具有线群结构的输入缓冲ATM交换网络在双优先级业务下的性能分析

本文对具有线群结构的输入缓冲ＡＴＭ交换网络在双优先级业务下的时延和吞吐率性能进行了分析。借助概率母函数的方法，给出了高低优先级信元在缓冲器中的队长分布，时延分布平均队长和平均时延以及交换网络最大吞吐率的封闭表达式，并通过计算机仿真验证了分析结果的精确性。由于所采用的分析方法克服了传统的数值叠代计算方法的复杂性，因此，在ＡＴＭ交换网络的工程设计中具有重要的实际意义。     

ATM组播交换系统的一种信元调度算法

对于输入缓冲和输出缓冲ATM组播交换系统,目前主要有两种信元调度算法:窗口调度算法和输出缓冲算法。这两种算法分别用于输入缓冲和输出缓冲系统中,其缺点是对处理器速度和存储器访问速度要求较高。笔者给出的算法对交换网络的处理速度和存储器访问速度要求不高。可以大大改善了交换机的延迟-吞吐率性能。     

高速信元交换调度算法研究

输入缓存交换结构的特点是缓存器和交换结构的运行速率与端口速率相等、实现容易,但存在队头阻塞(HOL),其吞吐率只有约58%.采用虚拟输出排队方法(VOQ)和适当的信元调度算法可消除HOL,使吞吐率达到100%.本文通过仿真对几种调度算法:PIM、iSLIP和LPF进行了全面地研究、比较和评价.     

实现虚拟输出队列调度的神经网络方法

基于虚拟输出队列（VOQ）缓存的Crossbar交换结构,提出了一种Hopfield神经网络（HNN）控制的信元交换调度方法.通过选取合适的能量函数,并在其中采用一种新的队列优先级函数,实现了信元的高效交换控制.计算机模拟结果表明,该算法可以将吞吐率提高到0.998,信元丢失率大大降低,时延特性也有很大改善.     

一种改进的多输入队列的神经网络调度算法

提出一种改进的ATM交换机多输入队列的神经网网络调度算法（IMIQM）,其调度策略采用每条入线在同一时隙内可传送多于1个信元的策略,并提出一种用于Hopfield神经网络（HNN）控制信元调度的新的能量函数。利用计算机进行仿真模拟,在业务流模型和负荷相同的情况下,当交换机规模N为150、多输入队列（开窗数）为5时,IMIQM的最大吞吐率可以达到0．904,普通的多输入队列法（MIQM）为0．856,而窗口方法（WM）为0．886。结果表明,IMIQM与MIQM、WM相比提高了吞吐率,或在吞吐率相同的情况下IMIQM更容易用光电子技术实现,且由于HNN的高度并行的数据处理能力,能够实现大规模交换结构的实时调度。     

输入缓冲结构ATM交换网络的窗口接入机理研究

本文了输入缓冲结构ＡＴＭ交换网络的窗口接入机理，首先分析了一种传统的相关窗口接入（ＤＷＡ）机理的最大吞吐率性能，然后，提出了一种独立的窗口接入（ＩＷＡ）机理，ＩＷＡ能彻底消除采用传统的ＤＷＡ机理时在输入缓冲器窗口中存在的队头阻塞现象，借助于概率母函数的方法分析了采用该ＩＷＡ机理的输入缓冲ＡＴＭ交换网络的时延和吞吐率性能，给出了求解平均信元时延和最大吞吐率的封闭显式，分析表明，ＩＷＡ机理的性能比传统     

星载Clos网络的全分布式容错调度算法

针对星载交换结构受空间辐射影响造成的可靠性严重下降问题,该文提出了一种支持全分布式调度的三级Clos网络及其全分布式容错(Fully Distributed Fault Tolerant, FDFT)调度算法,以提高星载交换结构在交叉点故障下的容错能力。该Clos网络的中间级和输出级采用联合输入交叉点队列,以支持Clos网络和交换单元内部的全分布式调度。FDFT采用一种分布式故障检测算法获得交叉点故障信息。基于对交叉点故障影响范围的分析,FDFT在输入级采用一种容错信元分发算法,实现无故障路径的负载均衡。理论分析证明,当任一输入/输出级交换单元故障个数不超过(m-n)或所有中间级交换单元故障个数不超过(m-n)时,其中m, n分别为输入级交换单元输入、输出端口数,FDFT能够达到100%吞吐率。仿真结果进一步验证,故障随机发生情况下,FDFT能够抵抗比故障任意发生情况下更多的故障,且在不同的业务场景下具有良好的吞吐率和时延性能。     

AMT交换中的群输出技术及应用

在ＡＴＭ交换网络的设计中，采用一个地址代表多个物理输出口的方法实现ＡＴＭ信元的选路，并进而在输出端分路输出的群输出技术可很好地利用网络业务的统计特征，获得高的网络性能和硬件需要量。本文叙述了群输出技术的原理，分析了其性能，并通过例子说明它在交换网络设计中的应用。     

编码TCP的建模与性能分析

研究了无线网络端到端分组丢失和编码纠错对TCP协议工作过程的影响机制,基于三维Markov链建模描述TCP拥塞窗口和可用窗口的变迁过程,在忽略慢启动阶段的条件下,以最大窗口尺寸、端到端分组丢失率和编码冗余系数为输入参数,通过数值计算求解编码TCP的吞吐率,据此定量分析影响编码TCP性能的因素。基于NS2的模拟实验结果表明基于Markov链的数值计算结果具有较高的准确度。     

多平面ATM交换网络结构及其性能分析

本文提出一种新的多平面ＡＴＭ交换网络结构。该结构比单平面结构有更好的性能,并且在网络平扩容和冗余备份等方面均具有优良的特性。通过采用虚拟队列和概率母函数的方法,分析了在随机均匀业务模型下该交换网络缓存器的平均队长、平均信元时延和交换网络最大吞吐率等性能参数的封闭表达式,计算机仿真结果表明了分析结果具有很高的精确度。该分析方法不需复杂的叠代算法,在交换机的工程设计中同时也具有重要的实际意义。     

Performance study of an input and output queueing ATM switch with a window scheme and a speed constraint

In this paper, we study the performance of an input and output queueing switch with a window scheme and a speed constraint. The performance of a non-blocking ATM switch can usually be improved by increasing the switching speed. Also, the performance of a switch can be improved using a window scheme by relaxing the first-in-firstout (FIFO) queueing discipline in the input queue. Thus, one can expect that a combined scheme of windowing and a speed constraint can improve further the performance of the packet switch. Here, we analyze the maximum throughput of the input and output queueing switch with a speed constraint combined with windowing, and show that it is possible to obtain high throughput with a small increment of speed-up and window size. For analysis, we model the HOL queueing system as a virtual queueing system. By analyzing the dynamics of HOL packets in this virtual queueing model, we obtain the service probability of the HOL server as a function of output contention capabilities. Using the result, we apply the flow conservation relation to this model and obtain the maximum throughput. The analytical results are verified by simulation.     

The impact of multihop wireless channel on TCP performance

This paper studies TCP performance in a stationary multihop wireless network using IEEE 802.11 for channel access control. We first show that, given a specific network topology and flow patterns, there exists an optimal window size W* at which TCP achieves the highest throughput via maximum spatial reuse of the shared wireless channel. However, TCP grows its window size much larger than W* leading to throughput reduction. We then explain the TCP throughput decrease using our observations and analysis of the packet loss in an overloaded multihop wireless network. We find out that the network overload is typically first signified by packet drops due to wireless link-layer contention, rather than buffer overflow-induced losses observed in the wired Internet. As the offered load increases, the probability of packet drops due to link contention also increases, and eventually saturates. Unfortunately the link-layer drop probability is insufficient to keep the TCP window size around W'*. We model and analyze the link contention behavior, based on which we propose link RED that fine-tunes the link-layer packet dropping probability to stabilize the TCP window size around W*. We further devise adaptive pacing to better coordinate channel access along the packet forwarding path. Our simulations demonstrate 5 to 30 percent improvement of TCP throughput using the proposed two techniques.     

PERFORMANCE ANALYSIS OF AN INPUT-BUFFERED ATM SWITCHING FABRIC WITH INDEPENDENT WINDOW-ACCESS SCHEME

In this paper, an Independent Window-Access(IWA) scheme is proposed, and the performance of an input-buffered ATM switching fabric with the IWA scheme is analysed by means of a probability generating function approach, the closed formulas of the average cell delay and the maximum throughput are given, and results show that the IWA scheme makes the switching fabric have better performances than traditional window-access scheme. The computer simulation results are in good agreement with these analytical results.     

High-throughput cell scheduling for broadband switching systems

The authors consider the output contention problem with a view towards increasing the throughput for asynchronous transfer mode (ATM) switching systems. A cell scheduling algorithm for increasing the throughput is proposed. The maximum throughput is increased up to 0.957. The efficiency (output trunk utilization/input trunk utilization) is almost equal to 100% and is independent of the switch size and traffic load. A switching system implemented with this cell scheduling algorithm is also proposed. The switching network usually consists of a sorting network followed by a routing network. Here, it is sufficient for a sorting network to establish input-output paths through it simultaneously without conflicts, and it is not necessary to append a routing network. In addition, a parallel mesh-connected architecture of a component of the switching system is proposed to speed up the cell scheduling of the system. Consequently, this approach can offer an effective alternative to ATM switching systems     

Rerouting network: a high-performance self-routing switch forB-ISDN

A high-performance self-routing switch is proposed for ATM (asynchronous transfer mode) switch systems. Switching performance is enhanced by a rerouting algorithm applied to a particular multistage interconnection algorithm. The interconnection algorithm offers many access points to the output and resolves output contention by layering buffers at each switching stage. The author analyzes switching performance and shows that this switch can be easily engineered to have high throughput and low cell loss probability by increasing the number of switching stages. The author also illustrates that the number of switching stages required for a given cell loss probability shows gradual growth with increasing switch size. Analysis shows that the proposed switch is robust even with respect to nonuniform traffic     

FIFO交换网络:一种保持信元次序完整性的多路径ATM交换结构

本文提出了一种新型的自选路由ＡＴＭ多路径交换结构，采用虚拟ＦＩＦＯ缓冲器技术，即能保持信元次序的完整性，又避免了螺旋式交换结构中虚拟信元引起的饱和吞吐量、延迟和信元丢失性能的下降。在均匀通信量和非均匀通信量情况下分析了它的性能，结果表明其最大可达到的饱和吞吐量为７／８，延迟和信元丢失率都比螺旋式结构小很多。同时，该系统无需内部加速，适于ＶＬＳＩ集成。     

Video transmission strategy in multi-rate and multi-node IEEE 802.11 networks

The video transmission strategy VQCW (video queue contention window) was proposed for video transmission fair problem in multi-rate and multi-node IEEE 802.11 networks.The strategy was based on node queue selective packet drop and contention window dynamic adjustment.It deduced a maximum throughput model according to initial contention window size because of the relation between throughput and initial contention window size.This model can provide theoretical upper limit for improving throughput.The theoretical modeling and NS simulation show that the proposed strategy can maintain both video transmission quality and high network overall throughput.     

Design and performance analysis of an asynchronous non-blocking switch with window policy

In this paper, we propose an architecture of an asynchronous non-blocking switch. The switch structure is relatively simple, but it has an advantage in that the window scheme can easily be implemented. Many switch structures synchronized with time slots have been proposed, but they are not efficient when implementing a window scheme. The asynchronous switch proposed in this paper with its implementation of a window scheme can increase its maximum throughput up to 1 in the case of minimum changeover time and large packet size. We also investigate the delay characteristics of the asynchronous switch. In the analysis of delay characteristics, we make some approximations. However, the results of the analysis are in good agreement with simulation results. In addition, the maximum throughput of the switch with finite window size is investigated.