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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. 课程名称: 计算机网络. 课程对象 :通信工程 电子信息 电气工程 计算机. 课程学分: 3. 课程学时: 68 学时. 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 edition Jim Kurose, Keith Ross

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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


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课程名称:计算机网络

课程对象:通信工程 电子信息

电气工程 计算机

课程学分:3

课程学时:68学时

课程基本信息

1、 课程属性

Computer Networking


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课程基本信息

2、教材选用

  • Computer Networking: A Top Down Approach Featuring the Internet,4rd edition

    • Jim Kurose, Keith Ross

    • Addison-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 Internet

#2 Application Layer

#3 Transport Layer

#4 Network Layer and Routing

#5 Link Layer and Local Area Networks

Computer Networking


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课程基本信息

3、课程群关系

Computer Networking


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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。

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。


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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


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自顶向下方法和互联网为实例

实验探究(30)

个人课后作业

课堂

讲授

(17)

团队调研报告

团队研究项目

个人读书报告

开放实验

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,使学生成为课堂精彩的一部分!

Computer Networking


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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


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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


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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!

Computer Networking


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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

“成就驱动”

7

7


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人人教学网站

  • 课程主站http://zhan.renren.com/dawnet

    • X-pechttp://zhan.renren.com/xpectteam

    • 霸气爷们波http://zhan.renren.com/820930374

    • 春田花花幼儿园http://zhan.renren.com/cthhyey

    • 七星阁http://zhan.renren.com/qxging

    • 相聚岛http://zhan.renren.com/darlingnet

    • 真我风采http://zhan.renren.com/junzicreat

    • 火力全开http://zhan.renren.com/dqhkzc

    • 愤怒的小强http://zhan.renren.com/fennudexiaoniao

    • 梦之翼http://zhan.renren.com/mengzhiyinet

    • 非常6+1 http://zhan.renren.com/xhwnet

Computer Networking


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团队进度安排

Computer Networking


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个人作业

17%

10%

13%

10%

50%

探究报告

团队作业

100%

期末考核

实验考核

课程考核成绩

Computer Networking


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单元说课

第二章 第2&3次课

HTTP协议

Computer Networking


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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。

Computer Networking


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1.课程导入

Computer Networking


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2.基本概念

Computer Networking


Some jargon

2: Application Layer

Some jargon

  • Web page consists of objects

    • Object can be HTML file, JPEG image, Java applet, audio file,…

  • Web page consists of base HTML-file which includes several referenced objects

  • Each object is addressable by a URL

  • Example URL(Uniform Resource Locator):

Http://www.nbu.edu.cn/images/run1.gif

path name

host name

Protocol


Http overview

2: Application Layer

HTTP: hypertext transfer protocol

Web’s application layer protocol

client/server model

client:

browser that requests,

receives,

“displays” Web objects

server:

Web server sends objects

in response to requests

HTTP 1.0: RFC 1945

HTTP 1.1: RFC 2068

HTTP overview

HTTP request

PC running

Explorer

HTTP response

HTTP request

Server

running

Apache Web

server

HTTP response

Mac running

Navigator


Http overview continued

2: Application Layer

Uses TCP:

client initiates TCP connection (creates socket,>1024,dynamic) to server(fixed,port 80)

server accepts TCP connection from client

HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server),again,….

TCP connection closed

HTTP overview (continued)


Http request message

2: Application Layer

HTTP request message

  • two types of HTTP messages: request, response

  • HTTP request message:

    • ASCII (human-readable format)

request line

(GET, POST, HEAD commands)

GET /index.html HTTP/1.1

Host: www.nbu.edu.cn

User-agent: Mozilla/4.0

Connection: close

Accept-language:cn

(extra carriage return, line feed)

header lines

Carriage return,

line feed

indicates end of message


Method types

2: Application Layer

HTTP/1.0

GET

POST

HEAD

asks server to leave requested object out of response

HTTP/1.1

GET, POST, HEAD

PUT

uploads file in entity body to path specified in URL field

DELETE

deletes file specified in the URL field

Method types


Http response message

2: Application Layer

HTTP response message

status line

(protocol status code

status phrase)

HTTP/1.1 200 OK

Connection close

Date: Thu, 06 Aug 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 ...

header lines

data, e.g.,

Requested HTML file


Http response status codes

2: Application Layer

200 OK

request succeeded, requested object later in this message

301 Moved Permanently

requested object moved, new location specified later in this message (Location:)

400 Bad Request

request message not understood by server

404 Not Found

requested document not found on this server

505 HTTP Version Not Supported

HTTP response status codes

In first line in server->client response message.

A few sample codes:


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3.理论实验融合探究教学

Computer Networking


Diy now 2 1 http get response

2: Application Layer

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


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2: Application Layer

探究任务与问题


Diy now 2 2 http

2: Application Layer

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“Continuationornon-HTTPtraffic DATA”或“TCP Segment of a Reassembled PDU ”


Diy now 2 3 http post response

2: Application Layer

DIY!now 2.3 基本的HTTP post/Response

  • 访问mail.nbu.edu.cn

  • 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


Reading works 2 1 web

2: Application Layer

Reading-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


Diy now 2 4 html

2: Application Layer

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;


Diy now 2 5 html

2: Application Layer

DIY!now 2.5 多重对象的HTML文档

  • 再次访问google首页;

  • 观察后续多个图片的下载过程;


Persistent http

2: Application Layer

Nonpersistent HTTP issues:

requires 2 RTTs per object

OS overhead for each TCP connection

browsers often open parallel TCP connections to fetch referenced objects

Default in HTTP/1.0

Persistent HTTP

server leaves connection open after sending response

subsequent HTTP messages between same client/server sent over open connection

Persistent without pipelining:

client issues new request only when previous response has been received

one RTT for each referenced object

Persistent with pipelining:

default in HTTP/1.1

client sends requests as soon as it encounters a referenced object

as little as one RTT for all the referenced objects

Persistent HTTP(难点)


Nonpersistent http

2: Application Layer

Suppose user enters URL www.nbu.edu.cn

1a. HTTP client initiates TCP connection to HTTP server (process) at www.nbu.edu.cn on port 80

Nonpersistent HTTP

(contains

5 text files,

1 css file,

31 gif images)

1b. HTTP server at host www.nbu.edu.cn waiting for TCP connection at port 80. “accepts” connection,

then notifying client

2. HTTP client sends HTTP request message (containing URL) into TCP connection socket.

Message indicates that client wants object index.html

3. HTTP server receives request message, forms response message containing requested object,

and sends message into its socket

time


Nonpersistent http cont

2: Application Layer

5. HTTP client receives response message containing html file, displays html. Parsing html file, finds 31 referenced jpeg objects and other files

Nonpersistent HTTP (cont.)

4. HTTP server closes TCP connection.

time

6. Steps 1-5 repeated for each of 31 jpeg objects and other files


Nonpersistent http1

2: Application Layer

Nonpersistent HTTP issues:

requires 2 RTTs per object

OS must work and allocate host resources for each TCP connection

but browsers often open parallel TCP connections to fetch referenced objects

NonPersistent HTTP

RTT

Index.html

RTT

RTT

1

RTT

RTT

2

RTT

3

.

.

.

35

Total (index.html+36files)

= 2RTT*37 + transmit time

>74RTT

RTT

36

RTT

time

time


Persistent http1

2: Application Layer

Persistent HTTP

server leaves connection open after sending response

subsequent HTTP messages between same client/server are sent over connection

Persistent HTTP

RTT

Index.html

RTT

RTT

1


Persistent http2

2: Application Layer

Persistent without pipelining:

client issues new request only when previous response has been received

one RTT for each referenced object

Persistent HTTP

RTT

Index.html

RTT

1

RTT

2

RTT

3

.

.

.

35

36

RTT

Total (index.html+36files)

= 2RTT+RTT*36 + transmit time

>38RTT

time

time


Persistent http3

2: Application Layer

Persistent with pipelining:

default in HTTP/1.1

client sends requests as soon as it encounters a referenced object

as little as one RTT for all the referenced objects

Persistent HTTP

RTT

RTT

Index.html

RTT

1

3

4 . . . 35

36

RTT

2

Total (index.html+36files)= 2RTT+2RTT + transmit time>4RTT


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2: Application Layer

NoPersistent with pipelining:

RTT

RTT

Index.html

RTT

1

2

3 . . . 35

36

RTT

Total (index.html+36files)= 2RTT+2RTT + transmit time>4RTT


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2: Application Layer

Persistent with pipelining, Issume MAX conection=8

RTT

RTT

Index.html

RTT

1

3

4 . . . 8

9

RTT

2

12 . . . 16

17

11

RTT

10

19

20 . . . 24

25

RTT

18

28 . . . 32

33

27

RTT

26

36

35

RTT

34

Total (index.html+36files)= 2RTT+RTT*6 + transmit time>8RTT


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2: Application Layer

NoPersistent with pipelining, Issume MAX conection=8

RTT

RTT

Index.html

RTT

2

3 . . . 7

8

1

RTT

RTT

10

11 . . . 15

16

9

RTT

RTT

18

19 . . . 23

24

17

RTT

RTT

26

27 . . . 31

32

25

RTT

RTT

36

34

35

33

RTT

Total (index.html+36files)= 2RTT+2RTT*5 + transmit time>12RTT


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4.单元小结与分析

Computer Networking


Team works 2 1

2: Application Layer

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?


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We are all the wonderfulpart of course.

宁波大学信息科学与工程学院

2012


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