Dynamic retransmission control for reliable mobile multicast

Most existing multicast protocols adopt a static retransmission scheme(unicast or multicast) to retransmit lost packets.In the mobile multicast environment,static multicast retransmission mode may lead to congestion in the receivers‘ wireless interfaces,while static unicast mode may result in great network load.Both static unicast and multicast retransmission modes will cause a performance loss.This paper logically divides the mobile multicast network into fixed and mobile parts,and focuses on the mobile part.Then this paper analyzes the retransmission costs when multicast or unicast mode is chosen.Two main parameters are used to compare their efficiencies:the average air-interface utilization of each receiver and the average network load.Based on the results of analysis,two new algorithms,called NLPA(Network Load Priority Algorithm)and AUPA(Air-interface Utilization Priority Algorithm)are presented.Finally,simulation results conclude that,with proper parameters,both NLPA and AUPA can dynamically alternate between unicast and multicast retransmission modes acording to the conditions of network and receiver,and avoid congestion in receivers‘ wireless interfaces as well as great network load,with a better use of network and terminal resources.     

Reliability analysis of a data transmission model for multicast

As computer systems have been widely used, Internet, which is a network-of-network, has been greatly developed and rapidly spread all over the world. In addition to unicast transmissions of point-to-point, multicast transmissions of one-to-many and many-to-many have been recently used. This paper considers a stochastic model where data are transmitted through multicast. The data are divided into n packets at a transmission server, and their packets are transmitted successively to each receiver of multicast group. Positive (ACK) or negative (NAK) acknowledgements are returned from each receiver, by depending on whether he or she has received all packets, correctly or not. When the server has received NAK, retransmissions only for receivers with NAK are made. The mean time until the data transmission succeeds is analytically derived and an optimal policy which maximizes the throughput is discussed. Finally, numerical examples are given under suitable conditions.     

基于网络编码和多访问点协作的视频多播方案

随着智能手机和平板等无线设备的普及,基于互联网的视频浏览成为无线设备的重要功能。然而,由于无线网络的链路间存在干扰、可靠性较低,为了提高视频多播传输的可靠性,文中分析了覆盖区域发生重叠的访问点间相互协作对于提高系统增益和系统公平性的作用,提出一种基于网络编码和多访问点协作的视频多播方案。该方案首先将每个视频划分为大小相同的报文段,并利用RLNC机制对每个段的报文进行编码。然后以使用户接收到的报文数量的期望值最大化的同时,实现公平调度为目标,考虑了访问点间的完全干扰和非完全干扰两种模型,将访问点间的传输范围发生重叠时的视频多播问题建模为线性规划优化问题,提出了双阶段启发式算法来进行求解,该算法通过利用多个访问点来获取空间和时间分集增益,提高了数据传输的可靠性,通过允许发生干扰的访问点并行传输数据,提高了系统效用。最后的仿真实验也验证了本文方案在接收报文总量、解码报文数量和公平性方面的有效性。     

Genetic fingerprinting for copyright protection of multicast media

Generally speaking, comparing to the unicast or broadcast methods, it is more efficient to transmit multimedia data via the multicast method to massive users. However, the ease of delivery of multimedia data may cause the copyright of such multimedia to be easily infringed upon, and the fingerprinting scheme is one of effective means for conquering this problem. Fingerprint embedding process often generates the multimedia contents into many different versions, which have to be transmitted via the unicast method. In this paper, we propose a new genetic fingerprinting scheme for copyright protection of multicast video. In this method, the encryption and decryption keys, which aim at scrambling and descrambling multimedia contents, are first produced with genetic algorithms. Next, multimedia data are then encrypted and multicast to all users. At the same time, a secure channel is employed to unicast a designated decryption key to each user. When a user deploys the designated key to decrypt the received data, a corresponding fingerprint would be embedded into the contents. Once upon the reception of the fingerprinted multimedia content, the embedded fingerprint can be extracted shortly, and the copyright can be confirmed and assured. Experimental results demonstrate that the proposed method can transmit multimedia data to clients effectively and cause only a slight degradation in perceptual quality.     

IPv6视频网格中基于用户端的网络性能测量

在具有服务质量保证的IPv6视频网格系统中,视频数据采用TCP协议传输。该文根据TCP协议传输的特点,采用基于客户端的被动测量技术,实现了对用户实际获得的视频流网络性能参数延迟、带宽、抖动的测量,提出了迟到包率的概念和计算方法。     

基于集成FEC和层次传输的可靠组播的流控技术

端系统能力和网络带宽的异构性给大规模组播的流控带来很大困难。本文将前向纠错（ＦＥＣ）技术与层次传输相结合,较好地解决了异构环境下可靠组播的流控问题。我们给出了传输调度和信道速率分配的算法,讨论了差错控制问题。性能分析和模拟表明,该方法对大规模、异构组播组可显著减少平均传输时间并且有效地利用网络带宽。只需较少数目的组播组就能得到性能的很大提高。软件ＦＥＣ编码器的速度能够匹配当前的网络条件,算法易于实     

一种基于遗传算法有时延约束的选播路由算法

选播是一种新型的网络服务，是IPv6的一个新特性。与单播、组播一样，都是IP的一种通信模式。本文在分析选播通信服务的基础上，提出了一种改进的遗传算法以求解有时延约束的选播路由问题。仿真实验结果表明，该算法是有效且切实可行的。     

OPNET环境下的PIM—SM组播路由协议仿真

IPv6组播技术作为下一代互联网的核心技术之一,相对于IPv4组播技术具有更大的优越性。文章首先对PIM-SM组播协议在IPv6上实现PIM-SM涉及的问题进行了论述,然后在OPNET网络仿真模型中实现了对IPv6和IPv4混合网络场景的配置,进行组播的仿真实验比较单播与组播网络的性能,系统地分析了PIM-SM协议在OPNET中的实现。     

Novel association control strategies for multicasting in relay-enabled WLANs

Multicast is a fundamental communication service in Wireless Local Area Networks (WLANs). Unfortunately, multicast packets are transmitted at the base rate needlessly, which prevents rich multimedia contents from being delivered to users. To this end, a number of prior studies have proposed to increase multicast capacity whereby an Access Point (AP) transmits at the highest data rate that can be decoded by all subscribers. Another approach is by controlling subscriber-AP associations such that a given objective, e.g., AP load, is met. Moreover, they have also proposed using relays to help boost stations with weak channel condition. In this paper, we propose an approach that exploits association control, high number of APs and relays simultaneously to improve the performance of multicast in WLANs. We show that the problem is NP-hard by reducing it from the Maximum Coverage with Group Budget (MCG) problem. We then propose a number of heuristics that consider two types of relays: non-subscribers and subscribers. The former are stations that are not part of any multicast groups whereas the latter comprise of stations that are actively receiving multicast packets. Our extensive simulation studies with varying APs, station numbers, and multicast transmission rates show the efficacy of our heuristics in reducing the average and maximum AP load, and are able to support a higher number of users at high multicast rates. Specifically, they result in up to 83% reduction in AP load, and support up to 17% and 53% more users in low and high rate multicast scenarios respectively.     

高效的动态组播群通信认证签字方案

由于组播群组的动态性和数据传送的不可靠性,相对于点到点通信,组播通信的安全认证更为复杂.在组播数据发送源认证问题中,签字的速度和长度是实现认证的主要障碍.为了解决这个问题,通过引入新的认证技术——认证矩阵,提出了一个有效的适用于大数量动态的群组和不可靠数据传送的组播认证签字方案.相对于目前的组播包认证方案,该方案可显著地降低签字长度,提高签字速度,并可提供不可抵赖服务,可应用于如多媒体数据传输、多方会议以及远程教育等广泛的应用领域.     

基于IP组播的告知服务器的以太网实现

同步协作是计算机支持的协同工作研究的一个重要领域,告知服务器为群组的同步协作提供了感知的实现技术,告知服务要求有效地向群组用户投递事件消息。ＩＰ组播技术是 服务 通讯技术,被广泛用于视音频群组通信,但目前许多告知服务器实现仍然采用点对 通信技术,在多媒体远程协作系统中,直接利用ＩＰ组播技术实现了可靠的告知服务,并初步分析了ＩＰ组播在以太网络上的实现方式和实现可靠笥的条件。     

A cross-layer approach for multiuser multiplexing on IP mobility

In general, content distribution and multicasting can be implemented from proxies and gateways in the network on a static host in wired/wireless network environments. However, if an end point host moves to different wireless access networks, it will have a problem in many situations. For example, consideration of contents like the level of required service quality for network search, handoff, connection and call time, and caching and load balancing is necessary. Unlike previous studies, this article analyzes additional costs related to Fast Handover and compares the performance of group of pictures and data transmission delay time. For this, first, the total additional cost was divided into signaling cost and packet transmission cost, and results of the comparison calculated for video data transmission delay time and traffic overhead are presented. This article proposes service quality improvement methods by acquiring multiuser channel state information for multicast video-streaming transmission with a method implemented between network layers. Channel state information of each user in the multicast group is used as information for the transmission of multicast packets. Thus, through simulation like real-time traffic, the optimum traffic transmission state is maintained. As a result of the simulation, we found that video-streaming service performance for multicast users improved by applying the approach method between layers. This article proposes optimization methods of a cross-layered approach for wireless network multimedia communication systems and video-streaming application services.     

Impact of device unavailability on the reliability of multicast transport in IEEE 802.11 networks

Multicast transport is an efficient solution to deliver the same content simultaneously to many receivers. This transport mode is mainly used these days to deliver real-time video streams. However, multicast transmissions support over IEEE 802.11 networks does not provide any feedback policies, which implies a definite loss of missing packets. This impacts the reliability of the multicast transport and the application employing it. An alternative to improve the reliability of multicast streaming over 802.11 networks is to prevent packet losses. In this perspective, it is necessary to identify the loss causes and to perform the required prevention actions. It is well known that collisions and path loss are two fundamental sources of transmission failures. Their impact can be eliminated by means of collision prevention and data rate adaptation. However, several works show that the loss rate of multicast packets may be considerable even in collisions-free environments and using an appropriate transmission rate. Particularly they show that losses may have a bursty nature which does not correspond to the bit error rate model of the PHY layer as defined by the chipset manufacturers. Therefore, in this paper, we carry out a thorough investigation of the loss causes in wireless networks. We show that device unavailability may be the principal cause of the significant packet losses that occur and their bursty nature. Particularly, our results show that the CPU overload may incur a loss rate of 100%, and that the delivery ratio may be limited to 35% when the device is in the power save mode.     

IETF softwire unicast and multicast framework for IPv6 transition

IPv6 protocol plays an important role in the next generation of Internet （NGI）. It is expected that the elegant coexistence of IPv4 and IPv6 is the key point of IPv6 transition. To solve the transition problem, we propose a mesh unicast framework and a multicast framework in this paper. We describe two reference models for the mesh unicast framework, and put forward two potential solutions for the multicast framework. A Linux-based prototype is implemented for IPv4 over IPv6 scenario and a test bed is deployed with 8 nodes on CERNET2. The deployment demon- strates the advantages of the framework.     

Interest-suppression-based NDN live video broadcasting over wireless LAN

Named data networking (NDN) is a new Internet architecture that replaces today’s focus on where – addresses and hosts with what – the content that users and applications care about. One of NDN’s prominent advantages is scalable and efficient content distribution due to its native support of caching and multicast in the network. However, at the last hop to wireless users, often the WiFi link, current NDN implementation still treats the communication as multiple unicast sessions, which will cause duplicate packets and waste of bandwidth when multiple users request for the same popular content. WiFi’s built-in broadcast mechanism can alleviate this problem, but it suffers from packet loss since there is no MAC-layer acknowledgement as in unicast. In this paper, we develop a new NDN-based cross-layer approach called NLB for efficient and scalable live video streaming over wireless LAN. The core ideas are: using WiFi’s broadcast channel to deliver content from the access point to the users, a leader-based mechanism to suppress duplicate requests from users, and receiver-driven rate control and loss recovery. The design is implemented and evaluated in a physical testbed comprised of one software AP and 20 Raspberry Pi-based WiFi clients. While NDN with multiple unicast sessions or plain broadcast can support no more than ten concurrent viewers of a 1Mbps streaming video, NDN plus NLB supports all 20 viewers, and Received December 29, 2015; accepted April 28, 2016 E-mail: zhxp@tsinghua.edu.cn can likely support much more when present.     

基于混合式分级流标签的IPv6组播通信

IPv6网络协议引入流标签概念,在路由器转发提供QoS支持。针对IPv6多媒体组播通信的需要,提出一种混合式流标签分级定义方案实现IPv6组播通信的QoS支持,在IPv6实验网上进行多媒体组播通信模拟测试,结果表明该方案能够提供满意的QoS支持。     

基于免疫算法的分层覆盖组播技术研究

为了克服传统的实时流媒体数据单播I、P组播等传输方式浪费网络带宽,甚至导致服务器过载的缺陷,提出了基于免疫算法的覆盖网络应用层组播树的构建方法。该方法以节点间网络延迟和节点的度作为约束条件,采用免疫算法划分组播岛、找出使整个系统"花费"最小的组播服务节点,实现了组播服务节点的全局最优选取。仿真结果表明,该方法有效可行,较采用传统的遗传算法具有更快的收敛速度和更高的搜索能力。     

IPv 6 下视频组播系统的设计与实现

介绍了IPv6组播技术特点及原理,并根据下一代网络的特点,给出了在下一代网络中部署IPv6组播服务的设计思路,利用IPv6组播技术和流媒体技术构建了一个基于IPv6的视频组播系统,经测试组播视频流畅,实现了视频的IPv6组播应用。