一种3GPP LTE网络的TCP拥塞控制方法

现有的传输控制协议(TCP)拥塞控制机制源自有线网络,未考虑无线基站介质访问控制(MAC)层调度器的特性,影响了TCP协议在长期演进(LTE)系统上的传输性能。提出一种跨层的TCP拥塞控制方法,由MAC层和TCP共同解决TCP虚假超时问题。此方法中,MAC层提供超时信息,TCP层识别出虚假超时后调整数据速率,从而避免系统性能损失,保证MAC层稳定工作。仿真结果表明,在保证用户公平性的同时,新方法可以有效解决虚假超时问题,提高用户实际吞吐量。     

移动WiMAX网络下行链路TCP吞吐量公平性的跨层优化

该文提出了一种移动WiMAX网络中的TCP公平性跨层优化模型,设计了基于此模型的cross-layer TCP改进协议。利用端节点链路层的速率信息和在基站BS(Base Station)处预分配ACK分组所需带宽的策略改善了下行终端的QoS (Quality of Service)指标,保证了下行终端和上行终端的吞吐量公平性。仿真结果表明cross- layer-TCP改进协议能够在保持原有系统吞吐量的前提下改善下行终端的公平性。     

混合网络下的TCP拥塞控制跨层优化算法

针对混合网络中并行链路间TCP流的不公平性,提出一种新的算法.此算法利用跨层设计的思想,以传输层的数据重传率为参数来调整TCP流不公平性,也就是说MAC层上的竞争窗口将根据重传率的动态变化而改变,其目的在于抑制并行链路TCP流接入信道能力的不公平性.并且用仿真工具NS2进行仿真的结果表明,采用改进算法后的网络公平性指数比未改进前提高了17.9％.该算法能明显改善并行链路间TCP流的不公平性.     

一种基于数据重传率的无线自组织网络TCP公平性策略

IEEE 802.11 MAC协议被广泛应用于多跳无线网络的研究与示范网中,802.11协议采用RTS/CTS策略减少了隐终端 问题对无线TCP性能的影响。但在多条并行链路间,隐终端问题的存在使得中间链路节点不能有效的接入到信道,导致TCP性能和公平性严重下降。该文提出了一种新的基于传输层数据重传率方法,对于受到严重干扰的中间链路不断获取它的数据重传率,在重传率增加时动态减少802.11退避计时器竞争窗口大小,增加其接入信道能力,从而提高其TCP性能和公平性。仿真结果证明,使用基于传输层数据重传率方法,不仅能基本上保证并行链路TCP的稳定性,还可以极大地提高中间链路TCP公平性。     

基于TCP的移动网络时延优化研究与实践

针对网络时延问题,深入研究在线视频、实时对战游戏等应用的业务特征,聚焦传输层信令特征,基于TCP,研究移动网络时延优化关键技术,突破常规TCP信令交互思路,研究并应用TCP ACK分裂、Quick ACK及智能预调度等技术,优化交互流程与空中接口调度机制,有效缩短网络时延,提升用户感知。实践证明此方法可行、有效,具备较大的推广价值。     

无线自组网与Internet互连中TCP流公平性分析与改进

通过实验与分析揭示了基于IEEE 802.11 MAC的无线自组网与Internet互连时TCP流间的不公平性现象及其产生原因,并基于网关带宽占用对互连环境下TCP流间的公平性进行定义,提出了一种基于网关动态带宽控制的TCP流公平性解决方案TCP-GAFC。TCP-GAFC只在网关节点上进行实现,无需修改TCP协议和MAC协议,具有很好的适用性和可扩展性。仿真实验表明,TCP-GAFC显著地改进了互连环境下TCP流间的公平性,并能达到合理的总吞吐量。     

基于拥塞反馈的Semi-TCP优化方法

Semi-TCP根据无线多跳网络的特性,利用跨层设计的思想,端到端的拥塞控制调整为节点之间逐跳的拥塞控制,将传输层的拥塞控制下移到MAC层,形成递归逐跳的拥塞控制,旨在提高拥塞控制的效率和拥塞处理的即时性。现有的算法要通过增加或修改MAC控制帧的方式来实现拥塞的控制,因而需要对节点已安装的MAC层协议做适当的修改。文中提出了一种基于拥塞反馈的优化方法,不需要对传统TCP协议进行太多的修改。在EXata平台上进行了仿真,证明了该优化方法的有效性。     

无线ad hoc网络中基于帧传输效率的拥塞控制方法

提出以一种基于帧传输效率的MAC层拥塞通告机制,当中间节点检测到帧传输效率小于某一阈值时,通过ECN通告使发送方主动降低发送速率.该机制只需在链路层完成,不需改变现有的传输层协议.仿真结果表明该方法能较大地提高网络的效率,尤其在多流情况下比原有的TCP协议的吞吐量提高了50%左右,同时能够保证多流之间的公平性.     

WLAN中TCP性能改进的跨层方案仿真

随着无线网络的迅速发展,如何改进TCP在无线网络中的传输性能这一课题,已经成为国内外研究的热点.文章分析了现有的几种典型的TCP改进方案,并在此基础上介绍一种新的跨层方案.通过在传输层和链路层之间引入ARQ Snoop代理,在链路层检测并重传ARQ分组的同时,协调WLAN MAC子层的ARQ机制与TCP的ARQ策略.     

基于跨层公平性准则的自适应无线资源分配方法

该文提出了一种新的公平性准则,它既适用于实时业务又适用于非实时业务,是一种对物理层和MAC层联合优化的跨层公平性准则。基于该准则提出了一种新的跨层自适应资源分配方案。仿真结果显示,该方案不仅可以较好地满足用户提出的QoS要求,而且可以保证用户间服务质量满意度的公平性。     

A Cross-layer Dual Queue Approach for Improving TCP Fairness in Infrastructure WLANs

Fairness is one of the most important performance measures in IEEE 802.11 Wireless Local Area Networks (WLANs), where channel is accessed through competition. In this paper, we focus on the fairness problem between TCP uplink and downlink flows in infrastructure WLANs from the cross-layer perspective. First, we show that there exists a notable discrepancy between throughput of uplink flow and that of downlink flow, and discuss its root cause from the standpoint of different responses to TCP data packet drop and TCP ACK packet drop at the access point (AP) buffer. In order to mitigate this unfairness, we propose a dual queue scheme, which works in a cross-layer manner. It employs two separate queues at the AP, one for the data packets of downlink TCP flows and another for the ACK packets of uplink TCP flows, and selects these queues with appropriate probabilities so that TCP per-flow fairness is improved. Moreover, we analyze the behavior of the dual queue scheme and derive throughputs of uplink and downlink flows. Based on this analysis, we obtain the optimal queue selection probabilities for fairness. Extensive simulation results confirm that the proposed scheme is effective and useful in resolving the TCP unfairness problem without deteriorating overall utilization.     

高效公平的EPON TCP性能调节机制

 提出了一个基于效用的EPON公平性指标算法.通过建立一个基于ACK特征包的ACK压缩和解压缩机制,消除了上游ONU的ACK对下游ONU下行数据流的影响,在保证ONU之间的公平性的同时,提高了带宽的使用效率.通过建立一个效用分类器,在维护了优先级机制扩展性的前提下,提高了并发的同业务类业务流之间的公平性.通过建立一个时延公平调度机制,在保证带宽的使用率前提下,保证了ONU的业务类之间的时延公平性.仿真结果很好验证了本机制的优点.     

REFWA: An Efficient and Fair Congestion Control Scheme for LEO Satellite Networks

This paper examines some issues that affect the efficiency and fairness of the Transmission Control Protocol (TCP), the backbone of Internet protocol communication, in multi-hops satellite network systems. It proposes a scheme that allows satellite systems to automatically adapt to any change in the number of active TCP flows due to handover occurrence, the free buffer size, and the bandwidth–delay product of the network. The proposed scheme has two major design goals: increasing the system efficiency, and improving its fairness. The system efficiency is controlled by matching the aggregate traffic rate to the sum of the link capacity and total buffer size. On the other hand, the system min-max fairness is achieved by allocating bandwidth among individual flows in proportion with their RTTs. The proposed scheme is dubbed Recursive, Explicit, and Fair Window Adjustment (REFWA). Simulation results elucidate that the REFWA scheme substantially improves the system fairness, reduces the number of packet drops, and makes better utilization of the bottleneck link. The results demonstrate also that the proposed scheme works properly in more complicated environments where connections traverse multiple bottlenecks and the available bandwidth may change over data transmission time.     

TCP在不可靠网络环境中的性能分析及其服务质量控制

本文对TCP在拥塞丢失和非拥塞丢失同时存在的不可靠网络环境中的性能进行了理论分析,给出了TCP吞吐量,延时以及分组丢失概率的简明表达式.同时针对多个TCP连接共享一条限速链路时服务质量不均衡问题,提出了轮询丢弃策略和惩罚丢弃策略两种服务质量控制策略.仿真结果表明,轮询丢弃策略可以提高限速链路的总吞吐量,而惩罚丢弃策略可以提高TCP连接之间的公平性.     

Scheduling schemes for multimedia service in wireless OFDM systems

Scheduling schemes play a key role in the system performance of broadband wireless systems such as WLANs/WMANs. Maximal SNR and round robin are two conventional scheduling strategies that emphasize efficiency and fairness, respectively. The proportional fair scheme provides a trade-off between efficiency and fairness, and has been well studied in TDMA and CDMA systems. In this article we extended the PF scheduling scheme to OFDM-based BWSs (OPF). In addition, we propose three variations: adaptive OPF (AOPF), multimedia AOPF (MAOPF), and normalized MAOPF (NMAOPF) in order to meet the QoS requirements for multirate services in multimedia systems. The adaptive modulation and coding schemes in time varying and frequency selective fading are considered. The system performances of the algorithms are compared in terms of efficiency (throughput and mean packet delay) and fairness (user satisfaction rate and average user rate). Joint physical and media access control layer simulation results show that AOPF and MAOPF can improve throughput at the cost of fairness, and NMAOPF can provide the highest throughput without losing fairness.     

An explicit and fair window adjustment method to enhance TCP efficiency and fairness over multihops Satellite networks

Transmission control protocol (TCP) is the most widely used transport protocol in today's Internet. Despite the fact that several mechanisms have been presented in recent literature to improve TCP, there remain some vexing attributes that impair TCPs performance. This paper addresses the issue of the efficiency and fairness of TCP in multihops satellite constellations. It mainly focuses on the effect of the change in flows count on TCP behavior. In case of a handover occurrence, a TCP sender may be forced to be sharing a new set of satellites with other users resulting in a change of flows count. This paper argues that the TCP rate of each flow should be dynamically adjusted to the available bandwidth when the number of flows that are competing for a single link, changes over time. An explicit and fair scheme is developed. The scheme matches the aggregate window size of all active TCP flows to the network pipe. At the same time, it provides all the active connections with feedbacks proportional to their round-trip time values so that the system converges to optimal efficiency and fairness. Feedbacks are signaled to TCP sources through the receiver's advertised window field in the TCP header of acknowledgments. Senders should accordingly regulate their sending rates. The proposed scheme is referred to as explicit and fair window adjustment (XFWA). Extensive simulation results show that the XFWA scheme substantially improves the system fairness, reduces the number of packet drops, and makes better utilization of the bottleneck link.     

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．     

Optimizing uplink TCP-ACK transmission in WiMAZ OFDMA systems

In WiMAX networks, a bandwidth request-grant process is required for uplink operation. However, the process is not optimized for TCP, since the uplink ACK stream is disrupted due to the following: (a) The process consists of several stages which in turn introduce big transmission delay; and (b) it requires additional uplink bandwidth which is significant compared to the ACK packet size. In this paper, the authors propose a new ACK transmission scheme, where ACK packets are combined with a bandwidth request (BR) header. Through simulation, it is demonstrated that the proposed scheme reduces the overheads of TCP-ACK transmissions effectively.     

Improving network service quality with explicit TCP window control

We describe in this paper a new TCP rate control scheme based on a simple recursive algorithm. The idea behind the algorithm is to match the offered network load to the available resources by modifying at an intermediate network element, the receiver's advertised window in TCP acknowledgments returning to the source. We show through simulations that the scheme can efficiently control TCP traffic to limit queue buildups and buffer requirements at the network nodes, resulting in significant improvements in delay, packet loss rates, fairness, throughput and link utilization. Copyright © 2001 John Wiley & Sons, Ltd.