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，随着产品（带宽×延迟）的增长，需要填充管道的拥塞窗口。变得相当大，特别是在越野赛道上。在这种情况下，TCP中一个众所周知的问题是选择。初始窗口. .最近，由于通过无线链路（例如，无线局域网、卫星链路、UMTS等）游牧访问Internet的日益普及，出现了新的挑战。无线链路的数据速率不断上升，已接近802.11a无线局域网的50Mbps，为移动用户提供了有效的骨干业务扩展。然而，无线链路往往会引入与拥塞无关的随机数据包错误和丢失。这对传统的TCP协议（例如，TCP New Reno和TCP SACK）造成了问题，它们将任何丢失解释为缓冲区溢出（即，作为拥塞的症状），从而不必要地减少拥塞窗口，从而导致性能损失。性能的下降与连接的（带宽x长度）乘积成正比，并且在高带宽NGI环境中可能相当显著，特别是在包括。最后一跳无线局域网、UMTS链路或高带宽卫星。文献中已经报道了几种增强高带宽无线链路上TCP拥塞控制的方法（例如TCP Peach， TCP Westwood (TCPW)）。其中一些改进相当成功。例如，TCPW，一种使用瓶颈带宽共享估计的TCP变体。在损失时调整拥塞窗口，在大泄漏管道中显示出可扩展性和良好的链路利用率。，（即大带宽延迟积，不可忽略的随机丢包）。本提案是关于在有线/无线路径上对TCP性能进行系统的实验研究。这项调查将包括迄今为止在文献中提出的各种TCP增强的比较。它将考虑一组具有代表性的实验环境和应用场景。我们最近在TCPW互联网实验中通过有损路径进行大文件传输，这在一定程度上激发了我们提出这个项目的动机。在这个项目中，研究人员将扩大范围，包括广泛的TCP无线增强技术。研究人员将确定每种方案的优缺点，描述最适合的流量/网络环境，更一般地说，开发与无线媒体特性、TCP拥塞控制参数和性能结果相关的模型。综上所述，鉴于：(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TCP协议的性能下降，(3)修改后的TCP无线版本（仍保留基本的端到端范式）提供了令人鼓舞的改进，研究人员认为这是一个非常合适的时机，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对无线TCP协议进行系统的、基于实验的评估。

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.