Evaluation of ABR traffic management under various system time scales

In this paper, the effects of various time scales on the management of ABR (Available Bit Rate) traffic using feedback based control is studied. Since delay tolerable, the ABR applications can be allocated the remaining resources after CBR (Constant Bit Rate) and VBR (Variable Bit Rate) applications have been accommodated. To avoid excessive losses the transmission rate of the ABR applications should be modulated by the amount of remaining resources. That is, the ABR rate should be controlled through a feedback based rate control mechanism. In this paper, a network link shared by remote ABR and VBR applications is considered and the impact of various system time scales on the effectiveness of the feedback based flow control scheme is investigated by formulating and studying a tractable analytical model. These time scales are expressed in terms of the network transmission speed, the minimum tolerable ABR rate and the rate of change of the VBR source rate. While the negative impact of a decreased network time scale on the effectiveness of this control scheme is well established, the impact of the ABR and VBR time scales has not been investigated in the past. It turns out that for a given network time scale, the induced cell losses can be significantly reduced for increased ABR and/or VBR time scales and thus, the latter time scales should be taken into consideration while evaluating the effectiveness of an adaptive feedback based flow control mechanism. This study also suggests that higher efficiency can be achieved by enforcing large ABR time scales, leading to the introduction of a new class of transmission policies.     

ABR业务流量控制中的显速率反馈

ABR(Available Bit Rate)业务可以提高ATM网络的利用率,能让用户LAN通过广域网进行高吞吐量、低丢失率的互通。可以预计,未来ATM网上的数据业务将主要用ABR连接来传输。ABR业务中的首要问题是流量控制。文章在比较了几种流量控制方案后,认为显速率反馈是ABR业务流量及拥塞控制的一个有效方法,是完善ABR业务的一个重要手段,并对显速率算法作了进一步研究。     

A switching mechanism for ATM ABR traffic control

Many rate control mechanisms for ABR service have been proposed in literature, based on heuristics. In this paper, we propose a new rate-based control mechanism for ABR service. A controller that switches between a Rough Adjustment Method (RAM) and a Delicate Adjustment Method (DAM) is used in the mechanism to achieve a fast response as well as stability. The convergence of the mechanism can still be guaranteed even if there is a large delay in the system, which is theoretically proven in this paper. Simulation results are used to illustrate the effectiveness of this new mechanism.     

Performance of ATM available bit rate for bursty TCP sources and interfering traffic

The Available Bit Rate (ABR) service has been shown to enable persistent, greedy data sources to efficiently utilize ATM network resources. However, the throughput for bursty TCP over ABR data traffic in the presence of interfering traffic may not be as good as for persistent ABR sources without interfering traffic. This paper shows that in a comparison of rate based ABR schemes (EPRCA and ERICA) and a credit based ABR scheme (QFC), QFC performance is significantly better than rate based ABR schemes for bursty data traffic with bursty interfering traffic.     

基于速率的反馈拥塞控制的最优化问题研究

基于速率的反馈拥塞控制用于ＡＴＭ网络中可用位速率（ＡＢＲ）流量控制。可用位速率业务需要最优和稳定的流量控制器来保证高的吞吐量和保证网络的稳定性。本文采用线性控制理论来设计基于速率的流量控制器。这个控制器是一个简单的比例控制器,使用品质因数来优化参数。文中证实了最优化控制器对系统参数的最小依赖性。     

Auditory brainstem response classification for threshold detection using estimated evoked potential data: comparison with ensemble averaged data

Auditory brainstem response (ABR) has become a routine clinical tool in neurological and audiological assessment. ABR measurement process with ensemble averaging is very time-consuming and uncomfortable for subjects due to the more repetition of single trials. This condition also restricts the wide usability of ABR in clinical applications. Therefore, the reduction in repetitions has a great importance in ABR measurements. In this study, 488 ABR responses are used for creating two different data sets. The first set is created conventionally by ensemble averaging of 1,024 single trials for each ABR pattern. The second set is obtained from the first estimated 64 single trials of the same records for each ABRs. Estimation is realized by using a nonlinear adaptive filtering algorithm. In classification stage, a powerful classifier integrated with a feature selection algorithm is performed for each data set. In result, the classification performance for estimated ABR data with 64 repetitions is better than the classification performance of the ensemble averaged data with 1,024 repetitions. The proposed system is resulted in an accuracy of 96% for estimated ABRs. So, the proposed system can effectively be used for threshold detection in auditory assessment providing a high accuracy. While the obtained results contribute to the practical ABR usage in clinics, the great significance of it arises from the reduction in repetitions via estimation of ABRs.     

基于模糊逻辑的ABR显式流量控制算法

面向连接的ATM网络通过一系列的流量管理机制为各种应用提供纯粹的服务质量(QoS)保证，其中ABR业务流量控制的作用尤显重要．显式速率(Explicit Rate,ER)控制是一种有效的机制，有效性、公平性和算法复杂度是各种显式速率控制算法所面临的主要问题．该文将ABR业务流基于速率的端到端闭环反馈控制抽象为控制理论中典型的调节系统，运用不依赖对象模型的模糊控制理论设计了一种新的流量控制算法——模糊速率控制算法(FRCA)．仿真试验表明FRCA的综合性能良好：保证了最大—最小公平性的实现；在LAN和WAN上均有较好的适应能力；算法的复杂度低；队列长度的控制能力强；易于硬件实现．     

Binary ABR flow control over ATM networks with uncertainty using discrete-time variable structure controller

A binary available bit rate （ABR） scheme based on discrete-time variable structure control （DVSC） theory is proposed to solve the problem of asynchronous transfer mode （ATM） networks congestion in this paper. A discrete-time system model with uncertainty is introduced to depict the time-varying ATM networks. Based on the system model, an asymptotically stable sliding surface is designed by linear matrix inequality （LMI）. In addition, a novel discrete-time reaching law that can obviously reduce chatter is also put forward. The proposed discrete-time variable structure controller can effectively constrain the oscillation of allowed cell rate （ACR） and the queue length in a router. Moreover, the controller is self-adaptive against the uncertainty in the system. Simulations are done in different scenarios. The results demonstrate that the controller has better stability and robustness than the traditional binary flow controller, so it is good for adequately exerting the simplicity of binary flow control mechanisms.     

Binary ABR flow control over ATM networks with uncertainty using discrete-time variable structure controller

A binary available bit rate (ABR) scheme based on discrete-time variable structure control (DVSC) theory is proposed to solve the problem of asynchronous transfer mode (ATM) networks congestion in this paper. A discretetime system model with uncertainty is introduced to depict the time-varying ATM networks. Based on the system model, an asymptotically stable sliding surface is designed by linear matrix inequality (LMI). In addition, a novel discrete-time reaching law that can obviously reduce chatter is also put forward. The proposed discrete-time variable structure controller can effectively constrain the oscillation of allowed cell rate (ACR) and the queue length in a router. Moreover, the controller is self-adaptive against the uncertainty in the system. Simulations are done in different scenarios. The results demonstrate that the controller has better stability and robustness than the traditional binary flow controller, so it is good for adequately exerting the simplicity of binary flow control mechanisms.     

Correctness and performance of the ATM ABR rate control scheme

We study both correctness and performance of the source/destination protocols of the available bit rate (ABR) service in asynchronous transfer mode (ATM) networks. Although the basic protocol for rate-based congestion management is relatively simple, the protocol specification has to cope with several “real-world” cases such as failures and delayed/lost feedback which introduce complexity. Rigorous proof of the correct functioning of the protocol based on a formal specification is necessary. We use a formal model to show that the ABR source/destination protocol is free of livelocks, so that under all conditions both resource management (RM) and data cells will be transmitted. Furthermore, if there are data cells available, then the ABR protocol is deadlock free; otherwise, the system goes to a desirable sleep state waiting for data cells, as long as certain parameters are set appropriately at connection setup. We also show that the network options of explicit forward congestion indication (EFCI) and explicit rate (ER) interoperate correctly.In addition to ensuring the correct functioning of the protocol, it is essential that pathological situations do not result in very poor performance, which we view as another form of “incorrect operation”. We derive conditions that ensure that the source's allowed cell rate (ACR) is stable in the presence of delayed or lost feedback RM cells. We arrive at bounds on the number of consecutive RM cell losses tolerated while the ACR rate remains stable. We also provide an asymptotic estimate of ACR and the allowable RM cell loss probability to ensure that ACR is stable, statistically.The ABR protocol contributes to the feedback delay in two ways: the source delay of sending out the probe forward RM (FRM) cells and the destination delay of turning around the backward RM (BRM) cell. We provide a worst-case analysis of the delay in turning around RM cells at the destination station and the worst-case inter-departure time of FRM cells from the source.     

多时滞ATM网络中ABR 流量的积分滑模控制

针对含有多个时滞的异步传输模式(ATM)网络的拥塞问题,设计了积分滑模控制器,对可用比特率(ABR)业务流量进行控制,并引入预估器来补偿输入时滞.所设计的控制算法不但能够克服变化的ABR带宽给闭环系统带来的不利影响,而且还能保证含有多输入时滞闭环系统的稳定性,同时还可实现带宽按权重分配和缓冲队列长度的跟踪.     

基于网络状态预测的提前控制

高速网络的大带宽延迟乘积使其于传统反馈机制的ＡＢＲ难以对高可变ＶＢＲ快速响应,造成速率的不匹配。为了提高反馈控制方法的有效性,充分利用高优先级ＶＢＲ业务剩余的可用带宽,文中提出基于预测的提前控制模式,根据ＡＢＲ信源的不同反馈延迟对未来时间段ＶＢＲ占用带宽进行预测,并利用未来ＡＢＲ可用带宽估算值为相应的ＡＢＲ进行速率分配,从而实现速率的精确匹配。高速网络ＶＢＲ业务的强相关性使相对精确的时间序列预测成     

Mechanical Verification of an Ideal Incremental ABR Conformance Algorithm

The Available Bit Rate protocol (ABR) for ATM networks is well adapted to data traffic by providing minimum rate guarantees and low cell loss to the ABR source end system. An ABR conformance algorithm for controlling the source rates through an interface has been defined by ATM Forum, and a more efficient version of it has been designed by Rabadan and Klay. We present in this work the first complete mechanical verification of the equivalence between these two algorithms. The proof is involved and has been supported by the PVS theorem prover. It has required many lemmas, case analysis, and induction reasoning for the manipulation of unbounded scheduling lists. Some ABR conformance protocols have been verified in previous works. However, these protocols are approximations of the one we consider here. In particular, the algorithms assume a bound on the number of rates to be scheduled.     

Automatic classification of auditory brainstem responses using SVM-based feature selection algorithm for threshold detection

This paper presents a novel system for automatic recognition of auditory brainstem responses (ABR) to detect hearing threshold. ABR is an important potential signal for determining objective audiograms. Its detection is usually performed by medical experts with often basic signal processing techniques. The proposed system comprises of two stages. In the first stage, for feature extraction, a set of raw amplitude values, a set of discrete cosine transform (DCT) coefficients and a set of discrete wavelet transform (DWT) approximation coefficients are calculated and extracted from signals separately as three different sets of feature vectors. These features are then selected by a modified adaptive method, which mainly supports to the input dimension reduction via selecting the most significant feature components. In the second stage, the feature vectors are classified by a support vector machine (SVM) classifier which is a powerful advanced technique for solving supervised binary classification problem due to its generalization ability. After that the proposed system is applied to real ABR data and it is resulted in a very good sensitivity, specificity and accuracy levels for DCT coefficients such as 99.2%, 94.0% and 96.2%, respectively. Consequently, the proposed system can be used for recognition of ABRs for hearing threshold detection.     

环隙气升式生物反应器三维CFD建模与仿真

气升式生物反应器被广泛地用于低耗氧微生物发酵过程中,如维生素C的发酵生产。采用计算流体力学对一个缩小的、工业环隙气升式生物反应器内的流体流动进行了建模与仿真,寻找该反应器内流体流动状态的规律。结果表明,在通气量比较小的情况下,生物反应器内的流体流动是极为复杂的,气含率分布和液体速度分布都存在着很大的不均匀性。但通过三维CFD仿真可以近似地确定流态接近CSTR和PFR的区域,从而为简化的CSTR-PFR组合流动模型的建模提供依据。     

A proportional feedback scheme for ATM networks

Available bit rate (ABR) service class is proposed by Asynchronous Transfer Mode (ATM) Forum to provide the “best-effort” services like traditional TCP/IP traffic. It is designed to make use of the remaining bandwidth not used by VBR and CBR. However, the bursty nature of ABR traffic makes it difficult to prevent buffers on ATM switches from overflowing. A number of schemes have been proposed for ABR traffic control. In this paper, a proportional scheme that is rate-based hop-by-hop flow control is proposed. A mathematical model is built to analyze the hop-by-hop flow control scheme. It is shown the scheme can utilize full bandwidth without any cell loss. It is also shown the scheme has low queuing delay and fast transient response.     

基于短声和扫频音的听觉脑干诱发电位比较研究

听觉脑干诱发电位检测(Auditory Brainstem Response,ABR)是一种客观检测听力损失的常用方 法。短声作为一种宽频信号,其诱发的 ABR 通常被认为是 ABR 检测的金标准。但由于人体耳蜗基底 膜行波具有延迟特性,短声不能同时刺激整个耳蜗基底膜产生兴奋,导致诱发的 ABR 波形因不同相而 产生衰减。为解决这一局限性,该研究设计了一种扫频音刺激,根据耳蜗基底膜的延迟特性重新调整 不同频率成分出现的时间,以诱发 ABR 信号。实验通过将所设计的扫频 ABR 方法和传统的短声 ABR 方法的波质量进行比较发现,在不同的刺激强度和刺激速率下,扫频 ABR 的波形形态均明显优于短声 ABR 的。此外,在不同的响应叠加次数下,所设计的扫频音比短声诱发 ABR 能更快地诱发出 ABR 波 形。该文所提出的扫频 ABR 方法有望提高 ABR 在听力损失诊断中的灵敏度。     

二进制ABR流量控制算法的建模与分析

面向连接的ATM网络通过一系列的流量管理机制为各种应用提供纯粹的服务质量保证（QoS)，其中ABR业务流量控制的作用尤其重要，在二进制流量控制方案中，信元速率和队列长度的大幅振荡降低了链路利用率，严重地影响了算法的效率，但它的简洁性对设计高性能交换机又极具吸引力，该文基于流体流理论建立了二进制流量控制的分析模型，并用仿真试验验证了模型的正确性，通过小信号局部线性化方法得到源终端系统调节速率的线性模型，分别将标准EFCI算法和作者改进的基于概率标识的p-EFCI算法等效为带继电器特性的饱和特性的非线性环节，用控制理论中描述函数的分析方法研究了两种算法的稳定性，在理论上为p-EFCI算法在鲁棒性方面优于EFCI算法找到了根据。     

模糊控制在ATM流量管理中的应用

应用模糊控制理论,研究了ATM网络的流量管理问题。将ABR（Available Bit Rate)业务的流量控制抽象为一时滞系统的控制问题,指出了一种模糊速率流量控制算法,实现了带宽在各个ABR虚连接中公平有效地分配。仿真结果表明算法具有良好的综合性能。