Packet video and its integration into the network architecture

Packet video is investigated from a systems point of view. The most important issues relating to its transmission are identified and studied in the context of a layered network architecture model, leading to a better understanding of the interactions between network and signal handling. The functions at a particular layer can thereby be made less dependent on network implementation and signal format. In the layered network model, the higher layers provide format conversion, hierarchical source coding, error recovery, resynchronization, cost/quality arbitration, session setup and tear-down, packetization, and multiplexing. Provisions from the network layers pertain mainly to real-time transmission. Special consideration is given to hierarchical source coding, error recovery, statistical behavior, and timing aspects. Simulation results indicating practical solutions to some of the issues raised are presented for a hierarchical packet-video subband coding system     

Packet video error concealment with Gaussian mixture models.

In this paper, Gaussian mixture modeling is applied to error concealment for block-based packet video. A Gaussian mixture model for video data is obtained offline and is thereafter utilized online in order to restore lost blocks from spatial and temporal surrounding information. We propose estimators on closed form for missing data in the case of varying available neighboring contexts. Our error concealment strategy increases peak signal-to-noise ratio compared to previously proposed schemes. Examples of improved subjective visual quality by means of the proposed method are also supplied.     

Packet scheduling with playout adaptation for scalable video delivery over wireless networks

In this paper, we propose a playout deadline-aware packet scheduling for scalable video delivery over wireless networks. We develop a novel playout adaptation algorithm to reduce playback interruptions by jointly considering the active playout buffer status and adaptive playout rate. We also propose a packet priority analysis method based on the layer information of Scalable Video Coding (SVC). Based on the priority of the video packet and the adaptive playout-deadline, an optimal packet scheduling algorithm is proposed. Packets are selected for transmission to minimize the quality degradation caused as well as to reduce the playout latency. We also adopt a benchmark for the packet priority analysis by calculating the distortion impact of each packet with the consideration of the packet dependency in SVC. When compared with the state-of-the-art algorithms as well as the benchmark, our proposed scheduling algorithm shows a good trade-off between the video quality and the playout latency.     

Packet prioritization for H.264/AVC video with cyclic intra-refresh line

Insertion of a cyclic intra-refresh line is a lightweight way of mitigating spatio-temporal error propagation in a video stream transmitted over a mobile network. This paper presents low-complexity yet effective prioritization based on slice position within a video frame relative to the cyclic refresh line. Two prioritization schemes are compared. The first is a region-based method, while the second, which is packet-based, improves packet classification. Experimental results indicate that, the packet-based scheme can achieve video quality gains of up to 4 dB, compared to when the scheme is not used. The proposed schemes require no decoder modifications and do not introduce an increase in bitrate or in computational complexity.     

Packet loss visibility across SD,HD, 3D,and UHD video streams

The trend towards video streaming with increased spatial resolutions and dimensions, SD, HD, 3D, and 4kUHD, even for portable devices has important implications for displayed video quality. There is an interplay between packetization, packet loss visibility, choice of codec, and viewing conditions, which implies that prior studies at lower resolutions may not be as relevant. This paper presents two sets of experiments, the one at a Variable BitRate (VBR) and the other at a Constant BitRate (CBR), which highlight different aspects of the interpretation. The latter experiments also compare and contrast encoding with either an H.264 or an High Efficiency Video Coding (HEVC) codec, with all results recorded as objective Mean Opinion Score (MOS). The video quality assessments will be of interest to those considering: the bitrates and expected quality in error-prone environments; or, in fact, whether to use a reliable transport protocol to prevent all errors, at a cost in jitter and latency, rather than tolerate low levels of packet errors.     

Optimal Packet Length for Packet Voice Communication

It is shown that for typical operating parameters, the optimal packet length for a single link packet voice system is of the order of 300-700 bits. This is contrary to both the optimal length of a data packet (approximately 1000 bits), and documented experimental implementations of such network architecture for voice (approximately 1000 bits).     

走出IP网络的“迷宫”

11月17日,美国百科帝(Packet Design)公司的首席技术官Cengiz Alaettinoglu博士到中国访问。Cengiz博士在管理广域网的路由分析技术领域享有知名地位,曾任互联网工程任务组(IETF)路由政策系     

Packet by Packet Analysis in Contemporary Network Simulators

This article presents a comparative study of three hybrid network simulators: OPNET’s Modeler and ns-2, as well as NCTUns. In order to fulfill this, the simulated results were compared with the results obtained from a real network testbed using a packet by packet analysis methodology. Using a generic network based in an experimental network and modeled in the three simulators, the experimental comparison consisted in introducing data traffic in six different scenarios, combining traffic patterns of Constant Bit Rate (CBR) and a File Transfer Protocol session (FTP). The first objective is to corraborate the precision of the used models in the simulation to create this traffic patterns. Second, to test the network response to these types of traffic, all these by using the same packet by packet analysis methodology. The results obtained from the simulators were compared against the results obtained from the testbed network. The results obtained in this study showed that ns-2 presents good results in the simulation of CBR traffic, while the Modeler from OPNET presents an outstanding traffic simulation in terms of the FTP traffic. Nevertheless, some problems were detected in the three simulators, but NCTUns was the one that presented the most number of errors and problems in the overall results. These types of studies at the packet by packet level are important to validate the models used in the simulations that are based in components and applications used in grand scale simulations.     

Packet phone

Why would anyone want to transmit voice over the creaky, packet-based Internet? In this paper, the author looks for some answers to the great conundrum of modern communications     

Packet forwarding

A packet network is viewed as consisting of two major interacting layers: a lower layer responsible for the determination of a set of paths that can be used to carry packet flows, and an upper layer responsible for actually sending the flows over these paths, on a per-packet basis. A systematic review is provided of the various techniques that can be used to perform the actual packet-by-packet routing operation at the upper layer, called the packet forwarding function. The function components of a routing system and its characteristics (responsiveness to changes in network state and degree of centralization) are discussed. Five routing techniques are then examined, namely source, directory, destination, global-path, and channel-link-path routing     

Packet Pacing in Small Buffer Optical Packet Switched Networks

In the absence of a cost-effective technology for storing optical signals, emerging optical packet switched (OPS) networks are expected to have severely limited buffering capability. To mitigate the performance degradation resulting from small buffers, this paper proposes that optical edge nodes “pace” the injection of traffic into the OPS core. Our contributions relating to pacing in OPS networks are three-fold: first, we develop real-time pacing algorithms of poly-logarithmic complexity that are feasible for practical implementation in emerging high-speed OPS networks. Second, we provide an analytical quantification of the benefits of pacing in reducing traffic burstiness and traffic loss at a link with very small buffers. Third, we show via simulations of realistic network topologies that pacing can significantly reduce network losses at the expense of a small and bounded increase in end-to-end delay for real-time traffic flows. We argue that the loss-delay tradeoff mechanism provided by pacing can be instrumental in overcoming the performance hurdle arising from the scarcity of buffers in OPS networks.      

分组网络中包调度算法研究

下一代因特网要支持QoS(quality of service)实现,而包调度又是QoS实现的关键技术之一。文中对现有的包调度算法进行了分类,分析和比较了各类算法的技术特点与性能优劣,讨论了包调度算法研究今后的发展方向。     

A Scalable Packet Sorting Circuit for High-Speed WFQ Packet Scheduling

A novel implementation of a tag sorting circuit for a weighted fair queueing (WFQ) enabled Internet protocol (IP) packet scheduler is presented. The design consists of a search tree, matching circuitry, and a custom memory layout. It is implemented using 130-nm silicon technology and supports quality of service (QoS) on networks at line speeds of 40 Gb/s, enabling next generation IP services to be deployed.     

Round-Robin分配方式下多径传输的重排序性能分析

基于包分配的多径传输在接收端所引起的数据包乱序严重影响TCP的传输性能。针对此问题,从排队论的角度出发对Round-Robin分配方式下多径传输的重排序问题进行了分析。从数据包的乱序率、重排序时间和端到端总时间3个方面考察了路径差异与路径数目对多径传输的性能的影响。结果表明,在采用两条路径传输时,应使得两条路径的传输速率近似相同;在路径传输速率相同的条件下,为明显地提升多径传输的重排序性能,路径数目应不超过4条。     

基于输入队列的光分组交换短包抢先调度

光分组交换的输出队头阻塞引起分组的平均排队时延增加.分析了可变长分组的特点,提出了基于抢先方式的短包抢先调度(PSPP)算法,以减少分组在输入排队中的平均等待时间.在PSPP算法中,短包可以抢占长包的传输时间,获得优先的服务.分析和仿真结果表明,当到达业务负载为中或较低时,短包优先调度算法使短包的平均排队时延接近零,所有分组的平均等待时延减小,该算法还保证具有实时特性的TCP业务获得较低的平均等待时延.     

不同长度分布下的光分组交换性能研究

通过分析不同分组长度分布(PLD)对光分组交换(OPS)性能的影响,以便为OPS在不同长度业务下配置不同的冲突解决方案.研究了光分组在固定长度分布、指数分布和因特网经验长度分布下分别对没有光纤延迟线(FDL)和有FDL下的OPS的性能影响.分析和仿真表明,因特网经验长度分布的业务在没有FDL缓存的条件下,获得最低的分组丢失率(PLR)性能;而固定长度分布的业务,仅在OPS配置有FDL时才可以获得最低的PLR性能.     

数字电视传送流丢包和丢包率研究

定义了数字电视传送流丢包,并通过实验指出丢包对电视信号有重要影响,建议把定义的丢包率作为评价数字电视信号传输质量的客观指标之一.为此,提出了两种分析丢包和统计丢包率的算法,并进行了实验验证.     

弹性分组数据（RRR）环技术

随着各电信运营商大力开展宽带域网建设，如何提代电信级的数据服务变得越来越重要。本文详细阐述了新型的弹性分组数据环（RPR）技术的特征，以及RPR技术与SDH、以太网技术相比在环形拓扑结构上支持数据业务的优势。