基于多个网络接口的DASH系统设计与实现

对基于HTTP协议的动态自适应流媒体来说,客户端可以根据不同的网络状况自适应地调整请求的视频比特率。当前DASH的研究主要集中于单链路的比特率切换算法的设计。而考虑到移动终端拥有多个网络接口以及短视频的播放流行度,开发一个基于LTE/Wi-Fi的多接口DASH系统——PASM(Predictive Adaptive Streaming system over LTE/Wi-Fi Multiple access networks)。PASM从两个互补方面提高了DASH性能,一方面,减少了由于两条链路异构性造成的视频块的乱序到达,充分利用两条链路的带宽之和进行DASH传输,提高了请求视频的质量;另一方面,在剩余请求视频时长不多时,采用一种更加激进的视频比特率请求算法,减少了带宽的不充分利用,提高了视频的平均比特率。实验结果表明,在各种链路带宽差异的网络下,PASM保证了视频比特率的平滑切换,同时提高了视频平均比特率。     

基于模数的WiMAX网络高负载自适应冲突解决算法

根据现有的部分研究结果发现,IEEE 802.16标准中使用的截断二进制指数后退算法在解决网络冲突时效率很低;并且当网络的负载增多时,该算法的运行性能更差.在此基础上,提出了一种基于模数的自适应冲突解决算法来优化WiMAX网络的冲突解决过程.该算法将所有用户站按照当前时间帧内的传输机会数量分为多个小组,并且要求用户站只能通过特定的传输机会发送请求.与此同时,为了保证整个网络的高性能,本算法要求基站和用户站根据上一轮请求过程中的平均冲突概率和传输机会使用率来调整当前时间帧内的传输机会数量,以及挑选部分用户站参与带宽请求,保证了WiMAX网络在高负载情况下的运行性能.模拟结果表明,本算法在WiMAX网络运行过程中能够较好地解决请求过程中的冲突,对网络性能提高较大.     

基于贡献度的自适应P2P流媒体数据调度算法

在P2P流媒体系统中,数据调度算法是决定视频播放质量和系统性能的核心部分。针对当前P2P流媒体数据调度算法未能考虑节点带宽和服务能力的差异,从而造成对系统资源利用不充分的问题,提出一种基于贡献度的自适应(CBA)流媒体数据调度算法。算法定义节点贡献度来衡量节点的数据上传和可用带宽情况,预先向部分节点传输准备数据。并根据数据块优先级、带宽估计情况和节点贡献度等信息进行自适应调整,确定数据块请求的提供方和次序。仿真实验表明,CBA算法能充分地利用节点可用带宽,降低流媒体的启动延迟和服务器负载,改善系统的整体性能。     

支持多集群数据并行的On-demand文件传输算法

数据密集型应用通常需要在广域网分布式共享计算环境中高效地传输海量数据。并行处理中,大量的数据需要在生成集群、存储集群、处理集群间进行传输。针对该传输问题提出了一个支持多集群数据并行传输的按需文件传输算法(On-demand File Transfer),该算法以批量传输请求的整体完成时间最小为目的,根据集群内部快速传输的特点,实现目的端并行,分散单个节点的传输负载;在传输路径上,采用多重路径和多跳路径分割方法实现并行传输。对于批量传输请求,依据每个请求的传输负载,全局按需分配带宽,以解决传输路径的带宽冲突,从而充分利用当前网络带宽,快速传输批量传输请求。     

基于MPEG视频流的动态带宽分配算法

ATM是兴起的宽带网标准,基于报文的视频正是宽带网上的一个典型应用.变位率视频的传输方法为恒定的视频质量提供了可能,但是在传输过程中,报文的丢失、延迟和延迟抖动等因素都会影响视频质量,因此有必要提供QoS保证.提出了两种新的在ATM网上进行MPEG视频传输的动态带宽分配算法,一种是动态计算算法,另一种是动态虚拟缓存算法.在这些算法中,根据允许的丢包率,动态地调整MPEG视频带宽以保证QoS.     

一种应用于DVB-RCS卫星通信系统的存储优化带宽请求算法

DVB-RCS 卫星通信系统中,已有的带宽请求算法多注重于队列延迟以及带宽利用率等性能的提高而未考虑卫星终端的存储优化针对此问题,提出了一种应用于 DVB-RCS 卫星通信系统的存储优化带宽请求算法,该算法通过预测到达数据流的容量来实现对发送队列中数据总量的控制,同时兼顾对传输时延以及传输效率的平衡。仿真表明,该算法能够合理控制系统的存储容量,并且在优化带帘利用率、控制时延抖动等方面与已有算法相比具有同样的高性能.     

基于Donet的P2P流媒体直播优化调度算法

为了提高P2P流媒体系统的整体性能,改善节点的播放质量,针对现有调度算法启动延迟大和节点带宽利用率不高问题,提出了一种可动态调节各节点中待请求紧急数据的流媒体直播优化调度算法(LOSA).该算法不仅考虑了流媒体直播的时间特性,同时还考虑了如何减少紧急数据请求的等待时间以及对Peer节点上传带宽的充分利用.实验结果表明,LOSA算法缩短了终端用户观看视频的延迟,提高了媒体流的连续性.     

WLAN与EPON融合接入网上行带宽分配算法

为了提高带宽的利用率,提出一种WLAN与EPON融合接入网上行带宽分配算法。该算法将无线终端接入的业务分为不同的服务等级,以实现不同业务Qo S保证。首先,ONU-AP给各个无线终端STA分配带宽,采用IEEE 802.11E协议的简单调度算法给语音业务和一般数据业务分配带宽,利用视频流的平均速率估算视频业务的传输带宽。其次,光线路终端OLT给各个ONU-AP分配带宽,OLT根据语音业务速率和当前视频业务流量分别估算语音、视频业务在下一个轮询周期的带宽,并将剩余带宽在重负载终端中二次分配,最后给一般数据业务分配带宽。通过仿真实验,结果表明:与传统算法相比,该算法的网络时延和丢包率明显降低,实现了带宽资源的合理分配。     

WiMAX网络中基于优先级的视频分组调度算法

无线视频传输是网络传输的研究热点,在WiMAX网络中,实时轮询业务(rtPS)的典型应用是实时视频传输,当前使用较多的是先进先出(FIFO)和最早到达期限数据优先(EDF)队列调度算法,其中EDF算法多用于多业务之间的资源分配,而非单个业务流队列的出对调度。在视频优先级以及WiMAX网络为单个视频流分配带宽限定的条件下进行调度算法的研究,以期待在带宽有限的情况下得到更高的视频服务质量。     

基于视点预测的全景视频码率自适应策略

为解决全景视频传输中存在的视频卡顿多、用户体验质量（quality of experience,QoE）低等问题,研究当前主流的视点自适应传输方案,提出一种基于视点预测的码率自适应策略（VPBAS）。首先,构建了一种基于长短期记忆网络和全卷积网络的视点预测模型,模型将视点数据和视频显著性信息进行特征融合,实现不同模态数据的相互补充和修正,提高视点预测的准确率;然后,客户端采用随机森林算法预测当前的可用带宽,并根据视点预测结果和可用带宽信息为视频分块选择码率。最后,客户端把选择的码率信息定期发送给服务器,服务器根据反馈的信息向客户端推送最佳码率的全景视频流,这种交互过程在视频播放期间不断地重复,直至客户端观看完毕。实验结果表明,与现有传输方案相比,VPBAS能有效提高带宽受限情况下的视频观看体验。     

An efficient delay-constrained ARQ scheme for MMT packet-based real-time video streaming over IP networks

The MPEG has recently Querydeveloped a new standard, MPEG media transport (MMT), for the next-generation hybrid media delivery service over IP networks considering the emerging convergence of digital broadcast and broadband services. On account of the heterogeneous characteristics of broadcast and broadband networks, MMT provides an efficient delivery timing model to enable inter-network synchronization, measure various kinds of transmission delays and jitters caused by the transmission delay, and re-adjust the timing relationship between the MMT packets to ensure synchronized playback. By exploiting the delivery timing model, it is possible to accurately estimate the round-trip time (RTT) experienced during MMT packet transmission. Based on the measured RTT, we propose an efficient delay-constrained automatic repeat request (ARQ) scheme, which is applicable to MMT packet-based real-time video streaming service over IP networks. In the proposed ARQ scheme, the receiver buffer fullness at the time of packet loss detection is used to compute the arrival deadline, which is the maximum allowed time for completing the requesting and retransmitting of the lost MMT packet. Simulation results demonstrate that the proposed delay-constrained ARQ scheme can not only provide reliable error recovery, but it also achieves significant bandwidth savings by reducing the number of wastefully retransmitted packets that arrive at the receiver side and exceed the allowed arrival deadline.     

基于Linux的网络直播平台设计与实现

不同带宽用户对流媒体直播服务器的音频/视频质量有不同需求,为此,设计并实现一个基于Linux平台的网络直播平台。该平台采用MPEG4IP编码库的方法实现MPEG4软编码,利用实时传输协议传输数据的方法实现客户端直播请求,通过调用简单媒体接口库的方法实现视频在Linux平台的显示播放。实验结果证明,该网络直播平台传输效果较好,并且其稳定性和负载均衡性均达到设计要求。     

视频编码中考虑模式选择的位率优化控制

本文在传统位率控制方法的基础上提出一种新算法,即基于宏块的最佳位率控制算法．主要思想是在考虑还宽,比特率和缓冲区大小的同时,考虑不同宏块模式的选择对位率的影响,文中给出了一些相关结果并将其与传统方法所得数据相比较,结果表明在多数位率条件下用本算法得到的ＰＳＮＲ比传统方法要好．     

Adaptive bandwidth allocation based on playback tunnel to support video on demand service over ATM networks

This paper focuses on adaptive bandwidth allocation (ABA) for transporting pre-stored VBR compressed video data across networks in support of video-on-demand (VoD) service. Two key issues are addressed. Firstly, a simplified dynamic programming method based on playback tunnel is proposed to predict the bandwidth which can be dynamically allocated for transporting video segment to guarantee that the playback buffer neither underflows nor overflows. Secondly, ABA schemes with different criteria including middle-tunnel ABA (MT-ABA) and reduced-bandwidth-variability ABA (RBV-ABA) are investigated. The proposed ABA schemes are evaluated by a set of real-life MPEG video traces. The obtained results show that the RBV-ABA scheme outperforms MT-ABA scheme in terms of peak rate, traffic burstiness and bandwidth variability. On the other hand, the MT-ABA scheme is more significant for avoiding the playback buffer overflow or underflow than that of RBV-ABA.     

Enhancing aggregate QoS for video streaming

The IETF's Differentiated Services architecture is designed to provide different types or levels of service for Internet traffic. One of its key features is that traffic flows are aggregated so that routers in the core network only need to distinguish a relatively small number of aggregate flows, even if those flows consist of hundreds or thousands of individual flows. However, network-level QoS differentiation may not satisfy the requirements of many QoS-sensitive applications such as live video streaming, where end-to-end delay and reliability must be guaranteed.

This paper investigates application-level service differentiation for MPEG video streaming in a Diff-Serv-aware MPLS network infrastructure, along with routing support at the network layer. Based on the fact that MPEG video has become one of the most popular formats for Internet (wired and wireless) users, our approach enhances aggregate QoS for video streaming by employing existing application-level knowledge of the MPEG video structure; therefore it requires neither a new video compression algorithm nor additional bandwidth. Several MPEG video dispersion models are proposed and analyzed. Simulation results show that two such strategies are superior to the other tested. In addition, a new routing scheme is proposed to support searching the ‘best’ paths for efficient multi-path video streaming. Through extensive simulations, we demonstrate that our approaches improve the aggregate QoS of MPEG video streams, as well as overall network efficiency.     

A fuzzy control scheme for video transmission in Bluetooth wireless

This paper is concerned with transmission of Moving Picture Expert Group (MPEG) video over a Bluetooth wireless network using a fuzzy approach. MPEG Variable Bit Rate (VBR) video sources suffer from long delay and excessive loss due to the sudden bursts in bit rate. Constant Bit Rate (CBR) encoding scheme may work well for a network with a guaranteed bandwidth. However, a Bluetooth channel is subject to wireless interference and can never guarantee a constant bandwidth. Subsequently, it is impossible to transmit a CBR video over Bluetooth wireless without data loss or image quality degradation. To resolve this problem, a fuzzy control system is introduced at the Host Controller Interface (HCI). The system consists of a traffic-shaping buffer whose role is to prevent excessive back-to-back cells being generated during the peak transmissions of MPEG video sources. The output bit rate of the traffic-shaping buffer is controlled by a fuzzy controller to ensure that the video stream from the host conforms to the traffic condition of the Bluetooth channel. Another fuzzy controller regulates the average arrival bit rate to the traffic-shaper to guarantee that the buffer is neither full nor empty. Computer simulation results demonstrate that the use of the fuzzy controllers reduces excessive data loss at the HCI as compared with an open loop VBR/CBR video transmission in Bluetooth.     

VoD系统中基于优先级的准入控制和带宽分配策略

本文针对VoD系统中不同客户对视频服务质量的不同要求,提出一种基于优先级的准入控制和带宽动态分配策略。在准入控制时,综合考虑请求的优先级和并发流占用的实际带宽等因素,在保证为高优先级请求预留较多固定带宽的同时提高并发流个数;在服务过程中,根据优先级和网络状况动态调整每个流的带宽,使丢包率低于一定的阈值,并保证在相同的网络状态下为高优先级请求提供较高的视频服务质量。     

一种无线实时流媒体增强型自适应FEC控制机制

无线网络动态的信道特性和带宽有限等特点,使得在无线环境下为流媒体应用提供QoS保证面临更大的挑战。提出一种用于无线实时流媒体传输的增强型自适应前向纠错控制策略,以提高接收方的播放质量。该策略采用跨层设计的方法,根据当前的网络状态,自适应地调整MPEG视频帧的发送速率,在视频源数据和冗余数据之间动态分配网络带宽。仿真结果表明,该策略能使接收方获得最大的可播放帧率,有效提高流媒体传输的可靠性和实时性。     

Low cost pre-stored video transmission across networks

This paper proposes a simple, practical and low-cost dynamic segmentation and bandwidth allocation scheme, called middle point, to transmit pre-stored video from source to playback destination across networks. The proposed scheme is based on two concepts, playback tunnel and bandwidth tunnel, to determine the segmentation boundary and transmission bandwidth with the objective of reducing transmission cost while guaranteeing the playback buffer neither underflows nor overflows. The performance of the proposed scheme is evaluated by a set of real-life MPEG video traces and also compared with the well-known optimal smoothing scheme. The obtained results show that the proposed scheme can be easily implemented with low complexity and low transmission cost.