A differentiated services architecture for multimedia streaming in next generation Internet

This paper presents a Differentiated Services (Diffserv or DS) architecture for multimedia streaming applications. Specifically, we define two types of services in the context of Assured Forwarding (AF) per hop behavior (PHB) that are differentiated in terms of reliability of packet delivery: the High Reliable (HR) service and the Less Assured (LA) service. We propose a novel node mechanism called Selective Pushout with Random Early Detection (SPRED) that is capable of simultaneously achieving the following four objectives: (1) a core router does not maintain any state information for each flow (i.e., core-stateless); (2) the packet sequence within each flow is not re-ordered at a node; (3) packets from HR service are delivered more reliably than packets from LA service at a node during congestion; and (4) packets from TCP traffic are dropped randomly to avoid global synchronization during congestion. We show that SPRED is a generalized buffer management algorithm of both tail-dropping and Random Early Detection (RED), and combines the best features of pushout (PO), RED and RED with In/Out (RIO) mechanisms. Simulation results demonstrate that under the same link speed and network topology, network nodes employing our Diffserv architecture have substantial performance improvement over the current Best Effort (BE) Internet architecture for multimedia streaming applications.     

Controlling mean queuing delay under multi-class bursty and correlated traffic

This paper presents an adaptive queue management scheme to maintain queuing delay in a router at a required level based on a comprehensive analytical model under aggregated Internet traffic flows from various traffic classes. The proposed scheme uses a closed-loop feedback control mechanism to constrain the average queuing delay by regulating traffic arrival rate implicitly through a movable queuing threshold. A discrete-time queuing model is developed to derive the relationship between average queuing delays and queuing thresholds based on a traffic model that models aggregated Internet traffic through superposition of N MMBP-2 arrival processes. The queuing threshold is adjusted dynamically with reference to the relationship derived in the analytical model and also feedback of average queuing delay measurement. Packets are dropped dynamically with respect to the changes of queuing threshold and the packet loss events serve as implicit congestion indicators. Matlab is used to perform queuing analysis and simulation. Statistical evaluation is performed to show the efficiency and accuracy of the analytical and simulation results.     

Dynamic queue level control of TCP/RED systems in AQM routers

One main TCP congestion control objective is, by dynamically adjusting the source window size according to the router queue level, to stabilize the buffer queue length at a given target, thereby achieving predictable queueing delay, reducing packet loss and maximizing link utilization. One difficulty therein is the TCP acknowledging actions will experience a time delay from the router to the source in a TCP system. In this paper, a time-delay control theory is applied to analyze the mechanism of packet-dropping at router and the window-updating in TCP source in TCP congestion control for a TCP/RED dynamic model. We then derive explicit conditions under which the TCP/RED system is asymptotically stable in terms of the instantaneous queue. We discuss the convergence of the buffer queue lengths in the routers. Our results suggest that, if the network parameters satisfy certain conditions, the TCP/RED system is stable and its queue length can converge to any target. We illustrate the theoretical results using ns2 simulations and demonstrate that the network can achieve good performance and converge to the arbitrary target queues.     

主动队列管理中P I 字节模式和包模式

主动队列管理(AQM)是近年来TCP端到端拥塞控制的一个研究热点，其中PI拥塞控制机制是建立在RED拥塞控制基础上的一种控制机制．PI机制基于两种方法控制网络拥塞现象：跟踪实时队列长度及拥塞情况下以一定概率丢弃到达队列的数据包．以上方法的计算可以基于包数目或字节数，而方法选择的不同对网络会产生不同的影响．仿真量化性地测定使用不同队列计算和标注方法情况下对通信性能产生的影响．同时，PI控制器与RED控制器在相同模式和参数设置下进行比较，可显示出PI控制具有一定的优越性．     

Nonlinear RED: A simple yet efficient active queue management scheme

Among various active queue management schemes (AQM), random early detection (RED) is probably the most extensively studied. Unlike the existing RED enhancement schemes, we replace the linear packet dropping function in RED by a judicially designed nonlinear quadratic function. The rest of the original RED remains unchanged. We call this new scheme Nonlinear RED, or NLRED. The underlying idea is that, with the proposed nonlinear packet dropping function, packet dropping becomes gentler than RED at light traffic load but more aggressive at heavy load. As a result, at light traffic load, NLRED encourages the router to operate in a range of average queue sizes rather than a fixed one. When the load is heavy and the average queue size approaches the pre-determined maximum threshold (i.e. the queue size may soon get out of control), NLRED allows more aggressive packet dropping to back off from it. Simulations demonstrate that NLRED achieves a higher and more stable throughput than RED and REM, another efficient variant of RED. Since NLRED is fully compatible with RED, we can easily upgrade/replace the existing RED implementations by NLRED.     

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.     

基于ECN的实时多媒体的实时多媒体流TCP友好控制

随着Internet上多媒体应用的日益增加,实时多媒体流的TCP友好控制成为当前的研究热点。该机制基于RTP/RTCP协议,以ECN的方式将拥塞状况通知发送端,在路由器中采用RED队列管理策略,在端主机采用TCP友好的速率调节机制。ECNBCC机制具有TCP友好的特性并且可以对网络早期拥塞作出反应,从而降低丢包率和网络延时,该机制也可用于无线网络多媒体流的拥塞控制。     

一种链路负载自适应的主动队列管理算法

随机早检测(random early detection,简称RED)是IETF推荐部署的主动队列管理(active queue management,简称AQM)算法.RED存在参数难以配置、无法得到与流量无关的平均队长等问题.ARED(adaptive RED)是RED的自适应版本,它根据平均队长动态调节最大标记概率参数,从而得到稳定的平均队长.但ARED没有克服瞬时队列长度振荡问题,且在动态流量环境下性能明显降低.分析了ARED性能问题的原因,并提出了一种链路负载自适应的主动队列管理算法LARED(load adaptiveRED).LARED具有两个特点:自适应链路负载、快速响应队长变化.分析和仿真实验表明,与ARED等其他AQM算法相比,LARED在保持高链路利用率和低时延的同时可以得到稳定的瞬时队长,并且具有良好的响应性和鲁棒性.     

Investigation of the M2/G2/1/∞,N queue with restricted admission of priority customers and its application to HSDPA mobile systems

This paper investigates a queuing system for QoS optimization of multimedia traffic consisting of aggregated streams with diverse QoS requirements transmitted to a mobile terminal over a common downlink shared channel. The queuing system, proposed for buffer management of aggregated single-user traffic in the base station of High-Speed Downlink Packet Access (HSDPA), allows for optimum loss/delay/jitter performance for end-user multimedia traffic with delay-tolerant non-real-time streams and partially loss tolerant real-time streams. In the queuing system, the real-time stream has non-preemptive priority in service but the number of the packets in the system is restricted by a constant. The non-real-time stream has no service priority but is allowed unlimited access to the system. Both types of packets arrive in the stationary Poisson flow. Service times follow general distribution depending on the packet type. Stability condition for the model is derived. Queue length distribution for both types of customers is calculated at arbitrary epochs and service completion epochs. Loss probability for priority packets is computed. Waiting time distribution in terms of Laplace–Stieltjes transform is obtained for both types of packets. Mean waiting time and jitter are computed. Numerical examples presented demonstrate the effectiveness of the queuing system for QoS optimization of buffered end-user multimedia traffic with aggregated real-time and non-real-time streams.     

Adaptive Head-to-Tail: Active Queue Management based on implicit congestion signals

Active Queue Management is a convenient way to administer the network load without increasing the complexity of end-user protocols. Current AQM techniques work in two ways; the router either drops some of its packets with a given probability or creates different queues with corresponding priorities. Head-to-Tail introduces a novel AQM approach: the packet rearrange scheme. Instead of dropping, HtT rearranges packets, moving them from the head of the queue to its tail. The additional queuing delay triggers a sending rate decrease and congestion events can be avoided. The HtT scheme avoids explicit packet drops and extensive retransmission delays. In this work, we detail the HtT algorithm and demonstrate when and how it outperforms current AQM implementations. We also approach analytically its impact on packet delay and conduct extensive simulations. Our experiments show that HtT achieves better results than Droptail and RED methods in terms of retransmitted packets and Goodput.     

典型AQM算法的性能评价模型

利用GI/M/1/N排队系统和Internet业务流量自相似性的特点建立了一个评价AQM算法在非响应业务流量下性能的分析模型,提出了利用模型的分析计算结果而不是模拟或实验手段评价AQM算法性能的新方法.同模拟或实验手段相比,该方法能更深刻地刻画AQM算法在实际网络环境中的性能.用该模型分析比较3个经典的AQM算法——TD、RED和GRED的性能,所得的结果同其他研究者利用模拟或实验方法所得的结果一致.     

自相似网络流量可预测性及其在AQM中的应用

从网络流量的自相似性带来的可预测性入手,小结了两类常用的预测方法,并对其进行了比较;然后根据已有预测算法,将预测结果引入经典主动队列管理机制——RED算法中,提出了基于流量预测的RED算法;最后通过仿真实验表明,该算法能较好地控制平均队列长度,提高主动队列管理的性能。     

Multi-indicator Active Queue Management Method

A considerable number of applications are running over IP networks. This increased the contention on the network resource, which ultimately results in congestion. Active queue management (AQM) aims to reduce the serious consequences of network congestion in the router buffer and its negative effects on network performance. AQM methods implement different techniques in accordance with congestion indicators, such as queue length and average queue length. The performance of the network is evaluated using delay, loss, and throughput. The gap between congestion indicators and network performance measurements leads to the decline in network performance. In this study, delay and loss predictions are used as congestion indicators in a novel stochastic approach for AQM. The proposed method estimates the congestion in the router buffer and then uses the indicators to calculate the dropping probability, which is responsible for managing the router buffer. The experimental results, based on two sets of experiments, have shown that the proposed method outperformed the existing benchmark algorithms including RED, ERED and BLUE algorithms. For instance, in the first experiment, the proposed method resides in the third-place in terms of delay when compared to the benchmark algorithms. In addition, the proposed method outperformed the benchmark algorithms in terms of packet loss, packet dropping, and packet retransmission. Overall, the proposed method outperformed the benchmark algorithms because it preserves packet loss while maintaining reasonable queuing delay.     

一种基于连接的增强拥塞控制机制

文中针对越来越多的网络应用不采用端拥塞控制机制而导致非公平占用网络带宽问题,介绍了在路由器内部实现基于连接调度的增强拥塞控制方法。路由器使用公平排队调度算法代替传统的先来服务调度算法,可隔离和保护基于漏桶控制的连接。但采用基于窗口反馈拥塞控制机制ＴＣＰ连接会对数据包丢失敏感,路由器使用公平排队调度算法还需要结合相应的缓冲管理方法,才能保证ＴＣＰ连接获取公平的吞吐量。文中还讨论了基于连接的排队数据包     

基于排队模型的包链测量方法特征分析

基于单跳路由器的排队模型,研究了受背景流量影响下的探测包链排队行为。随着背景流量影响程度的不同,分析得出无背景流量排队、短背景流量排队、长背景流量排队和多背景流量排队等四种具有不同时延变化分布特征的典型探测包链排队行为。仿真实验通过调整包链发送速率,模拟了不同的背景流量影响程度,发现探测包链的包时延变化有不同的分布特征,与分析的四种典型探测包链排队行为特征基本一致。     

CARED: Cautious Adaptive RED gateways for TCP/IP networks

Random Early Detection (RED) is a widely deployed active queue management algorithm that improves the overall performance of the network in terms of throughput and delay. The effectiveness of RED algorithm, however, highly depends on appropriate setting of its parameters. Moreover, the performance of RED is quite sensitive to abrupt changes in the traffic load. In this paper, we propose a Cautious Adaptive Random Early Detection (CARED) algorithm that dynamically varies maximum drop probability based on the level of traffic load to improve the overall performance of the network. Based on extensive simulations conducted using Network Simulator-2 (ns-2), we show that CARED algorithm reduces the packet drop rate and achieves high throughput as compared to RED, Adaptive RED and Refined Adaptive RED. Unlike other RED based algorithms, CARED algorithm does not introduce new parameters to achieve performance gain and hence can be deployed without any additional complexity.     

面向分层移动IPv6 网络的动态指针推进机制

基于指针推进机制的分层移动IPv6方案因未考虑移动锚点管理域的影响,导致较高的注册和报文分发开销.提出一种面向分层移动IPv6网络的动态指针推进机制(dynamic pointer forwarding scheme for HMIPv6 networks,简称DPF-HMIPv6),移动节点可根据所选移动锚点的管理域大小,动态调整指针推进机制.若所选移动锚点的管理域大于特定阈值,则移动节点通过在接入路由器间构建指针链来避免频繁地向移动锚点注册;若所选移动锚点的管理域小于阈值,则移动节点通过在移动锚点间构建指针链来避免频繁地向家乡代理注册.数值分析和仿真实验的结果表明,该方案能够有效解决现有方案存在的问题,显著降低分层移动IPv6网络的开销.     

PowerTrust: A Robust and Scalable Reputation System for Trusted Peer-to-Peer Computing

We propose a new fair scheduling technique, called OCGRR (output controlled grant-based round robin), for the support of DiffServ traffic in a core router. We define a stream to be the same-class packets from a given immediate upstream router destined to an output port of the core router. At each output port, streams may be isolated in separate buffers before being scheduled in a frame. The sequence of traffic transmission in a frame starts from higher-priority traffic and goes down to lower-priority traffic. A frame may have a number of small rounds for each class. Each stream within a class can transmit a number of packets in the frame based on its available grant, but only one packet per small round, thus reducing the intertransmission time from the same stream and achieving a smaller jitter and startup latency. The grant can be adjusted in a way to prevent the starvation of lower priority classes. We also verify and demonstrate the good performance of our scheduler by simulation and comparison with other algorithms in terms of queuing delay, jitter, and start-up latency     

A scheduler ASIC for a programmable packet switch

While the Internet is successful in supporting traditional data-only traffic, an integrated services Internet is inevitable with the emergence of new applications such as voice, video, multimedia, and interactive video conferencing. Such an integrated services network should support a wide range of applications with diverse quality of service requirements and traffic characteristics. Provision for quality of service in packet networks in general, and in the Internet in particular, is the focus of most of the recent developments in switching and routing system design. We designed a generic, single-queue scheduler engine for use in a programmable packet switch/router to handle IP packets, ATM cells, or a combination of both. Comprising 275,000 gates, the 0.35-micron ASIC is incorporated into a prototype programmable packet switch     

基于扩充的GIX/M/1/N排队系统的主动队列管理算法性能评价模型

为了评价主动队列管理(AQM Active Queue Management)算法的性能,通过在标准的排队系统GIX/M/1/N中嵌入主动队列管理(AQM)算法的方法,建立了一个扩充的GIX/M/1/N排队系统。利用该扩充的GIX/M/1/N排队系统和Internet业务流量自相似性的特征,提出了一种评价AQM算法在非响应业务流量下的性能的分析方法,并据此评价了TD,RED,GRED和Adaptive RED等4个经典的AQM算法。为了验证该分析方法的合理性,利用NS2进行了一系列的仿真实验。结果表明,该分析方法所得结果与仿真实验所得结果一致,因此该分析方法能用于评价AQM算法的性能。