ACK报文拥塞对网络性能影响的研究

为了提高网络性能和安全、设计更有效地队列拥塞控制算法,通过研究现有的一些主动队列拥塞控制算法发现:大多数的拥塞控制算法的实现是基于队列长度或平均队列长度,这使得算法在提高网络整体性能上具有局限性。本文在现有的网络队列拥塞控制算法的基础上,将ACK信息确认报文传输状态引入到队列拥塞控制算法研究的系统中,通过仿真实验发现:ACK数据报文的传输状态在很大程度上影响着网络的吞吐量、数据包的传输延迟等。     

Deterministic model and transient analysis of virtual circuits

A model for a virtual circuit in the form of a tandem of servers that process incoming packets using a FIFO (first-in, first-out) discipline is proposed. The service times are assumed to be known completely. These may differ from packet to packet and from server to server. The model permits a variety of buffer or transit time constraints to be incorporated into the model. Several results that help one to understand the transient behavior of a virtual circuit are presented. On the basis of these results, a number of schemes that may be used to determine the time when the next packet must be sent over the network are presented. Transit delay and throughput are used to evaluate a given schedule. Solutions are given for maximum throughput, minimum transit delay, and maximum throughput under transit delay constraints. It is expected that these results will have a substantial bearing on the study of congestion control policies in computer networks, particularly those based on predicting network behavior     

基于NS2的RED和BLUE算法仿真及结果分析

随着因特网的迅速发展,网络拥塞日益严重,近年来提出了许多基于路队列管理的拥塞机制,本文分析了RED和BLUE的设计思想和算法实现。通过NS2网络仿真平台,在相同的数据流的情况下对两种算法的性能和原理进行对比,对仿真结果进行丢包率、吞吐量、平均时延等指标的分析和比较,给出结论。     

车联网中基于K均值聚类的拥塞控制方法

针对十字路口下车辆密度过大时造成的车联网拥塞问题,提出基于K-means聚类的车联网拥塞控制方法。在IEEE802.11P协议模型的基础上,引入处理高并发数据的拥塞控制模块,利用网络层分簇时V2V相对距离值作为K-means聚类算法帧分类的相似度区分值,与VANET的网络标准参数建立拥塞控制方法 (KCC),避免同一类车辆节点交互不同步和高密度节点情况下网络拥塞概率过高等问题。仿真结果表明,KCC与CSMA/CA相比有较好的平均时延、平均吞吐量、丢包率、冲突概率等性能。     

NNRA-CAC: NARX Neural Network-based Rate Adjustment for Congestion Avoidance and Control in Wireless Sensor Networks

A wireless sensor network (WSN) is an application area that is valuable in various fields, such as healthcare monitoring, environmental monitoring, and so on. Application areas require WSNs with high throughput and low degree of packet loss. Due to congestion in the network, the throughput of the network is affected, which imposes the need for congestion control in the network. This article proposes a method, titled NARX Neural network-based Rate Adjustment (NNRA) for avoiding and controlling congestion in the network. Initially, congestion in the network is avoided by dropping packets and the NNRA is used to control congestion in the network when congestion is present. Performance analysis is carried out in terms of throughput, delay, size of the queue, packet loss, and the level of the congestion using two setups. The results of the proposed method are compared with the existing methods to prove the effectiveness of the proposed method. The proposed method attained a maximum throughput at a rate of 0.9585 and minimum values for delay, queue size, packet loss, and the congestion level.     

基于自适应转发的大数据通信带宽时延感知拥塞控制技术

大数据通信带宽时延会导致通信拥塞故障,影响通信网络的正常运行,为此提出基于自适应转发的大数据通信带宽时延感知拥塞控制技术。根据通信网络的组成结构和通信原理,构建大数据通信网络模型。在该模型下,采集大数据通信带宽时延,通过特征提取与匹配,感知当前通信网络的拥塞状态。针对处于拥塞状态的通信信道,在考虑通信带宽的情况下,计算拥塞控制量,利用自适应转发技术调度并分配通信带宽,在差分流传输控制协议的支持下,实现大数据通信带宽时延感知拥塞控制。通过拥塞控制效果测试实验得出结论：与传统拥塞控制技术相比,在优化设计技术的控制作用下,移动通信网络的吞吐量有所增加,带宽时延降低了149.3ms,同时通信误码率降低了0.037%,即优化设计技术在拥塞控制效果方面具有明显优势。     

An expert system for real-time traffic management in wireless local area networks

The paper explores delay-based congestion and flow control and the offloading of real-time traffic from wireless local area networks (WLANs) to mobile cellular networks (MCNs) in multihomed devices. The control system developed is based on an embedded hierarchical expert system. It adjusts transceivers’ traffic flow(s) for prevailing network conditions to achieve application-dependent delay and throughput limits. In wireless networks, delay and throughput depend on the packet size, packet transmission interval, and node connection density. Therefore, the controller on the destination node monitors average one-way delay and the change of one-way delay of the incoming traffic. On this basis, it adjusts the packet size and transmission interval of the source node by transmitting a control command to the source. If the prevailing level of traffic in the network exceeds its capacity despite of the control actions taken, devices prepare for developed asynchronous offloading of traffic to another access network.The control model was validated via simulation of Voice over Internet Protocol (VoIP) traffic in the OMNeT++ network simulator. The results demonstrate that the expert system developed is able to regulate packet sizes to match the prevailing application-dependent optimum and transfer traffic to another network if the network exceed its capacity no matter the control actions taken. Although this work is motivated mainly by issues of congestion and flow control of WLAN systems and the simulations and results were prepared for the IEEE 802.11b system, the approach and techniques are not limited to these systems, but they are applicable for other packet switched access networks (PSANs), too.     

一种无线传感器网络的优化速率控制方法

拥塞控制是无线传感器网络中的一个关键性问题。从解决拥塞问题出发,提出了一个基于优化速率的拥塞控制算法ORCC。算法构建了一个分布式的分簇网络结构,利用缓冲的占用情况进行拥塞检测,并使用基于优化理论的速率调节策略来保证网络吞吐量的稳定,从而通过求解出的最优解来实现簇内节点效用的最大化。仿真实验表明,ORCC算法不仅能有效缓解网络拥塞,降低平均延迟,还具有较好的网络传输公平性。     

基于改进BBR的数据报拥塞控制协议

数据报拥塞控制协议(Datagram Congestion Control Protocol,DCCP)是提供拥塞控制和不可靠传输特点的实时多媒体基础协议,DCCP中的CCID2算法仍然采用AIMD的控制机制,这种传统的Loss-Base拥塞控制模型已经不适用于目前高BDP的网络环境,容易引起缓冲区膨胀现象,导致网络延迟增加和抖动等问题.与Loss-Base的算法相比,BBR算法可以有效地控制网络延时,最大限度避免网络排队的情况,在丢包率较高的情况下仍可以保持一定的带宽利用率和较低的链路延时,因此适合于DCCP实时流媒体的应用的协议.本文在DCCP中引入了BBR算法并做相应的改进,增加了丢包率检测模型,使用延时与带宽积模型的拥塞控制算法对上述问题进行改进.通过模拟实验证明,本方法在高负载情况下连接的平均延迟相比CCID2降低了20%,在丢包率较高的环境下也能保持良好的吞吐量.     

TCP传输中往返时延偏移智能响应机制研究

为了提高高丢包率环境下的TCP传输性能,提出一种往返时延偏移智能响应机制。对往返时延偏移值进行标准化处理得到标准延迟因子,用这个因子对拥塞窗口增长和减小量进行修正,实现拥塞窗口增长速度随往返时延偏移自适应调整,能够区分随机丢包和网络拥塞。开发Linux内核模块实现了往返时延偏移智能响应机制,可快速部署到所有基于AIMD策略的拥塞控制机制。仿真结果表明,使用往返时延偏移智能响应机制,平均吞吐量超过cubic算法57%,能够有效提升高丢包率环境的带宽利用率。     

多信道无线Mesh网络的路由协议

针对单径路由协议不能充分利用多信道无线Mesh网络的信道资源的问题,提出了一种基于拥塞控制的并行多径路由协议PMRP。该协议将一个数据流分配到多条路径同时传输,当所有路径都发生中断时,才重新寻找路由;并采取相应的拥塞感知技术,避免拥塞节点再转发新的数据流。仿真结果证明：与无线自组网按需平面距离矢量路由协议（AODV）协议相比,PMRP在网络负载较大时,能有效地减小端到端延迟,提高数据包的成功投递率,增加网络的整体吞吐量。     

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.     

基于模糊控制的ad hoc网络TCP算法研究

TCP协议是针对固定可靠网络设计的一种传输协议,它把数据包丢失或延迟的原因都归结为网络拥塞。在移动自组网上直接应用TCP 协议,网络性能会因比特出错率高等原因大幅下降。针对无线自组织网络高误码的基本特征,基于TCP Vegas协议和环回时间的均值和方差改变趋势,采用不同的控制策略调节发送端的数据发送速率,从而优化传输控制协议的吞吐量,提高网络资源的利用率。仿真研究结果表明,与传统的传输控制协议相比,该算法具有更高的吞吐量和稳定的拥塞控制窗口。     

一种适用于Ad Hoc网络的拥塞控制算法

Ad hoc网络是一种无基础设施、无中心控制的分布式自组织网络,在紧急情况下能够迅速搭建.目前,在IEEE802.11协议基础上所搭建的ad hoc网络面临的主要问题是在信道达到饱和时,其链路层时延明显增加,以至于其上层的协议无法正常工作.本文提出了一种结合链路层及传输层的拥塞控制算法,通过对传输层拥塞窗口的控制、以及引入报文生命期及优先级,使得网络即使在大业务量时,链路层依然能够保持很低的时延,同时大幅度地提高传输层吞吐率.最后通过仿真,验证了该算法的有效性.     

控制无线实时传输的改进TFRC算法

为了解决实时数据在无线网络中传输中所遇到的拥塞控制问题,结合延迟抖动大小和丢失事件率,对基于用户数据报协议(UDP)的TFRC的拥塞判断机制进行了改进,以使其适用于无线实时传输.改进后的协议减少了因比特传输错误引起的拥塞控制,使得无线实时数据的吞吐率更加平滑.通过NS2仿真环境对改进前后的算法进行了实验对比,结果表明,改进的TFRC协会能为无线实时数据传输提供更好的速率控制策略.     

基于BPNN端到端时延预测的多路传输调度

针对移动异构网络环境网络参数动态变化、多路传输过程中数据包乱序引发的吞吐量下降等问题,提出一种基于BP神经网络(back propagation neural network,BPNN)端到端时延预测的多路传输调度方法,通过BP神经网络的构建、训练和学习,实现对端到端传输时延的更准确预测,以此为基础,对子流拥塞状况及网...     

基于NS2的路由器算法Droptail和RED的分析与比较

随着因特网的迅速发展,网络拥塞问题日益严重,近年来提出了许多基于路由器的拥塞控制机制。本文详细分析了基于路由器的弃尾（Droptail）和随机早期检测RED拥塞控制 机制的设计思想和算法实现。基于NS2网络仿真平台,分别在不同数据流和相同数据流情况下对两种算法的性能和原理进行了对比研究;对仿真结果进行吞吐量、延迟、振荡、丢包率等各项QoS指标的详细分析和比较,并给出了相应结论。     

认知无线Mesh网络信道接入与路由协议研究*

针对认知用户可用频谱动态变化,数据链路由于无可用的授权信道而无法建立,导致路径中断的问题,引入了具有拥塞感知能力的多径路由协议。认知用户可通过在多条路径中选择具有SOP交集的下一跳节点进行通信,降低主用户在授权信道上出现对认知用户数据传输带来的干扰;并在路由协议中采用了拥塞控制技术,通过对节点的拥塞情况进行感知,可有效避免瓶颈节点的出现。仿真结果表明,该协议在认知无线Mesh网络中,能较好地减小端到端延迟,提高数据包的成功投递率,增加网络的整体吞吐量。     

一种用于片上网络的拥塞感知哈密尔顿最短路径路由算法

类脑处理器能够支持多种脉冲神经网络SNN的部署来完成多种任务。片上网络NoC能够用较少的资源和功耗解决片上复杂的互连通信问题。现有的类脑处理器多采用片上网络来连接多个神经元核,以支持神经元之间的通信。SNN在时间步内瞬时突发的通信会在短时间内产生大量的脉冲报文。在这种通信行为下,片上网络会在短时间内达到饱和,造成网络拥塞。片上网络中非拥塞感知路由算法会进一步加剧网络拥塞状态,如何在每一个时间步内有效处理这些数据包,从而降低网络延迟,提高吞吐率,成为了目前需要解决的问题。首先对SNN的瞬时猝发通信特性进行了分析;然后提出一种拥塞感知的哈密尔顿路径路由算法,以降低NoC平均延迟和提高吞吐率;最后,使用Verilog HDL实现该路由算法,并通过模拟仿真进行性能评估。在网络规模为16×16的2D Mesh结构的片上网络中,相对于没有拥塞感知的路由算法,在数量猝发模式和概率猝发模式下,所提出的拥塞感知路由算法的NoC平均延迟分别降低了13.9%和15.9%;吞吐率分别提高了21.6%和16.8%。     

基于拥塞控制的无线传感器网络数据汇集树生成算法

针对无线传感器网络数据汇集应用中, 由于数据流量大, 相邻路径之间容易发生串扰、信道竞争和冲突, 造成拥塞问题, 提出了基于拥塞控制的无线传感器网络数据汇集树生成算法(Data gather tree algorithm based on congestion control, DGT-CC). DGT-CC算法通过层次发现、邻居发现、启发式搜索和流量均衡策略构造一棵最短路径最小拥塞权值树. 理论分析证明DGT-CC算法收敛, 并能够构造一棵最短路径最小拥塞权值树, 仿真实验表明DGT-CC算法在丢包率、网络吞吐量和时延方面都较普通的最短路径树具有更好的性能.