一种基于链路传输延迟的MPTCP拥塞控制算法*

由于传统TCP拥塞控制算法直接应用到MPTCP(Multipath Transport Control Protocol)中存在公平性问题,以及不能有效地发挥多路径传输的优势,因而从公平性方面对MPTCP现有拥塞控制算法进行研究.研究发现,现有的MPTCP拥塞控制算法均受到相同的回路时间限制.提出一种基于链路延迟的RTT补偿算法(Compensating for RTT mismatch,C-RTT ).该算法通过设置网络带宽占用比参数以及对MPTCP连接的子流设置侵略因子,从而保证瓶颈链路处MPTCP数据流和TCP数据流公平地共享可用带宽.最后通过NS3仿真实验证明,该算法能够有效地补偿链路中因RTT不等引起的公平性问题,并避免链路之间数据的非周期抖动,且保证了多路径传输的优越性.     

基于局域信息少数者博弈的拥塞控制算法

针对目前已有的拥塞控制算法普遍存在资源利用率低下、RTT不公平和多瓶颈链路不公平等问题,分析了网络拥塞控制中的博弈现象,考虑网络局域信息在拥塞控制过程中的影响,建立了一种基于局域信息少数者博弈的拥塞控制模型,提出并实现了一种基于局域信息少数者博弈的拥塞控制算法。仿真实验表明,该算法在保证瓶颈链路资源利用率的同时,有效地解决了异构RTT流的不公平性问题,实现了多瓶颈链路下的最大最小公平性。     

一种拥塞感知的TFRC协议慢启动算法

 本文分析了TFRC(TCP-Friendly Rate Control)协议在慢启动阶段采用类似TCP协议的倍增发送速率机制存在的问题,提出了一种利用回路响应时间(Round Trip Time,RTT)来自适应调节慢启动阶段速率的算法.通过分析实际RTT值和EWMA(Exponentially Weighted Moving Average)处理后的平均RTT值来感知网络当前的拥塞状况,以调节发送速率的激进程度.仿真实验表明,该方法对TFRC协议具有明显的改进作用,减少了慢启动阶段结束时的报文丢失率,提高了协议的传输平稳度和吞吐量,从而能更有效地适应多媒体流的传输要求.     

输入排队中抢占式的短包优先调度算法

调度算法决定了输入排队交换结构的性能.本文根据Internet业务特征提出调度算法应保证短包的高优先级和低延迟.已有包方式调度中,长包信元的连续传输将造成短包长时间等待.为解决该问题,本文设计了一种低复杂度抢占式交换结构,并提出了相应的抢占式短包优先调度算法(P-SPF).短包优先可减小TCP流的RTT,并由此提高TCP之性能.通过排队论分析和实际业务源模型下仿真可知:P-SPF取得短包近似为零的平均包等待时间,同时达到94%的系统吞吐量.     

OBS网络中一种基于优先级的偏射路由机制

提出了一种基于优先级的偏射路由机制,该机制通过分割偏射优先级低的突发包来保证高优先级突发包的QoS.仿真结果表明,高优先级突发包的丢失率比低优先级的要低,并且突发包的丢失率随数据信道数目的增加而降低.该机制不仅能够有效地降低突发包的丢失率,而且能够为高优先级突发包提供很好的QoS保障.     

一种基于速率的组播拥塞控制算法及其性能分析

大部分组播拥塞控制机制都是将包丢失作为网络拥塞的信号,存在丢包、响应速度慢以及由此引起的协议间不公平等缺陷.本文提出了一种新的基于速率拥塞控制算法通过对拥塞的早期检测,进行及时反馈,发送端通过调节数据包的发送间隔进行拥塞避免和控制,使网络能够对拥塞做出快速反应,更有效地利用网络资源.实验结果表明,在相同的配置下,采用该拥塞控制算法的网络在吞吐量、灵敏性和公平性等性能上均优于原先的算法.     

一种新的缓存空间动态分配机制及其分组丢失率分析

本文提出了一种适于分组交换机或路由器的缓存空间的动态分配机制:附加缓存块按需分配机制ABBA,在给出其排队模型"M/M/1/K(2K)"的基础上,导出了其矩阵形式的稳态概率分布和分组丢失概率,并通过理论和仿真两种途径将分组丢失率性能与典型的缓存空间的静态分配系统进行了分析比较.最后分析了附加块动态分配决策机制应考虑的几个重要因素并给出了相应的动态分配算法.     

业务自相似性对光突发交换调度算法影响分析

使用泊松业务流模型对光突发交换网络进行性能分析不能准确地反映网络状态。该文从理论上对突发包长度进行了推导,对基于时间门限汇聚机制下突发包数据流自相似程度进行了计算机仿真测量,并利用自相似业务流模型对光突发交换网络中比较常用的LAUC和LAUC-VF调度算法进行了性能仿真。仿真结果表明:基于时间门限的汇聚机制能够有效地降低数据流自相似程度,数据流的自相似特性对LAUC算法的影响并不非常明显,但对LAUC-VF算法的性能则产生了比较严重的影响,其突发包丢失率较泊松流平均增加了近3个百分点。     

TCP-H：基于三重判决的TCP拥塞控制

在异构无线网络中存在高误码、切换、信号衰落等链路特性,使传统的TCP拥塞控制机制受到了挑战。在不增加开销的情况下,基于丢包检测、RTT时间和ACK返回速率三重判决,提出了一种新的TCP拥塞控制机制（TCP—H）。仿真结果表明,TCP—H增强了对拥塞和随机差错的区分能力,满足公平性要求,改进的最小RTT计算方法解决了在低延迟向高延迟网络切换的时Vegas,Westwood等算法存在的最小RTT更新问题,有效提高了在异构无鲅网络环埔下TCP的性能．     

光突发交换网络中一种基于LAUC的批调度算法

为了降低突发丢失率和调度复杂度,提出了一种基于LAUC的批调度算法.该算法首先缓存多个突发控制包,当最大缓存时间到达时,根据突发到达顺序批调度处理缓存中的突发控制包,并采用LAUC算法来为突发预留信道资源.其优势在于:计算复杂度与LAUC一样低,因为它只增加了突发控制包缓存和改变了LAUC算法的调度顺序;突发丢失率比较低,仿真结果表明它的突发丢失率比LAUC算法要低,当最大缓存时间大于偏置时间的最大差值时,它的突发丢失率比LAUC-VF算法还要低.     

Performance evaluation of high speed TCP over optical burst switching networks

Study of TCP performance over OBS networks has been an important problem of research lately and it was found that due to the congestion control mechanism of TCP and the inherent bursty losses in the Optical Burst Switching (OBS) network, the throughput of TCP connections degrade. On the other hand, High Speed TCP (HSTCP) was proposed as an alternative to the use of TCP in high bandwidth-delay product networks. HSTCP aggressively increases the congestion window used in TCP, when the available bandwidth is high and decreases the window cautiously in response to a congestion event. In this work, we make a thorough simulation study of HSTCP over OBS networks. While the earlier works in the literature used a linear chain of nodes as the network topology for the simulation, we use the popular 14-node NSFNET topology that represents an arbitrary mesh network in our study. We also study the performance of HSTCP over OBS for different bandwidths of access networks. We use two different cases for simulations where in the first HSTCP connections are routed on disjoint paths while in the second they contend for resources in the network links. These cases of simulations along with the mesh topology help us clearly distinguish between the congestion and contention losses in the OBS network and their effect on HSTCP throughput. For completeness of study, we also simulate TCP traffic over OBS networks in all these cases and compare its throughput with that of HSTCP. We observe that irrespective of the access network bandwidth and the burst loss rate in the network, HSTCP outperforms TCP in terms of the throughput and robustness against multiple burst losses up to the expected theoretical burst loss probability of 10⁻³.     

A buffer management algorithm for improving up/down transmission congestion protocol fairness in IEEE 802.11 wireless local area networks

The fair allocation of the resources is an important issue in wireless local area network (WLAN) because all wireless nodes compete for the same wireless radio channel. When uplink and downlink transmission congestion protocol (TCP) flows coexist in WLAN, the network service is biased toward the uplink TCP flows, and the downlink TCP flows tend to starve. In this article, we investigate the special up/down TCP unfairness problem and point out that the direct cause is the uplink acknowledgement (ACK) packets occupy most buffer space of access point. We thus propose a buffer management algorithm to ensure the fairness among uplink and downlink TCP flows. In order to limit the greedy behavior of ACK packets, the proposed algorithm adjusts the maximum size of buffer allocated for the ACK packets. Analysis and simulation results show that the proposed solution not only provides the fairness but also achieves 10–20% lower queue delay and higher network goodput than the other solutions. Copyright © 2012 John Wiley & Sons, Ltd.     

A rate control scheme for adaptive real-time applications in IP networks with lossy links and long round trip times

Currently there is no control for real-time traffic sources in IP networks. This is a serious problem because real-time traffic can not only congest the network but can also cause unfairness and starvation of TCP traffic. However, it is not possible to apply current solutions for Internet to the networks with high bandwidth-delay products and high bit error rates. The channel errors may result in inaccurate congestion control decisions and unnecessary rate throttles leading to severe performance degradation. This problem is amplified in the links with high bandwidth-delay products, since the link is inefficiently utilized for a very long time until the unnecessary rate throttle is recovered. In this paper, a new Rate Control Scheme, RCS, is introduced for real-time interactive applications in networks with high bandwidth-delay products and high bit error rates. RCS is based on the concept of using dummy packets to probe the availability of network resources. Dummy packets are treated as low priority packets and consequently they do not affect the throughput of actual data traffic. Therefore, RCS requires all the routers in the connection path to support some priority policy. A new algorithm is also proposed to improve the robustness of the RCS to temporal signal loss conditions. The delay-bound considerations for real-time traffic sources using RCS rate control scheme are also investigated. Simulation experiments show that in environments with high bandwidth-delay products and high bit error rates, RCS achieves high throughput performance without penalizing TCP connections.     

光突发交换网络中多跳公平分割丢弃方法的研究

光突发交换网络被认为是一种新的IP over WDM网络,也是下一代互联网的发展趋势。 该文给出了一个在光突发交换网络中解决多跳分割丢弃不公平性的改进方法,该方法不但保留了原有方法的可以保证多跳网络中数据包丢失率的一致性优点,而且还减小了损失,增大了网络吞吐量。最后通过仿真验证了该方法的有效性,对实际网络的设计有一定的理论指导意义。     

Loss estimation and control mechanism in bufferless optical packet-switched networks based on multilayer perceptron

Artificial neural networks (ANNs) are well-known estimators for the output of broad range of complex systems and functions. In this paper, a common ANN architecture called multilayer perceptron (MLP) is used as a fast optical packet loss rate (OPLR) estimator for bufferless optical packet-switched (OPS) networks. Considering average loads at the ingress switches of an OPS network, the proposed estimator estimates total OPLR as well as ingress OPLRs (the OPLR of optical packets sent from individual ingress switches). Moreover, a traffic policing algorithm called OPLRC is proposed to control ingress OPLRs in bufferless slotted OPS networks with asymmetric loads. OPLRC is a centralized greedy algorithm which uses estimated ingress OPLRs of a trained MLP to tag some optical packets at the ingress switches as eligible for drop at the core switches in case of contention. This will control ingress OPLRs of un-tagged optical packets within the specified limits while giving some chance for tagged optical packets to reach their destinations. Eventually, the accuracy of the proposed estimator along with the performance of the proposed algorithm is evaluated by extensive simulations. In terms of the algorithm, the results show that OPLRC is capable of controlling ingress OPLRs of un-tagged optical packets with an acceptable accuracy.     

3G-WLAN融合网络中一种新的双模终端设计

设计了一种能够在3G与WLAN融合网络中智能切换的双模终端模型.为了实现两种网络之间的无缝切换,提出了网络接口选择算法.该算法通过提前注册和认证机制减少了垂直切换时延,并采用提前切换的方法减少了垂直切换时数据包丢失.仿真结果验证了设计和算法具有良好性能.     

Improved ant colony-based multi-constrained QoS energy-saving routing and throughput optimization in wireless Ad-hoc networks简

In order to establish a route supporting multi-constrained quality of service（QoS）, increase network throughput and reduce network energy consumption, an improved ant colony-based multi-constrained QoS energy-saving routing algorithm（IAMQER） is proposed. The ant colony algorithm, as one of the available heuristic algorithms, is used to find the optimal route from source node to destination node. The proposed IAMQER algorithm, which is based on the analysis of local node information such as node queue length, node forwarding number of data packets and node residual energy, balances the relationship between the network throughput and the energy consumption, thus improving the performance of network in multi-constrained QoS routing. Simulation results show that this IAMQER algorithm can find the QoS route that reduce average energy consumption and improves network packet delivery ratio under the end-to-end delay and packet loss ratio constraints.     

Using constrained preemption to improve dropping fairness in optical burst switching networks

In this paper, we propose a new scheme to tackle the “beat down” unfairness problem in optical burst switching networks. In the new scheme, the control packets of bursts with higher preemptive metric value are allowed to preempt the channel resources reserved earlier for bursts with lower preemptive value. However, the control packets of preempted bursts continue to make wasted channel reservations in successive optical cross connects along the burst lightpaths and may also preempt other data bursts. Unchecked preemptions, therefore, can degrade the throughput of the network and induce reverse unfairness. Our scheme uses carefully designed constraints to avoid excessive wasted channel reservations, reduce cascaded useless preemptions, and maintain healthy throughput levels. The extensive simulation results show that the constrained preemption scheme improves fairness compared to previous methods without degrading network throughput.     

有线-无线混合IP网络多媒体传输算法研究

提出了一种端到端的在异构的有线．无线混合IP网络上多媒体传输的改进算法WMTA（wireless multimedia transmission algorithm）。通过研究Gilbert无线差错模型仿真环境中包的长度与丢包率的关系,发现包长与丢包率呈线性增长的关系。基于上述观察,算法通过交替发送大小数据包探测随机和拥塞丢包数,并根据两种丢包的程度进行速率控制。针对不同网络状态转换时算法更新慢的缺点,添加了更新因子K,使算法在网络状态转换时能迅速适应当前网络的状态。仿真结果表明,与现有算法相比,WMTA无论是在运行单个流还是存在竞争流情况下,都能够达到更高的吞吐量和带宽利用率,有效地提高了网络中多媒体传输的服务质量（QoS）。     

OFDM系统中视频传输的调度算法研究

针对OFDM系统,提出了一种基于视频内容的跨层调度方案。该方案采用了基于生存期的包排序策略,根据视频包的生存期大小进行排序,保证视频包能在生存期内发送到接收端,减少丢包数目。同时,采用跨层设计的思想,综合考虑了信道状况和视频包特性,如视频包生存期、重要性、解码器采用的错误掩藏方法,提出改进的比例公平调度算法,不仅有效地利用了多用户分集来进一步提高数据吞吐量,也充分考虑了视频的重要性和时延约束。实验结果表明,采用内容感知的跨层调度算法,解码端的视频质量得到有效提高,从而可以提高主观感知质量。