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Network Homework Solution

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Submitted By 1994281124
Words 270
Pages 2
复习题:
4.答:不同意。如课本中所述,所有的通信会话都有客户端和服务器端。在P2P文件共享应用中,接收文件的一方是客户端,发送文件的一方是接收端。

5.答:目的主机的IP地址和目的端口号。

9.答:SSL运行在应用层。SSL socket从应用层获取未加密的数据,加密后,传递给TCP socket。如果应用程序的开发者想要用SSL来强化UDP,他必须把SSL代码包含到应用程序中。

12.答:当用户第一次访问网站时,网站返回一个cookie号。cookie号存储在用户的主机上,由浏览器管理。在每一次后续的访问(或购物)时,浏览器将cookie号发回站点。因此站点知道这个用户(更准确的说,是这个浏览器)在访问站点。

16.答:报文通过从Alice的主机发送到邮件服务器,使用HTTP协议。Alice的邮件服务器将报文发送到Bob的邮件服务器,使用SMTP协议。Bob将报文从他的邮件服务器传输到他的主机,使用POP3协议。
17.
[pic]
Figure: A sample mail message header
Received:该首部表示SMTP服务器发送和接受邮件报文的序列号,包含各自的时间戳。
这个例子中有4个“Received:”首部。这意味着这和邮件报文在到达接受者的邮箱之前经过了5个不同的SMTP服务器。
● 第四个“Received:”首部表示邮件报文从发送者的SMTP服务器流向传输服务器链中的第二个SMTP服务器。发送者的SMTP服务器的地址是65.55.135.123,第二个SMTP服务器是by 130fd.bay130.hotmail.msn.com。
● 第三个“Received:”首部表示邮件报文从服务器链中的第二个SMTP邮件服务器流向第三个SMTP服务器,然后继续。
● 最后,第一个“Received:”首部表示邮件报文从服务器链中的第四个SMTP服务器流向最后一个SMTP服务器(例如,接受者的邮件服务器)。
Message-id: 报文的编号是BAY130- F26D9E35BF59E0D18A819AFB9310@phx.gbl (by by130fd.bay130.hotmail.msn.com)。Message-id是一个在报文创建时,由邮件系统分配的独一无二的字符串。
From: 表示邮件发送者的email地址。在上面的例子中,发送者是prithuladhungel@hotmail.com
To: 表示邮件接受者的email地址。在上面的例子中,接受者是prithula@yahoo.com
Subject: 表示邮件的标题(如果发送者指定)。在上面的例子中,发送者指定的标题是“Test mail”
Date: 发送者发送邮件时的日期和时间。在这个例子中,发送者发送邮件的日期是19th May 2007,时间是23:52:36 GMT。
Mime-version: 邮件使用的MIME版本。在这个例子中是1.0。
Content-type: 在邮件报文主体的内容的类型。在这个例子中,是“text/html”。
Return-Path: 指定当邮件接受者想回复发送者时,回复邮件的发送地址。也被发送者的邮件服务器用来在发送错误时,返回不可发送的邮件报文。在这个例子中,返回路径是prithuladhungel@hotmail.com。

习题:
1. a) F b) T c) F d) F

4.答:a)请求的文档的URL是http://gaia.cs.umass.edu/cs453/index.html。“Host”域表示服务器名,“/cs453/index.html”表示文件名。
b)浏览器运行的是版本1.1,在第一个对之前。
c)浏览器请求的是一个持久连接。由:Connection: keep-alive可知。
d)这是一个欺骗性的问题。这个信息没有包含在HTTP报文的任何地方。所以,没有办法通过单独的看HTTP报文交换来得到这个信息。我们可以通过IP数据报(载有包含HTTP Get请求的TCP段)来回答这个问题。

5.答:a)状态码是200及“OK”表示服务器能够成功找到文件。回复时间是:Tuesday, 07 Mar 2006 12:39:45 Greenwich Mean Time。
b)文档index.html最后修改时间是:Saturday 10 Dec 2005 18:27:46 GMT。
c)返回文档共3874字节。
d)返回文档的前5个字节是:
Received: from 65.55.135.123 by by130fd.bay130.hotmail.msn.com with HTTP; Sat, 19 May 2007 23:52:36 GMT
From: "prithula dhungel"
To: prithula@yahoo.com
Bcc:
Subject: Test mail
Date: Sat, 19 May 2007 23:52:36 +0000
Mime-Version:1.0
Content-Type: Text/html; format=flowed
Return-Path: prithuladhungel@hotmail.com

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