Single server queueing model for data multiplexing in analog speech

Finite buffer behavior of an asynchronous time division multiplexed (ATDM) channel is investigated. Mixed data comprising of single character and burst (String of characters) is asynchronously multiplexed in analog speech on the channel. A queueing model with limited buffer capacity, mixed input traffic (Poisson and burst Poisson arrivals), constant transmission rate (while serving) and server interruptions through a first order Markov process is studied for the purpose. Our results indicate that for a given traffic intensity, buffer behavior in this system lies between that for Poisson input arrivals and that for burst Poisson input arrivals. Therefore, the buffer should be designed for the pure burst Poisson arrivals as it may be treated as the worst case design for the pure Poisson and the mixed arrivals as well.     

高射频步枪参数对枪口响应影响的分析

建立具有13刚体和31自由度的被动态人-枪相互作用模型,采用弹簧-阻尼方法进行肌肉模拟,利用逆向动力学方法确定各关节上的初始驱动力.考虑设计参数间的相互耦合影响,分析射频、缓冲簧刚度和预压力以及缓冲行程等参数对枪口响应的影响.基于多体系统动力学模型进行参数的灵敏度分析和优化.分析结果表明:射频增加对于3发点射情况下的枪口精度是有利的;对于第3发以后的射击,只有枪械缓冲装置与人体系统的合理匹配才能有效减小人体被动态下枪口的跳动位移.     

基于模糊控制的ATM网络VBR视频传输平滑策略

VBR视频传输的突发性是影响ATM网络服务质量的关键因素,文中通过模糊控制方法对视频传输流量的阈值进行监控,实现了接入的平滑并可动态调整传输速度。文中以传输流量及这发级作为评价指标进行分析,结果表明VBR视频传输自适应平滑策略的实效性。     

An optical burst reordering model for time-based and random selection assembly strategies

Contention resolution schemes in optical burst switched networks (OBS) as well as contention avoidance schemes delay burst delivery and change the burst arrival sequence. The burst arrival sequence usually changes the packet arrival sequence and degrades the upper layer protocols performance, e.g., the throughput of the transmission control protocol (TCP).In this paper, we present and analyze a detailed burst reordering model for two widely applied burst assembly strategies: time-based and random selection. We apply the IETF reordering metrics and calculate explicitly three reordering metrics: the reordering ratio, the reordering extent metric and the TCP relevant metric. These metrics allow estimating the degree of reordering in a certain network scenario. They estimate the buffer space at the destination to resolve reordering and quantify the number of duplicate acknowledgements relevant for investigations on the transmission control protocol.We show that our model reflects the burst/packet reordering pattern of simulated OBS networks very well. Applying our model in a network emulation scenario, enables investigations on real protocol implementations in network emulation environments. It therefore serves as a substitute for extensive TCP over OBS network simulations with a focus on burst reordering.     

基于模糊逻辑和路由器辅助的MCC算法

针对端到端组播拥塞控制的局限性,提出一种基于模糊逻辑和路由器辅助的组播拥塞控制算法FLRA-MCC。在FLRA-MCC中,主动路由器实时监测网络状态,利用模糊逻辑计算缓冲区调节因子a,从而自动调节缓冲区大小以缓解拥塞,并且只在发生较重拥塞时,才向源端反馈拥塞信息以通知源端减小发送速率。仿真结果表明,该算法能够保证网络吞吐量的稳定性,较好地吸收突发流,同时以更小的丢包率传输数据。     

Energy-efficient scheduling in multi-core servers

In this paper we develop techniques for analyzing and optimizing energy management in multi-core servers with speed scaling capabilities. Our framework incorporates the processor’s dynamic power, but it also accounts for other intricate and relevant power features such as the static (leakage) power and switching overhead between speed levels. Using stochastic fluid models to capture traffic burst dynamics, we propose and study different strategies for adapting the multi-core processor speeds based on the observable buffer content, so as to optimize objective functions that balance energy consumption and performance. The strategies can be non-hysteretic (i.e., the processor speed depends on current buffer level relative to the buffer thresholds) or hysteretic (i.e., it matters in which direction the buffer thresholds are crossed). It is shown that, under rather general conditions, strategies which use more threshold levels are more efficient with respect to power consumption; however, most of the efficiency gain is achieved with 1 or 2 thresholds only. In addition, the optimal power consumptions of the different strategies are only very mildly sensitive to perturbations in the input parameters, implying the highly advantageous property that the performance is robust to estimation errors in the system’s input traffic parameters.     

OBS网络中基于突发的可用信道数组及其调度算法

信道调度算法是提高光突发交换(OBS)网络性能的关键技术之一.现有的数据信道调度算法多是基于单一突发的模式,即每个突发的控制分组(BCP)到达后就立即被调度处理,其效率的提高已迭极限.首次提出基于突发的可用信道数组的概念,将对每个突发仅搜索一次信道组的状况并保存有关信息,从而有效提高系统的调度效率.该设计的调度器能有效减少对信道状况的多次扫描,进一步改善OBS网络的性能.     

光突发交换网络中无缓存冲突解决模型的研究

光突发交换网络被认为是未来光网络发展的趋势,而突发包在节点的冲突问题却是光突发交换网络中一个非常需要解决的问题,目前很多情况下使用的光缓存技术虽然可以缓解冲突问题,但是却增加了节点结构的复杂性和噪声。论文首先提出一种基于优先级的冲突解决方法,并给出了突发包的封装格式,然后利用三种无缓存的冲突解决模型对不同优先级突发包的冲突问题进行了详细的叙述和比较。     

Buffer Coding for Reliable Transmissions over Wireless Networks

In-network caching is a useful technique for reducing latency and retransmission overhead of lost packets for reliable data delivery in wireless networks. However, in-network caching is challenging to implement in memory constrained devices such as RFIDs and sensors, and also in Wireless LAN (WLAN) gateways for large-scale deployments. In this paper we propose a novel technique for management of in-network caches using XOR coding for optimizing the use of limited buffer space in presence of random and burst packet losses. We identify two critical parameters, coding degree and coding distance for the coding scheme. As a case-study we implement our approach over Snoop and evaluate its performance for WLANs. We further propose a self-adaptive algorithm that tunes coding degree on the fly based on the measured coding behavior and packet loss probability. Using simulations in ns-2, we observe that in our simulation settings, when the size of the retransmission buffer in the gateway is less than 16 packets per TCP flow, the throughput can be enhanced by up to 30% for random losses and up to 20% for burst losses.     

交叉流水线多队列缓冲报文转发技术

IP报文封装为链路帧是路由器设计必不可少的技术。提出了一种通用的多通道报文封装和转发的处理器结构．利用FPGA内部存储资源，采用流水线和多队列缓存区相结合，显著提高了小报文线速转发和突发流量传输的性能。     

Parallel simulation of statistical multiplexers

The simulation of high-speed telecommunication systems such as ATM (Asynchronous Transfer Mode) networks has generally required excessively long run times. This paper reviews alternative approaches using parallelism to speed up simulations of discrete event systems, and telecommunication networks in particular. Subsequently, a new simulation method is introduced for the fast parallel simulation of a common network element, namely, a work-conserving finite capacity statistical multiplexer of bursty ON/OFF sources arriving on input links of equal peak rate. The primary performance measure of interest is the cell loss ratio, due to buffer overflows. The proposed method is based on two principal techniques: (1) the derivation of low-level (cell level) statistics from a higher level (burst level) simulation and (2) parallel execution of the burst level simulation program. For the latter, atime-division parallel simulation method is used where simulations operating at different intervals of simulated time are executed concurrently on different processors. Both techniques contribute to the overall speedup. Furthermore, these techniques support simulations that are driven by traces of actual network traffic (trace-driven simulation), in addition to standard models for source traffic. An analysis of this technique is described, indicating that it offers excellent potential for delivering good performance. Measurements of an implementation running on a 32 processor KSR-2 multiprocessor demonstrate that, for certain model parameter settings, the simulator is able to simulate up to 10 billion cell arrivals per second of wallclock time.     

OBS网络中基于缓存和分割的冲突解决方法研究

光突发交换网络被认为是一种新型的IPoverWDM光网络,其中突发包在核心路由器中发生的冲突问题是一个关键的研究课题。解决冲突的方法可以分为利用缓存和不利用缓存两大类。目前对这两种方法进行的单独研究很多,这就存在有很大的局限性,因为独立的研究并不能灵活适应网络环境的需求,这样就不能达到优化网络的目的。本文针对这样的局限性,首先列出了几种光缓存结构,而后以一种结构较优越的缓存结构和分割策略进行了综合性能比较,分析了两种策略各自的优势,得出的一些有用结论对于以后实际光突发交换网络的优化设计具有一定的理论指导意义。     

基于改进粒子群优化算法的PID控制器整定

由传统的Z-N(Ziegler-Nichols)整定公式得出的PID参数,不能得到最佳的控制性能.为此,本文提出一种基于适应度指数定标和边界缓冲墙相结合的改进型粒子群算法,应用于PID参数的整定.首先采用适应度指数定标的选中概率,挑选出粒子进行随机变异;其次对越界的粒子进行缓冲,保证粒子落在寻优空间内以增加粒子种群多样性,同时调整种群粒子个数、社会和认知因子以提高寻优效率.在仿真实验中,将改进的粒子群算法分别应用于5种不同的工业过程,整定他们的PID参数.对误差绝对值乘以时间积分的性能指标(ITAE)做最小化,得到了相应的PID参数,验证了这里提出的改进型粒子群算法的有效性.     

基于自相似流量的一种新的队列管理算法

鉴于网络流量的自相似特性,结合应对该特性可采用的两种主要措施,提出了一种应对该特性的一种新的队列管理算法。算法包括两部分,一是缓冲区管理算法,另一是队列调度算法。新算法在缓冲区管理上采用了一种“伪扩充”缓冲区的方法。“伪扩充”维持缓冲区总空间的不变的情况下,按照策略增加一个用于处理自相似突发流量的队列。针对“扩充”后的缓冲区,采用基于静态优先级和轮询的队列调度算法。从理论上分析了,两部分的结合产生的新的队列管理算法在应对自相似突发流量中的有用性。     

A simulation study of bursty data traffic with hybrid source smoothing in an ATM node

In this paper, we study the mean delay and maximum buffer requirements at different levels of burstiness for highly bursty data traffic in an ATM node. This performance study is done via an event-driven simulation program which considers both real-time and data traffic. We assume that data traffic is loss-sensitive. A large buffer (fat bucket) is allocated to data traffic to accommodate sudden long burst of cells. Real-time traffic is delay-sensitive. We impose input traffic shaping on real-time traffic using a leaky-bucket based input rate control method. Channel capacity is allocated based on the average arrival rate of each input source to maximize the utilization of channel capacity. Simulation results show that both the maximum buffer requirements and mean node delay for data traffic are directly proportional to the burstiness of its input traffic. Results for mean node delay and cell loss probability of real-time traffic are also analyzed. The simulation program is written in C++ and has been verified using the zero mean statistics concept by comparing simulation results to known theoretical or observed results.     

ABS: Adaptive buffer sizing for heterogeneous networks

Most existing criteria [3], [5], [9] for sizing router buffers rely on explicit formulation of the relationship between buffer size and characteristics of Internet traffic. However, this is a non-trivial, if not impossible, task given that the number of flows, their individual RTTs, and congestion control methods, as well as flow responsiveness, are unknown. In this paper, we undertake a completely different approach that uses control-theoretic buffer size tuning in response to traffic dynamics. Motivated by the monotonic relationship between buffer size and loss rate and utilization, we design a mechanism called Adaptive Buffer Sizing (ABS), which is composed of two Integral controllers for dynamic buffer adjustment and two gradient-based components for intelligent parameter training. We demonstrate via ns2 simulations that ABS successfully stabilizes the buffer size at its minimum value under given constraints, scales to a wide spectrum of flow populations and link capacities, exhibits fast convergence rate and stable dynamics in various network settings, and is robust to load changes and generic Internet traffic (including FTP, HTTP, and non-TCP flows). All of these demonstrate that ABS is a promising mechanism for tomorrow’s router infrastructure and may be of significant interest for the ongoing collaborative research and development efforts (e.g., GENI and FIND) in reinventing the Internet.     

A performance model for an asynchronous optical buffer

We investigate the behaviour of an asynchronous optical buffer by means of a continuous-time queuing model. Through a limit procedure, previously obtained results for a discrete-time queuing model are translated to a continuous-time setting. We also show that the same results can be obtained by a direct analysis using Laplace transforms. Closed-form expressions are obtained for the cases of exponentially distributed burst sizes, deterministic burst sizes and mixtures of deterministic burst sizes.

The performance of asynchronous optical buffers shows the same characteristics as that of synchronous optical buffers: a reduction in throughput due to the creation of voids on the outgoing channel and a burst loss probability that is strongly influenced by the choice of fiber delay line granularity. The optimal value of the latter depends on the burst size distribution and the offered load.     

Performances of burst admission control schemes with cell multiplexing in ATM networks

In this paper, we consider two burst admission control (BAC) schemes with cell multiplexing. One is the burst admission by threshold (BAT) scheme which uses the BAC function by comparing a threshold value with the queue size on the epoch receiving a burst request. Another is the burst admission by prediction of cell losses (BAPCL) scheme, which is based on the fact that it is possible to calculate the queue sizes at burst release times when there is a burst request. By a multi-level model with an MMDP/D/1/K queuing system, the performance and the effect of the two schemes are studied in view of burst and cell levels. Also, the performance of the peak bit-rate reservation (PBRR) scheme without cell buffering is considered with a backoff state. By numerical examples, we discuss the dependence of system performances on the traffic and the system parameters. In order to show the increase of multiplexing gain by the BAC schemes with cell multiplexing, we compare the admissible loads of the BAT and BAPCL schemes with those of the PBRR and the pure cell multiplexing schemes, where we can see that the BAT scheme has almost the same performance as the BAPCL scheme though the latter is superior to the former for most cases, especially for the stringent cell-loss sensitive case.     

基于分段IFS分形重建的流量模型

网络流量模型是网络仿真和网络行为研究中的一个基本问题。在分段IFS分形编码重建的基础上提出了一个新的网络流量模型,它基于实际流量的分形重建,所得重建流量变化趋势接近初始流量。在调节因子θ的作用下,重建流量的Hurst参数可以在一定范围内变化,同时重建流量自相关函数曲线与原始流量类似。因此,为网络流量仿真建模研究提供了一种新的选择。     

Min-max control of uncertain multi-inventory systems withmultiplicative uncertainties

In this note, we consider production-distribution systems with buffer and capacity constraints. For such systems, we assume that the model is not known exactly. More precisely, the entries of the matrix representing the system structure may be affine functions of some uncertain time-varying parameters that take values within assigned bounds. We give stabilizability conditions that can be checked, in principle, by solving a min-max problem on the surface of the state-space (buffer level space) unit ball. Then, we consider a special case in which each uncertain parameter affects a single column of the system matrix and is independent of all the other ones. In this case, we propose a mixed integer linear programming algorithm to check the stabilizability conditions and we provide a stabilizing control in an explicit form