【作者】 徐昌彪；

【导师】 杨士中； 隆克平；

【作者基本信息】 重庆大学 ， 电气工程， 2002， 博士

【摘要】 当代通信技术的发展，极大地提高了人们传递信息和获取信息的能力。然而，迄今为止，仍然不能实现对任何人、任何时间、任何地点和任何内容的信息交换。显然，要改变这种状况，必须依赖于无线通信及移动通信技术的发展和应用。因为，第一、无线网络能极大地减少建设成本，如节省了铺设电缆和维护电缆的开支；第二，无线网络能够在有线网络无法实现的地方建立，这对偏远的乡村尤其具有实际意义；第三，无线网络实现了无处不在的互连网访问。与有线网络相比，无线网络通常表现出高误码率、传输时延及时延抖动大、有限的链路带宽以及移动终端的频繁移动等特性，使网络通信性能和业务服务质量难于保证。这样，传统的TCP/IP协议也就无法直接适用于无线环境。同样，目前针对话音业务设计的移动通信网也不适于传送数据和多媒体业务。对无线网络中关键理论与技术的研究已成了当前网络领域一个重要的研究课题。本文集中探讨了无线网络下的TCP核心技术，以期能为改善无线网络下的TCP性能提供有价值的参考。TCP是目前Internet中广泛采用的传输控制协议，为各主机之间提供可靠按序的传输服务，在保障网络通信性能方面起着非常重要的作用。TCP设计主要针对系统稳定性、协议兼容性、业务公平性、资源利用率以及拥塞控制等问题。正如上面所述，由于无线网络具有一些有别于有线网络的固有特性，使基于有线网络而设计的TCP技术无法直接适用于无线网络。下面是本文在无线TCP方面完成的主要研究工作：1．探讨了无线网络下的TCP策略。主要涉及TCP差错控制策略、基于拥塞丢包的TCP拥塞控制策略以及基于误码丢包的TCP速率调节策略；2．讨论了无线网络下的TCP拥塞裁决技术和无线网络下的TCP隐式丢包检测技术；3．提出了一种显式误码丢包通知机制。即便是在高误码率、多段无线链路下，此机制亦能够有效快速地将误码丢包信息显式地告之数据源端；4．提出了两种基于拥塞丢包的TCP拥塞控制机制：D_AIMD和基于资源加权分配的TCP拥塞控制。D_AIMD主要解决TCP存在的数据发送速率波动性较大的问题；基于资源加权分配的TCP拥塞控制能够实现TCP业务间网络资源的加权分配，从而可有效实现服务质量的相对保证，改善网络的通信性能；5．提出了两套基于误码丢包的TCP速率调节方案：基于速率和基于窗口的TCP速率调节。其中每一套速率调节方案又可有多种具体的实现方式。短期内误码丢包较严重时，可以通过数据发送速率的降低来有效避免不必要的误码丢包，<WP=5>从而提高数据发送的可靠性，减少移动设备不必要的能源消耗和系统的额外开销，同时又不会过多降低系统吞吐量和加大系统时延。本文内容安排大致是这样的：第1章概述无线网络通信、无线TCP技术研究现状以及本文的主要工作；第2章简要介绍OSI参考模型与TCP/IP模型；第3章介绍基于有线网络而设计的TCP技术；第4章探讨无线网络中的TCP策略，主要涉及TCP差错控制策略、基于拥塞丢包的TCP拥塞控制策略以及基于误码丢包的TCP速率调节策略；第5章讨论无线网络下的丢包检测技术，详细分析一种显式误码丢包通知机制；第6章讨论无线网络中基于拥塞丢包的TCP拥塞控制，详细分析两种拥塞控制方案，给出仿真结果分析；第7章讨论无线网络中基于误码丢包的TCP速率调节，详细分析两套速率调节机制，给出仿真结果分析。更多还原

【Abstract】 With the fast development of communication, the abilities of transmitting and catching information have been enhanced greatly. However, so far it hasn’t been achieved to exchange information wherever. Obviously, it is only wireless communication to reach the goal for the reasons of cheaper cost, building network wherever, internetworking wherever and so on. Comparing to wired network, there are many different characteristics in wireless environments, such as higher error rate, longer delay, lower bandwidth, frequent mobility and so on, which result in difficulty to guarantee network performances and qualities of service. So traditional TCP/IP protocols can’t be directly adapted to wireless networks. The study of key theories and technologies for wireless networks has been becoming an important task in communication field. This paper will focus on TCP key technologies over wireless networks. TCP, transmission control protocol for providing reliable service, has being widely used in Internet. TCP plays an important role in guaranteeing network performances. The design of TCP mainly aims at system stability, protocol compatibility, traffic fairness, resource utility, network congestion control and so on. As for the reasons presented above, TCP can’t be directly adapted to wireless networks. The study of wireless TCP are as follows: I TCP strategies for wireless networks dealing with error control, congestion control and corruption-based TCP rate adjustment; II Technologies about TCP congestion verdict and implicit loss detection of TCP packet under wireless environment; III A novel explicit error bit notification mechanism. It is very efficient to adopt this mechanism to notify corruption loss information to TCP sender even under high bit error rate and multi-hop wireless environment; IV Two suits of congestion-based TCP congestion control mechanisms. One mechanism can efficiently mitigate the fluctuation of data sending rate in steady state while quickly tracing network state changes, and another can easily perform network resources allocation by weight between traffics under the similar communication environments. V Two suits of corruption-based TCP rate adjustment mechanisms respectively<WP=7>1`belonging to rate-based and window-based. Due to the mechanisms, unnecessary data lost by corruption can be greatly avoided through the decrease of data sending rate while heavy data loss rate by corruption lasts short time, which may lead to higher reliability, unnecessary energy consumption of mobile devices and less system overheads with light influence to throughput and delay. The paper is organized as follows: Chapter 1 briefly introduces wireless communication, overview of wireless TCP technologies and works in the paper. Chapter 2 outlines OSI reference framework and TCP/IP architecture. Chapter 3 briefly explains TCP in wired networks. Chapter 4 discusses TCP strategies over wireless networks dealing with error control, congestion control and corruption-based TCP rate adjustment. Chapter 5 discusses detection of data lost by corruption or congestion in wireless networks, and analyzes a novel explicit bit error notification mechanism for wireless networks. Chapter 6 details two suits of congestion-based TCP congestion control mechanisms. Chapter 7 gives two suits of corruption-based TCP rate adjustment mechanisms.更多还原