計算機網(wǎng)絡(luò)原理習(xí)題答案匯編

1、學(xué)習(xí) 好資料Review QuestionsSection 2.11） List five non-proprietary（非專有的） Internet applications and theapplication-layer protocols that they use.列舉五種非專用的英特網(wǎng)應(yīng)用以及它們所使用的應(yīng)用層協(xié)議。applicationsprotocolse-mailSMTPWEBHTTPstreaming multimediaHTTP,RTPfile transferFTPremote terminal accessTelnet2） For a communication s

2、ession（會議）between two hosts, which host is theclient and which is the server?對倆主機之間的通信會話，哪個主機是客戶機，哪個主機是服務(wù)器？The process which initiateSt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 pro

3、cess running on another host?運行在一臺主機上的進程使用什么信息標(biāo)識運行在另一臺主機上的進程？The IP address of the destination host and the port number of the destination socket.4） List the various network-application user agents that you use on a dailybasis.列舉你每天都會使用的網(wǎng)絡(luò)應(yīng)用程序用戶代理。Web browser E-mail application user agentFile Transf

4、er user agentP2p user agent audio/video user agent5) Referring to Figure 2.1-2, we see that not none of applications listed in thetable require both "no data loss" and "timing". Can you conceive of an application that requires no data loss and that is also highly time sensitive?參

5、見圖 2.1-2 ， 我們可以看到表中所列舉的應(yīng)用沒有一個既要求沒有數(shù)據(jù)丟失又要求定時。 你能設(shè)想出一個應(yīng)用，既既要求沒有數(shù)據(jù)丟失又要求定時嗎？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?握手協(xié)議的意義？A protocol uses handshaking if the two communicating entities first exchange c

6、ontrol 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?為什么 HTTP ， FTP ， SMTP ， POP3 和 IMAP 都運行在 TCP 協(xié)議而不是UDP 協(xié)議上？The applications associatedwith those protocols

7、require that all application data be received in the correct order and without gaps. TCP provides this service whereas UDP does not.更多精品文檔學(xué)習(xí) 好資料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. (認 證)

8、Describe how this can be done with cookies.考慮一個電子商務(wù)網(wǎng)站需要保留每一個客戶的購買記錄，描述如何使用 HTTP 認證；描述這是如何 用 cookies 來實現(xiàn)的。When the user first visits the site, the site returns a cookie number.This cookienumber is stored on the user s host and is managed by the browser. During each subsequent visit (and purchase), th

9、e 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 流水線) and persistent HTTP without pipelining (沒有流水線的持久HTTP 連接) ? Whichof the two is use

10、d 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

11、 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 theIf-modified-since:header line to forcea responsemessage with the 304 Not Modifiedstatus code.用 Telnet 向 web 服務(wù)器發(fā)送一條多行的請求報文。 在該請求報文中包含 If-mo

12、dified-since:首部行，迫使響應(yīng)報文中出現(xiàn)304 Not Modified 狀態(tài)碼。11) Why is it said that FTP sends control information "out of band"?( 頻帶外的)為什么說FTP 在“帶外“發(fā)送控制信息？FTP uses two paralle(l 平行的)TCP connections, one connectionfor sending control information (such as a request to transfer a file) and another connect

13、ionfor 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 orHotmail) sends a message to Bob, who accesses his

14、 mail from his mail serverusing 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.假設(shè) Alice 使用一個基于 web 的電子郵件賬戶向 Bob 發(fā)送郵件， 而 Bob 使用 POP3 協(xié)議訪問他的郵件服務(wù)器來獲取郵件。討論信息是如何從

15、Alice 的主機到 Bob 的主機的。一定要列出在兩臺主機間移動信息所用的應(yīng)用層協(xié)議。Message is sent from Alice s host to her mail server over HTTP. Alice mail server then sendshte 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 wh

16、ose only data is a MicrosoftExcel attachment. What might the header lines (including MIME lines) look like?假定你發(fā)送一封電子郵件，唯一的數(shù)據(jù)就是一個表格附件?？赡艿氖撞啃?包含 MIME 行)是什么 樣的？From: 123To: 456Subject: helloMIME-Version: 1.0Content-Transfer-Encoding: base64Content-Type: Application/MS-Excel更多精品文檔學(xué)習(xí)-好資料14) Print out the

17、 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報文的首部，在 Received 中，首部行有多少行？分析該報文首部行的每一行。15) From a user's perspective, what is the difference between the download-and-delete mode and the dow

18、nload-and-keep mode in POP3?從用戶的觀點來看， POP3 中“下載并刪除”模式和“下載并保留”模式有什么區(qū)別？With download and delete, after a user retrieveS®.0) its messages from a POP server, the messages are deleted. This poses a problem for the nomadic (游動的) user, who may want to access the messages from many different machines (

19、office PC, home PC, etc.).In the download and keep configuration酉己置),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 machi

20、ne (including very old messages).16) Redraw Figure 2.5-4 for when all queries from the local nameserver are iterative.重繪時，從本地域名服務(wù)器所有查詢迭代圖 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?每一臺英特網(wǎng)主

21、機都至少有一個本地域名服務(wù)器和一個權(quán)威域名服務(wù)器。這兩種服務(wù)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(代理服務(wù)器)to the DNS system: the host first queries its local name server for a mapping;the local name s

22、erverthen obtainsthe mapping on the behalf of (代表) the querying host.18) Is it possible that an organization's Web server and mail server haveexactly the same alias(另 Ll 名) for a hostname (e.g., )? What would be the"type" for the RR that contains the hostname of the mail server?一個機構(gòu)的we

23、b服務(wù)器和郵件服務(wù)器可以有有完全相同的主機別名嗎？包含了郵件服務(wù)器的主機 名的RR有什么樣的類型？Yes。An organization mail server and Web server can have the samealias for a host name. The MX record is used to map the mail server host name to its IP address.19) Use nslookup to find a Web server that has multiple IP addresses. Does theWeb server of

24、 your institution (school, company, etc.) have multiple IP addresses?使用nslookup 找到一個 Web服務(wù)器有多個IP地址。貴機構(gòu)的 Web服務(wù)器(如學(xué)校，公司，等)是否有多個IP地址？c:>nslookup Server: Address:3Non-authoritative answer:Name:cernetnews.si Addresses:0305121.194.0,2060708121.19

25、4.0,209121.194.0,210Aliases: edu.si c:>nslookup Server: pri Address:3Name:Address:65't have multiple IP address.My insititution doesnSections 2.6-2.920) The UDP server described in Section 2.7 only needed one socket, whereasthe TCP server described in Section 2.6 nee

26、ded two sockets. Why? If the TCPserver were to support n simultaneous（同時發(fā)生的）connections, each from adifferent client host, how many sockets would the TCP server need?2.7節(jié)描述的UDP服務(wù)器僅需要一個套接字，而 2.6節(jié)描述的TCP服務(wù)器則需要兩個套接字。為什么？如果TCP服務(wù)器要支持n個并行連接，且每個連接都來自不同的客戶機主機，那么 TCP服 務(wù)器需要多少個套接字？With the UDP server, there is

27、no welcoming socket, and all data from different clients enters the server through this one socket. With the TCP server, there is a welcoming socket, and each time a client initiates （發(fā)起）a connection to the server, a newsocket is created. Thus, to support n simultaneous connections, the server would

28、 neech+1 sockets.21) For the client-server application over TCP described in Section 2.6, why must the server program be executed before the client program? For the client-server application over UDP described in Section 2.7, why may the client program be executed before the server program?更多精品文檔學(xué)習(xí)-

29、好資料在 2.6 節(jié)所描述的運行于TCP 上的客戶機-服務(wù)器應(yīng)用程序， 為什么服務(wù)器程序要先于客戶機程序運行？在 2.7 節(jié)描述的運行于UDP 上的客戶機-服務(wù)器應(yīng)用程序，為什么客戶機程序要先于服務(wù)器程序運行？For the TCP application, as soon as the client is executed, it attempts to initiate a TCP connection with the server. If the TCP server is not running, then the client will fail to make a connect

30、ion.For the UDP application, the client does not initiate connections(or attempt to communicate with the UDP server) immediately upon executionPROBLEMS1) True or false.a) Suppose a user requests a Web page that consists of some text and twoimages. For this page the client will send one request messa

31、ge and recievethree response messages?假設(shè)一個用戶請求一個網(wǎng)頁，包含一些文本和兩個圖像。這個頁面的客戶端將發(fā)送一個請求消息和接收三個響應(yīng)消息？Fb) True or false. Two distinct Web pages (e.g., /research.html and /students.html) can be sent over the same persistent connection?真或假。兩種截然不同的網(wǎng)頁(例如， / research.html和 www.mit.e

32、du / students.html )可發(fā)送相同的持久連接？Tc) With non-persistent connections between browser and origin server,it is possible for a single TCP segment to carry two distinct HTTP requestmessages? 瀏覽器和源服務(wù)器之間的非持久連接，它有可能為一個單一的 TCP 段進行兩個不同的 HTTP 請求消息？Fd) The Date: header in the HTTP response message indicates when

33、 the在 HTTP 響應(yīng)消息頭指示的object in the response was last modified?最后修訂在響應(yīng)對象時？2) Read RFC 959 for FTP. List all of the client commands that are supported by theRFC.FTP 閱讀 RFC 959 。列出所有的客戶端支持的命令是由 RFC 。Access control commands:USER, PASS, ACT, CWD, CDUP, SMNT, REIN, QUITTransfer paramete r（參數(shù)） commands:PORT,

34、 PASV, TYPE STRU, MODEService commands:RETR, STOR, STOU, APPE, ALLO, REST, RNFR, RNTO, ABOR, DELE, RMD, MRD, PWD, LIST, NLST, SITE, SYST, STAT, HELP, NOOP3) Read RFC 1700. What are the well-known port numbers for the "simple file transfer protocol" （sftp）? For the "network news transf

35、oer protocol" （nntp）?閱讀RFC 1700 中。什么是簡單文件傳輸協(xié)議"（SFTP ）眾所周知的端口號？對于 新聞聯(lián)播 transfoer 協(xié)議”（NNTP ） ?4) Suppose within your web browser you click on a link to obtain a web page.Suppose that the IP address for the associated URL is not cached（緩存） in yourlocal host, so that a DNS look up is necessary

36、 to obtain the IP address. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur（產(chǎn)生）a RTT of RTT 1，RTT n. Further supposethat web page associated with the link contains exactly one object, a smallamount of HTML text. Let RTT0 denote （表示

37、）the RTT between the local host andthe server containing the object. Assuming zero transmission time of the object, how much time elapses（流逝）from when the client clicks on the link until theclient receives the object.假定在你的瀏覽器中，你點擊一個超鏈接來獲得一個web頁面。假定相關(guān)的URL的IP地址沒有緩存在你的本地主機上，因此必須進行DNS查詢以獲得IP地址。假設(shè)你的主機從 D

38、NS獲得IP地址之前，已經(jīng)訪問了 n個DNS服務(wù)器，相繼產(chǎn)生的 RTT依次為RTT1 , RTTn 。進一步假設(shè)，與 連接相關(guān)的web網(wǎng)頁只含有一個對象，即少量的HTML文本。讓RTT0表示本地主機和包含對象的服務(wù)器之間的RTT。假設(shè)對象傳輸時間為 0,從客戶點擊連接到接收到對象需要多長時間？The total amount of time to get the IP address isRTT1RTT2RTTn .Once the IP address is known, RTTo elapses to set up the TCP connection andanother RTTo el

39、apsesto request and receive the small object. The total response time is2RTToRTT1RTT2RTTn5) Referring to question (4), suppose the page contains three very smallobjects. Neglecting transmission times, how much time elapses with (a)nonpersistent HTTP with no parallel TCP connections, (b) nonpersisten

40、tHTTP with parallel connections, (c) persistent HTTP with pipelining.提到的問題(4),假設(shè)該頁面包含三個非常小的物體。忽略的傳輸時間，間隔時間多長(一)非持久的HTTP 沒有并行的TCP連接，(b )與并行連接的非持久的HTTP , (c)與持久HTTP流水線。1)RTT1RTTn2RTTo3 2 RTTo= 8RTT RTTRTT.b)RTT1 3-RTTn2RTTo2RTTo= 4RTT RTT - : RTT.c)RTTiRTTn 2RTToRTTo= 3RTTo RTT1 一 一 RTTn6) Two HTTP re

41、quest methods are GET and POST. Are there any other methodsin HTTP/1.0? If so, what are they used for? How about HTTP/1.1 ?兩個HTTP請求方法是GET和POST 。在HTTP/1.0是否有任何其他的方法？如果是這樣，它們是什么使用？關(guān)于 HTTP/1.1 的怎么樣？7) Write a simple TCP program for a server that accepts lines of input from a client and prints the lines

42、 onto the server's standard output. (You can do this by 更多精品文檔學(xué)習(xí) 好資料modifying the TCPServer.java program in the text.) Compile and execute your program. On any other machine which contains a Web browser, set the proxy server in the browser to the machine in which your server program is running;

43、also configure the port number appropriately. Your browser should now send its GET request messages to your server, and your server should display the messages on its standard output. Use this platform to determine whether your browser generates conditional GET messages for objects that are locally

44、cached.寫一個簡單的 TCP 服務(wù)器接受從客戶端的輸入線和輸出到服務(wù)器的標(biāo)準(zhǔn)輸出線方案。（您可以通過修改文本 TCPServer.java 方案。）編譯和執(zhí)行程序。在任何其他機器，其中包含一個Web 瀏覽器，在瀏覽器中設(shè)置代理服務(wù)器在您的服務(wù)器程序運行的機器，也適當(dāng)配置的端口號。您的瀏覽器現(xiàn)在應(yīng)該 GET 請求消息發(fā)送到您的服務(wù)器，您的服務(wù)器上顯示的消息，它的標(biāo)準(zhǔn)輸出。利用這一平臺，以確定是否您的瀏覽器生成本地緩存的對象，有條件的 GET 消息。8) Read the POP3 RFC, RFC 1939.What is the purpose of the UIDL POP3comma

45、nd?閱讀的 POP3 RFC ， RFC 1939 中。 UIDL POP3 命令的目的是什么？UIDL abbreviates (是 的縮寫) “ uniqu-eID listing ” . When a POP3 client issues the UIDL command, the server responds with the unique message ID for all of the messages present in the users mailbox. This command is useful for “ download and keep ” . By kee

46、ping a file that lists the messages retrieved in earlier sessions, the client can use the UIDL command to determine which messageson the server have already been seen.9) Install and compile the Java programs TCPClient and UDPClient on one host and TCPServer and UDPServer on another host.a) Suppose y

47、ou run TCPClient before you run TCPServer. What happens? Why?b) Suppose you run UDPClient before you run UDPServer. What happens?Why?c) What happens if you use different port numbers for the client and server sides?10) Rewrite TCPServer.java so that it can accept multiple connections. (Hint: Youwill need to use threads.)重寫TCPS