Transport Protocols for the Wired/Wireless NGI: Implementation and Experimental Evaluation

下一代互联网(NGI)对传输协议(TCP)的高效运行提出了可扩展性挑战。特别是，随着乘积(带宽x延迟)的增长，填充管道所需的拥塞窗口。变得相当大，特别是在越野线路上。在这种情况下，TCP中的一个众所周知的问题是.Initial窗口的选择。最近，由于游牧民族通过无线链路(如无线局域网、卫星链路、UMTS等)接入互联网的日益流行，出现了新的挑战。无线链路上的数据速率一直在不断上升，接近802.11a无线局域网上的50 Mbps，从而为移动用户提供了有效的骨干服务扩展。然而，无线链路往往会引入与拥塞无关的随机分组错误和丢失。这给传统的TCP协议(例如，TCPNew Reno和TCPSACK)带来了问题，其将任何丢失解释为缓冲区溢出(即，作为拥塞的症状)，并因此不必要地减少拥塞窗口，从而导致性能损失。性能下降与连接的(带宽x长度)乘积成正比，在高带宽NGI环境中可能非常显著，尤其是在包括最后一跳无线局域网、UMTS链路或高带宽卫星在内的跨国路径上。在文献中已经报告了在高带宽无线链路上增强TCP拥塞控制的几种方法(例如，TCP Peach、TCP Westwood(TCPW))。其中一些改进相当成功。例如，TCPW，一种使用瓶颈带宽份额估计的TCP变体。为了在丢失时调整拥塞窗口，在大型泄漏管道中表现出了可扩展的特性和良好的链路利用率(即大带宽延迟乘积和不可忽略的随机分组丢失)。该方案是关于对有线/无线路径上的TCP性能进行系统的实验研究。这项调查将包括对目前文献中提出的各种TCP增强进行比较。它将考虑一组具有代表性的实验环境和应用场景。建议的项目在一定程度上是由我们最近在TCPW互联网上通过有损路径传输大文件的积极经验所推动的。在这个项目中，研究人员将扩大范围，包括大量的TCP无线增强技术。研究人员将确定每种方案的优缺点，确定其最适合的流量/网络环境，更广泛地说，开发将无线媒体特征、TCP拥塞控制参数和性能结果联系起来的模型。总而言之，考虑到：(1)游牧计算和无线接入高速有线互联网的重要性日益增加；(2)在无线路径上观察到传统的TCP协议的性能降级；以及(3)修改后的无线版本的TCP(仍保留基本的端到端范例)提供了令人鼓舞的改进，研究人员认为，现在是由一个包括协议开发人员、应用程序开发人员和网络测量专家的团队参与系统的、基于实验的无线TCP协议评估的非常合适的时机。

The Next Generation Internet (NGI) poses scalability challenges to the efficient operation of the transport protocol (TCP). In particular, as the product (bandwidth x delay) grows, the congestion window required to .fill the pipe. becomes quite large, especially on cross-country links. One well known problem in TCP in this scenario is the selection of the .initial window.. More recently, new challenges have emerged because of the increasing popularity of nomadic access to the Internet via wireless links (e.g., wireless LANs, satellite links, UMTS, etc). The data rates on wireless links have been constantly on the rise, approaching the 50Mbps on 802.11a wireless LANs and thus providing an effective extension of backbone services to mobile users. However, wireless links tend to introduce random packet errors and loss that are not correlated to congestion. This creates problems to conventional TCP protocols (e.g., TCP New Reno and TCP SACK), which interpret any loss as a buffer overflow (i.e., as a symptom of congestion) and thus reduce the congestion window unnecessarily with consequent loss in performance. The drop in performance is proportional to the (bandwidth x length) product of the connection and can be quite significant in the high bandwidth NGI environment, especially on cross country paths including .last hop wireless LANs, UMTS links, or high bandwidth satellites. Several approaches to enhance TCP congestion control over high bandwidth wireless links have been reported in the literature (e.g., TCP Peach, TCP Westwood (TCPW)). Some of these enhancements have been quite successful. For example, TCPW, a TCP variant that uses bottleneck bandwidth share estimation. to adjust the congestion window upon loss, has shown scalable properties and good link utilization in large leaky pipes., (i.e. large bandwidth delay product, and non negligible random packet loss). This proposal is about carrying out a systematic, experimental investigation of performance of TCP over wired/wireless paths. This investigation will include the comparison of various TCP enhancements proposed so far in the literature. It will consider a representative set of experimental environments and application scenarios. The proposed project is in part motivated by our recent positive experience with TCPW Internet experiments of large file transfers over lossy paths. In this project the researchers will broaden the scope to include a vast gamut of TCP wireless enhancement techniques. The researchers will identify the pros and cons of each scheme, characterize the traffic/network environment for which it is best suited, and, more generally, develop models that relate wireless media characteristics, TCP congestion control parameters and performance results. In summary, given: (1) the increasing importance of nomadic computing and wireless access to the high speed wired Internet; (2) the performance degradations observed in conventional TCP protocols over wireless path, and (3) the encouraging improvements offered by modified, wireless versions of TCP (which yet retain the basic end to end paradigm), the researchers believe this a very appropriate time to engage in a systematic, experimentally based evaluation of wireless TCP protocols by a team that includes protocol developers, applications developers and network measurement experts.