2014-2015学年上学期2013级中期考试试卷答案.doc

云南大学2014至2015学年上学期软件学院2013级计算机网络原理期中考试试卷（闭卷）满分：100分 考试时间：100分钟 任课教师：王世普学院： 专业： 学号： 姓名： （注意：答题可以用中文、也可以用英文）得分表：题号一二三四五总分得分第一题答题卡：小题号12345678910回 答ACDBBBABAB第二题答题卡：小题号12345回 答一、单项选择题（每个选项1分，共10分，请将选择结果填入第一题答题卡）1 （1） is the protocol suite for the current Internet.（1）A. TCP/IPB. NCPC.UNIXD.ACM2A JPEG image is sent as email ,What is the content-type （2） .（2）Amultipart/mixedBmultipart/imageCimage/JPEGDimage/basic3A user want to send some information to Web server using HTTP protocol, the request line method is （3） .（3）AGETBPATCHCMOVEDPOST 4If a TCP segment carries data along with an acknowledgment, this technology is called （4） acknowledgment.（4）A. backpacking B. piggybacking C. piggyingD. mothers help5UDP is a （5） transport layer protocol that simply allow data to be exchanged without （6） . So it requires other protocols to handle error processing and （7） .（5）AconnectionBconnectionlessCjoinDdisconnection（6）AdatagramsBacknowledgementsCdataDsegment（7）AretransmissionBsendCreceiveDacknowledgements6A user requests a Web page that consists of a basic HTML file and 3 JPEG image files. dtrans denoting the time to transfer a file. The total time is (8) to request the Web page in persistent connections mode?（8）A. 4(2RTT+ dtrans)B. 2RTT+4 dtransC. RTT+4 dtransD.4(RTT+ dtrans)7Host A sends a TCP segment (Seq = 43, ACK = 103) to host B and Host B replies with a TCP segment (Seq = 103, ACK = 57). The payload length of the TCP segment from host A to host B is ( 9 ) .（9）A14 bytes.B43 bytes.C46 bytes.D57 bytes.8As a data packet moves from the lower to the upper layers, header are （10） .（10）A. addedB. subtractedC. rearrangedD. modified二、判断正误（每个问题1分，共5分。正确的打“”、错误的打“”，请将判断结果填入第二题答题卡）1. The DNS defines a distributed, hierarchical database that provides only hostname to IP address mappings. ( )2. The “Last-Modified:” header line in the HTTP response message indicates when the object in the response message was last modified. ( )3If sequence number is k bit, then the send window maximum size of GBN protocol is equal to 2k-1.( )4The UDP header checksum is recomputed at every routers.( )5Suppose that the last SampleRTT in a TCP connection is equal to 1 sec. Then Timeout for the connection will necessarily be set to a value = 1 sec. ( )三、回答下列问题（每个问题5分，共30分）1For a communication session between two hosts, which host is the client and which is the server? 要点：通信的发起者（请求者）是客户，通信的接受者（服务者）是服务器。2What is the difference between persistent HTTP with pipelining and persistent HTTP without pipelining?要点：前者在一个TCP连接期间可以传送多个WEB页面；后者在一个TCP连接期间只能传送一个WEB页面。3What are the two types of services that the Internet provides to its applications? What are important characteristics of each of these services? 要点：面向连接的服务（连接管理、正确可靠、按序交互、流控制、拥塞控制）；无连接服务（不需建立连接、不可靠、每个报文独立传送，无流控制和拥塞控制）4Why is it said out of band (带外的) that FTP sends control information?要点：TCP数据连接是主连接，不能提供FTP命令的传输；TCP控制连接仅仅是传输FTP命令和执行状态，因而是数据通道之外的通道，故属于“带外”信道。5Please list the main transmission mediums used in the computer network. 要点：铜线、光纤、（地面）无线、卫星6What are the differences Congestion Control and flow control. 要点：范围不同（全网；通信双方）、目的不同（防止接收端缓冲区溢出；防止网络拥塞）四、计算题（共25分）1. Suppose host A communicates with host B through TCP, sometime host A sends 10 bytes data to host B, then host B responds with 100bytes data. Analyze the necessary 2.Suppose host A communicates with host B through TCP, sometime host A sends 115 bytes data to host B, then host B responds with 100bytes data. Analyze the necessary ACK numbers and the Sequence number in the segments sent between host A and host B . Please give the analysis procedure (8 分)Seq=45,ACK=108Seq=108,ACK=160Seq=160,ACK=208Host AHost B要点(第1种理解，将红色部分视为错误)：ACK是期望接收的段的序号；当B收到一个数据为115字节、序号为45的段，就意味着期望接收的下一个段的序号应该是45+115=160；当S收到来自B的一个数据为100字节、序号为108的段后，则意味着期望接收的段的序号是108+100=208.第2种理解，将红色部分视为第一个来回、2后为第二个来回：A发10Bytes，B回100Bytes；A发115Bytes，B回100BytesSeq=45,ACK=108Seq=108,ACK=55Seq=55,ACK=208Host AHost BSeq=208,ACK=1702 UDP and TCP use 1s complement sum for their checksums. Suppose you have the following three 16-bit words: 1100100110010101, 1010011101110101, 0110010111001101. What is the 1s complement sum of these words? （7分）1100100110010101+10100111011101011011100010000101010111000100001011+011001011100110101101011011011000+0sum1101011011011000checksum0010100100100111答案：00101001001001113Consider two hosts, Host A and B, connected by a single link of rate R bps. Suppose that the two hosts are separated by m meters, and suppose the propagation speed along the link is s meters/second, and the size of packet is L bits. （10分）(1) Express the propagation delay, dprop in terms of m and s.dprop = m/s(2) Determine the transmission delay dtrans in terms L and R. dtrans =L/R(3) If R=1000 Mbps, m=120km, s=3108m/s and L=1000 Bytes, please compute：dprop =120103/(3108)秒=410-4秒=0.4毫秒=400微秒dtrans=10008/(1000106)=810-6秒=810-3毫秒=8微秒五、综合题（共30分）1Match the following tasks to one of the TCP/IP layers: （7分）(1) Transmission of Data Segment ( 传送层 )(2) ASCII changed to EBCDIC ( 应用层 )(3) Transmission of data frame( 链路层 )(4) Provides log-in and logout procedures ( 应用层 )(5) Selects a destination network ( 网络层 )(6) Provides services for the network applications( 应用层 )(7) Provides E-mail and file transfer services ( 应用层 )3. Please answer the following questions. (1) Consider the following HTTP GET message. Answer the following questions, indicating where in the message below you find the answer. ( 4分 )GET /info/2012-10-18/0-1-411.html http/1.1Host: User-agent: Mozilla/4.0Accept-language: enKeep-Alive:300Connection:keep-aliveQuestions:a. What is the URL of the document requested by the browser?/info/2012-10-18/0-1-411.htmlb. What version of HTTP is the browser running?HTTP 1.1c. Does the browser request a non-persistent or a persistent connection?a persistent connectiond. What is domain name of the server?Y(2)The text below shows the reply sent from the server in response to the HTTP GET message in the question above (1). Answer the following questions, indicating where in the message below you find the answer. 即：解释带数字标注的那些行的含义和作用 (6 分)HTTP/1.1 200 OKContent-Length: 19572Content-Type: text/htmlLast-Modified: Sun, 30 Sep 2012 07:23:15 GMTAccept-Ranges: bytesServer: Microsoft-IIS/6.0X-Powered-By: ASP.NETDate: Thu, 25 Oct 2012 21:26:48 GMTConnection: Keep-AliveQuestions:HTTP/1.1 200 OKHTTP1