Analysis of bandwidth aggregation techniques for combined use of satellite and xDSL broadband links

The availability of multiple technologies to access the Internet is even more common in today's connectivity scenarios. As an example, smartphones make use of 3G/4G data technology but, when a Wi‐Fi access point is available, they switch from 3G/4G (which typically is a paid per volume service) to the wireless local access. The same principle is applicable for fixed access, when terrestrial ADSL or optical fiber and satellite technologies can be typically available in the same place. This paper focuses on the simultaneous availability of different access technologies with the capability to use them in combination, to offer better performance than the traditional single technology access.     

并行多路传输中数据调度算法的研究

针对传统并行多路传输中数据调度算法存在的问题,基于MPTCP协议,提出了带宽预测和前向时延的数据调度算法(data-scheduling algorithm using bandwidth estimation and forward trip-time,DA-BEFT)。该算法充分考虑子流间传输时延差较大的影响,结合性能好的重传选路策略,减轻接收端因数据乱序导致的缓存阻塞,提高整个连接吞吐量。通过仿真实验验证了DA-BEFT在子流时延差变化时能够提高带宽利用率,提高网络的吞吐量。     

PTCP Incast in Data Center Networks

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.     

多源协作的传输控制机制

多路径传输控制协议（Multipath Transmission Control Protocol,MPTCP）是传输控制协议的一种扩展,实现端到端动态地利用多个地址建立多条传输路径,从而提高网络传输质量和可靠性.但是,MPTCP仍存在局限,能够解决端到端已确定的多路径调度问题,但难以实现不同端以及变化端间的路径协作.智慧协同网络是一种新型的未来网络体系,其核心思想是通过网络组件的智慧协作,最大限度优化利用网络资源,提高网络工作效率.本论文提出了基于智慧协同网络的多源协作传输控制机制,实现了传输控制协议从单源多路径向多源多路径的突破.具体来说,首先刻画了一种智慧协同网络的多源协作传输架构,引入子源协作传输方法,并详细介绍了多源协作机制的理论模型、报文格式以及子源协作管理的核心工作流程.通过仿真实验验证,多源协作传输控制机制能够将拥塞窗口平均利用率从51%提升至96%,并提高网络利用率和吞吐量.     

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.     

利用SDN实现可编程无线局域网多径接入管理

WiFi接入点（Access Point,AP）被广泛部署在学校、商场和机场等公共场所,满足用户随时随地的使用需求.然而,管理大规模的WiFi网络仍是一个亟待解决的难题,设备间的差异性造成难以在无线局域网中提供集中的接入管理.同时,由于各种新服务、新应用的推动,使得传统无线局域网中的网络资源利用率低及接入点负载不均衡的问题目益严重.因此,本文引入SDN思想,将协议无关转发（POF）技术应用到无线局域网中,提出一种深度可编程无线局域网架构,实现集中接入管理.同时,综合考虑信号强度（RSSI）、实时网络流量等因素,提出一种基于多路径TCP （MultiPath TCP,MPTCP）的无线AP接入管理机制,充分利用各AP的带宽资源,避免在拥塞的路径上继续传输数据,从而均衡底层AP负载.     

基于MPTCP的前向预测数据调度方法

现有MPTCP的数据调度方案无法满足多路径的动态变化,出现链路传输性能降低的问题.通过对每条路径上的ACK数、往返时延进行预测,提出一种前向预测速度调度方法.利用NS-3对该算法仿真,表明该算法能提高吞吐量,更加合理,并使负载更加均衡.     

IPv6+MPTCP技术对上层应用支撑的验证

通过对TCP/IPv4地址结构和Socket API的研究,重构了MPTCP/IPv6的地址结构及Socket API软件,扩展了SRS开源流媒体服务器对IPv6的支持。以此为基础,编译了MPTCP内核及扩展的SRS、配置了相应的路由表,最终实现了基于IPv6+MPTCP的视频直播平台实例,有效验证了二者结合的有效性及可用性。结果表明：（1）MPTCP多路径并发传输技术具有良好的负载均衡能力;（2）MPTCP多路径冗余机制可实现无缝切换,提升网络的鲁棒性;（3）IPv6+MPTCP+RTMP三个协议具有良好的兼容性;（4）该直播平台为开发基于IPv6+MPTCP技术的下一代互联网万物相联应用提供了一个范例。     

基于灰色马尔科夫预测的移动多路传输调度算法

多路径传输控制协议通过聚合多路径带宽提高资源利用率及网络吞吐量。在无线异构网络环境中,由于网络性能不稳定、传输路径性能差异等因素容易导致数据包乱序及缓冲区阻塞,对网络多路传输性能造成负面影响。为在有限的接收缓冲区内对数据包实施合理调度,基于灰色预测模型GM （1,N）与马尔科夫优化的前向传输时间（FTT）预测模型,提出一种自适应多路传输数据调度算法GMM-S。通过对未来时刻子流FTT的准确预测实现子流传输性能的有效评估,并以此作为数据分发依据进行传输数据的多子流动态调整。仿真实验结果表明,与RR和LowRTT算法相比,该算法可有效解决接收端数据包乱序问题,同时提升网络吞吐量。     

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.