有门限的动态双队列缓存管理策略性能分析

对共享缓存分组交换机提出了按需分配缓存的具有门限的动态双队列缓存管理策略.具有门限的动态双队列特性,在提高不同优先级业务服务公平性以提供服务质量保证的同时,也提高了缓存的整体有效利用率.据此对该系统建立了M1 M2/M/1/K (K)的排队模型,给出了相应的Q矩阵,利用矩阵几何解方法对模型求解得到了稳态概率分布.最后做了相应的性能分析,定量给出了不同优先级分组的队长分布、丢失概率等的计算公式.     

Performance analysis of multimedia based web traffic with QoS constraints

During the recent years, there has been a tremendous growth in the development and deployment of multimedia based networked applications such as video streaming, IP telephony, interactive games, among others. These applications, in contrast to elastic applications such as email and data sharing, are delay and delay jitter sensitive but can tolerate certain level of packet loss. A vital element of end-to-end delay and delay jitter is the random queueing delays in network switches and routers. Analysis of robust mechanisms for buffer management at network routers needs to be carried out in order to reduce end-to-end delay for traffic generated by multimedia applications. In this context, a threshold based buffer management scheme for accommodating multiple class multimedia traffic in network routers has been analysed. This technique effectively controls the allocation of buffer to various traffic classes according to their delay constraints. The forms of the joint state probabilities, as well as basic performance measures such as blocking probabilities are analytically established at equilibrium. Typical numerical experiments are included to illustrate the credibility of the proposed mechanism in the context of different quality of service (QoS) grades for various network traffic classes. This model, therefore, can be used as a powerful tool to provide a required grade of service to a particular class of multimedia based web traffic in any heterogeneous network.     

Modeling and performance analysis for IPv6 traffic with multiple QoS classes

This paper focuses on the modeling and performance analysis for IPv6 traffic with multi-class QoS in virtual private networks (VPN). The multi-class QoS is implemented on differentiated service basis using priority scheme of 4 bits defined in the packet header of IPv6. A VPN-enabled IP router is modeled as a tandem queuing system in which each output link consists of two parallel priority output queues. The high-priority queue is used to carry the delay sensitive traffic while the low-priority queue is used to carry the delay insensitive traffic. On the other hand, multiple thresholds are implemented in each queue, respectively, for packet loss priority control. The performance analysis is done using fluid flow techniques. The numerical results obtained from the analysis show that the differentiated service based on the priority schemes defined in IPv6 is able to effectively satisfy the multi-class QoS requirement for supporting multimedia services in VPN. The performance trade-off between the delay sensitive traffic and delay insensitive traffic in terms of traffic throughput, packet loss probability and end-to-end delay in VPN networks is presented.     

Control of queueing delay in a buffer with time-varying arrival rate

Quality of Service (QoS) is of extreme importance in accommodating the increasingly diverse range of services and types of traffic in present day communication networks and delay is one of the most important QoS metrics. This paper presents a new approach for constraining queueing delay in a buffer to a specified level as the arrival rate changes with time. A discrete-time control algorithm is presented that operates on a buffer (queue) which incorporates a moveable threshold. An algorithm is developed that controls the delay by dynamically adjusting the threshold which, in turn, controls the arrival rate. The feasibility of the system is examined using both theoretical analysis and simulation.     

多信道有限缓存下混合业务接入控制的排队性能研究

基于无线通信网的运行机制和实时性、非实时性混合业务对无线通信网络的不同服务质量（QoS）要求,设计了有限缓存下实时性业务优先接入控制策略,并建立了无线通信网络在有限缓存下混合业务带有优先接入控制的多服务台离散时间排队模型Geom₁±Geom₂/Geom₁, Geom₂/s, s（PP）/n+s, s.精确划分了系统的状态组成,分析了系统性能和状态转移概率,获得了系统的稳态分布、平均队长、损失率、以及信道的平均利用率.最后,对所建模型进行数值模拟,得到各业务到达率、服务率、信道个数、缓冲器容量与各业务损失率的关系.针对网络拥塞控制,本文提出通过增加信道个数、提高优先级业务的服务率能有效地降低两类业务的损失率.     

An efficient fuzzy system for traffic management in high-speed packet-switched networks

 In this paper we present a novel buffer management scheme based on fuzzy logic. We deal with the problem of managing traffic flows with different priorities within the same buffer. The aim is to guarantee the QoS of high-priority traffic, and at the same time exploit unused buffer resources to accommodate best-effort traffic in order to maximize the total throughput. The scheme we propose can be applied both to ATM and IP networks. The performance evaluation of the fuzzy priority control scheme shows that it outperforms any static threshold mechanism and, as far as the total throughput is concerned, it is very close to that of the push out mechanism considered in literature as an ideal mechanism. Finally, we address some implementation issues of the control system and propose the design of a new cost-effective VLSI fuzzy processor.     

Performance evaluation for DRED discrete-time queueing network analytical model

Due to the rapid development in computer networks, congestion becomes a critical issue. Congestion usually occurs when the connection demands on network resources, i.e. buffer spaces, exceed the available ones. We propose in this paper a new discrete-time queueing network analytical model based on dynamic random early drop (DRED) algorithm to control the congestion in early stages. We apply our analytical model on two-queue nodes queueing network. Furthermore, we compare between the proposed analytical model and three known active queue management (AQM) algorithms, including DRED, random early detection (RED) and adaptive RED, in order to figure out which of them offers better quality of service (QoS). We also experimentally compare the queue nodes of the proposed analytical model and the three AQM methods in terms of different performance measures, including, average queue length, average queueing delay, throughput, packet loss probability, etc., aiming to determine the queue node that offers better performance.     

区分服务中一种动态概率优先级调度算法*

提出了一种动态概率优先级算法DPP,针对一类对延时和丢包率要求相对较高的应用,根据AF1队列长度动态调整概率计算参数p,有效地解决了由于突发流量带来的QoS性能下降问题。不同实验环境下的仿真结果表明,DPP算法有效改善了突发性对分组平均排队延时的影响,减少了分组丢包率。     

Loss probability estimation and control for OFDM/TDMA wireless systems considering multifractal traffic characteristics

In this paper, we analyze the queueing performance in terms of loss rate of an OFDM (orthogonal frequency-division multiplexing)/TDMA (time division multiplexing access) based wireless system taking into account the multifractal behavior of the wireless traffic flows. To this end, first, we show evidences of multifractal characteristics on wireless traffic traces. These findings motivated us to propose a traffic policing and control scheme based on a multifractal envelope process in order to maintain the traffic flows well-behaved, i.e., in accordance to the desired QoS parameters. Furthermore, by assuming a multifractal traffic model, we derive a data loss probability equation for wireless traffic flows that was applied to the OFDM/TDMA based wireless system. Simulations and comparisons to other methods were carried out in order to verify the efficiency of the proposed traffic policing scheme as well as of the loss probability estimation approach.     

多门限随机早期丢弃及仿真研究

CIOQ交换结构通常在输入端口侧采用基于VOQ结构的输入排队,为了实现VOQ队列报文的优先级区分丢弃,文章在实验的基础上给出了一种支持DiffServ结构中QoS的多门限随机早期丢弃（MTRED）队列管理机制。并通过大规模业务流量下的仿真对不同丢包门限的设置进行了深入的研究,最后给出了相关结论。     

A simple fluid model for servicing priority traffic

We consider a simple priority queueing system with two different types of traffic, high and low priority. Each type of traffic generates arrivals to its own buffer that are modeled by continuous fluid flows. The input flow into the high priority buffer is Markov modulated, while the input rate into the low priority buffer is constant. The fluid is transmitted from the buffers with the high priority buffer having priority over the low priority buffer. The problem for the joint distribution of the buffer contents is derived and solved explicitly. Approximations are constructed for the tail behavior of the buffer content     

On the time scales in video traffic characterization for queueing behavior

To guarantee quality of service (QoS) in future integrated service networks, traffic sources must be characterized to capture the traffic characteristics relevant to network performance. Recent studies reveal that multimedia traffic shows burstiness over multiple time scales and long range dependence (LRD). While researchers agree on the importance of traffic correlation, there is no agreement on how much correlation should be incorporated into a traffic model for performance estimation and dimensioning of networks.In this article, we present an approach for defining a relevant time scale for the characterization of VBR video traffic in the sense of queueing delay. We first consider the Reich formula and characterize traffic by the Piecewise Linear Arrival Envelope Function (PLAEF). We then define the cutoff interval above which the correlation does not affect the queue buildup. The cutoff interval is the upper bound of the time scale which is required for the estimation of queue size and thus the characterization of VBR video traffic. We also give a procedure to approximate the empirical PLAEF with a concave function; this significantly simplifies the calculation in the estimation of the cutoff interval and delay bound with little estimation loss.We quantify the relationship between the time scale in the correlation of video traffic and the queue buildup using a set of experiments with traces of MPEG/JPEG-compressed video. We show that the critical interval, i.e. the range for the correlation relevant to the queueing delay, depends on the traffic load: as the traffic load increases, the range of the time scale required for estimation for queueing delay also increases. These results offer further insights into the implication of LRD in VBR video traffic.     

Analysis and modeling of a threshold based priority queueing system

This paper proposes a threshold based priority scheme to provide adequate quality of service to high priority traffic while providing the best possible service to low priority traffic. Two thresholds are used to control the average waiting time of each class of traffic in the queue. The proposed threshold based priority scheme is analyzed based on the three-dimension Markov chain. According to the results, the parameters of this scheme can be tuned dynamically to achieve the delay requirement of each class of traffic.     

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.     

Analysis of priority queueing system based on thresholds and its application to signaling system no. 7 with congestion control

We analyze a priority queueing system with congestion control based on thresholds. A priority queue with a triple of thresholds consisting of an abatement threshold, an onset threshold and a discard threshold was investigated by San-qi Li. We extend Li's model to a priority queue with N triples of thresholds and obtain the stationary probabilities of queue length by using the Embedded Markov chain method. We obtain the loss probability and the mean delay of packet of each class. We apply our result to signaling system no. 7 network with a congestion control based on thresholds.     

Performance analysis of a threshold-based dynamic TXOP scheme for intra-AC QoS in wireless LANs

The IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has been proposed for provisioning of differentiated Quality-of-Service (QoS) between various Access Categories (ACs), i.e., inter-AC QoS, in Wireless Local Area Networks (WLANs). However, the EDCA lacks the support of the intra-AC QoS provisioning, which is indispensable in practical WLANs since the network loads are always asymmetric between traffic flows of ACs with the same priority. To address the intra-AC QoS issue, this paper proposes a Threshold-Based Dynamic Transmission Opportunity (TBD-TXOP) scheme which sets the TXOP limits adaptive to the current status of the transmission queue based on the pre-setting threshold. An analytical model is further developed to evaluate the QoS performance of this scheme in terms of throughput, end-to-end delay, and frame loss probability. NS-2 simulation experiments validate the accuracy of the proposed analytical model. The performance results demonstrate the efficacy of TBD-TXOP for the intra-AC QoS differentiation.     

基于QoS的路由器队列管理

新一代互联网必然要满足服务质量(QoS)的要求，本文讨论了新一代互联网路由器输入端缓冲区队列管理和内存管理的一个方案，提出了二级队列的基本结构拥塞控制与门限值的设定方法，使所提方案能够支持多级QoS和动态内存分配。     

一种动态优先级调度算法与OPNET仿真

提供服务质量保证是目前lnternet的重要研究课题之一,其核心问题是实现不同业务流的分类转发。本文分析了基于EDF的优先级队列PQBEDF算法,由于PQBEDF方案中动态优先级随时间片变化过快从而降低了高优先级队列服务质量,针对这个不足我们引入阈值来控制计数器一个时间片以后是否加1,从而为每类业务的信元保证一个最小的服务速率。     

Fuzzy-based rate control for real-time MPEG video

We propose a fuzzy logic-based control scheme for real-time motion picture expert group (MPEG) video to avoid long delay or excessive loss at the user-network interface (UNI) in an asynchronous transfer mode (ATM) network. The system consists of a shaper whose role is to smooth the MPEG output traffic to reduce the burstiness of the video stream. The input and output rates of the shaper buffer are controlled by two fuzzy logic-based controllers. To avoid a long delay at the shaper, the first controller aims to tune the output rate of the shaper in the video frame time scale based on the number of available transmission credits at the UNI and the occupancy of the shaper's buffer. Based on the average occupancy of the shaper's buffer and its variance, the second controller tunes the input rate to the shaper over a much larger time scale by applying a closed-loop MPEG encoding scheme. With this approach, the traffic enters the network at an almost constant bit rate (with a very small variation) allowing simple network management functions such as admission control and bandwidth allocation, while guaranteeing a relatively constant video quality since the encoding rate is changed only in critical periods when the shaper buffer “threatens” to overflow. The performance of the proposed scheme is evaluated through numerical tests on real video sequences