Review Questions Section 2.1
1) List five non-proprietary（非专有的） Internet applications and the
application-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。
applications e-mail WEB streaming multimedia file transfer remote terminal access
protocols SMTP HTTP HTTP ,RTP FTP Telnet 2) For a communication session(会议) between two hosts, which host is the
client 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 daily
basis.
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 agent File Transfer user agent P2p user agent
audio/video user agent
5) Referring to Figure 2.1-2, we see that not none of applications listed in the table require both \application 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 2.2-2.5
6) What is meant by a handshaking protocol? 握手协议的意义？
A protocol uses handshaking if the two communicating entities first 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 each of 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）? Which of 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 in the 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 \（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’s mail server then sends the message to Bob’s mail server over SMTP. Bob then 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) look like?
假定你发送一封电子邮件，唯一的数据就是一个表格附件。可能的首部行（包含MIME行）是什么样的？
From: 123@xxx.com To: 456@yyy.com Subject: hello
MIME-Version: 1.0
Content-Transfer-Encoding: base64 Content-Type: Application/MS-Excel
14) Print out the header of a message that you have recently received. How many Recieved: header lines are there? Analyze each of the header lines in the message.
打印出你最近收到的报文的首部，在Received中，首部行有多少行？分析该报文首部行的每一行。
15) From a user's perspective, what is the difference between the download-and-delete mode and the download-and-keep mode in POP3? 从用户的观点来看，POP3中“下载并删除”模式和“下载并保留”模式有什么区别？
With download and delete, after a user retrieves（取回） its messages from a POP server, the messages are deleted. This poses a problem for the nomadic （游动的）user, who may want to access the messages from many different machines (office PC, home PC, etc.).
In the download and keep configuration（配置）, messages are not deleted after the user retrieves the messages. This can also be inconvenient, as each time the user retrieves the stored messages from a new machine, all of
non-deleted messages will be transferred to the new machine (including very old messages).
16) Redraw Figure 2.5-4 for when all queries from the local nameserver are iterative.
重绘时，从本地域名服务器所有查询迭代图2.5-4。
17) Each Internet host will have at least one local name server and one
authoratative name server. What role does each of these servers have in DNS? 每一台英特网主机都至少有一个本地域名服务器和一个权威域名服务器。这两种服务器在域名解析中起什么作用？
A host authoritative name server provides the official translation of a hostname to an IP address (among other things). A host local name server is a proxy(代理服务器) to the DNS system: the host first queries its local name server for a mapping; the local name server then obtains the mapping on the behalf of（代表） the querying host.