信息中心网络内数据重传算法的优化

对于信息中心网络（ICN）中原始数据恢复机制的网络带宽利用率低下的问题，提出一种基于网络编码的实时数据重传（NC-RDR）算法。首先，根据网络的实时状态对网络中丢失的数据包进行统计；然后，将网络编码结合到信息中心网络中，对统计的丢失的数据包进行组合编码；最后，将编码后的数据包重传发送给接收端。对提出的方案进行分析，仿真结果表明，与基于网络编码的多播数据恢复（NC-MDR）算法相比，在传输带宽（平均传输次数）方面，降低了约30%，因此，在信息中心网络中，该算法能有效地减少网络重传次数，提高网络传输效率。     

多描述编码与网络编码在无线传感器网络中的应用

多描述编码可以有效地防止图像数据的丢失,防止对单份数据的依赖,保证接收端收到图像的质量。网络编码可以有效提高网络带宽利用率。为了适应数据在无线传感器网络中的可靠传输,并节省网络的带宽,提出将多描述编码与网络编码相结合的思想,以多条路径传输为基础,将其应用在无线传感器网络中。     

基于RTP的MPEG-4视频监控系统的设计

简述了MPEG-4标准的特性和RTP/RTCP协议的概念,详细说明了将MPEG-4码流映射到RTP净荷的方法,最后在此基础上提出了一种基于网络的远程视频监控系统的设计方案.该方案首先给出了系统的设计框架,然后分别阐述了发送端和接收端的具体实现流程.实验结果表明,采用RTP/RTCP协议传输MPEG-4码流能有效利用网络带宽,并且图像质量有较大的提高.     

基于缓冲技术的网络带宽自适应码流控制策略

码流控制是网络多媒体服务中需要解决的主要问题之一.该文依据码流控制的主要影响因素--网络带宽,提出了一种基于网络带宽自适应的缓冲技术方案,先在接收端实时探测网络带宽反馈给网络服务发送端,按照网络带宽选择编码不同的数据分层,并进行了缓冲处理,然后输出传送码流,使得网络服务在适应网络不同带宽需求上具有灵活性.实验表明,使用该文带宽自适应缓冲技术方案,提高了预编码的MPEG视频流的传输质量.     

一种MPEG码流网络带宽自适应传输策略

提出一种基于QoS的MPEG码流自适应网络带宽的传输策略，采用MPEG压缩编码技术，实现多媒体数据实时传输协议RTP，在发送端(前端)根据接收端(后端)的反馈信息预测网络状况，并据此通过选帧技术实现对发送码率的动态调整，使其适应网络带宽的变化。     

网络灾备的传输补偿技术研究

本文研究了当前计算机网络中进行重要数据事故灾备时存在速度慢、可靠性低等问题,提出利用信息学缟码理论中的线性纠错码LECC来改善此状况。线性纠错码方法对数据进行分块冗余编码,在不可靠信道(如 Internet)上传输编码块。接收端只要接收到足够数量的编码块,就可解码出初始数据信息,而不管哪些数据包丢失了,缩短了包应答及丢失包重传的时间,提高了信道的可靠性及传榆效率。     

一种自适应的视频流化前向纠错算法

网络视频应用经常会受到数据包丢失或错误以及网络带宽资源不足的干扰.相关研究表明:在多数情况下,动态变化的网络带宽和丢包率是影响视频流化质量的关键因素.因此,为了保证视频质量,可以采用前向纠错(forward error correction,简称FEC)编码来提高视频数据传输的可靠性;同时,为了适应网络状态的变化,发送端可以调节视频数据的发送速率,并在视频源数据与FEC数据之间合理分配网络传输带宽.首先通过对视频流结构的分析,在充分考虑帧之间的依赖关系和帧类型的基础上提出了一种帧的解码模型.在此基础上,建立了用于在视频源数据和FEC数据之间分配网络带宽资源的优化算法.实验表明,该模型可以有效地适应网络状态的变化,并通过优化分配网络带宽资源来使接收端获得最大的可播放帧率.     

MPEG-4视频编码及网络传输中的误码研究

本文通过MPEG-4视频编码及码流语法结构的分析，系统总结了MPEG-4视频流在容错方面的特性。在此基础上，结合解码器针对MPEG-4视频流网络传输的特点，提出了相关的错误检测和恢复方法。     

基于CDMA网络的自适应图像传输算法

针对CDMA环境多变和带宽分配的特点,本文提出了一种自适应图像传输算法。发送端通过接收端反馈的TCP数据包判断网络状况,结合CDMA网络中传输数据帧长特征,调节UDP数据包的发送时间和数据包大小,从而自适应CDMA网络带宽的变化,充分利用网络的可靠带宽。最后,给出了算法的测试结果。测试结果表明,该算法能够快速地跟随CDMA网网络带宽变化,也可以应用于其它窄变带宽的网络中。     

IP网络MPEG-4视频流的自适应差错掩盖算法

针对IP网络上的MPEG-4视频传输,采用面向差错控制的打包方案,提出了一种结合时域差错恢复和空域差错恢复方法的快速自适应差错恢复混合算法。该算法根据视频帧的编码模式、丢失宏块的邻域宏块的编码模式、运动程度和运动矢量一致性自适应地选择差错恢复方法。仿真实验结果验证了自适应算法具有较好的差错恢复能力。     

An adaptive control for video transmission over bluetooth

This paper is concerned with transmission of a moving picture expert group (MPEG) video stream over a Bluetooth channel, using an adaptive neuro-fuzzy technique. MPEG variable bit rate (VBR) video sources over a network generally experience long delay and unacceptable data loss, due to high variations in bit rate. Furthermore, transmission rate could be unpredictable in a Bluetooth network due to interferences by other wireless devices or general Bluetooth channel noises. Subsequently, it is almost impossible to transmit VBR data sources over Bluetooth without excessive delay or data loss. In this work, an adaptive scheme is introduced so that the controller may adjust itself to the current state of the system under control. This paper utilizes a traffic-shaping buffer to prevent excessive back-to-back transmissions of MPEG VBR data sources. A novel adaptive neuro-fuzzy scheme regulates the output rate of the buffer to ensure that the video stream from the host conforms to the traffic conditions of the Bluetooth channel during the transmission period. The computer simulation results show that the use of the neuro-fuzzy controller reduces excessive delay and data loss at the host-controller-interface, as compared with a conventional VBR video transmission and a rule-based fuzzy controller (RBF1) in Bluetooth.     

基于RTCP的闭环码率调控和流量整形策略

网络监控系统中的实时视频质量容易受网络带宽影响。针对此问题,提出了一种基于RCTP控制报文的闭环码率调控策略,即通过分析RTCP接收者报包(Receiver Report, RR)的反馈信息,调整编码器码率,以自适应网络承载能力;又进一步针对H. 264码流传输的高突发性,提出了码流流量整形策略,用以抑制数据突发,从而避免因突发引起的瞬时网络阻塞,减小网络丢包。实验结果表明,本策略有效地降低了码流的传输丢包率,提高了实时视频质量。     

一种嵌入视频流的丢包自测量方法

现有的丢包主动测量方法是通过探测流的丢包信息去推测网络的丢包特性,进而推测特定应用流的丢包,测量结果不能准确获知某一给定应用流的丢包情况.由于丢包通常属于短时间、小概率事件,要更加准确地测量丢包就意味着需延长测量时间,或者提高探测流的发送速率以及时发现丢包,这将不可避免地增加网络的额外负载.分析了不同类型帧损伤的影响,并以MPEG-4,H264 视频为研究对象,通过对其码流结构特点及RTP 封装策略的分析,提出一种将测量信息嵌入到视频用户数据域(User_Data)的丢包测量方法PLBU(packet loss measurement based on User_Data).该方法利用视频码流信息完成对丢包的探测,不影响视频的正常播放,不需要注入新的探测流,极大地降低了因测量而引入的额外负载.NIST Net 及Planetlab 等实验结果表明,该算法不仅丢包测量准确性高,且可提供丢包所属视频帧类型等信息,如视频中I,P,B 帧的数据包丢失的情况.借助该测量方法,服务提供商可评测网络视频流丢包,并分析视频体验质量(QoE)变化情况,且不受视频流在网络传输中的优先级影响.     

User-Oriented QoS Analysis in MPEG-2 Video Delivery

We address the problem of video quality prediction and control for high-resolution video transmitted over lossy packet networks. In packet video, the bitstream flows through several subsystems (coder, network, decoder); each of them can impair the information, either by data loss or by introducing some delay. However, each of these subsystems can be fine-tuned in order to minimize these problems and to optimize the quality of the delivered signal, taking into account the available bitrate. The assessment of the end-user quality is a non-trivial issue. We analyse how the user-perceived quality is related to the average encoding bitrate for variable bit rate MPEG-2 video. We then show why simple distortion metrics may lead to inconsistent interpretations. Furthermore, for a given coder setup, we analyse the effect of packet loss on the user-level quality. We then demonstrate that, when jointly studying the impact of coding bit rate and packet loss, the reachable quality is upperbound and exhibits one optimal coding rate for a given packet loss ratio.     

Fuzzy-based rate control for real-time MPEG video

We propose a fuzzy logic-based control scheme for real-time motion picture expert group (MPEG) video to avoid long delay or excessive loss at the user-network interface (UNI) in an asynchronous transfer mode (ATM) network. The system consists of a shaper whose role is to smooth the MPEG output traffic to reduce the burstiness of the video stream. The input and output rates of the shaper buffer are controlled by two fuzzy logic-based controllers. To avoid a long delay at the shaper, the first controller aims to tune the output rate of the shaper in the video frame time scale based on the number of available transmission credits at the UNI and the occupancy of the shaper's buffer. Based on the average occupancy of the shaper's buffer and its variance, the second controller tunes the input rate to the shaper over a much larger time scale by applying a closed-loop MPEG encoding scheme. With this approach, the traffic enters the network at an almost constant bit rate (with a very small variation) allowing simple network management functions such as admission control and bandwidth allocation, while guaranteeing a relatively constant video quality since the encoding rate is changed only in critical periods when the shaper buffer “threatens” to overflow. The performance of the proposed scheme is evaluated through numerical tests on real video sequences     

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.     

Control Mechanisms for Error-Resilient MPEG-2 Video Communications over ATM Networks

The design of digital video communications systems is a very active research area. Due to the stringent requirement of video and characteristics of networking technologies, the provisioning of control mechanisms guaranteeing a certain level of service is essential for the success of distributed video applications. In this paper, we study the use of different schemes for the robust transmission of MPEG-2 video over ATM networks. We compare error-resilience performance of two data-partitioning schemes for MPEG-2 bit stream transmitted over ATM networks where two layers of priority traffic are supported with different cell discarding schemes. The effectiveness of the different control mechanisms is quantitatively evaluated in terms of cells loss rates, end-to-end delay and cell loss distributions. Our results show that the use of control mechanisms at various levels of the protocol stack is essential for the deployment of error resilient video applications.     

基于MPEG 4的无线视频传输方案的研究*

提出一种基于MPEG4的无线视频传输非等重误码保护方案。根据信道反馈的丢包率信息,自适应选择输出视频流的保护模式。在丢包信道中,对MPEG4码流中运动信息和纹理信息采取不同的保护力度,使用FEC重点保护运动信息数据提高其对误码的鲁棒性。在无丢包信道中,不对数据进行保护,降低打包开销,减少冗余数据。     

基于小波EBCOT的图像IP网络传输控制策略

为了使当前“尽力而为”的网络提供视频流服务时满足QoS要求，文章提出一种基于小波EBCOT的图像IP网络传输控制策略．通过采用基于小波EBCOT的渐进可分级编码方法，对压缩后的比特流按其重要性分层打包传输，同时根据对当前网络可用带宽的估计及信道状态的判断，区分网络拥塞及不可靠传输两种不同情况进行自适应不等重丢包保护AUPLP．软件仿真表明，该文算法可大大增强小波EBCOT编码后数据的抗误码能力，在发生数据拥塞时有助于缓解网络的过负载状况，在发生不可靠传输时接收端解码图像能平均提高1．2dB的PSNR。     

Traffic specifications for the transmission of stored MPEG video onthe Internet

Guarantees of quality-of-service (QoS) in the real-time transmission of stored video on the Internet is a challenging task for the success of many video on demand (VoD) applications. Two QoS classes have been specified by the IETF Integrated Services (intserv) Working Group: Guaranteed Services and Controlled-Load Services. For both of them, it is necessary to provide traffic sources with the capability of calculating the traffic characteristics to be declared to the network, Tspec, on the basis of a limited set of parameters statistically characterizing the traffic and the required level of QoS. The target of this paper is to develop an algorithm for the evaluation of the Tspec parameters which characterize the video stream when a given QoS is required. To this end an analytical framework modeling an MPEG stored-video server and the access network node is introduced. The video emission process is modeled with a switched batch Bernoulli process (SBBP), and performance in the video-server smoother is analytically evaluated. Then the token bucket at the network access point, loaded by the output traffic of the video-server smoother, is modeled to calculate the probability of marking nonconforming data packets