基于Agent实现组播在广域网中的传输

针对目前Internet中大部分路由器不支持组播数据传输的问题，本文基于Agent技术提出了一种实现广域网内组播数据传输的方法。该方法使用了基于Agent的通信模型．组播会话中的每个成员通过其上运行的Agent实现数据收发；并将能够实施IP组播通信的网络范围看作是一个组播域，在每个组播域中自动选择一个Agent作为主Agent(MA)，组播域中的其他Agent为备份Agent(BA)；在组播域内利用IP组播进行数据传输，在组播域间利用主Agent之间的TCP连接进行数据传输．从而使得组播通信能够跨越路由器的障碑。此外还实现了BA向MA的自动升级．保证了组播会话的可靠性和连续性。     

卫星网络中基于UDP的可靠数据传输协议

在卫星网络中,标准的传输控制协议TCP不能充分发挥网络的性能。论文通过分析卫星网络的特点提出了一个基于UDP的应用层传输协议UDT-Sat。该协议使用基于带宽估计的拥塞控制和基于选择性负向确认的快速重传机制实现数据高效可靠的传输。实验表明,UDT-Sat在卫星网络中具有很高的带宽利用率,同时保持了良好的公平性和稳定性。     

基于跳到跳信息的卫星网络传输控制协议研究

设计了一种适用于卫星网络的传输控制协议TPSN。该协议使用异步跳到跳确认,快速恢复成段丢失数据,并采用基于检测窗口的端到端选择性否定应答(SNACK)机制,减少协议控制信息,保证数据可靠传输。在跳到跳可靠性保证机制基础上传输网络负载,实现在避免网络拥塞条件下高效利用网络带宽资源,并保证具有不同端到端往返时延的异种数据流之间的公平性。仿真结果表明TPSN能够在长延迟、误码率高、链路频繁切换的卫星网络中保证高效的带宽利用、可靠的数据传输以及各数据流之间的公平。     

基于ACK和NAK的可靠组播传输协议的性能分析和比较

本文在目前各种可靠组播传输协议的基础上,归纳构建了两类基本的可靠组播传输协议—基于确认(ACK)的和基于否定确认(NAK)的可靠组播传输协议.在典型的组播网络系统模型基础上,对这两类协议以及一种主要的改进协议在占用网络带宽和可扩展性方面的性能特点进行了定性的分析和比较.性能分析结果表明,基于否定确认且采用否定确认压缩策略(NAK Compression)的可靠组播传输协议成功传输组播数据包所需要的带宽较小,具备良好的可扩展性.     

电视与广播

TN93 02021600基千ACK和NAK的可靠组播传输协议的性能分析和比较/王斌,刘增基,李红滨,张冰(西安电子科大综合业务网国家重点实验室)11电子学报一2001,29(10)一1314一1318在目前各种可靠组播传轴协议的基础上,归纳构建了两类基本的可靠组播传输协议一基于确认(ACI勺的和基于否定确认(NAK)的可靠组播传输协议.在典型的组播网络系统模型基础上,对这两类协议以及一种主要的改进协议在占用网络带宽和可扩展性方面的性能恃点进行了定性的分析和比较.性能分析结果表明,基于否定确认且采用否定确认压缩策略(NAK Compression)的可靠组播传翰…     

SDN交换机及其星载交换的实现方案初探

随着互联网技术和应用的不断发展,网络中的新技术、新业务层出不穷,网络的复杂度越来越高。传统的卫星网络已难以满足高吞吐量、灵活多变的业务需求。针对传统卫星网络中的问题,业界提出在卫星网络引入SDN技术,实现软件定义卫星网络SDSN。对现有SDN交换机的实现方式进行归纳总结,针对卫星网络特殊环境分析卫星结点中SDN星载交换设备的系统功能,并提出一种基于OpenFlow协议的SDN星载交换机实现方案。     

MPLS网络中DiffServ组播算法

文章提出一种在多协议标签交换(MPLS)网络中边界路由器实现组播和区分服务的算法,该算法利用处于分支点的边界路由器之间的标签交换路径来传输组播数据包,同时引入了信息管理点,用于计算、管理和调整组播树,实现全域的服务质量.描述了算法的具体细节和实现原理,也评价了该算法的可行性和优越性.     

基于卫星网络的移动可靠组播技术

本文首先介绍了基于卫星网络的可靠组播的优势,然后详细讨论了移动可靠组播及卫星网络可靠组播所面临的新的问题,最后提出了卫星网络中移动可靠组播的解决方案。     

试验IP网组播丢包问题研究

IP组播技术实现了IP网络中点到多点的高效数据传送,因为组播能够有效地节约网络带宽降低网络负载,所以在实时数据传送和语音图像数据等诸多方面都有广泛的应用。由于传输环境、协议配置或端口流量等原因,在实际应用中可能会发生传输数据丢失的现象。针对组播传输丢包问题,分析了某类试验IP网络协议及组播传输环境特点,提出了几种解决方案并进行了试验验证。     

基于覆盖组播网络的实时视频传输方案的设计

本文设计了一种基于覆盖组播网络的流媒体传输系统,通过在网络中部署数据流转发中间服务器(intermediate server,IMS),构建一层覆盖组播网络,实现流媒体的应用层组播,提高数据传输效率,减少数据网络冗余;同时通过度和延时受限的路由算法,均衡网络流量;根据视频编码的特点,在应用层进行网络过滤,自适应调节视频发送码率,避免了网络阻塞,保证了流媒体的可靠传输.本系统部署简单,通过现场测试,达到了较好的效果.     

Transport protocols in multicast via satellite

In a wide variety of broadband applications, there is a need to distribute information to a potentially large number of receiver sites that are widely dispersed from each other. Communication satellites are a natural technology option and are extremely well suited for carrying such services because of the inherent broadcast capability of the satellite channel. Despite the potential of satellite multicast, there exists little support for multicast services over satellite networks. Although several multicast protocols have been proposed for use over the Internet, they are not optimized for satellite networks. One of the key multicast components that is affected when satellite networks are involved in the communication is the transport layer. In this paper, we attempt to provide an overview of the design space and the ways in which the network deployment and application requirements affect the solution space for transport layer schemes in a satellite environment. We also highlight some of the issues that are critical in the development of next generation satellite multicast services. Copyright © 2004 John Wiley & Sons, Ltd.     

A New Transport Protocol for Broadcasting/Multicasting MPEG-2 Video Over Wireless ATM Access Networks

Because of the telecommunications de-regulation act and progress in wireless technologies, we will see the co-existence of heterogeneous broadband access infrastructures in the broadband video service industry in the near future. In this paper, we addressed the error control issue when transmitting MPEG-2 video streams over wireless access networks for broadband video broadcast or multicast services. An end-to-end transport protocol based on ATM and wireless ATM technologies is proposed. For video services, the underlying transport network should be transparent and quality should be maintained uniformly over all the segments whether wireline or wireless links. For network resources to be used efficiently, error control should be applied locally on the wireless segments so as to avoid the excessive overhead over the reliable wireline portions. Because a broadband video broadcast or multicast service is a one-to-multiple point service, FEC is the most prevalent error control mechanism. Due to the important role of MPEG-2 control information in the decoding process, priority MPEG-2 control information has to be differentiated from MPEG-2 data information, and excess error protection has to be allocated to it in order to achieve satisfactory QoS. Therefore, a header redundancy FEC (HRFEC) scheme for error control is applied at the local distribution centers before the MPEG-2 encoded video streams are transmitted over the wireless channels. HRFEC is an FEC-based selective protection scheme, which allocates extra error protection to important control information. Simulation results show that the quality of the reconstructed video sequence is vastly improved by using HRFEC, when the channel condition is poor.     

Satellite Internet services using DVB/MPEG-2 and multicast Webcaching

Communication satellites can be used to broadcast large volumes of data directly to extensive user groups. With the latest generation of high-powered direct broadcast satellites and the changing traffic and usage patterns in the Internet, new ways of using satellites for delivering data directly to the end user have become viable alternatives to terrestrial point-to-point networks. In this article the software architecture of a distributed system, which has been successfully implemented and which supports online and offline interactive multimedia services, is presented. It is based on a method of carrying Internet datagrams over DVB/MPEG-2 transport systems, intended for digital television. It relies on a configuration using a broadband forward channel and a separate, usually narrowband, return channel. The forward link is usually provided by a geostationary satellite, whereas the return channel uses a different network technology, such as dialup connection, a direct Ku-band return link, a LEO satellite network, or an LMDS local distribution system. A generic multicast system is presented which exploits the inherent capabilities of satellites to reach a large number of customers. The reliable multicast strategy chosen is shown to handle multiple applications, each with different reliability and timing requirements     

On Multicast Routing for Wavelength-Routed WDM Networks with Dynamic Membership

Future broadband networks must support integrated services and offer flexible bandwidth usage. In our previous work in [1], we explored the optical link control (OLC) layer on the top of optical layer that enables the possibility of bandwidth on-demand (BoD) service directly over wavelength division multiplexed (WDM) networks. Today, more and more applications and services such as video-conferencing software and Virtual LAN service require multicast support over the underlying networks. Currently, it is difficult to provide wavelength multicast over optical switches without optical/electronic conversions although the conversion takes extra cost. In this paper, based on the proposed wavelength router architecture (equipped with ATM switches to offer O/E and E/O conversions when necessary), a dynamic multicast routing algorithm is proposed to furnish multicast services over WDM networks. The goal is to join a new group member into the multicast tree so that the cost, including the link cost and the optical/electronic conversion cost, is kept as low as possible. The same algorithm can be applied to other wavelength routing architectures with redefinition of electronic copy cost. The effectiveness of the proposed wavelength router architecture as well as the dynamic multicast algorithm is evaluated by simulation.     

Scalable architecture and evaluation for multiparty conferencing over satellite links

This paper describes the architecture of a proposed multiparty conferencing system for satellites. Different conferencing models are discussed and compared. A session initiation protocol (SIP)-based conference signaling model and an extension to protocol-independent multicast sparse mode that supports quality-of-service (QoS) in DiffServ networks are proposed, as particularly suitable for multiparty conferencing applications over satellite links. The paper also presents key issues and potential solutions of scalable QoS multicast services for multiparty conferences over satellite. End-to-end QoS parameters for voice and video are measured and analyzed on a prototype.     

TCP/IP enhancements for satellite networks

With the emerging market for high-mobility remote access broadband services, satellite networks are becoming increasingly popular. Although the ubiquitous TCP/IP protocol is widely used to provide reliable data delivery in terrestrial networks, it faces many challenges in satellite environments. These stem from the inherent features of satellite channels, such as large delays, increased error rates, and bandwidth asymmetry. To address these concerns, a variety of solutions have been proposed. These include direct TCP enhancements to better tune the TCP/IP stack and additional selective acknowledgment mechanisms. Other proposals use advanced interworking to reduce sensitivity to various channel features. Examples include multiple TCP sessions, link-layer interworking, and ACK control schemes. Improving onboard satellite features (buffer management, flow control) can also provide benefits for TCP/IP transport. The objective of this article is to present the various solutions and discuss their possible trade-offs. Overall, there exists a rich set of alternatives to meet the challenges in this important arena     

Key Management in Secure Satellite Multicast Using Key Hypergraphs

Satellite networks play an important role in today’s information age because they can provide the global coverage services. Information security is an important concern in satellite multicast communications, where eavesdropping can be performed much easier than the fixed terrestrial networks. In this work, a novel multicast key management scheme based on key hypergraph for satellite networks on a predefined communication scenario is proposed. We use logical key hierarchy and distributed-logical key hierarchy as reference models for performance comparisons. It is shown that the proposed multicast key management scheme is scalable to large dynamic groups and minimizes satellite bandwidth usage.     

Satellite ATM networks: a survey

Satellite ATM networks have significant advantages over terrestrial ATM networks. Satellites provide unique advantages such as remote coverage with rapid deployment, distance insensitivity, bandwidth on demand, immunity to terrestrial disasters, and offering broadband links. Satellite ATM networks will play an important role in the rapidly evolving information infrastructure. However, there are several obstacles which need to be overcome so that satellite ATM networks can operate in full service. The objective of this survey is to present the state of the art in satellite ATM networks and to point out open research problems. We explain the satellite ATM network architecture and cover the requirements and technical barriers for seamless integration of ATM and satellite networks. We describe the feasibility of the existing ATM cell transport methods, and deal with conventional and new satellite link access methods, and some error control schemes for the satellite environment. We then describe the problems of the proposed traffic and congestion control schemes, followed by the error performance of the Transmission Control Protocol (TCP) and Service-Specific Connection-Oriented Protocol (SSCOP) for the satellite ATM network. We present basic requirements and a possible architecture for local area-metropolitan area network (LAN-MAN) interconnection using satellite ATM and then discuss the requirements for multimedia services in satellite ATM networks     

多重业务的宽带承载

多重业务的迅速发展和其拥有的多媒体、互动等新特征，使宽带网络难以有效地实现统一承载，并进而成为多重业务发展的障碍。要实现在宽带网络中可运营、可管理、可增值地承载多重业务，需要全面采用新技术。在各种新技术中，高宽带的网络技术使网络资源更丰富；服务质量（QoS）技术实现多重业务的差异化服务，从而保证业务的服务质量；强大的组播技术有效地控制和保障多媒体业务的开展；安全保障技术为多重业务提供高质量、完善的安全运营机制；高可靠性技术为宽带网络承载多重业务提供可靠、不间断地运营机制。     

Multicast Broadcast Services Support in OFDMA-Based WiMAX Systems [Advances in Mobile Multimedia]

Multimedia stream service provided by broadband wireless networks has emerged as an important technology and has attracted much attention. An all-IP network architecture with reliable high-throughput air interface makes orthogonal frequency division multiplexing access (OFDMA)-based mobile worldwide interoperability for microwave access (mobile WiMAX) a viable technology for wireless multimedia services, such as voice over IP (VoIP), mobile TV, and so on. One of the main features in a WiMAX MAC layer is that it can provide'differentiated services among different traffic categories with individual QoS requirements. In this article, we first give an overview of the key aspects of WiMAX and describe multimedia broadcast multicast service (MBMS) architecture of the 3GPP. Then, we propose a multicast and broadcast service (MBS) architecture for WiMAX that is based on MBMS. Moreover, we enhance the MBS architecture for mobile WiMAX to overcome the shortcoming of limited video broadcast performance over the baseline MBS model. We also give examples to demonstrate that the proposed architecture can support better mobility and offer higher power efficiency.