一种改进的基于Smith原则的计算机高速通信网络的拥塞控制方案

1.引言 ATM网络是一类虚拟的电路交换网络,它融入了电路交换技术和包交换技术。在这两个系统融入以前它们是独立的,若要互相通信必须获得彼此的通信参数才能建立虚拟连接。而ATM网络通过存储技术和统计复用来共享网络资源,网络资源的共享使得通信费用大大减少。ATM是以定长的信元(cell)作为高速通信信息的载体,它具有高速、低比特错误率、动态分配带宽和高复合能力的优点,这些使得它非常适宜于需要保证服务质量(Quality of Service,QoS)的多媒体数据流。由于多媒体业务流的特性,常引起网络拥塞并降低服务的质量。因此必须采取一定的流量管理控制机制来避免网络的拥塞。     

具有显式反馈的拥塞控制系统研究进展

近年来越来越多的高带宽光纤网络和长时延的卫星网络融入到Internet中来。研究发现，传统TCP协议的拥塞控制机制随着网络带宽和延迟的增大而趋于不稳定。研究这种高带宽时延乘积网络环境下的拥塞控制机制成为热点研究课题，其中一个重要趋势就是采用显式反馈方法。本文讨论了基于IP网络中的显式反馈机制，包括传统ECN、各种类ECN机制以及新的拥塞控制协议；分析了各种机制的特点，总结了现有研究的问题并指出了几个值得继续研究的要点。     

Stable Queue Management in communication networks

Since Active Queue Management (AQM) was recommended by the Internet Engineering Task Force (IETF) as an efficient way to overcome performance limitations of Transmission Control Protocol (TCP), several studies have proven control theory to be a promising field for the design and analysis of congestion control in homogenous communication networks. AQM is gaining increased importance due to reports of buffer-induced latencies throughout the Internet. The increasing volume and diversity of traffic types (i.e., data, voice, and video) suggests that traffic management mechanisms, in general, and AQM schemes, specifically, must not only focus on the critical issue of congestion control but must also consider the QoS demands of heterogeneous traffic. However, to combine quality-of-service provisioning with congestion control, AQM design needs to be reconsidered. In this paper, we propose a state feedback controller design scheme for heterogeneous networks preserving the closed-loop system stability. Delay dependant stability conditions of the closed loop system are derived based on the Lyapunov-Krasovskii method. The proposed approach offers flexible choice of control parameters allowing the network administrator to control fairness and response time for each individual source node in a network of multiple links with different delay properties. The performance and robustness of the proposed controller were illustrated and analyzed using event-based computer simulations.     

Energy-aware IP traffic engineering with shortest path routing

Internet energy consumption is rapidly becoming a critical issue due to the exponential traffic growth and the rapid expansion of communication infrastructures worldwide. We address the problem of energy-aware intra-domain traffic engineering in networks operated with a shortest path routing protocol. We consider the problem of switching off (putting in sleep mode) network elements (links and routers) and of adjusting the link weights so as to minimize the energy consumption as well as a network congestion measure. To tackle this multi-objective optimization problem with priority (first minimize the energy consumption and then the network congestion), we propose a Mixed Integer Linear Programming based algorithm for Energy-aware Weights Optimization (MILP-EWO). Our heuristic exploits the Interior Gateway Protocol Weight Optimization (IGP-WO) algorithm for optimizing the OSPF link weights so as to minimize the total cost of link utilization. The computational results obtained for eight real network topologies and different types of traffic matrices show that it is possible to switch off a substantial number of nodes and links during low and moderate traffic periods, while guaranteeing that network congestion is low enough to ensure service quality. The proposed approach is also validated on two networks of emulated Linux routers.     

显式流量控制协议XCP研究

显式流量控制协议(XCP)能提高网络带宽利用率并改善带宽分配的公平性，本文分析了TCP在带宽时延乘积较大时所存在的性能问题，说明了XCP体系结构和流量控制规则，并对XCP与TCP的带宽时延乘积方面进行了性能比较。     

基于窗口的端到端拥塞控制:网络稳定性与效率

拥塞窗口算法对网络稳定性和效率的影响表现在平衡状态附近。分组级递增量越小网络稳定性越强；往返时间级递增量的一阶导数越小网络效率越大．在以上研究的基础上，进而提出一种新拥塞控制算法的基本思想：根据拥塞反馈信号估计可用带宽，分组速率能快速收敛到并能长期保持在可用带宽附近．     

Logarithmic window increase for TCP Westwood+ for improvement in high speed,long distance networks

The majority of current Internet applications uses Transmission Control Protocol (TCP) for ensuring reliable end-to-end delivery of data over IP networks. The resulting path is, generally speaking, characterized by fairly large propagation delays (of the order of tens to hundreds of milliseconds) and increasing available bandwidth. Current TCP¹performance is far from representing an optimal solution in such operating conditions. The main reason lies in the conservative congestion control strategy employed, which does not let TCP to exploit the always increasing available path capacity. As a consequence, TCP optimization has been an active research topic in the research community over the last 25 years, boosted in the last few years by the widespread adoption of high-speed optical fiber links in the backbone and the emergence of supercomputing networked applications from one side and tremendous growth of wireless bandwidth in network access from another. This has led to the introduction of several alternative proposals for performing congestion control. Most of them focus on the effectiveness of bandwidth utilization, introducing more “aggressive” congestion control strategies. However, such approaches result often in unfairness among flows with substantially different RTTs, or do not present the inter-protocol fairness features required for incremental network deployment.In this paper, we propose TCP LogWestwood+, a TCP Westwood+ enhancement based on a logarithmic increase function, targeting adaptation to the high-speed wireless environment. The algorithm shows low sensitivity with respect to RTT value, while maintaining high network utilization in a wide range of network settings. The performance, fairness and stability properties of the proposed TCP LogWestwood+ are studied analytically, and then validated by means of an extensive set of experiments including computer simulations and wide area Internet measurements.     

基于NetFPGA的VCP网络的设计与实现

可变结构拥塞控制协议（VCP）是一种可适应于高带宽时延乘积网络的显式拥塞控制协议,它仅用两个ECN比特位标记网络拥塞的反馈信息,达到较高的带宽利用率和公平性。但目前针对VCP的研究大部分都是基于离散事件仿真验证,文中设计并搭建一种VCP真实网络验证环境。基于Linux协议栈设计VCP网络端系统,基于NetFPGA平台设计VCP网络中间节点,形成完整的VCP网络架构。构建典型的VCP网络实验拓扑,与TCWDT相比,VCP在实际网络中可达到较好的性能。     

LIAD: Adaptive bandwidth prediction based Logarithmic Increase Adaptive Decrease for TCP congestion control in heterogeneous wireless networks

For accessing plentiful resources in the Internet through wireless mobile hosts, diverse wireless network standards and technologies have been developed and progressed significantly. The most successful examples include IEEE 802.11 WiFi for wireless networks and 3G/HSDPA/HSUPA for cellular communications. All IP-based applications are the primary motivations to make these networks successful. In TCP/IP transmissions, the TCP congestion control operates well in the wired network, but it is difficult to determine an accurate congestion window in a heterogeneous wireless network that consists of the wired Internet and various types of wireless networks. The primary reason is that TCP connections are impacted by not only networks congestion but also error wireless links. This paper thus proposes a novel adaptive window congestion control (namely Logarithmic Increase Adaptive Decrease, LIAD) for TCP connections in heterogeneous wireless networks. The proposed RTT-based LIAD has the capability to increase throughput while achieving competitive fairness among connections with the same TCP congestion mechanism and supporting friendliness among connections with different TCP congestion control mechanisms. In the Congestion Avoidance (CA) phase, an optimal shrink factor is first proposed for Adaptive Decreasing cwnd rather than a static decreasing mechanism used by most approaches. Second, we adopt a Logarithmic Increase algorithm to increase cwnd while receiving each ACK after causing three duplicate ACKs. The analyses of congestion window and throughput under different packet loss rate are analyzed. Furthermore, the state transition diagram of LIAD is detailed. Numerical results demonstrate that the proposed LIAD outperforms other approaches in goodput, fairness, and friendliness under diverse heterogeneous wireless topologies. Especially, in the case of 10% packet loss rate in wireless links, the proposed approach increases goodput up to 156% and 1136% as compared with LogWestwood+ and NewReno, respectively.     

Unreliable transport protocol using congestion control for high-speed networks

Currently there is no control for the real-time traffic of multimedia applications using UDP (User Datagram Protocol) in high-speed networks. Therefore, although a number of high-speed TCP (Transmission Control Protocol) protocols have been developed for gigabit-speed (or faster) links, the real-time traffic could also congest the network and result in unfairness and throughput degradation of TCP traffic. In this paper, a new unreliable transport protocol, FAST DCCP, is presented for the real-time traffic in high-speed networks. FAST DCCP is based on the DCCP protocol and adopts the FAST scheme to realize congestion control. Some modifications have been made to the mechanisms inherited from DCCP so as to let the proposed protocol can efficiently operate under a large size window. In addition, an enhanced protocol, EEFAST DCCP, using the measurements of one-way delay to dynamically adjust the window size is also proposed to improve the throughput of FAST DCCP with the effect of reverse traffic. Simulation results show that FAST DCCP not only can satisfy the requirements of real-time data delivery, but also perform well in bandwidth utilization and fairness in high-speed networks. Meanwhile, EEFAST DCCP is able to effectively conquer the throughput degradation caused by the reverse traffic.