Impact of Network Dynamics on User's Video Quality: Analytical Framework and QoS Provision

We develop an analytical framework to investigate the impacts of network dynamics on the user perceived video quality. Our investigation stands from the end user's perspective by analyzing the receiver playout buffer. In specific, we model the playback buffer at the receiver by a G/G/1/? and G/G/1/N queue, respectively, with arbitrary patterns of packet arrival and playback. We then examine the transient queue length of the buffer using the diffusion approximation. We obtain the closed-form expressions of the video quality in terms of the start-up delay, fluency of video playback and packet loss, and represent them by the network statistics, i.e., the average network throughput and delay jitter. Based on the analytical framework, we propose adaptive playout buffer management schemes to optimally manage the threshold of video playback towards the maximal user utility, according to different quality-of-service requirements of end users. The proposed framework is validated by extensive simulations.     

Conditioned asymptotics for tail probabilities in large multiplexers

Consider a buffer whose input is a superposition of L independent identical sources, and which is served at rate sL. Recent work has shown that, under very general circumstances, the stationary tail probabilities for the queue of unfinished work Q in the buffer have the asymptotics P[Q > Lb] ≈ e^−LI(b) for large L. Here the shape function, I, is obtained from a variational expression involving the transient log cumulant generating function of the arrival process.

In this paper, we extend this analysis to cover time-dependent asymptotics for Markov arrival processes subject to conditioning at some instant. In applications we envisage that such conditioning would arise due to knowledge of the queue at a coarse-grained level, for example of the number of current active sources. We show how such partial knowledge can be used to predict future tail probabilities by use of a time dependent, conditioned shape function. We develop some heuristics to describe the time-dependent shape function in terms of a reduced set of quantities associated with the underlying arrivals process and show how to calculate them for renewal arrivals and a class of ON-OFF arrivals. This bypasses the full variational calculation of the shape function for such models.     

Port partitioning and dynamic queueing for IP forwarding

With the increase of internet protocol (IP) packets the performance of routers became an important issue in internet/working. In this paper we examine the matching algorithm in gigabit router which has input queue with virtual output queueing. Dynamic queue scheduling is also proposed to reduce the packet delay and packet loss probability. Port partitioning is employed to reduce the computational burden of the scheduler in a switch which matches the input and output ports for fast packet switching. Each port is divided into two groups such that the matching algorithm is implemented within each pair of groups in parallel. The matching is performed by exchanging the pair of groups at every time slot. Two algorithms, maximal weight matching by port partitioning (MPP) and modified maximal weight matching by port partitioning (MMPP) are presented. In dynamic queue scheduling, a popup decision rule for each delay critical packet is made to reduce both the delay of the delay critical packet and the loss probability of loss critical packet. Computational results show that MMPP has the lowest delay and requires the least buffer size. The throughput is illustrated to be linear to the packet arrival rate, which can be achieved under highly efficient matching algorithm. The dynamic queue scheduling is illustrated to be highly effective when the occupancy of the input buffer is relatively high.Scope and purposeTo cope with the increasing internet traffic, it is necessary to improve the performance of routers. To accelerate the switching from input ports to output in the router partitioning of ports and dynamic queueing are proposed. Input and output ports are partitioned into two groups A/B and a/b, respectively. The matching for the packet switching is performed between group pairs (A, a) and (B, b) in parallel at one time slot and (A, b) and (B, a) at the next time slot. Dynamic queueing is proposed at each input port to reduce the packet delay and packet loss probability by employing the popup decision rule and applying it to each delay critical packet.The partitioning of ports is illustrated to be highly effective in view of delay, required buffer size and throughput. The dynamic queueing also demonstrates good performance when the traffic volume is high.     

Application-driven,energy-efficient communication in wireless sensor networks

Several sensor network applications based on data diffusion and data management can determine the communication transfer rate between two sensors beforehand. In this framework, we consider the problem of energy efficient communication among nodes of a wireless sensor network and propose an application-driven approach that minimizes radio activity intervals and prolongs network lifetime. On the basis of possible communication delays we estimate packet arrival intervals at any intermediate hop of a fixed-rate data path. We study a generic strategy of radio activity minimization wherein each node maintains the radio switched on just in the expected packet arrival intervals and guarantees low communication latency. We define a probabilistic model that allows the evaluation of the packet loss probability that results from the reduced radio activity. The model can be used to optimally choose the radio activity intervals that achieve a certain probability of successful packet delivery for a specific radio activity strategy. Relying on the probabilistic model we also define a cost model that estimates the energy consumption of the proposed strategies, under specific settings. We propose three specific strategies and numerically evaluate the associated costs. We finally validate our work with a simulation made with TOSSIM (the Berkeley motes’ simulator). The simulation results confirm the validity of the approach and the accuracy of the analytic models.     

Class-specific quality of service guarantees in multimedia communication networks

We consider the problem of quality-of-service (QoS) provisioning in modern high-speed, multimedia, communication networks. We quantify QoS by the probabilities of loss and excessive delay of an arbitrary packet, and introduce the model of a multiclass node (switch) which provides network access to users that may belong to multiple service classes. We treat such a node as a stochastic system which we analyze and control. In particular, we develop an analytical approach to estimate both the delay and the buffer overflow probability per service class, based on ideas from large deviations and optimal control. We exploit these performance analysis results by devising a call admission control algorithm which can provide per class QoS guarantees. We compare the proposed approach to alternative worst-case and effective bandwidth-based schemes and argue that it leads to increased efficiency. Finally, we discuss extensions to the network case in order to provide end-to-end QoS guarantees.     

Computing steady state probabilities in λ(n)/G/1/K queue

In this paper a recursive method is developed to obtain the steady state probability distribution of the number in system at arbitrary and departure time epochs of a single server state-dependent arrival rate queue λ(n)/G/1/K in which the arrival process is Markovian with arrival rates λ(n) which depend on the number of customers n in the system and general service time distribution. It is assumed that there exists an integer K such that λ(n) > 0 for all 0 n < K and λ(n) = 0 for all n K. Numerical results have been presented for many queueing models by suitably defining the function λ(n). These include machine interference model, queues with balking, queues with finite waiting space and machine interference model with finite waiting space. These models have wide application in computer/communication networks.     

An output queueing analysis of multipath ATM switches

The performance of output buffers in multipath ATM switches is closely related to the output traffic distribution, which characterizes the packet arrival rate at each output link connected to the output buffer of a given output port. Many multipath switches produce nonuniform output traffic distributions even if the input traffic patterns are uniform. Focusing on the nonuniform output traffic distribution, we analyze the output buffer performances of several multipath switches under both uniform and nonuniform input traffic patterns. It is shown that the output traffic distributions are different for the various multipath switches and the output buffer performance measured in terms of packet loss probability and mean waiting time improves as the nonuniformity of the output traffic distribution becomes higher.     

高吞吐量的核心无状态公平队列算法

提出了一种优化的核心无状态公平队列凋度算法(xCSFQ),在CSFQ的基础上,根据缓冲区占用率和数据流到达速率决定丢包概率,缓存管理上采用基于CHOKC原理的机制进行缓存管理,解决了CSFQ链路利用率低的问题,提高了带宽在UDP流和TCP流之间分配的公平性,最后对算法进行了仿真分析。     

Per-stream loss behavior of ∑MAP/M/1/K queuing system with a random early detection mechanism

In this paper, the matrix-analytic approach is applied to explore the per-stream loss behavior of the multimedia traffic under RED scheme. We constructed a ∑MAP/M/1/K queuing model for the RED mechanism with multimedia traffic which follows a continuous-time Markovian arrival process (MAP). In addition to evaluating the long-term per-stream packet drop probabilities, we examine the bursty nature of per-stream packet drops by means of conditional statistics with respect to dropped periods and the probability that the queuing system stays in the dropped period. The dropped period corresponds to having more than a certain number of packets in router buffer; non-dropped period corresponds to the opposite. These performance measures describe the quality of service provided by the router to particular multimedia traffic streams in the presence of background multimedia traffic.     

Initial-interval driven biasing of nodal concentration along a fixed curve

Element size transitioning in the construction of spatial meshes for finite element models is often controlled by biasing the concentration of nodes, towards one end or the other, along each of a set of curves in the model. A simple, common and efficient scheme to implement such nodal concentration biasing along a given curve is to require that the nodal spacings δ_i be (sequence) terms bⁱδ₀ of a geometric series. Current practice takes the parameter value b, or its equivalent, as an independent input, so that the initial nodal spacing δ₀ must be a computed output. This is the most straightforward approach, but the lack of direct control over the value δ₀ is a significant shortcoming. In an element size transitioning scenario, δ₀ is often a parameter for which the model builder/analyst has independent quantitative information. It may represent the a priori known thickness of a thin bond or weld, for example. A more rational choice for these cases, proposed by this paper, is a scheme for which δ₀ is an independent input parameter instead of b. The parameter b is computed by a convergence-guaranteed algorithm for which the existence of b as a single-valued function of its input is proven.     

Framework based on stochastic L-Systems for modeling IP traffic with multifractal behavior

This paper presents and compares a set of traffic models, and associated parameter fitting procedures, based on so-called stochastic L-Systems, which were introduced by biologist A. Lindenmayer as a method to model plant growth. Starting from an initial symbol, an L-System generates iteratively sequences of symbols, belonging to an alphabet, through successive application of production rules. In a traffic modeling context, the symbols are interpreted as packet arrival rates or mean packet sizes, and each iteration is associated to a finest time scale of the traffic. These models are able to capture the multiscaling and multifractal behavior sometimes observed in Internet traffic. We describe and compare four traffic models, one characterizing the packet arrival process, and the other three characterizing both the packet arrival and the packet size processes. The models are tested with several measured traffic traces: the well-known pOct Bellcore, a trace of aggregate WAN traffic and two traces of specific applications (Kazaa and Operation Flashing Point). We assess the multifractality of these traces using Linear Multiscale Diagrams. The traffic models are evaluated by comparing, for the measured traffic and for traffic generated according to the inferred models, the probability mass function, the autocovariance function and the queuing behavior. Our results show that the L-System based traffic models that characterize both the packet arrival and packet size processes can achieve very good fitting performance in terms of first- and second-order statistics and queuing behavior.     

The 0—1 Integer Programming Problem in a finite ring with identity

We define the 0—1 Integer Programming Problem in a finite field or finite ring with identity as: given an m × n matrix A and an n × 1 vector b with entries in the ring R, find or determine the non-existence of a 0—1 vector x such that Ax = b. We give an easily implemented enumerative algorithm for solving this problem, along with conditions that spurious solutions occur with probability as small as desired. Finally, we show that the problem is NP-complete if R is the ring of integers modulo r for r ≥ 3. This result suggests that it will be difficult to improve on our algorithm.     

The departure process of an N/G/1 queue

The departure process of an N/G/1 queue is investigated. The arrival process called an N process is a versatile point process and includes, for example, a Markov-modulated Poisson process, which is comprised of models of packetized voice and video traffic arrival processes. The first passage analysis yields LSTs of distributions of the interdeparture times. Emphasis is on the interdeparture times of an N/D/1 queue. Numerical examples show that correlation of interarrival times is likely to be preserved in interdeparture times, and that the departure of a voice packet multiplexer can be expected to be smoothed for a normal load. The result in this paper enables evaluation of the smoothing effect of burst traffic through nodes in Asynchronous Transfer Mode networks.     

Dimensioning shared-per-node recirculating fiber delay line buffers in an optical packet switch

Optical buffering based on fiber delay lines (FDLs) has been proposed as a means for contention resolution in an optical packet switch. In this article, we propose a queuing model for feedback-type shared-per-node recirculating FDL optical buffers in asynchronous optical switching nodes. In this model, optical packets are allowed to recirculate over FDLs as long as the total number of recirculations is less than a pre-determined limit to meet signal loss requirements. Markov Modulated Poisson Process (MMPP)-based overflow traffic models and fixed-point iterations are employed to provide an approximate analysis procedure to obtain blocking probabilities as a function of various buffer parameters in the system when the packet arrival process at the optical switch is Poisson. The proposed algorithm is numerically efficient and accurate especially in a certain regime identified with relatively long and variably-sized FDLs, making it possible to dimension optical buffers in next-generation optical packet switching systems.     

Optimal and nearly optimal algorithms for approximating polynomial zeros

We substantially improve the known algorithms for approximating all the complex zeros of an n^th degree polynomial p(x). Our new algorithms save both Boolean and arithmetic sequential time, versus the previous best algorithms of Schönhage [1], Pan [2], and Neff and Reif [3]. In parallel (NC) implementation, we dramatically decrease the number of processors, versus the parallel algorithm of Neff [4], which was the only NC algorithm known for this problem so far. Specifically, under the simple normalization assumption that the variable x has been scaled so as to confine the zeros of p(x) to the unit disc x : |x| ≤ 1, our algorithms (which promise to be practically effective) approximate all the zeros of p(x) within the absolute error bound 2^−b, by using order of n arithmetic operations and order of (b + n)n² Boolean (bitwise) operations (in both cases up to within polylogarithmic factors). The algorithms allow their optimal (work preserving) NC parallelization, so that they can be implemented by using polylogarithmic time and the orders of n arithmetic processors or (b + n)n² Boolean processors. All the cited bounds on the computational complexity are within polylogarithmic factors from the optimum (in terms of n and b) under both arithmetic and Boolean models of computation (in the Boolean case, under the additional (realistic) assumption that n = O(b)).     

Platoon架构下VANETs车间通信过程及性能分析

智能车辆编组platoon的稳定运行需要车辆间实时可靠的信息传输来保证.针对应用专用短程通信（DSRC）技术来实现车载自组织网路（VANETs）车间通信的platoon架构,提出了一种车间通信网络性能的分析方法,分别对platoon组内智能车辆间通信和多个platoons组间通信的过程进行了分析.该方法采用长度有限的M/G/1/K排队模型分析数据包到达媒体访问控制（MAC）层的排队过程,得到不同网络负载下缓冲区排队状态的平稳分布;并且在缓冲区可能处于空闲状态时,利用Markov模型分析方法得到不同车辆位置的车间通信性能.研究结果表明：网络数据流量、信道条件、MAC层缓冲区排队过程、争用信道退避过程以及platoon参数对车间通信的包传输时延和包丢失概率等网络性能有显著影响,数值分析结果验证了专用短程通信技术下的车间通信具有较小的信息传输延时,能够满足platoon稳定运行的要求.     

Performance analysis of a discrete-time queuing system with a correlated train arrival process

In this paper, we present an exact transient and steady-state discrete-time queuing analysis of a statistical multiplexer with a finite number of input links and whose arrival process is correlated and consists of a train of a fixed number of fixed-length packets. The functional equation describing this queuing model is manipulated and transformed into a mathematical tractable form. This allows us to derive the transient probability generating function (pgf) of the buffer occupancy. From this transient pgf, time-dependent performance measures such as transient probability of empty buffer, transient mean of buffer occupancy and instantaneous packet overflow probabilities are derived. By applying the final-value theorem, the corresponding exact expressions for the steady-state pgf of the queue length and packet arrivals are derived. We also show how the transient analysis provides insights into the derivation of the system's busy period distribution. Closed-form expressions for the mean packet and message delays are also provided. The paper presents significant results on the transient and steady-state analysis of statistical multiplexers with N input links and correlated train arrivals.     

基于改进模糊支持向量回归模型的机场能源需求预测

针对离群点在机场能源数据的预测和分析中存在干扰等问题,建立了一种基于改进模糊支持向量回归(FSVR)的机场能源需求预测模型。首先,采用模糊统计法对测试样本集、系统参数和模型输出进行分析,推导出符合其数据分布的基本隶属函数形式;其次,结合例证法、专家经验法对隶属函数进行"再学习",逐步修改和完善正态隶属函数a、b参数值,半梯形隶属函数边界参数值及三角隶属函数p、d参数值,以此消除或减少不利数据挖掘的离群点,同时保留有效关键点;最后,结合支持向量回归(SVR)算法,建立预测模型,并验证了该模型的可行性。实验结果表明,与反向传播(BP)神经网络方法相比,FSVR方法的预测准确率提高了2.66%,对离群点的识别率提高了3.72%。