多路径TCP拥塞控制算法研究

首先介绍了多路径传输协议的几种典型的拥塞控制算法,然后对MPTCP协议进行了理论分析,包括MPTCP拥塞控制算法在瓶颈链路TCP公平性、平衡拥塞能力以及flap现象,实验分析表明LINKED INCREASES算法效果最好。最后,指出其存在的问题,并指出了进一步的研究方向。     

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。     

TCP在无线环境中的性能改进技术研究

对TCP拥塞控制算法作了一些改进,以适应于无线链路传输环境.基本方法是根据TCP测量的RTT值动态估计当前链路可用带宽,重新计算并设置拥塞窗口cwnd值.仿真显示,改进后的TCP应用于无线环境性能有了较大的改进.     

一种异构网络TCP拥塞控制算法

针对互联网中端对端带宽、时延和丢包率等的差异性日益加剧,导致TCP传输性能严重退化,该文提出一种链路自适应TCP拥塞控制算法(INVS)。INVS在拥塞避免阶段初期采用基于指数函数的凸窗口增长函数,以提高链路利用率;在窗口增长函数中引入了自适应增长因子实现窗口增长速率与链路状态相匹配;采用了自适应队列门限的丢包区分策略以提高无线环境下TCP的性能。性能分析和评估表明,INVS提高了TCP拥塞控制算法的吞吐量、公平性、链路利用率和RTT公平性。     

基于RTT的TCP流带宽公平性保障机制

TCP端到端的拥塞控制机制使得TCP连接获得的瓶颈带宽反比于RTT(数据包往返时间)。为了缓解TCP对于RTT较小流的偏向,区分服务的流量调节机制在RTT较小的流取得目标速率且获得多余资源的情况下可以确保RTT较大流不至于饥饿。现有的基于RTT的流量调节机制在网络拥塞程度较轻时非常有效,但是当网络拥塞程度较重时,由于对RTT较大流的过分保护而导致RTT较小流饥饿。因此,通过引进自适应的思想提出了改进方法,其主要思想就是根据网络的拥塞程度自适应地调整对RTT较大流的保护程度。大量的仿真试验表明所提的机制能有效保障TCP流的带宽公平性并且比现有的方法具有更好的强壮性。     

基于MPTCP的非对称多链路传输调度方法述评

随着通信及网络技术的发展,移动终端设备往往配备多个网络接口,具有多链路的网络接入能力。为实现多链路传输,互联网工程任务组提出了新型的多路径传输控制协议（Multipath Transmission Control Protocol,MPTCP）。如何合理进行MPTCP数据包调度为用户提供更大带宽、提高数据传输可靠性,并最大化网络资源利用率,成为网络通信领域的重要课题。首先,介绍了MPTCP的基本功能和其在数据调度中面临的主要挑战;然后,针对非对称多链路下的MPTCP传输调度算法,从减少数据包乱序、降低传输延迟、提高链路利用率,以及结合强化学习四个角度分析和比较了近年来的多路径传输相关研究;最后,结合当前研究热点展望了MPTCP的未来发展趋势。     

区分服务网络中直接拥塞反馈机制与动态流量调节

IP服务质量是目前国际上的一个研究热点,IETF为此而定义了区分服务体系结构.然而,该体系中存在不公平问题.本文提出了一种直接拥塞反馈机制(DCCS),配合网络边缘的动态流量调节(DTC)算法,能够为该体系提供很好的公平性.该机制不仅能保证响应流与非响应流之间的公平性,而且能解决响应流(如TCP)自身由于分组长度,微流数目及环回时延(RTT)等因素而产生的差异.     

多路径传输控制协议技术综述

随着互联网的应用发展,用户对带宽的需求日益增大。同时,伴随着宽带接入技术的发展,终端可以同时具有多条网络链接,然而传统传输控制协议(TCP)采取单路通信,因而造成资源浪费。为此,IETF专门提出了多路径TCP(MPTCP)来实现TCP的多路传输,从而提高链路利用率和协议鲁棒性。本文对国内外MPTCP的最新研究成果进行了总结,包括MPTCP的体系结构、路由和拥塞控制等内容,可为国内研究者进一步深入研究提供参考。     

网络拥塞与流量控制

文章主要研究了TCP/IP中主要采用的拥塞控制算法,讨论了目前TCP/IP中常用的AIMD算法的稳定性、收敛性、公平性,及其约束条件,并进一步将MAIMD算法和AIMD算法进行了比较。最后仿真了两用户不同RTT时的状态轨迹和公平指数轨迹。     

CB-HSTCP:高速网络中的公平TCP算法

通过实验发现HSTCP存在严重的RTT(Round Trip Time)不公平性,另外发现拥塞时存在大量的包丢失.用模型对RTT不公平现象进行了分析,并分析了包丢失问题.提出了CB-HSTCP算法,包括CW机制和Block-pacing机制,用于改善公平性和降低包丢失率.为衡量算法性能,提出了一个相对公平性标准.通过分析并使用ns2进行模拟实验,证实该方案在保证HSTCP性能的基础上,解决了RTT不公平性问题、降低了包丢失率,同时具有良好的扩展性和TCP友好性.     

数据中心网络中的MPTCP Incast（英文）

In recent years,dual-homed topologies have appeared in data centers in order to offer higher aggregate bandwidth by using multiple paths simultaneously.Multipath TCP(MPTCP) has been proposed as a replacement for TCP in those topologies as it can efficiently offer improved throughput and better fairness.However,we have found that MPTCP has a problem in terms of incast collapse where the receiver suffers a drastic goodput drop when it simultaneously requests data over multiple servers.In this paper,we investigate why the goodput collapses even if MPTCP is able to actively relieve hot spots.In order to address the problem,we propose an equally-weighted congestion control algorithm for MPTCP,namely EW-MPTCP,without need for centralized control,additional infrastructure and a hardware upgrade.In our scheme,in addition to the coupled congestion control performed on each subflow of an MPTCP connection,we allow each subflow to perform an additional congestion control operation by weighting the congestion window in reverse proportion to the number of servers.The goal is to mitigate incast collapse by allowing multiple MPTCP subflows to compete fairly with a single-TCP flow at the shared bottleneck.The simulation results show that our solution mitigates the incast problem and noticeably improves goodput in data centers.     

Multipath congestion control algorithm based on link capacity

Factors such as link differences and TCP friendliness constraints lead to the problem of unfair bandwidth allocation when the TCP congestion control mechanism was applied directly to multi-path transmission.To address the problem,it was proposed that a multipath congestion control algorithm was based on link capacity.The proposed algorithm which was based on the concept of feedback regulation achieved multipath joint congestion control by establishing the M/M/1 cache queue model to adjust the throughput rate of senders.Experimental results show the proposed algorithm can improve the multipath transmission bandwidth utilization and the multipath congestion control algorithm responsiveness,and ensure the fairness of multipath transmission.     

TCP Window Control for Variable Bandwidth in Wireless Cellular Networks

Most of TCP schemes in wireless networks assume that the bandwidth of the bottleneck link remains constant over time. However, in wireless cellular networks, to effectively manage the limited resources, the bandwidth is controlled based on radio condition over time. Such varying bandwidth can cause the networks congestion or underutilization. In this letter, we propose a new window control algorithm to improve TCP performance in wireless cellular networks with variable bandwidth. Simulation results illustrate that our proposal improves the performance of TCP in terms of fairness and link utilization     

Towards end-host-based identification of competing protocols against TCP in a bottleneck link

Classical Transmission Control Protocol (TCP) designs have never considered the identity of the competing transport protocol as useful information to TCP sources in congestion control mechanisms. When competing against a TCP flow on a bottleneck link, a User Datagram Protocol (UDP) flow can unfairly occupy the entire link bandwidth and suffocate all TCP flows on the link. If it were possible for a TCP source to know the type of transport protocol that deprives it of link access, perhaps it would be better for the TCP source to react in a way which prevents total starvation. In this paper, we use coefficient of variation and power spectral density of throughput traces to identify the presence of UDP transport protocols that compete against TCP flows on bottleneck links. Our results show clear traits that differentiate the presence of competing UDP flows from TCP flows independent of round-trip times variations. Signatures that we identified include an increase in coefficient of variation whenever a competing UDP flow joins the bottleneck link for the first time, noisy spectral density representation of a TCP flow when competing against a UDP flow in the bottleneck link, and a dominant frequency with outstanding power in the presence of TCP competition only. In addition, the results show that signatures for congestion caused by competing UDP flows are different from signatures due to congestion caused by competing TCP flows regardless of their round-trip times. The results in this paper present the first steps towards development of more ’intelligent’ congestion control algorithms with added capability of knowing the identity of aggressor protocols against TCP, and subsequently using this additional information for rate control.     

An implementation of Min–Max optimization for multipath SCTP through bandwidth estimation based resource pooling technique

Multipath transport protocols like Stream Control Transmission Protocol (SCTP) and Multipath TCP (MPTCP) have been introduced in the past as alternatives to traditional single path transport protocols like TCP and UDP. Various approaches to divide the flow on multiple paths have also been proposed in the literature. In this work, we show that the bandwidth estimation based resource pooling (BERP) congestion control algorithm is a practical implementation of the Min–Max optimization approach for flow division and verify this through ns-2 based simulations.     

Delay-based congestion avoidance for TCP

The set of TCP congestion control algorithms associated with TCP-Reno (e.g., slow-start and congestion avoidance) have been crucial to ensuring the stability of the Internet. Algorithms such as TCP-NewReno (which has been deployed) and TCP-Vegas (which has not been deployed) represent incrementally deployable enhancements to TCP as they have been shown to improve a TCP connection's throughput without degrading performance to competing flows. Our research focuses on delay-based congestion avoidance algorithms (DCA), like TCP-Vegas, which attempt to utilize the congestion information contained in packet round-trip time (RTT) samples. Through measurement and simulation, we show evidence suggesting that a single deployment of DCA (i.e., a TCP connection enhanced with a DCA algorithm) is not a viable enhancement to TCP over high-speed paths. We define several performance metrics that quantify the level of correlation between packet loss and RTT. Based on our measurement analysis, we find that, although there is useful congestion information contained within RTT samples, the level of correlation between an increase in RTT and packet loss is not strong enough to allow a TCP-sender to improve throughput reliably. While DCA is able to reduce the packet loss rate experienced by a connection, in its attempts to avoid packet loss, the algorithm reacts unnecessarily to RTT variation that is not associated with packet loss. The result is degraded throughput as compared to a similar flow that does not support DCA.