Community Streaming With Interactive Visual Overlays: System and Optimization

Community streaming is an enhanced form of joint content viewing where a sense of community is reinforced by the addition of interactive visual overlays, controlled in real-time by viewers, on top of a shared video stream. As a concrete example, we describe a community video system called ECHO, where personalized avatars are overlaid on top of a real-time encoded video stream of an Internet game for multicast consumption. Recognizing that only the visual overlays are generated live, we propose schemes that encode and schedule the live and non-live portions of the overlaid video separately in order to exploit the difference in delay sensitivity of the two, leading to video streams that contain two sub-streams with different delay constraints. We show that, in the known channel case, a low complexity ldquoearliest deadline firstrdquo packet scheduling algorithm minimizes receiver buffer delay. We also analyze the case where multiple streams are multiplexed, which allows us to quantify the potential gains of allowing different delay constraints for different sub-streams. We show that a ldquowater fillingrdquo strategy maximizes the total number of streams that can be supported. Simulation results show that the bandwidth necessary to maintain low-latency for visual overlays is reduced by about 40% when our proposed sub-stream approach is used. For multiplexing of multiple streams, our approach can increase the number of supported streams (e.g., a 30% increase when around ten streams are multiplexed).     

延迟容忍网络中多Ferry路由设计及改进

针对延迟容忍网络多Ferry路由设计方案MRT-Tree中普通节点的缓存和能量消耗过多的不足之处,提出了星型拓扑多Ferry路由设计MRT-Star.新设计使用专用的缓存装置来取代普通节点作为转发节点,并改变了普通节点的分配方式和Ferry节点的交互方式.最后,通过数学计算和数学分析表明MRT-Star在不额外消耗普通节点的缓存和能量的同时,还能获得比MRT-Tree较低的数据传输延迟.     

车载自组织网络中基于定向传播的自适应路由协议

数据分组在转发过程中需要在其转发范围内寻找一个中继节点进行转发。为了降低转发过程中寻找中继节点的复杂程度,减少从源节点到达目的节点的平均跳数,提出了一种车载自组织网络中基于定向传播的自适应路由协议(Adaptive Routing Protocol Based on Directional Transmission,ARPBDT)。该路由协议有两个关键参数:转发角度和平均每跳前进距离。首先为了缩小转发范围,设置一个始终朝着目的节点方向的转发角度,以减少转发范围内的节点数以及寻找中继节点的计算量;其次为了减少平均跳数,在转发范围内根据前进距离自适应地选择较优或次优的邻居节点作为中继节点进行转发。仿真结果表明,与OBDR相比,所提路由协议的平均跳数较少,平均每跳前进距离较大,能够使数据分组快速地到达目的节点。     

基于P2P的流媒体点播系统中客户端缓存的研究

在Internet上提供大规模的VoD服务是一项具有挑战性的工作.首先提出一种基于P2P(peer to peer)方法的VoD服务体系PP_VoD,该系统通过在每个节点中开辟一段缓存空间来保存其最近所接收到的数据,以便为后续到达的节点提供服务,最后对该系统中客户端的缓存空间进行了详细的讨论.     

一种用于协作通信系统的频率同步算法

在协作通信领域中频率同步已成为研究的焦点之一。由于其系统特性,载波频率偏移（Carrier Frequency Offset,CFO）普遍存在。考虑了协作通信系统中的多频偏估计问题,提出了一种新的用于协作通信系统的频率同步算法ECR,通过中继节点在转发前进行频率再补偿,使得中继节点转发的信号的发送频率均与源节点的发送频率保持一致,继而目的节点的频率同步问题得以简化,同时系统不会随着中继节点的增多而变得复杂。仿真结果表明,所提出的同步方法在协作通信系统中可以取得较好的系统性能。     

软件定义网络中协同存储数据面快速转发

针对利用具备存储能力的网内节点进行协同存储需依据周边缓存状态快速转发数据包的问题,提出了一种数据面快速转发方法。该方法采用在交换机内对每一端口维护两个布隆过滤器（BF）的方式,实现在数据面对于周边缓存状态的维护;同时扩展了协议无感知转发指令,该指令直接查询BF,依据所查询结果,采用优化的转发流程转发数据包,实现依据周边缓存状态的快速转发。实验结果表明:依据控制器所维护状态进行转发在输入速率为80 Kb/s即达到性能瓶颈,而所提方法可在111 Mb/s时线速转发数据包,且转发效率略优于协议无感知转发原本的直接转发指令;所采用的BF维护的方式内存开销最多仅为流表项维护周边缓存状态方式内存开销的20%。在具备存储能力的软件定义网络（SDN）中,采用所提方法可在数据面维护周边缓存状态,提升协同存储依据周边缓存状态转发数据包的效率。     

水声传感网中基于网络编码的协作传输算法

为提高水下数据传输可靠性,本文在随机线性网络编码的基础上提出一种协作数据传输算法。首先,为源节点寻找数据转发链路,让数据通过多条链路进行转发;其次,使用网络编码方法对数据包进行编码,避免转发节点转发重复数据包;最后,对各个节点的数据包传输时隙进行调度,避免节点间信号冲突。仿真结果表明,本文提出的算法在一定程度上提高了网络信道利用率和数据传输可靠性,且具有较好的稳定性。     

机会网络中基于能量消耗的缓存管理策略

为了减少机会网络中节点的能量消耗,均衡各节点之间能量使用情况,延长网络寿命,提出基于能耗的缓存管理策略。在节点缓存空间有限的情况下,所提出的算法根据周围邻居节点能量的使用情况,动态调整节点用于缓存转发消息空间的大小,从而减少节点在存储-转发过程中的能量消耗。同时,为了避免传统休眠机制的能耗路由算法中由于目的节点休眠而导致消息投递失败的情况,引入了新的Inactive节点状态。实验仿真表明,与定时休眠机制的能耗算法比较,采用基于能量消耗的缓存管理策略能够使得机会网络中所有节点的整体能耗降低50%左右,并且节点之间能耗的标准差降低80%以上。     

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.     

SmartPeerCast: a Smart QoS driven P2P live streaming framework

The P2P swarm technologies have been shown to be very efficient for medium scale content distribution systems in the last few years, such as the file sharing and video-on-demand (VOD) applications. However it is still an open topic about how to deploy the P2P paradigm for the real time video broadcasting (RTVB) applications. The P2P RTVB application is different from the cache based P2P system because it has more stringent restrictions for startup time and packet loss ratio. In this paper, an adaptive media broadcasting P2P framework named SmartPeerCast which employs the media transrating service to control the quality of service (QoS), is proposed. SmartPeerCast achieves a network awareness, codec awareness, and high performance RTVB service with four key designs: (1) It groups the newly joined peers into different quality clusters by their uploading capability. This clustering mechanism avoids the bandwidth bottleneck between the heterogeneous peers of the overall P2P overlay by only forwarding the same quality stream over the peers in the same cluster. (2) The streaming quality is adjusted adaptively between the sending and the receiving peers by a Smart QoS algorithm to compensate for the network jitters to reduce the receiving peer’s playback jitter. (3) The receiving peer monitors the data forwarding QoS of the sending peer to select the best suitable parent node dynamically. The SmartPeerCast uses this Smart QoS framework to implement an incentive mechanism to award the peers with high uploading contributions by migrating them to a higher quality cluster. (4) A transrating engine is used at the leaf nodes of the high quality cluster to forward the stream with suitable bits rate to the nodes of the low quality cluster; this transrating service not only can fully utilize the uploading bandwidth of the peers in the higher quality cluster but also avoids the bandwidth bottleneck of stream forwarding between the heterogeneous peers. Our experiment results and the real deployment show that SmartPeerCast can eliminate the bandwidth bottleneck and content bottleneck between the heterogeneous peers with a smaller startup time and packet loss and it is a high performance and medium scale P2P RTVB framework.     

混合架构下多请求模式的缓存替换模型研究

针对多类型多访问模式应用的需求,在GDSF算法的基础上,引入平均访问间隔和最近访问间隔两个特性以增强算法的适应性;建立缓存结构模型,通过双关键字索引机制,快速索引缓存对象,降低系统开销;对超过一定大小的文件采取后缀预取策略以增加缓存中数据对象的个数.在课题应用背景下,与传统算法的对比实验表明,该方法能够减少缓存的平均请求等待时间,提高对象命中率和字节命中率,增强了缓存替换算法对多类型多请求模式应用的适应性.     

基于匿名通信的在线匿名秘密举报方案

为保护举报者的身份隐私（身份信息和位置信息）不被包含举报受理机构在内的任意组织获取,提出一种在线匿名秘密举报方案。匿名举报者借助公开密钥算法通过随机转发的方法将加密举报信息发送给举报受理机构,加密举报信息经过网络中一系列中转节点的转发最终到达举报受理机构,任何中转节点和攻击者不能获取举报信息的明文,包含举报受理机构在内的所有节点以及外来攻击者无法取得举报人的身份隐私,如举报信息属实,举报机构可以对举报者进行奖励,同时仍然保持举报者的身份和位置信息不会泄露给举报受理机构或者任意第三方。由于中转节点是随机选择的,不依赖于某些特定节点,从而保证系统的健壮性。实验结果表明,该方案能够支持大型网络中多个举报者顺利完成举报,系统不会出现平均响应时间随节点个数增加而急剧增长的现象,具有良好的可靠性和稳定性。     

Defending Against Buffer Map Cheating in DONet-Like P2P Streaming

Data-driven Overlay Network (DONet)-like P2P system is especially suitable to support live stream applications, since its data structure can tolerate node dynamics quite well. However, optimal streaming demands the cooperation of individual nodes. If selfish nodes cheat about their buffer maps to reduce the forwarding burden, the overall streaming quality would be negatively affected. To defend against this kind of cheating, we design a trustworthy service-differentiation based incentive mechanism with low complexity in this paper. The mechanism is composed of the service-differentiation algorithm and the contribution-evaluation algorithm. Compared with other studies in this area, the primary characteristic of our mechanism lies in two aspects. Firstly, the contribution of each node is evaluated considering the features of live streaming, not just by the transferring bytes. Secondly, the potential cheating behavior of overlay nodes during the fulfillment of incentive algorithms can be avoided, which is usually not considered by other similar studies. Extensive simulations suggest that the algorithms are indeed effective for defending against buffer map cheating in DONet-like P2P streaming.      

基于RTP／RTCP的音视频同步方法研究

分析音频和视频同步的标准以及造成音视频不同步的原因,提出一种基于RTP／RTCP协议的音视频同步控制方法。以音频为主媒体,视频为从媒体,在接收端通过设置缓冲区实现音频流的媒体内同步,通过比较音视频数据包的时间戳判断同步关系,对视频采取重复或丢弃的方法实现音视频同步控制。在实验环境下模拟音视频流经网络传输后在接收端经过同步控制后播放和直接播放两种情况,表明,提出的同步方法能很好的纠正音视频不同步的现象。     

Integrating Fine-Grained Message Passing in Cache Coherent Shared Memory Multiprocessors

This paper considers the use of data prefetching and an alternative mechanism, data forwarding, for reducing memory latency caused by interprocessor communication in cache coherent, shared memory multiprocessors. Data prefetching is accomplished by using a multiprocessor software pipelined algorithm. Data forwarding is used to target interprocessor data communication, rather than synchronization, and is applied to communication-related accesses between successive parallel loops. Prefetching and forwarding are each shown to be more effective for certain types of architectural and application characteristics. Given this result, a new hybrid prefetching and forwarding approach is proposed and evaluated that allows the relative amounts of prefetching and forwarding used to be adapted to these characteristics. When compared to prefetching or forwarding alone, the new hybrid scheme is shown to increase performance stability over varying application characteristics, to reduce processor instruction overheads, cache miss ratios, and memory system bandwidth requirements, and to reduce performance sensitivity to architectural parameters such as cache size. Algorithms for data prefetching, data forwarding, and hybrid prefetching and forwarding are described. These algorithms are applied by using a parallelizing compiler and are evaluated via execution-driven simulations of large, optimized, numerical application codes with loop-level and vector parallelism.     

Maximum data delivery probability-oriented routing protocol in opportunistic mobile networks

Some recent studies utilize node contact patterns to aid the design of routing protocol in Opportunistic Mobile Networks (OppNets). However, most existing studies only utilize one hop contact information to design routing protocol. In order to fully utilize nodes’ collected contact information to improve the performance of data forwarding, in this paper we focus on exploiting node contact patterns from the multi-hop perspective. We first give the definition of opportunistic forwarding path, and propose a model to calculate the maximum data delivery probability along different opportunistic forwarding paths. Second, based on the maximum data delivery probability, we propose a novel approach to improve the performance of data forwarding in OppNets based on two forwarding metric. The proposed forwarding strategy first manages to forward data copies to nodes have higher centrality value at the global scope. Afterwards, maximum data delivery probability to the destination is evaluated, to ensure that data is carried and forwarded by relays with higher capability of contacting the destination. Finally, extensive real trace-driven simulations are conducted to compare the proposed routing protocol with other existing routing protocols in terms of delivery ratio and delivery cost. The simulation results show that our proposed routing protocol is close to Epidemic Routing in terms of delivery ratio but with significantly reduced delivery cost. Additionally, our proposed routing protocol outperforms Bubble Rap and Prophet in terms of delivery ratio, and the delivery cost of our proposed routing protocol is very close to that of Bubble Rap.     

基于PTS的视频流集群同步显示技术

针对集群大屏拼接显示系统各节点机独立解码、视频流显示不同步的问题,本文分析了集群拼接显示系统的特点,提出了利用PTS信息实现集群内各节点机同步显示视频流的机制,研究了组播接收模块、Ts流拆包模块、视频解码模块和同步控制模块和拼接屏显示模块等视频流同步显示实现技术．研究试验结果证明了基于PTS的视频流集群同步显示技术的有效性．     

An advertisement-based peer-to-peer search algorithm

Most of the existing search algorithms for unstructured peer-to-peer (P2P) systems share one common approach: the requesting node sends out a keyword search query and the query message is repeatedly routed and forwarded to other peers in the overlay network. Due to multiple hops involved in query forwarding, the search may result in a long delay before it is answered. Furthermore, some incapable nodes may be overloaded when the query traffic becomes intensive or bursty.