基于实验 自顶向下 互联网特色 计算机网络.ppt

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1、,探究式示范建设课程汇报计算机网络,宁波大学信息科学与工程学院 王晓东/周宇,2012.6,Computer Networking,课程基本信息,1、 课程属性,Computer Networking,课程基本信息,2、教材选用,Computer Networking: A Top Down Approach Featuring the Internet，4rd editionJim Kurose, Keith RossAddison-Wesley.计算机网络自顶向下方法与Internet特色（第4版 影印版）高等教育出版社,#1 Computer Networks and the Inter

2、net#2 Application Layer#3 Transport Layer#4 Network Layer and Routing#5 Link Layer and Local Area Networks,Computer Networking,课程基本信息,3、课程群关系,课程基本信息,4、教学目标任务,本课程主要介绍计算机网络当前的主流技术、基本原理及应用领域中的各种工程问题。 学生通过本课程的学习，重点反映计算机网络的原理性知识，以及网络体系结构中众多协议的要点和基本概念，要求学生主要掌握计算机网络的基本原理，熟练掌握数据链路层、网络层和传输层、应用层的主要功能和核心协议思想。

3、运用自顶向下方法和internet特色，以TCP/IP协议为例重点介绍Internet应用层协议和可靠传输协议、流量和拥塞控制算法，并通过自主学习和探究实验进行计算机网络的协议分析，能够初步掌握计算机协议编程技术。,Computer Networking,课程基本信息,5、知识体系,课程知识核心体系：以协议原理为主并兼顾组网应用在学生的技术素质的培养上：以应用能力为主并兼顾开发能力课程意义：在信息专业学生的知识和技能体系结构中起着贯穿性的作用传授处理复杂问题、分层问题、构建问题等方法论和世界观。,Computer Networking,课程组织,让学生用自己动手实验探究的方法进行学习和应用，使

4、学生成为课堂精彩的一部分！,Computer Networking,课程特色一,理论和实验融合教学,在实验室上课，将实验和理论授课打通精讲多练，强化学生自学和探究环节用动手探究环节来驱动学生学习培养学生的实验能力和实践精神不光可以在理论不便讲授时采用实验分析辅助还可以在理论讲授后让学生马上动手实验验证和分析部分环节让学生先实验后提出问题、带着问题听课或者让学生自己分析、讨论和总结得出结论大大提高了学生的分析能力和学习兴趣,Computer Networking,课程特色二,技术和原理感知式教学,“通过今天的课程，我突然有了网络应用中数据包交换和传输的真实感受，就像当年海伦凯勒把手伸到水流中豁然

5、领悟水的含义一样，真的好兴奋哦！”很多学生在计算机网络课程探究式教学中都有过类似的感叹。,Computer Networking,课程特色三,应用和研究成就式教学,每班每组学生报告全程录像!,7,团队组织,5-6人一组（组长）每个小组一个小岛每个小组一个组名 团队任务：完成合作教学任务（同，协作完成）完成团队专项研究（异，开放实验）腾讯、微软、百度、淘宝等专题创建和维护团队博客（人人小站）展示团队成果越丰富越好越个性越好,7,“成就驱动”,Computer Networking,人人教学网站,课程主站http:/ http:/ http:/ http:/ http:/ Networking,团

6、队进度安排,Computer Networking,课程考核成绩,Computer Networking,单元说课,第二章 第2&3次课 HTTP协议,Computer Networking,单元教学内容与目标,学习内容：HTTP协议的特性，包括GET方法、服务器响应、单对象、多对象等知识。以宁大网站首页为例。前导知识：Wireshark抓包的基础。实验软件：开源的WIRESHARK。课前预习：学生课前预习HTTP协议的主要特性。教学组织：学生分成2人一组（每个实验岛6人），在实验室授课。师生一起动手实验并分析讨论，循序渐进的深入探究HTTP协议。学会自己如何一步一步的掌握协议知识。,Comp

7、uter Networking,1.课程导入,Computer Networking,2.基本概念,2: Application Layer,19,Some jargon,Web page consists of objectsObject can be HTML file, JPEG image, Java applet, audio file,Web page consists of base HTML-file which includes several referenced objectsEach object is addressable by a URLExample URL(U

8、niform Resource Locator):,Http:/ name,path name,Protocol,2: Application Layer,20,HTTP overview,HTTP: hypertext transfer protocolWebs application layer protocolclient/server modelclient: browser that requests, receives, “displays” Web objectsserver: Web server sends objects in response to requestsHTT

9、P 1.0: RFC 1945HTTP 1.1: RFC 2068,PC runningExplorer,Server runningApache Webserver,Mac runningNavigator,HTTP request,HTTP request,HTTP response,HTTP response,2: Application Layer,21,HTTP overview (continued),Uses TCP:client initiates TCP connection (creates socket,1024,dynamic) to server(fixed,port

10、 80)server accepts TCP connection from clientHTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server),again,.TCP connection closed,2: Application Layer,22,HTTP request message,two types of HTTP messages: request, responseHTTP request me

11、ssage:ASCII (human-readable format),GET /index.html HTTP/1.1Host: User-agent: Mozilla/4.0Connection: close Accept-language:cn (extra carriage return, line feed),request line(GET, POST, HEAD commands),header lines,Carriage return, line feed indicates end of message,2: Application Layer,23,Method type

12、s,HTTP/1.0GETPOSTHEADasks server to leave requested object out of response,HTTP/1.1GET, POST, HEADPUTuploads file in entity body to path specified in URL fieldDELETEdeletes file specified in the URL field,2: Application Layer,24,HTTP response message,HTTP/1.1 200 OK Connection closeDate: Thu, 06 Aug

13、 2004 12:00:15 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Mon, 22 Jun 2004 . Content-Length: 6821 Content-Type: text/html DEMO data data data data data .,status line(protocol status codestatus phrase),header lines,data, e.g., Requested HTML file,2: Application Layer,25,HTTP response status codes

14、,200 OKrequest succeeded, requested object later in this message301 Moved Permanentlyrequested object moved, new location specified later in this message (Location:)400 Bad Requestrequest message not understood by server404 Not Foundrequested document not found on this server505 HTTP Version Not Sup

15、ported,In first line in server-client response message.A few sample codes:,Computer Networking,3. 理论实验融合探究教学,2: Application Layer,27,DIY!now 2.1 基本的HTTP GET/Response,设置capture filter清空internet缓存完成一次简单的HTTP访问仔细观察HTTP的数据包结构分析GET和Response深入一步访问一个跳转网页，了解302状态码访问一个错误网页，体验404状态码,2: Application Layer,28,探究

16、任务与问题,2: Application Layer,29,DIY!now 2.2 得到较长的HTTP文档,通过浏览器访问一个较长的网页分析多个数据包传输的过程观察“Continuation or non-HTTP traffic DATA”或“TCP Segment of a Reassembled PDU ”,2: Application Layer,30,DIY!now 2.3 基本的HTTP post/Response,访问用任意用户名登录对捕获到的post和response进行分析研究chunked编码和set-cookie的作用,2: Application Layer,31,Re

17、ading-works 2.1 WEB数据传输安全,我们发现HTTP协议在GET、POST及其响应数据都是明文传输的，这在电子商务、电子政务应用中会出现商业利益和个人隐私问题，请通过动手实验或网络搜索调研：1 研究你所使用的WEB电子邮局是否存在账户、密码安全问题？2 目前有没有具有安全性更好的HTTP协议标准？提示：HTTPS和SSL,2: Application Layer,32,DIY!now 2.4带有内嵌对象的HTML文档,访问一个带两个图片的网页；观察和分析首页、两个图片的下载过程；,2: Application Layer,33,DIY!now 2.5 多重对象的HTML文档,再

18、次访问google首页；观察后续多个图片的下载过程；,2: Application Layer,34,Persistent HTTP（难点）,Nonpersistent HTTP issues:requires 2 RTTs per objectOS overhead for each TCP connectionbrowsers often open parallel TCP connections to fetch referenced objectsDefault in HTTP/1.0Persistent HTTPserver leaves connection open after

19、sending responsesubsequent HTTP messages between same client/server sent over open connection,Persistent without pipelining:client issues new request only when previous response has been receivedone RTT for each referenced objectPersistent with pipelining:default in HTTP/1.1client sends requests as

20、soon as it encounters a referenced objectas little as one RTT for all the referenced objects,2: Application Layer,35,Nonpersistent HTTP,Suppose user enters URL ,1a. HTTP client initiates TCP connection to HTTP server (process) at on port 80,2. HTTP client sends HTTP request message (containing URL)

21、 into TCP connection socket. Message indicates that client wants object index.html,1b. HTTP server at host waiting for TCP connection at port 80. “accepts” connection, then notifying client,3. HTTP server receives request message, forms response message containing requested object, and sends messag

22、e into its socket,time,(contains 5 text files, 1 css file,31 gif images),2: Application Layer,36,Nonpersistent HTTP (cont.),5. HTTP client receives response message containing html file, displays html. Parsing html file, finds 31 referenced jpeg objects and other files,6. Steps 1-5 repeated for each

23、 of 31 jpeg objects and other files,4. HTTP server closes TCP connection.,time,2: Application Layer,37,NonPersistent HTTP,Nonpersistent HTTP issues:requires 2 RTTs per objectOS must work and allocate host resources for each TCP connectionbut browsers often open parallel TCP connections to fetch refe

24、renced objects,RTT,RTT,time,time,Index.html,RTT,RTT,1,RTT,RTT,2,RTT,RTT,36,3.35,Total (index.html+36files)= 2RTT*37 + transmit time74RTT,2: Application Layer,38,Persistent HTTP,Persistent HTTPserver leaves connection open after sending responsesubsequent HTTP messages between same client/server are

25、sent over connection,RTT,RTT,Index.html,RTT,1,2: Application Layer,39,Persistent HTTP,Persistent without pipelining:client issues new request only when previous response has been receivedone RTT for each referenced object,RTT,RTT,time,time,Index.html,RTT,1,RTT,2,RTT,36,3.35,Total (index.html+36files

26、)= 2RTT+RTT*36 + transmit time38RTT,2: Application Layer,40,Persistent HTTP,Persistent with pipelining:default in HTTP/1.1client sends requests as soon as it encounters a referenced objectas little as one RTT for all the referenced objects,RTT,RTT,Index.html,RTT,1,RTT,2,4 . . . 35,3,36,Total (index.

27、html+36files)= 2RTT+2RTT + transmit time4RTT,2: Application Layer,41,NoPersistent with pipelining:,RTT,RTT,Index.html,RTT,1,RTT,3 . . . 35,2,36,Total (index.html+36files)= 2RTT+2RTT + transmit time4RTT,2: Application Layer,42,Persistent with pipelining, Issume MAX conection=8,RTT,RTT,Index.html,RTT,

28、1,RTT,2,4 . . . 8,3,9,Total (index.html+36files)= 2RTT+RTT*6 + transmit time8RTT,RTT,10,12 . . . 16,17,RTT,18,20 . . . 24,25,RTT,26,28 . . . 32,33,RTT,34,36,35,27,19,11,2: Application Layer,43,NoPersistent with pipelining, Issume MAX conection=8,RTT,RTT,Index.html,RTT,1,RTT,3 . . . 7,2,8,Total (inde

29、x.html+36files)= 2RTT+2RTT*5 + transmit time12RTT,RTT,9,RTT,11 . . . 15,10,16,RTT,17,RTT,19 . . . 23,18,24,RTT,25,RTT,27 . . . 31,26,32,33,RTT,34,35,RTT,36,Computer Networking,4.单元小结与分析,2: Application Layer,45,Team-works 2.1 一个连接并行下载多个？,前面实验研究了来自不同服务器和同一服务器多个对象的传输实例，我们也分析了HTTP的不同工作模式，现在讨论一下这样一种工作模式，即：一个TCP连接中并行下载多个HTTP对象。目前有没有存在这样的HTTP工作方式？这样的HTTP工作方式会带来什么问题？,宁波大学信息科学与工程学院,We are all the wonderful part of course.,2012,