VBR Video Source Characterization and a Practical Hierarchical Model

There are many ways to build up traffic models for VBR video sources. A frequently applied methodology is to use mathematical analysis based on realistic assumptions to set up a source model that generates traffic according to a stochastic process. In this case, the critical issue is the validation of the synthetic trace by comparing statistics to results obtained from measurements on the real source. In this paper, we choose a different and more practical approach to model the behavior of the real traffic source. Our model building philosophy is that we analyze and understand what happens with the video information on its way from the ingress to the multimedia terminal to the egress of the network card. Throughout this journey the information is processed by several mechanisms and we build an empirical model step by step based on our measurement-based observations. Besides understanding the traffic generation procedure, statistical analysis of VBR traffic traces captured from a number of video sequences was also carried out in several scenarios. Using the knowledge of encoding, encapsulation and scheduling processes and results of the trace analysis, a hierarchical source model is set up for modeling the multimedia terminal. Thereby our model imitates the generation of video frames and the inner working of each level of protocol hierarchy and tries to reproduce the complex behavior of the real source. We use the leaky bucket analysis for verification of the model in order to capture directly the behavior of the traffic in a queue.     

Reducing cell loss in banyan based ATM switching fabrics

In this paper, we propose a new technique for reducing cell loss in multi‐banyan‐based ATM switching fabrics. We propose a switch architecture that uses incremental path reservation based on previously established connections. Path reservation is carried out sequentially within each banyan but multiple banyan planes can be concurrently reserved. We use a conflict resolution approach according to which banyans make concurrent reservation offers of conflict‐free paths to head of the line cells waiting in input buffers. A reservation offer from a given banyan is allocated to the cell whose source‐to‐destination path uses the largest number of partially allocated switching elements which are shared with previously reserved paths. Paths are incrementally clustered within each banyan. This approach leaves the largest number of free switching elements for subsequent reservations which has the effect of reducing the potential of future conflicts and improves throughput. We present a pipelined switch architecture based on the above concept of path‐clustering which we call path‐clustering banyan switching fabric (PCBSF). An efficient hardware that implements PCBSF is presented together with its theoretical basis. The performance and robustness of PCBSF are evaluated under simulated uniform traffic and ATM traffic. We also compare the cell loss rate of PCBSF to that of other pipelined banyan switches by varying the switch size, input buffer size, and traffic pattern. Copyright © 2001 John Wiley & Sons, Ltd.     

Measured average cell rate‐based congestion avoidance scheme

Techniques for congestion control of available bit‐rate (ABR) traffic in ATM (asynchronous transfer mode) networks remain an important issue. Several congestion control schemes have been proposed to adjust the cell rates of sources with a modified or mean allowed cell rate. To make these schemes work effectively in practice, the modified or mean allowed cell rate must converge under all conditions. However, it is not easy to obtain an accurate value, and an inaccurate value could result in network performance degradation such as severe oscillations and considerable unfairness. Therefore, we propose a measured average cell rate‐based congestion avoidance for ABR traffic in ATM networks. The scheme has high throughput and achieves shorter queue lengths without congestion. With measured average cell rate, the scheme provides fast convergence to a start‐up virtual connection (VC) and rate of equalization from different initial conditions of the sources. Thus, this scheme provides better fairness among connections. Copyright © 2001 John Wiley & Sons, Ltd.     

一种按钮式数字电位器在视频数据混合器中的应用

介绍了按钮式非易失性数字电位器X9511的结构原理及特点,设计了它在收费站视频数据混合器（VDM）中应用的电路。该电路充分利用了X9511精度高、调节方便、性能稳定等优点,能够准确方便地调节视频图像上叠加字符的亮度及阴影的深度。     

重尾ON/OFF源模型生成自相似业务流研究

因为传统模型没有考虑网络业务流量各种时间尺度都具有突发性,因此是不完善的,一系列的测量结果表明,网络业务流量显示自相似性,重尾分布ON／OFF模型能比较好地解释自相似业务流的产生原因,可以把LAN上的业务分解为多个活动（active)主机对之间的业务流,本文通过系统的仿真实验研究了重尾ON／OFF源模型生成自相似流的机理,并与理论结果进行了对比,而且补充了理论结果。     

配电网中谐波源检测方法的研究

介绍了配电网中谐波源探测的一种新方法——临界阻抗法(CIM)。该方法的原理是比较戴维南等效回路中两个谐波电压源的大小,取较大的一个作为主谐波源。通过对于公共耦合点的电压和电流的测量可以引入临界阻抗的概念。进行了临界阻抗法在电网处于不同情况下的基本理论分析,并做了一系列的系统校验,阐明了临界阻抗法在谐波源检测中的正确性。     

多层多原理STLF评估系统

根据电力市场运营对短期负荷预测STLF(Short Term Load Forecast)高精度要求,提出多层多预测原理的STLF评估系统。系统由人机交互层、评估决策层、多原理预测层和数据库管理层构成。根据具体负荷特性、运行情况、评估结果自适应选择高精度原理的预测Agent执行。按评估系统多数据源的需求,采用ADO．NET实现复杂互联网环境下异构数据库的集成,构建负荷预测专用数据仓库,给出了负荷预测计算服务的Web Service实现方法。     

国际性大都市交通出行方式综合分析

通过对交通出行方式的汇总,确定两种主要的交通模式:即小汽车和公共交通. 通过对一些国际性大都市的主要交通出行方式和演变过程的分析对比,得出完善的城市公共交通系统是解决大城市交通问题的有效方式. 从而为我国大城市的合理交通出行方式确定未来发展方向,即为居民公共交通出行创造舒适、良好、经济的出行条件,并通过系列配套设施建设、政策管理手段,引导人们合理使用私人小汽车出行.     

北京市某商务居住综合区交通影响评估研究

交通影响评价是对城市土地开发或土地使用性质变更的项目,可能对城市交通所产生的影响进行定量评估并制定解决方案的过程. 近年来,北京市新建商务区以及纯住宅项目较多,新建项目建设完工投入使用后会给周边带来多大的交通量以及是否会恶化原有的交通环境,都需要通过交通影响评价来预决策. 现对北京市某商务居住综合区的交通影响评价进行了研究,提出了交通改善措施.     

基于LSP时延和拥塞的分布式自适应流量工程算法

研究多协议标签交换(MPLS)网络中的流量工程,提出了基于标签交换路径(LSP)时延和拥塞 来优化网络流量的算法。给出全网流量优化的数学模型,并根据该模型内在的层次性,设计 了分布式自适应流量工程算法。为了使算法具有实时性强、收敛速度快、稳定性较好、运算 和网络开销小等特点,在设计中,采用了禁忌搜索和算法参数的非线性调整来提高算法的性 能。仿真分析表明,该算法能够实现对网络性能的全面优化,适合应用于骨干网的流量优化.