SWFA: a new buffer management mechanism for TCP over ATM-GFR

We investigate packet discarding schemes for transport control protocol (TCP) over asynchronous transfer mode with guaranteed frame rate service. In this letter, we propose the selective weighted fair allocation (SWFA) scheme, which discards packets from selected sessions. 15 TCP connections with equal minimum cell rate (MCR) and unequal MCRs are simulated. The SWFA scheme with per-virtual connection (VC) queuing is compared with early packet discard (EPD) with first-in, first-out queuing, EPD with per-VC queuing, and differential fair buffer allocation with per-VC queuing. Our results show that SWFA with per-VC queuing achieves significant enhancement on throughputs, goodputs, and fairness.     

A new buffer management scheme for hierarchical shared memoryswitches

We study a multistage hierarchical asynchronous transfer mode (ATM) switch in which each switching element has its own local cell buffer memory that is shared among all its output ports. We propose a novel buffer management technique called delayed pushout that combines a pushout mechanism (for sharing memory efficiently among queues within the same switching element) and a backpressure mechanism (for sharing memory across switch stages). The backpressure component has a threshold to restrict the amount of sharing between stages. A synergy emerges when pushout, backpressure, and this threshold are all employed together. Using a computer simulation of the switch under symmetric but bursty traffic, we study delayed pushout as well as several simpler pushout and backpressure schemes under a wide range of loads. At every load level, we find that the delayed pushout scheme has a lower cell loss rate than its competitors. Finally, we show how delayed pushout can be extended to share buffer space between traffic classes with different space priorities     

Bandwidth estimation: metrics, measurement techniques, and tools

In a packet network, the terms bandwidth and throughput often characterize the amount of data that the network can transfer per unit of time. Bandwidth estimation is of interest to users wishing to optimize end-to-end transport performance, overlay network routing, and peer-to-peer file distribution. Techniques for accurate bandwidth estimation are also important for traffic engineering and capacity planning support. Existing bandwidth estimation tools measure one or more of three related metrics: capacity, available bandwidth, and bulk transfer capacity. Currently available bandwidth estimation tools employ a variety of strategies to measure these metrics. In this survey we review the recent bandwidth estimation literature focusing on underlying techniques and methodologies as well as open source bandwidth measurement tools.     

On synchronization techniques: performance and impact on time metrics monitoring

The paper presents an experimental comparison of device synchronization strategies to monitor quality of service (QoS) time metrics, such as the one‐way delay and the delay variation. The compared strategies are based on global positioning system (GPS), public Internet network time protocol (NTP) servers and ad hoc GPS‐based NTP servers with different treatments of the NTP traffic. The presented experimental results allow to quantitatively evaluate the level of performance achievable using each synchronization technique. Finally, considering a satellite test bed, we focus our analysis on two relevant aspects of time metrics monitoring: the impact of the synchronization errors on the metrics observation and the different values that can be measured when a metric is monitored at the application or data link level. Copyright © 2003 John Wiley & Sons, Ltd.     

3D IC floorplanning: Automating optimization settings and exploring new thermal-aware management techniques

The introduction of 3D chip architectures is an increasingly attractive integration solution due to the potential performance improvement, power consumption reduction and heterogeneous integration. Nevertheless, thermal distribution, evacuation and limitation constitute some of the key issues that can hinder widespread adoption of 3D integration technology. Efficient 3D floorplan algorithms have to be developed to address such complexity. In this paper we first discuss the implementation of such an algorithm and identify parameters that play a role in the solution quality. We then propose the use of a genetic algorithm to discover sets of parameters that guarantee good ?oorplan quality. Then, we present an improved thermal-aware ?oorplanner based on a new formulation of the cost function that minimizes not only peak temperature, but also thermal gradients. The temperature minimization goal is reinforced using a smart heuristic that guides 3D moves in the direction of placing power hungry blocks next to the heat sink. Experimental results show the ability of the method to reduce the temperature peak and gradient signi?cantly, while maintaining area, wirelength and computation time.     

一种自适应的FRED缓存管理算法

如何保证业务流的公平性,特别是在存在UDP业务流的情况下,有效地保护TCP流一直是一个热点研究课题.本文提出了一种自适应的FRED缓存管理算法AFRED,通过动态的调节分组丢弃的门限,保护了TCP流,提高了系统的公平性,同时保证了带宽利用的有效性.算法的复杂度与FRED相近,但是能获得更好地性能.     

快速buffer添加算法

在深亚微米设计中,连线延迟时间已经超过器件延迟时间,成为影响性能的瓶颈之一。在线网中插入缓冲器（buffer）是改善线延迟的一种有效方法,但是目前基于缓冲器块（bufferblock）的方法一般因其计算量比较大,算法比较慢,并且也增加布局（floorplan）的复杂性。为此本文提出并实现了一种新的快速算法来解决芯片顶层互连中缓冲器添加问题。     

Pushout with virtual thresholds buffer management scheme in a shared buffer ATM switch

In this paper we investigate the performance metrics of buffer management schemes. In general, the selective pushout (SP) scheme can support very low loss probability of the high‐priority cells, but it may cause unfairness of buffer allocation among different output queues and high overall cell loss probability. In order to fit the dynamic required performance metrics of ATM switches, a novel buffer management scheme called pushout with virtual thresholds (PVT) is proposed. In the PVT scheme, each output queue is guaranteed to increase in length until its virtual threshold (VT). Simulation results show the PVT can dynamically achieve the fairness and low overall cell loss probability or very low loss probability of the high priority cells by adequately adjusting the VT. Specially, when the VT = 0, the PVT control can be viewed as the SP control. Copyright © 2003 John Wiley & Sons, Ltd.     

Virtualized architectural heritage: new tools and techniques

Technology has come a long way in solving many of the early limitations of virtual reality (VR) and virtual worlds have quietly found growing acceptance in selected areas. However, issues of graphic quality and speed has dogged virtual world heritage developers, forcing simplistic representations and triggering criticism from the heritage community. In addition, until recently there was also a lack of inexpensive software and data standards (such as QuickTimeVR and Virtual Reality Modeling Language, or VRML) for creating visually realistic interactive environments. Although significant advances have been made, the accurate virtual representation of historic and cultural landmarks has been limited by a lack of tools to quickly, inexpensively, and accurately model reality. The representation of built heritage requires two distinct forms of 3D data, current, real-world conditions and virtual or theorized historical interpretations. We call the combination of the two forms virtualized as opposed to virtual. Despite the use of numerous measurement technologies in traditional heritage work, existing tools lacked the optimal mix of features required for virtualized architectural environments. Dissatisfied with available choices. We began an extensive analysis of available technologies. In this article, we review results in heritage projects with two emerging systems     

Estimating action potential thresholds from neuronal time-series: new metrics and evaluation of methodologies

The estimation of action potential thresholds is a subjective process, which we quantified by surveying experienced electrophysiologists via a software application that allowed them to select action potential thresholds from several presented neuronal time series. Independent of this survey, we derived two nonparametric techniques for automating the detection of an action potential threshold from the time-series of intracellular recordings. Both methods start with a phase-space representation of the action potential (dV/dt versus V). Method I detects the maximum slope in the phase space, while Method II detects the maximum second derivative in the phase space. These two methods, as well as five additional methods in the literature, were tested on three data sets representing a variety of action potential shapes, the same three datasets that were used in the electrophysiologist survey. The database of user responses was used to provide an external benchmark against which to statistically evaluate all seven methods. Method II, as well as the curvature-based Methods VI and VII, provided the best results tracking both absolute and relative changes in threshold versus the other nonparametric methods (peak of second and third time derivatives). The one parametric method evaluated, detection of threshold crossing of the first temporal derivative, performed comparably to these methods, provided that an appropriate threshold was chosen. We conclude that Methods II, VI, and VII were the best methods evaluated due to their performance across a wide range of action potential shapes and the fact that they are nonparametric. Our user database of responses may be useful to other investigators interested in developing additional methods in that it quantifies what has often been a subjective estimate.     

Optimal buffer management policies for shared-buffer ATM switches

Shared-buffer ATM switches can have severe cell loss under asymmetrical or heavy loading conditions, which makes buffer management essential. In this paper, we study the shared-buffer system under the class of all work-conserving pushout policies and derive the properties of the optimal policy, which gives the least-average expected total cell loss probability. In a 2×2 system with independent identically distributed Bernoulli arrivals, we show that the optimal policy can be characterized by a single threshold. In the case of correlated arrivals, modeled by a discrete batch Markovian arrival process, the optimal policy has multiple thresholds, one for each phase of the arrival process. For the N×N shared buffer ATM switch, we are unable to prove optimality of any policy, but we study the system via simulations. We provide a dynamic buffer management policy and compare its performance with that of static threshold-type policies     

Internet中分组丢弃缓存管理技术的研究

Internet中，基于分组丢弃的缓存管理技术是分组转发设备的重要功能模块，其算法对网络性能会产生重大影响。本文对现有主要的分组丢弃技术及其派生算法作了总结，并就存在的问题和不足提出了研究建议。     

机会网络缓存管理机制性能分析与比较

首先引入机会网络及相应的理论基础,包括机会网络的基本概念、网络架构以及研究方向;然后重点介绍了机会网络中典型的缓存管理机制,并深入分析了其优缺点;最后对机会网络中缓存管理机制进行了总结并对未来缓存设计目标予以展望.     

基于数据缓冲区动态分组的功耗管理策略

传统DPM策略通过适应请求分布降低功耗,效果受到限制.另一类策略主动改变请求分布,使其较好的满足DPM要求.数据缓冲区策略属于其中的典型,但现有的缓冲区策略未充分考虑实际系统的数据访问情况,对数据缓冲区的使用效率较低.本文针对此问题提出一种新颖的DGDB(Dynamic Grouping of Data Buffer)功耗管理策略.实验结果表明,在复杂数据访问情况下,DGDB策略具有更好的节能效果与稳定性.     

使用FPGA和IP Core实现定制缓冲管理

在通信网络系统中．流量管理的核心是缓存管理。队到管理和调度程序。本文结合使用FPGA及IP Core阐述缓存管理的结构工作原理及设计方法     

A new priority control of ATM output buffer

A new ATM output buffer management strategy with priority control function is proposed, based on four types of cell classes. This strategy can use system resource more effectively, meet the quality of service (QOS) requirements (i.e. cell loss probabilities and delay characteristics) of different services, and also can reduce the complexity of buffer. Furthermore, overload from lower priority traffic doesn't degrade the performance of higher priority traffic (i.e. cell loss rate and cell delay characteristics).     

一种具有自适应特性的SSO噪声抑制输出驱动电路

介绍了SSO噪声产生的原因,简要概述了常用的抑制SSO噪声的方法.在此基础上,提出了一种具有自适应特点的SSO噪声抑制输出驱动电路,并给出了较详细的分析和比较.     

Ambiguity of objective image quality metrics: A new methodology for performance evaluation

Objective image quality metrics try to estimate the perceptual quality of the given image by considering the characteristics of the human visual system. However, it is possible that the metrics produce different quality scores even for two images that are perceptually indistinguishable by human viewers, which have not been considered in the existing studies related to objective quality assessment. In this paper, we address the issue of ambiguity of objective image quality assessment. We propose an approach to obtain an ambiguity interval of an objective metric, within which the quality score difference is not perceptually significant. In particular, we use the visual difference predictor, which can consider viewing conditions that are important for visual quality perception. In order to demonstrate the usefulness of the proposed approach, we conduct experiments with 33 state-of-the-art image quality metrics in the viewpoint of their accuracy and ambiguity for three image quality databases. The results show that the ambiguity intervals can be applied as an additional figure of merit when conventional performance measurement does not determine superiority between the metrics. The effect of the viewing distance on the ambiguity interval is also shown.