计算机网络原理习题答案

Review QuestionsSection 2.11)List five non-proprietary（非专有的）Internet applications and theapplication-layer protocols that they use.列举五种非专用的英特网应用以及它们所使用的应用层协议。

2)For a communication session(会议) between two hosts, which host is theclient and which is the server?对俩主机之间的通信会话，哪个主机是客户机，哪个主机是服务器？The process which initiates（发起）the communication is the client; the process that waits to be contacted is the server.3) What information is used by a process running on one host to identify a process running on another host?运行在一台主机上的进程使用什么信息标识运行在另一台主机上的进程？The IP address of the destination host and the port number of the destination socket.3)List the various network-application user agents that you use on a dailybasis.列举你每天都会使用的网络应用程序用户代理。

Web browser E-mail application user agentFile Transfer user agentP2p user agentaudio/video user agent5) Referring to Figure 2.1-2, we see that not none of applications listed in the table require both "no data loss" and "timing". Can you conceive of anapplication that requires no data loss and that is also highly time sensitive?参见图2.1-2，我们可以看到表中所列举的应用没有一个既要求没有数据丢失又要求定时。

你能设想出一个应用，既既要求没有数据丢失又要求定时吗？There are no good examples of an application that requires no data loss and timing.Sections 2.2-2.56) What is meant by a handshaking protocol? 握手协议的意义？A protocol uses handshaking if the two communicating entitiesfirst exchange control packets before sending data to each other. SMTP uses handshaking at the application layer whereas HTTP does not.7) Why do HTTP, FTP, SMTP, POP3 and IMAP run on top of TCP rather than UDP?为什么HTTP，FTP，SMTP，POP3 和IMAP 都运行在TCP 协议而不是UDP协议上？The applications associated with those protocols require that all application data be received in the correct order and without gaps. TCP provides this service whereas UDP does not.8) Consider an e-commerce site that wants to keep a purchase record for eachof its customers. Describe how this can be done with HTTP authentication. （认证）Describe how this can be done with cookies.考虑一个电子商务网站需要保留每一个客户的购买记录，描述如何使用HTTP认证；描述这是如何用cookies来实现的。

When the user first visits the site, the site returns a cookie number.This cookie number is stored on the user’s host and is managed by the browser. During each subsequent visit (and purchase), the browser sends the cookie number back to the site. Thus the site knows when this user (more precisely, this browser) is visiting the site.9) What is the difference between persistent HTTP with pipelining（持久HTTP 流水线）and persistent HTTP without pipelining（没有流水线的持久HTTP连接）? Whichof the two is used by HTTP/1.1?In persistent HTTP without pipelining, the browser first waits to receive a HTTP response from the server before issuing a new HTTP request. In persistent HTTP with pipelining, the browser issues requests as soon as it has a need to do so, without waiting for response messages from the server.persistent HTTP with pipelining is used by HTTP/1.1。

10) Telnet into a Web server and send a muli-line request message. Include inthe request message the If-modified-since: header line to force a response message with the 304 Not Modified status code.用Telnet 向web 服务器发送一条多行的请求报文。

在该请求报文中包含If-modified-since:首部行，迫使响应报文中出现304 Not Modified 状态码。

11) Why is it said that FTP sends control information "out of band"?（频带外的）为什么说FTP在“带外“发送控制信息？FTP uses two parallel（平行的）TCP connections, one connection for sending control information (such as a request to transfer a file) and another connection for actually transferring the file.Because the control information is not sent over the same connection that the file is sent over, FTP sends control information out of band.12) Suppose Alice with a Web-based e-mail account (such as Yahoo! mail or Hotmail) sends a message to Bob, who accesses his mail from his mail server using POP3. Discuss how the message gets from Alice's host to Bob's host. Be sure to list the series of application-layer protocols that are used to move the message between the two hosts.假设Alice使用一个基于web的电子邮件账户向Bob 发送邮件，而Bob使用POP3 协议访问他的邮件服务器来获取邮件。

讨论信息是如何从Alice 的主机到Bob的主机的。

一定要列出在两台主机间移动信息所用的应用层协议。

Message is sent from Alice’s host to her mail server over HTTP. Alice’smail server then sends the message to Bob’s mail server over SMTP. Bob t hen transfers the message from his mail server to his host over POP3.13) Suppose that you send an e-mail message whose only data is a Microsoft Excel attachment. What might the header lines (including MIME lines) looklike?假定你发送一封电子邮件，唯一的数据就是一个表格附件。