支持Internet实时多媒体应用的Overlay技术研究

目前出现的大规模（large-scale）的多媒体应用对Internet提出了新的挑战。传统的IP组播（IP multicast，IPM）由于实现技术的复杂性，很难在Internet上推广。相反，基于叠加网络（overlay network，ON）的解决方案则受到各方面的关注。本文针对大规模实时多媒体应用需求，通过建立评价参数模型对ON协议进行研究。尤其时overlay组播（overlay multicast，OM）的QoS控制、可靠性以及可伸缩性机制进行了分析。与IPM相比，OM虽然有性能代价（performance penalty）问题，但是OM能方便、灵活地利用多种高层的功能实现，基于hop-by-hop方式有效地提供E2E（end—to-end）的可靠性和QoS保障，并且较好地支持TCP-friendliness，具有良好的可伸缩性。此外，0M的基础网络（infrastructure／underlay network）无关性，也使其容易在Internet中进行配置。以上特性使得OM成为支持Internet上大规模实时多媒体应用的最具前景的技术．     

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     

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。     

主动层次多目通信路由模型

许多应用需要IP多目通信.在Internet大规模应用IP Multicast时,有效的路由是关键.这样的多目路由协议必须是有效的、可伸缩的和增量可配置的.但是传统的Internet路由对性能是不敏感的,不能平衡负载和处理拥塞.现有的大多数多目通信路由协议不仅负责数据转发,还负责路由树的构造,这给路由器带来了极大的复杂性,而且协议的配置是手动的、费时费钱的工作.该文提出一个主动层次式Multicast路由的体系结构,采用主动网络技术将多目通信路由协议的数据转发和控制机制分开,根据链路的状态信息用主动报文控     

Software-Defined Multicast for Over-the-Top and Overlay-based Live Streaming in ISP Networks

The increasing amount of over-the-top (OTT) live streams and the lack of global network layer multicast support poses challenges for a scalable and efficient streaming over the Internet. Content Delivery Networks (CDNs) help by delivering the streams to the edge of almost every Internet Service Provider (ISP) network of the world but usually also end there. From there on, the streams are to be delivered to the clients using IP unicast, although an IP multicast functionality would be desirable to reduce the load on CDN nodes, transit links, and the ISP infrastructure. IP multicast is usually not available due to missing control and management features of the protocol. Alternatively, Peer-to-Peer (P2P) mechanisms can be applied to extend the overlay multicast functionality of the CDN towards the clients. Unfortunately, P2P only improves the situation for the CDN but makes it more challenging for the ISP as even more unicast flows are generated between clients inside and outside the ISP network. To tackle this problem, a Software-Defined Networking-based cross-layer approach, called Software-Defined Multicast (SDM), is proposed in this paper, enabling ISPs to offer network layer multicast support for OTT and overlay-based live streaming as a service. SDM is specifically tailored towards the needs of P2P-based video stream delivery originating from outside the ISP network and can easily be integrated with existing streaming systems. Prototypical evaluations show significantly improved network layer transmission efficiencies when compared to other overlay streaming mechanisms, down to a level as low as for IP multicast, at linearly bounded costs.     

Ant colony-based algorithm for constructing broadcasting tree with degree and delay constraints

Heterogeneous ISP router policies prevent multimedia QoS applications, such as real-time media streaming, video conferencing, and distance learning, that require IP layer multicasting from wide deployment on the Internet. Thus, recent efforts have applied application layer multicast to implement such applications by organizing the multicast group in an overlay (virtual), peer-to-peer network. Such a communication scheme can be regarded as a broadcasting problem with degree and delay constraints in the overlay network. The degree and delay-constrained broadcasting problem with minimum-cost appears to be NP-complete. This study proposes an ant colony-based algorithm to solve the difficult broadcasting problem and compares it with some related methods. The results of a series of simulations show the efficiency and effectiveness of the proposed algorithm.     

组播QoS保障和拥塞控制的Overlay实现技术

由于配置困难以及控制技术的复杂性，IP组播（IP Mmulticast，IPM）至今仍未在Intemct上得到推广。而以Overlay方式在Intemet中提供灵活有效的组播服务则成为近年来网络研究的一个热点。如何在基于Overlay的Intemet组播（Overlay Multicast，OM）中实现有效的Qos和可靠性保证，这已成为OM研究的新课题。该文通过建立组播QoS的数学模型，对基于Overlay实现Intemet组播的QoS和拥塞控制的机制进行了分析和探讨。     

重叠网络中一种实现组播交换的有效排队机制

不断增长的诸如电信会议和视频点播等多媒体应用,需要Internet有效地提供高性能的组播支持,为此,人们设计了重叠网络,用以支持不断增长的组播应用.在重叠网络中,信息包的复制过程是由专门的组播服务节点 (Multicast Service Node,MSN) 来完成的.因此,急需对MSN的基本体系结构,特别是MSN的排队和调度方案进行设计,从而使其提供有效的组播支持.为MSN设计了一个具有高性能的排队方案,它能够同时支持单播和组播,而且能以合理的代价实现高链路效率.方法是使用动态按需依向量排队(per-vector queuing on-demand).仿真研究表明,与其它已有的排队方案相比,采用该排队方案的交换机能实现更大的网络吞吐量,具有更高的链路效率和更少的网络延时.     

Island Multicast: Combining IP Multicast With Overlay Data Distribution

Traditional overlay protocols use unicast connections to form delivery trees. While it can achieve global multicast across the Internet, it is not as efficient as IP multicast. In this paper, we integrate IP multicast into overlay data distribution to improve delivery efficiency. We investigate island multicast where unicast connections are used to connect multicast domains and IP multicast is used within multicast domains. We first explore a centralized island multicast protocol (termed CIM), which relies on a central server to construct a delivery tree. We then study a distributed protocol (termed DIM), where hosts can distributedly join islands and form a delivery tree. We study the key issues in both protocols. We also discuss how to apply these protocols to media streaming applications. We have evaluated both protocols on Internet-like topologies. We have also implemented a prototype for CIM and tested it on PlanetLab. The results show that our approaches can significantly im prove network performance as compared to pure overlay protocols. Our study shows that it is important to consider local multicast capability when designing overlay protocols.     

Enabling Contribution Awareness in an Overlay Broadcasting System

We consider the design of bandwidth-demanding broadcasting applications using overlays in environments characterized by hosts with limited and asymmetric bandwidth, and significant heterogeneity in upload bandwidth. Such environments are critical to consider to extend the applicability of overlay multicast to mainstream Internet environments where insufficient bandwidth exists to support all hosts, but have not received adequate attention from the research community. We leverage the multitree framework and design heuristics to enable it to consider host contribution and operate in bandwidth-scarce environments. Our extensions seek to simultaneously achieve good utilization of system resources, performance to hosts commensurate to their contributions, and consistent performance. We have implemented the system and conducted an Internet evaluation on PlanetLab using real traces from previous operational deployments of an overlay broadcasting system. Our results indicate for these traces, our heuristics can improve the performance of high contributors by 10-240% and facilitate equitable bandwidth distribution among hosts with similar contributions.     

Enhancing end-to-end availability and performance via topology-aware overlay networks

This paper proposes a novel overlay architecture to improve availability and performance of end-to-end communication over the Internet. Connectivity and network availability are becoming business-critical resources as the Internet is increasingly utilized as a business necessity. For example, traditional voice and military systems are turning into IP-based network applications. With these applications, even short-lived failures of the Internet infrastructure can generate significant losses.To satisfy these needs, the concept of overlay networks has been widely discussed. However, in the previous studies of overlay networks, a measurable number of path outages were still unavoidable even with use of such overlay networks. We believe that an overlay network’s ability to quickly recover from path outages and congestion is limited unless we ensure path independence at the IP layer. Hence, we develop a simple but effective overlay architecture increasing path independence without degrading performance. The proposed overlay architecture enhances prior studies in the following ways: (1) we deploy overlay nodes considering topology and latency information inside an ISP and also across ISP boundaries; (2) we use a source-based single-hop overlay routing combined with the above topology-aware node deployment; (3) we increase the usage of multi-homing environment at endhosts. In this framework, we develop measurement-based heuristics using extensive data collection from 232 points in 10 ISPs, and 100 PlanetLab nodes. We also validate the proposed framework using real Internet outages to show that our architecture is able to provide a significant amount of resilience to real-world failures.     

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.     

应用层组播研究进展

组播技术是一种针对多点传输和多方协作应用的组通信模型,有高效的数据传输效率,是下一代Internet应用的重要支撑技术。早期的组播技术研究试图在IP层提供组播通信功能,但IP组播的实施涉及到对现有网络基础设施的调整,因此,大规模应用受到限制。近两年来,随着Peer-to-Peer(P2P)研究的兴起,基于应用层的组播技术也逐渐受到广泛关注。应用层组播协议将组成员节点自组织成覆盖网络,在主机节点实现组播功能,为数据多点并发传输提供服务。将组播功能从路由器迁移到主机上能有效解决许多与IP组播有关的问题,但同时也带来了一些新的挑战。本文分析了目前应用层组播研究的主要内容及技术特点,描述了协议设计所涉及的关键技术及面临的主要挑战,总结了现有工作及相关进展。     

Optimal Content Location in Multicast Based Overlay Networks with Content Updates

The architecture of overlay networks should support high-performance and high-scalability at low costs. This becomes more crucial when communication, storage costs as well as service latencies grow with the exploding amounts of data exchanged and with the size and span of the overlay network. For that end, multicast methodologies can be used to deliver content from regional servers to end users, as well as for the timely and economical synchronization of content among the distributed servers. Another important architectural problem is the efficient allocation of objects to servers to minimize storage, delivery and update costs. In this work, we suggest a multicast based architecture and address the optimal allocation and replication of dynamic objects that are both consumed and updated. Our model network includes consumers which are served using multicast or unicast transmissions and media sources (that may be also consumers) which update the objects using multicast communication. General costs are associated with distribution (download) and update traffic as well as the storage of objects in the servers. Optimal object allocation algorithms for tree networks are presented with complexities of O(N) and O(N ²) in case of multicast and unicast distribution respectively. To our knowledge, the model of multicast distribution combined with multicast updates has not been analytically dealt before, despite its popularity in the industry.     

ACOM: Any-source Capacity-constrained Overlay Multicast in Non-DHT P2P Networks

rdquoApplication-level multicast is a promising alternative to IP multicast due to its independence from the IP routing infrastructure and its flexibility in constructing the delivery trees. The existing overlay multicast systems either support a single data source or have high maintenance overhead when multiple sources are allowed. They are inefficient for applications that require any-source multicast with varied host capacities and dynamic membership. This paper proposes ACOM, an any-source capacity-constrained overlay multicast system, consisting of three distributed multicast algorithms on top of a non-DHT overlay network with simple structures (random overlay with a non-DHT ring) that are easy to manage as nodes join and depart. The nodes have different capacities, and they can support different numbers of direct children during a multicast session. No explicit multicast trees are maintained on top of the overlay. The distributed execution of the algorithms naturally defines an implicit, roughly balanced, capacity-constrained multicast tree for each source node. We prove that the system can deliver a multicast message from any source to all nodes in expected O(log_c n) hops, which is asymptotically optimal, where c is the average node capacity and n is the number of members in a multicast group.     

Multicast tree rearrangement to recover node failures in overlay multicast networks

Overlay multicast makes use of the Internet as a low level infrastructure to provide multicast service to end hosts. The strategy of overlay multicast slides over most of the basic deployment issues associated with IP multicast, such as end-to-end reliability, flow and congestion control, and assignment of an unique address for each multicasting group.     

Effective distributed service architecture for ubiquitous video surveillance

Video surveillance systems are playing an important role to protect lives and assets of individuals, enterprises and governments. Due to the prevalence of wired and wireless access to Internet, it would be a trend to integrate present isolated video surveillance systems by applying distributed computing environment and to further gestate diversified multimedia intelligent surveillance (MIS) applications in ubiquity. In this paper, we propose a distributed and secure architecture for ubiquitous video surveillance (UVS) services over Internet and error-prone wireless networks with scalability, ubiquity and privacy. As cloud computing, users consume UVS related resources as a service and do not need to own the physical infrastructure, platform, or software. To protect the service privacy, preserve the service scalability and provide reliable UVS video streaming for end users, we apply the AES security mechanism, multicast overlay network and forward error correction (FEC), respectively. Different value-added services can be created and added to this architecture without introducing much traffic load and degrading service quality. Besides, we construct an experimental test-bed for UVS system with three kinds of services to detect fire and fall-incident features and record the captured video at the same time. Experimental results showed that the proposed distributed service architecture is effective and numbers of services on different multicast islands were successfully connected without influencing the playback quality. The average sending rate and the receiving rates of these services are quite similar, and the surveillance video is smoothly played.     

Multi-channel live streaming in service overlay network

Service overlay network (SON) provides an effective means to deploy quality of service (QoS)-guaranteed live streaming over today’s Internet. A major challenge in designing such a network is dealing with resource sharing among multiple channels. To achieve the best overall QoS in SON, we devise a new multi-channel live streaming scheme. First, we propose a multi-tree construction algorithm by infrastructure-based overlay multicast. The algorithm employs pre-allocated session degree constraints in overlay nodes to reserve resources for multiple channels, and constructs multiple trees by considering the total resource utilization of overlay nodes. Second, we propose a tree-aware queue scheduling algorithm to reduce the overlay processing delay in view of the entire overlay network. Scheduling priority is identified to trade off session priority with node location in different trees. From simulation and experimental results, the scheme achieves a differentiated control among different sessions, provides load balancing among overlay nodes, and improves the delay performance on SON.