101G09XT1[1].宁波大学计算机网络A.答案.docx

宁波大学 2009 / 2010 学年第 1 学期考试卷（/B） 课号：_ 101G09XT1 _ 课名： 计算机网络_一、 单选题，每题仅一个正确答案，每题1.5分，共30分： 1. Which is not a network communication links?D.Subway 2.Which is not the types of protocol data unit in TCP/IP?C.datetime 3.In which state the delays of router become small?A. La/R 0 4.When congest occur in network, which delay become large?B.queuing delay 5.Application protocol define the types of messages exchanged, which are: A.request & response messages 6.Which version of hypertext transfer protocol are used in default mode now?C.HTTP 1.1 7.The Http client works on which port:C.TCP port above 1024 8.To indicates end of message in Http, we can use:A.Carriage return and line feed 9.Which is not an email protocol:C.Emule 10. TCP retransmission can not be caused by:D. ACK 11. Which of the following measures the time from one segment transmission to ACK receipt:A. sample RTT 12. Which event will not be in TCP Receiver:C.Arrival of out-of-order segment higher-than-expect seq. # . No gap detected. 13.TCP Flow Control is a speed-matching service for matching: A.the sender rate to the receiving applications drain rate 14.Which one is not the mechanism of TCP Congestion Control:C.FIFO 15.In RDT protocol, which can increase the use of physical resources:C.Pipeline 16. Which one is not the Key Network-Layer Functions in todays internet:C. Connection setup 17. Which of the following IP address belongs to category C address?A. 210.98.3.4 18.Network address translation implement in NAT router, it must use:CNAT translation table 19. ICMP do not error reporting about:D. unknown username 20. In Ethernets CSMA/CD Jam Signal make sure: A.other transmitters are aware of collision二、多选题，每题有2-3个正确答案，请在正确项前打钩(全钩不给分)，每题2分，共20分：1. The communication services be provided to applications, It can be: A.connectionless B.connection-oriented2.Which are application architectures model in the internet? A.client/server model B.peer-peer model C.browser/server model3. User Agent is an interface with user “above” and network “below”, such as: A.Web: browser B.E-mail: mail reader D.Streaming audio/video: media player4.Ftp protocol can work in which model that listed: A.PASV model C.Port model5. The problems with centralized directory of P2P maybe: A.Single point of failure C.Performance bottleneck D.Copyright infringement6.Which services are not available in TCP: A.delay guarantees C.bandwidth guarantees7. In TCP congestion control, there are those State in TCP Sender: A. Congestion Avoidance C. Slow Start D. Timeout8.In TCP three way handshake, it will be: A.client host sends TCP SYN segment to server C.server host receives SYN, replies with SYN/ACK segment D.client receives SYN/ACK, replies with ACK segment9.Those are the routing in the Internet: A.RIP B.OSPF D.BGP10.Those are the Random Access Protocols： B.CSMA C.CSMA/CD三、名称缩写选择，请在匹配项上填写缩写编号，如果在下列18个选项中没有，可以在1920项中自主添加选项。共10分： 1 往返时间 20 可靠传输协议 13 网络接口卡 17 自治系统 12 网络地址翻译协议 5 用户数据报协议 10 协议数据单元 9 动态地址分配协议 19 Internet协议 3 生存时间-19.( IP )20.( RDT )四、问答题（共30分）1.（共10分）下图是运行RIP协议的一个网络：1.1 请描述该路由表的含义：（3分）答：该路由表说明了由路由器D到底各相邻网络和路由器的开销（距离），如w/A/2 表示由A路由器到w网络为2跳y/B/2 表示由B路由器到y网络为2跳z/B/7 表示由B路由器到z网络为7跳x/-/1 表示由D路由器到x网络为1跳(直接连接)v/-/- 表示由D路由器到v网络为1跳(直接连接)1.2 当网络上出现由A发给D的如下路由宣告后路由表的变化情况：（2分）答：z/B/7 = z/A/51.3 接着又出现由B发给D的如下路由宣告后路由表的变化情况：（2分）答：z/A/5 = z/B/31.4 请问上述路由表中hops的含义是什么？（2分） 该数值包含了网络的带宽和延时等信息吗？（1分）答：hops代表跳数（路由器个数）不包含带宽和延时。2、（共10分）如图所示为TCP协议头部结构，请对照该图回答如下问题：2.1 一个基本的TCP头部占多少个字节？（1分）比UDP的头部大还是小？（1分）答：20字节大（UDP为8字节）2.2 TCP连接建立时用到那几个字段？（2分）答：sp# dp# seq# A/S/ACK#等2.3 TCP连接拆除时用到哪几个字段？（2分）答：sp# dp# seq# F/S/ACK#等2.4 TCP流量控制主要使用了哪个字段？（1分）答：Receive window2.5 图中出现了number字样，其数值的单位是什么？（1分）两个number分别代表什么意义？（1分）答：byteSEQ#表示发送数据的第一个字节的编号ACK#表示希望下次接收到的数据的第一个字节的编号2.6 根据该结构TCP在发送数据时可以顺便确认对方刚才发送的数据，是如何实现的？（1分）答：在发送数据的时候用SEQ#记录当前数据的第一个字节的序号，在ACK#中携带对方刚才发过来数据的序号的下一个字节，顺便完成确认。3、（共10分）cache是信息技术中常用的一种方法，请回答：3.1 cache的一般作用是什么？（1分）答：缓存作用，提高性能和效率3.2 在http协议中client cache的基本原理是什么？（4分）答：利用条件get实现客户端缓存，当服务器端文件没有更新过就不需要重新下载，提高HTTP传输效率。3.3 在http协议中利用server cache有何作用？（3分）答：可以实现http代理（PROXY），提高局域网共享上网的效率、降低成本。3.2 在http协议中的CDNs应用可以起到什么作用？（2分）答：可以实现分布式内容发布服务。六、文献分析（10分）根据文献中提供的信息，回答以下问题：1. What is the value of MTU in Ethernet? （2分）答：15002. So, How many bytes can be carried by IP datagram？（2分）答：14803. Where is the IP datagram fragment operating? （2分）答：Router network layer4. Where is the IP datagram reassembly operating? （2分）答：Destination host (end system) network layer5. Which field of IP can be examined to determine the datagrams are actually fragments of the same bigger datagram？（2分）答： ID# (identification number) 第 5 页 共 5 页