Multicast)的视频会议系统,通过组播机制实现多点通信。该文提出的H.323终端接入网关MCU-M(MultipointControlUnitforMulticast)使组播视频会议环境支持基于H.323协议的呼叫接入,实现了这两类系统之间的互通,极大地扩展了组播视频会议环境的用户群。H.323终端接入网关原型还可以被进一步扩展为通用的信息互通平台,用来连接各种不同的多媒体终端。     

An overlay multicast protocol for live streaming and delay-guaranteed interactive media

In many collaborative multimedia applications, there is often a requirement for simultaneously supporting live streaming and shareable interaction. A major challenge in designing such an application by overlay multicast is how to simultaneously provide scalable live streaming and delay-guaranteed interactive media. Live streaming by overlay multicast incurs additional application-layer latency, which conflicts with the delay-sensitive property of interactive media. To handle this dilemma, in this paper, we propose a layered degree-constrained overlay multicast protocol, which organizes the overlay multicast tree as a layered degree-constrained core tree and an extended tree. The core tree maintains available resources in its top layers for subsequent two-way interaction, whereas the extended tree expands the core tree for one-way live streaming. Our simulation and experimental results show that the proposed overlay multicast protocol can simultaneously provide delay-guaranteed interactive media as well as scalable live streaming.     

Design, optimization and performance evaluation of a content distribution overlay for streaming

As an evolution of peer-to-peer (p2p) file-sharing applications, overlay-based networks are also adopted to efficiently distribute content with real-time constraints to a wide user population. In addition, they can be utilized to exploit application level strategies to overcome limitations imposed by the underlying network infrastructure, e.g., the lack of multicast support.In this perspective, the paper introduces an overlay Content Distribution Network (CDN) able to sustain the real-time delivery of data streams. To better use resources, and to face the churn affecting users, the control and optimization of the CDN are performed through a model predictive control scheme. Simulations of two use cases are provided to show the effectiveness of the proposed solution. In particular, the stream of multimedia and interactive grid data are considered.     

On Bandwidth-Efficient Overlay Multicast

In this paper, we propose a new multicast delivery mechanism for bandwidth-demanding applications in IP networks. Our mechanism, referred to as multiple-destination overlay multicast (MOM), combines the advantages of IP multicast and overlay multicast. We formulate the MOM routing problem as an optimization problem. We then design an algorithm based on Lagrangian relaxation on our formulation and propose a distributed protocol based on the algorithm. For network operators, MOM consumes less network bandwidth than both IP multicast and overlay multicast. For users, MOM uses less interface bandwidth than overlay multicast.     

LION: Layered Overlay Multicast With Network Coding

Recent advances in information theory show that the throughput of a multicast session can be improved using network coding. In overlay networks, the available bandwidth between sender and different receivers are different. In this paper, we propose a solution to improve the throughput of an overlay multicast session with heterogeneous receivers by organizing the receivers into layered data distribution meshes and sending substreams to each mesh using layered coding. Our solutions utilize alternative paths and network coding in each mesh. We first formulate the problem into a mathematical programming, whose optimal solution requires global information. We therefore present a distributed heuristic algorithm. The heuristic progressively organizes the receivers into layered meshes. Each receiver can subscribe to a proper number of meshes to maximize its throughput by fully utilizing its available bandwidth. The benefits of organizing the topology into layered mesh and using network coding are demonstrated through extensive simulations. Numerical results indicate that the average throughput of a multicast session is significantly improved (up to 50% to 60%) with only slightly higher delay and network resource consumption.     

Buffer-assisted on-demand multicast for VOD applications

Multicast communications is widely used by streaming video applications to reduce both server load and network bandwidth. However, receivers in a multicast group must access the multicast stream simultaneously, and this restriction on synchronous access diminishes the benefit of multicast because users in a video-on-demand service usually issue requests asynchronously, i.e., at anytime. In this paper, we not only formulate this streaming problem but also propose a new multicast infrastructure, called buffer-assisted on-demand multicast, to allow receivers accessing a multicast stream asynchronously. A timing control mechanism is integrated on intermediate routing nodes (e.g., routers, proxies, or peer nodes in a peer-to-peer network) to branch time-variant multicast sub-streams to corresponding receivers. Besides, an optimal routing path and the corresponding buffer allocations for each request must be carefully determined to maximize the throughput of the multicast stream. We prove that the time complexity to solve this routing problem over general graph networks is NP-complete, and then propose a routing algorithm for overlay networks to minimize server load. Simulation results demonstrate that buffer-assisted on-demand multicast outperforms many popular streaming methods.     

Distinguishing video quality through differential matrices

Multicast multi-layered communications must implement efficient control algorithms to address undesirable network behaviors. This paper proposes two multi-metric algorithms for computing the rates of the video layers and improve the global video quality of a multicast session. In fact, we show that a single-metric approach may degrade some network parameters without obtaining any substantial improvements. Our first algorithm combines three metrics and a set of weights in such a way that one metric can be prioritized. This leads to an improved quality of multicast sessions, as we show through a number of experiments. In networks where the available resources are highly variable, however, the stability of the video quality is compromised if absolute values of the metrics are adopted. We then propose a second algorithm that uses the relative values of the metrics on a per-entry basis. Computation of the global quality of the multicast session is based on a differential matrix that stores the metrics for each receiver. This scheme takes into account the dynamics of the available resources and the heterogeneity of receivers. The great benefit of this approach is that the global video quality is always improved for every loop of the algorithm.     

一种异构环境下覆盖多播网络路由算法

由于IP多播在部署上的困难,覆盖多播网络(overlay multicast networks,简称OMN)作为构建通用的多播服务平台的另一可行途径正不断为人们所认可.针对实时多媒体应用对带宽需求的异构性,研讨了异构环境下OMN的路由问题.通过对度约束模型进行扩展,描述了一种新的适应异构环境的OMN网络模型.采用分层的带宽分配策略,提出了一种异构环境下构造OMN最小延时半径多播树的启发式算法--分层的压缩树(1ayered compact tree,简称LCT)算法,并对其性质进行了理论证明和分析.仿真实验结果表明,随着分配带宽的减少,LCT算法能够有效地降低多播树的高度和网络资源使用量,并保持较低的多播树延时半径增幅.     

基于树与环应用层组播覆盖网的研究与比较

由于应用层组播在部署和实现方面的优势受到学术界的广泛关注.应用层组播协议在不同的覆盖网络拓扑结构(如树、网、环)下具有不同的性能特征.因此,比较应用层组播覆盖网的性能是评估覆盖网络拓扑优缺点的关键.在NS-2下对基于树、环的覆盖网络进行仿真.仿真结果表明,尽管环型覆盖网比树型覆盖网具有较高路径伸展度和较高链路强度,但在单个组播组成员失效或离开的情况下,它提供了恒定的、更低的节点度和较高数据传送率.     

支持实时多媒体传输的应用层组播系统

由于IP组播并未取得预期的成功，研究人员又提出了由终端主机来代替路由器实现群组通信功能。针对实时多媒体传输的特点以及目前单组播网络混合存在的现状，该文提出了一利，新的支持实时多媒体传输的应用层组播系统。在系统中，多个网关形成一层覆盖网，由网关完成数据的复制、分发以及组的成员管理，从而在应用层实现了群组通信的功能。     

QoS Path Monitoring for Multicast Networks

New network monitoring tools are necessary for supporting the deployment and the operations of multicast services on the Internet. Because of the peculiar characteristics of multicast routing (e.g., multicast forwarding trees) and the potential of message implosion problems, traditional network management tools are not sufficient for monitoring the quality of multicast delivery such as packet loss, delay, and jitter. Current multicast monitoring tools are either not scalable, limited in their functionality, or difficult to deploy in enterprise networks.In this paper, we present a new monitoring framework (called SMRM, SNMP-based multicast reachability monitoring) for multicast reachability based on SNMP. The SMRM framework is used for actively monitoring the health and the quality of service of multicast networks. SMRM provides a scalable real-time feedback on the packet loss, delay, and jitter of any selected segments of multicast delivery trees. In addition, NOC (network operations center) personnel can easily understand, deploy, and extend the SMRM framework in order to detect and isolate reachability and performance problems in multicast sessions. SMRM combines both distributed monitoring and centralized control, which offers scalability and simplicity. The integration of SMRM into SNMP is motivated by the wide distribution of SNMP agents in networks today, which significantly facilitates the deployment of SMRM is existing networks.     

WEBGOP: collaborative web services based on graph-oriented programming

WEBGOP is a programming architecture for collaborative Web services using graph-oriented programming. The motivation for the project comes from the realization that the integration of collaborative Web services lacks support. The aim of WEBGOP is to extend the Web from a client-server system to a structured multipoint system. A graph abstraction of the network provides the structure for the integration of Web services and facilitates their configuration and programming. Using WEBGOP, a logical graph representing a virtual-overlay network over the Internet is created to link up collaborative Web services. Web services are individually or jointly invoked through either unicast or multicast messages within the overlay network. All messages are based on the simple-object access protocol (SOAP). This forms an extension of the hypertext transfer protocol (HTTP) to support the distributed invocation of Web services. The Web services on different servers work collaboratively for a multipoint network application. This project provides a structured integration of Web services by extending the support of intermediary processing in a multipoint service. It also provides a rich network-programming interface for a new class of integrated Web applications while retaining the use of the Internet protocol and HTTP.     

多组共享式应用层组播算法

利用单播传输路径的重叠特性所构建的叠加组播树可以部分模拟IP层的有源组播,而单组会话中成员主机在网络中分布的不足可以通过多组会话中的主机来弥补。该文根据这一特点提出了一种基于多组会话成员共享的应用层组播算法,该方法采用了源主机和接收主机之间的单播传输路径和多组协作机制,为每个组播源建立单独的组播树。通过模型分析,该文算法所构建的组播树可以比单组会话计算方法获得较大优势的链路利用率。     

OverSim:可扩展的应用层组播网络仿真框架

应用层组播作为IP组播的一个可行替代方案日益成为Internet应用研究的一个热点。如何仿真大规模、动态的应用层组播覆盖网络已经成为应用层组播方案研究人员面临的一个共同问题。本文在分析当前几款主流的覆盖网络仿真软件的基础上,提出了采用基于OMNet++网络仿真环境的Over-Sim覆盖网络仿真框架来模拟大规模、动态的应用层组播覆盖网络,并在此基础上研究分析可扩展的应用层组播方案。最后我们采用OverSim实现了对应用层组播协议Scribe的仿真并对结果进行了分析。仿真结果表明,OverSim可以在有限的硬件环境下,稳定地仿真高达上万个节点的大规模动态覆盖网络,仿真过程中内存消耗较低,且与覆盖网络规模呈线性关系。     

面向混合网络的半覆盖组播路由协议

组播已在多个协议层上分别实现,但现有协议仍未兼顾对灵活性与效率的共同需求.总的来说,硬件组播和IP组播较为高效,而覆盖组播则更为灵活.在混合网络中,底层技术的差异使这一问题变得更为突出.为此提出了一种动态自组织的半覆盖组播路由协议HOMR(half overlay multicast routing).该协议把基于组内区域广播的IP组播、基于地址端口转换的覆盖组播以及对各类硬件组播的调用融入单一的模型,在各层组播间按需转换.HOMR具有与全覆盖组播相似的灵活性,模拟实验表明,HOMR在保持较低协议开销的同时,获得了与完全IP组播相近的转发效率.     

A Scalable Overlay Multicast Architecture for Large-Scale Applications

In this paper, we propose a two-tier overlay multicast architecture (TOMA) to provide scalable and efficient multicast support for various group communication applications. In TOMA, multicast service overlay network (MSON) is advocated as the backbone service domain, while end users in access domains form a number of small clusters, in which an application-layer multicast protocol is used for the communication between the clustered end users. TOMA is able to provide efficient resource utilization with less control overhead, especially for large-scale applications. It also alleviates the state scalability problem and simplifies multicast tree construction and maintenance when there are large numbers of groups in the network. To help MSON providers efficiently plan backbone service overlay, we suggest several provisioning algorithms to locate proxies, select overlay links, and allocate link bandwidth. Extensive simulation studies demonstrate the promising performance of TOMA     

移动自组织网络应用层组播研究

移动自组织网络的应用迫切要求组播支持。应用层组播是解决组播问题的一种有效的方案。针对目前移动自组网络中网络层组播出现的问题,深入研究了移动自组织网络应用层组播,并作了详尽的性能比较。深入分析了移动自组织网络覆盖组播的优势,并指出了移动自组织网络组播亟待解决的问题,为新的移动自组织网络应用层组播研究提供了非常有价值的研究方向。     

Ad hoc无线网络中的组播路由协议

由固定网络、基础结构移动网络和非基础结构无线网络组成的集成网络将成为未来互联网发展的趋势。同时,面向组计算和组通信的需求不断增长,要求未来的集成网络能为用户提供组播通信的功能。Adhoc无线网络是非基础结构无线网络的典型代表,具有带宽有限、拓扑结构易变和电池能源有限的特点,这些特性使得未来集成网络实现组播通信具有一定的挑战性。该文在分析Adhoc无线网络基本特性的基础上,综合评述了新近的Adhoc网络组播路由协议的研究现状,并对几种典型的Adhoc网络组播路由协议的特点进行了分类分析和比较,最后讨论了Adhoc无线网络组播路由协议的发展趋势和挑战。