计算机网络英文题库(附答案)chapter1(推荐文档)

Chapter 2 Application Layer1. In the following four descriptions, which one is correct?A In C/S architecture, clients communicate with each other directly.B In C/S architecture, client has a fixed well-known address.C In P2P architecture, peers communicate with each other directly.D In P2P architecture, peer has a fixed well-known address.2. In the context of a communication session between a pair of process, the process that initiates the communication is labeled as the , the process that waits to be contacted to begin the session is labeled as the .A client process, server processB sending process, receiving processC input process, output processD communicating process, connecting process3. A socket is the interface between within a host.A the network layer and the link layerB the link layer and the physical layerC the application layer and the transport layerD the transport layer and the network layer4. In the following applications, which one is a loss-tolerant application?A E-mailB file transferC instant messagingD real-time audio5. In the following applications, which one is a bandwidth-sensitive application?A E-mailB web applicationC real-time audioD file transfer6. The service of TCP can’t guarantee .A delivery of all data without errorB delivery of all data in the proper orderC the rate of deliveryD congestion control7. In the following applications, which one uses UDP?A E-mailB web applicationC file transferD DNS8. In the following descriptions about HTTP, which one is not correct?A HTTP uses non-persistent connections in its default mode.B HTTP uses TCP as its underlying transport protocol.C HTTP is a stateless protocol.D HTTP is client-server architecture.9. Suppose a web page consists of a base HTML file, 5 JEPG images and a java applet, and also suppose HTTP uses persistent connection without pipelining, the total response time is .A 2RTTB 8RTTC 12 RTTD 14RTT10. In HTTP response message, if the requested HTTP protocol version is not supported, the status code is .A 200B 301C 400D 5051~5CACDC6~10CDABD11. The port number of web application is .A 25B 20C 80D 5312. A network entity that satisfies HTTP requests on the behalf of an origin web server is .A server farmB server stackC proxy serverD edge server13. In the following descriptions about persistent connection, which one is not correct?A The server leaves the TCP connection open after sending a response.B Each TCP connection is closed after the server sending one object.C There are two versions of persistent connection: without pipelining and with pipelining.D The default mode of HTTP uses persistent connection with pipelining.14. FTP uses two parallel TCP connections to transfer a file, there are .A control connection and data connectionB receiving connection and sending connectionC client connection and sever connectionD program connection and process connection15. In the following descriptions about FTP, which one is correct?A FTP is p2p architecture.B FTP sends its control information out-of-band.C FTP uses persistent connection.D FTP is a stateless protocol.16.In the commands of FTP,which one does not have parameter?A USERB PASSC LISTD STOR17. The Internet mail system has three components which they are .A user agent, SMTP, POP3B SMTP, POP3, IMAPC user agent, SMTP, IMAPD user agent, SMTP, mail server18. If the status code in HTTP response message is 404, it means .A Request succeeded.B The requested document doesn’t exit on this server.C This is a generic error code indicating that the request could not be understood bythe server.D Requested object has been permanently mover.19. Comparison HTTP with SMTP, the correct is .A HTTP is a push protocol, and SMTP is a pull protocol.B In the default mode, both of them use persistent connection.C HTTP places all of the message’s objects into one message, and SMTP sends every object one by one.D HTTP requires each message to be in 7-bit ASCII format, and SMTP doesn’t impose this restriction.20. The headers in the MIME message must include except .A FromB Content-typeC Content-transfer-encodingD MIME version11~15CCBAB16~20DDBBD21. In the following protocol, which one is stateless?A POP3B SMTPC FTPD IMAP22. DNS means .A Data Name SystemB Data National SystemC Domain Name SystemD Domain National System23. There are three classes of DNS server except .A Root DNS serverB Local DNS serverC TLD server D Authoritative DNS server24. DNS provides some services except .A Host aliasingB Mail server aliasingC Load distributionD A single point of failure25.There are three architectures for locating content in P2P file sharing,KaZaA uses.A Centralized Directory（Napster）B Query Flooding(Gnutella)C Exploiting Heterogeneity(p141)D Incentive Priorities26.There are three architectures for locating content in P2P file sharing,Napster uses.A Centralized Directory(p137)B Query FloodingC Exploiting HeterogeneityD Incentive Priorities27.The following architectures in P2P file sharing,which is an overlay network?A Centralized DirectoryB Query Flooding(p139)C Exploiting HeterogeneityD Incentive Priorities28. The time it takes for a small packet to travel from client to server and then back to the client is .A round-travel timeB next-hop timeC round-trip timeD prefix-matching time29. Suppose A ( with a Web-based e-mail account ) sends a message to B ( who accesses his mail server using POP3), which application-layer protocol is not used?A HTTPB SMTPC POP3D IMAP30. In the four following options, which protocol is included in Mail Access Protocol?A SMTPB DHCPC IMAPD FTP31. In FTP commands, is used to send user password to the server.A UserB PassC RetrD Stor32. The function of the additional header field in MIME Content-Type is .A to convert the message body to its origin non-ASCII formB to determine what actions it should take on message bodyC to send an E-mail to the receiving user agentD to indicate what type the message is33. In the four following options, which application is organized as hybrid of C/S and P2P architecture?A E-mailB OICQC File transferD Web application34.In the four following options,which is not a centralized DNS design’s problem?A a single point of failureB traffic volumeC distant centralized databaseD slow(maintenance)35.In the following options, from the application developer’s perspective, which is not correct?A the network architecture is fixedB the network architecture provides a specific set of services to applicationsC the application architecture is designed by the physical devicesD the application architecture dictates how the application is organized over the various end systems36. There are three predominant architectures used in modern network applications, which one is not included?A the client-server architectureB the P2P architectureC a hybrid of the client-server and P2P architectureD a hybrid of the client-server and browser-server architecture37. In the following options about C/S architecture, which is not correct?A In C/S architecture, there is an always-on host, called the server.B In C/S architecture, there is an always-on host, called the client.C The server has a fixed, well-known address, called IP address.D Clients do not directly communicate with each other.38.are often used to create a powerful virtual server in C/S architecture.A PeersB Server farmC server stackD local server39. A process sends messages into, and receives messages from, the network through its .A socketB programC clientD peer40. Which one is not defined by an application-layer protocol?A the types of messages exchangedB the syntax of various message typesC the semantics of the fieldsD rules for determining when and how to translate the socket41. HTTP can use two types of connections, which are .A persistent and non-persistent connectionB connection with pipelining and without pipeliningC TCP and UDPD parallel and serial connection42. takes for a small packet to travel from client to server and then back to the client.A RDTB thresholdC RTTD overhead43. The default mode of HTTP uses .A non-persistent connection with pipeliningB non-persistent connection without pipeliningC persistent connection with pipeliningD persistent connection without pipelining44. In HTTP request messages, the request line has three fields, there are .A the method field, the URL field and the HTTP version fieldB the method, the connection and URL fieldC the user-agent, the method and HTTP version fieldD the user-agent, the URL and the HTTP version field45. In the header lines of HTTP request message, if the field of Connection is close, it specifies .A the host on which object residesB what type of the user agentC that the browser wants the server to close the connection after sending the requested objectD which language can the browser receive46. In HTTP response message, if the status code is 404, it means .A request succeeded and the information is returned in the responseB requested object has been permanently movedC the requested HTTP protocol version is not supported by the serverD the requested document does not exist on this server47. is a network entity that satisfies HTTP requests on the behalf of an origin Web server.A proxy serverB local serverC DNS serverD Web server48. In the following four options about web cache, which one is not correct?A A web cache is both a server and a client at the same time.B A web cache is purchased and installed by an ISP.C A web cache can raise the response time for a client request.D A web cache can reduce traffic on an institution’s access link to the Internet.49. The request message in the conditional GET must include the header line.A Last-ModifiedB Last-ReferencedC If-Modified-SinceD If –Referenced-Since50. FTP uses two parallel connections to transfer a file, they are .A TCP and UDP connectionB connection with pipelining and without pipeliningC control an data connectionD client-server and browser-server connection51. In FTP commands, which one is used to ask the server to send back a list of all files in the current remote directory?A USERB PASSC LISTD RETR52. In the Internet mail system, allow users to read, reply to, forward, save and compose message.A User agentsB mail serversC SMTPD TCP53. The two key MIME headers for supporting multimedia are .A Content-Type and MIME-VersionB Content-Type and Content-Transfer-EncodingC Content-Transfer-Encoding and MIME-VersionD MIME-Version and MIME-Type54. For Internet mail, the mail access protocol is used to .A transfer mail from the recipient’s mail server to the recipient’s user agentB transfer mail from the sender’s mail server to the recipient’s mail serverC translate the mail from the sender’s mail serverD translate the mail into the recipient’s mail server55. POP3 progresses through three phases, which they are .A authorization, translation and transactionB authorization, translation and updateC authorization, transaction and updateD translation, transaction and update56. In the following four services, which one can not provide by DNS?A Host aliasingB Mail server aliasingC translate hostname to IP addressesD translate MAC addresses to IP addresses57. There are three classes of DNS servers, there are .A root DNS server, top-level domain DNS server and local DNS serverB root DNS server, top-level domain DNS server and authoritative DNS serverC root DNS server, local DNS server and authoritative DNS serverD root DNS server, local DNS server and top-level domain DNS server58. In the following four options about POP3, which one is not correct?A The user agent employed only three commands: List, Retr and QuitB The server does not carry state information across POP3 sessionsC The port number is 110D The POP3 protocol does not provide any means for a user to create remote folders and assign messages to folders.59.A resource record in DNS distributed database is a four-tuple,which field can be ign ored?(p132)A Name B Value C Type D TTL60.In the following four options about DNSresource record,which one is correct?A The meaning of Name and Value depend on Type.B The meaning of Value and Type depend on Name.C If Type=A,then Name is a domain and Value is the IP address for the hostname.D If Type=MX,then Name is domain and Value is the IP address for the hostname.61.In the following four options about DNS messages,which one is not correct?A There are only two kinds of DNS message.(p133)B Both query and reply message have the same format.C The header section in DNS message has12bytes.D The authority section contains the resource records for the same that was originally q ueried.62.In DNS message,contains information about the query that is being made.(p133)A authority sectionB question sectionC answer sectionD additional section63.There are three techniques are employed in most any P2P file-sharing systems,which one is not include?（p144）A Request queuingB incentive prioritiesC parallel downloadingD Response queui ng64. In the following four options about P2P file-sharing, which one is not correct?A P2P file-sharing is highly scalable.B P2P file-sharing relies on P2P architecture.C The means for locating content in different P2P file-sharing are different.D P2P file-sharing systems not only share MP3s,but also videos, software, documents and images.65.In MIME header lines,specifies the name of the SMTP server that sent the messag e(from),the name of the SMTP server that received the message(by),and the time an which the receiving server received the message.A ReceivedB FromC ToD MIME-Version66. If the header line Connection is close, it means that the client wants .A persistent connection with pipeliningB persistent connection without pipeliningC nonpersistent connectionD not connection67. In HTTP request message, the entity body is empty with the method, but is used with the method.A GET, POSTB POST,GETC GET, HEAD D POST, HEAD68. In HTTP response message, if the Date: header ;one indicates the time Fri. 08 Aug. 2008 12:00:00 GMT, the Last-Modified: header line can not be .A Fri. 08 Aug. 2008 11:00:00 GMTB Fri. 08 Aug. 2008 11:30:00 GMTC Fri. 08 Aug. 2008 12:00:00 GMTD Fri. 08 Aug. 2008 12:30:00 GMT69. In the following four options, which one is not the part of cookie technology?A Cookie header lines in the HTTP response message and request message.B One cookie header file kept on the user’s end system and managed by the user’s browser.C A network entity that satisfies HTTP requests on the behalf of an origin Web server.D A back-end database at the Web site70. On-top of stateless HTTP, can be used to create a user session layer.A proxy serverB Web cacheC cookieD socket71. Processes communicate with each other by reading from and writing to .A programsB threadsC socketsD channels72. In the following four options about network architecture, which one is not correct?A The network architecture is fixed.B The network architecture provides a specific set of services to application.C The network architecture is designed by application developer.D The network architecture dictates how the application is organized over special server.73. In Client-Server architecture, the clients visit the server’s through .A client’s socketB client’s IP addressC server’s socketD server’s IP address74. can be thought of as a program that is running within end system.A processB threadC socketD context75. API means .A Application Program InterfaceB Application Process InterfaceC Appellation Program InterfaceD Appellation Process Interface76. One host can be running many network applications, so the system assigns them differentto distinguish each other.A IP addressB port numberC hostnameD section77. In the following four applications, which one is both bandwith-sensitive and require tight timing constraints?A real-time audioB file transferC E-mailD Web documents78. The port number of the Web server is .A 25B 20C 80D 808079. The port number of the mail server is .A 25B 20C 80D 808080. Look the URL /rjxy/index.html, the object’s path name is .A B /rjxyC /rjxy/index.htmlD index.html81. Each URL has components, they are .A transport protocol and object’s path nameB host name and object’s path nameC transport protocol and host nameD client name and server name1. Consider an HTTP client will request a WEB page from a WEB server. Suppose the URL of the page is /somedepartment /somedir/exp.html. The client does not want to use persistent connections and want to receive French version of the object. The user agent is Windows NT 5.1. Give the request message according to the given format.Request line:Header lines:2. Telnet into a Web server and send a multiline 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.Solution:Request line:Header lines:3. Suppose within you Web browser you click on a link to obtain a Web page. The IPaddress for the associated URL is not cached in your local host, so a DNS look-up is necessary 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 an RTT of RTT1,…，RTT n. Further suppose that the Web page associated with the link contains exactly one object, consisting of a small HTML text. Let RTT0 denote the RTT between the local host and the server containing the object. Assuming zero transmission time of the object, how much time elapses from when the client clicks on the link until the client receives the object?5. Suppose that you send an e-mail message whose only data is a microsoft excell attachment. What might the header lines (including MIME lines) look like?。

2.2 Network hardware-scale
2.2.1 Network hardware-scale
Personal Area Networks
2.2.2 Network hardware-scale
Local Area Networks
2.2.3 Network hardware-scale
applicatictions
Home applications
• • • •
Twitter Youtube Facebook Ubiquitous computing
• • • •
Smart phone GPS M-commerce Wearable computer
Mobile users
Social issues
Since computer scientists like to have their cake and eat it, too, we will use the hybrid model of Fig. 1-23 as the framework for this book.
4.1 Reference models-OSI
4.1 Reference models-OSI
4.2 Reference models-TCP/IP
4.3 Reference models- Used in This Book
目前在计算机网络领域有影响的标准化组织： 1、国际电信联盟（ITU) 2、国际标准化组织（ISO） 3、电子工业协会（EIA） 4、电气与电子工程师协会（IEEE） 5、ATM论坛
Network hardware Network software
Reference models

Chapter11-11.What are two reasons for using layered protocols?(请说出使用分层协议的两个理由)答：通过协议分层可以把设计问题划分成较小的易于处理的片段。

分层意味着某一层的协议的改变不会影响高层或低层的协议。

1-13. What is the principal difference between connectionless communication and connection-oriented communication?(在无连接通信和面向连接的通信两者之间，最主要的区别是什么？)答：主要的区别有两条。

其一：面向连接通信分为三个阶段，第一是建立连接，在此阶段，发出一个建立连接的请求。

只有在连接成功建立之后，才能开始数据传输，这是第二阶段。

接着，当数据传输完毕，必须释放连接。

而无连接通信没有这么多阶段，它直接进行数据传输。

其二：面向连接的通信具有数据的保序性，而无连接的通信不能保证接收数据的顺序与发送数据的顺序一致。

1-20. A system has an n-layer protocol hierarchy. Applications generate messages of length M bytes. At each of the layers, an h-byte header is added. What fraction of the network bandwidth is filled with headers?(一个系统有n层协议的层次结构。

应用程序产生的消息的长度为M字节。

在每一层上需要加上一个h字节的头。

请问，这些头需要占用多少比例的网络带宽)答：hn/(hn+m)*100%1-28. An image is 1024 x 768 pixels with 3 bytes/pixel. Assume the image is uncompressed. How long does it take to transmit it over a 56-kbps modem channel? Over a 1-Mbps cable modem? Over a 10-Mbps Ethernet? Over 100-Mbps Ethernet?(一幅图像的分辨率为1024 x 768像素，每个像素用3字节来表示。

Review Questions第一章1.Which characteristics of a multiterminal system make it different from a computer network?A processing power of multiterminal systems remained fully centralized, whilecomputer networks have a distributed processing power.一个多端系统处理能力仍然完全集中，而计算机网络具有分布式处理能力。

2.When were the first important results achieved in the field of joining computers using long-haul links?In the late 60s在60年代后期3.What is ARPANET?A.A network of supercomputers belonging to military organizations and research institutes in the United StatesB.An international scientific research networkC.The technology of creating WANsA is correct4.When did the first network operating systems appear?In the late 60s60年代后期5.In what order did the events listed here take place?A.The invention of WebB.The development of standard LAN technologiesC.The start of voice transmission in digital form through telephone networksThe invention of World Wide Web互联网的诞生6.Which of the events stimulated LAN development?Appearance of large-scale integrated circuits (LSI devices) resulted in invention of microcomputers which in its turn stimulated a research activity in the area of local computer networks (LANs). The adoption of personal computers was a powerful incentive for the development of LANs.大规模集成电路（LSI器件出现）导致这反过来刺激了研究活动在本地计算机网络（LAN）的微型计算机的发明。

Solution of Selected Exercises from the End of Chapter ExercisesChapter 1 - Introduction And Overview1.4 To what aspects of networking does data communications refer? Answer: Data communications refers to the study of low-level mechanisms and technologies used to send information across a physical communication medium, such as a wire, radio wave, or light beam.b5E2RGbCAP1.5 What is packet-switching, and why is packet switching relevant tothe Internet?Answer: Packet switching divides data into small blocks, called packets, and includes an identification of the intended recipient in each packet. Packet switching changed networking in a fundamental way, and provided the basis for the modern Internet. Packet switching allows multiple senders to transmit data over a shared network. p1EanqFDPw1.8 What is a communication protocol? Conceptually, what two aspects ofcommunication does a protocol specify?Answer: A communication protocol refer to a specification for network communication.Major aspects of a protocol are syntax (format> and semantics (meaning> of the protocol. DXDiTa9E3d1.9 What is a protocol suite, and what is the advantage of a suite? Answer:protocols are designed in complete, cooperative sets called suites or families, instead of creating each protocol in isolation.Each protocol in a suite handles oneaspect of communication。

《计算机⽹络》考题（英⽂选择题）Computer Networks – Exam1 Short questionsFor each question, please circle a single best answer.1.In the CSMA/CD protocol, what condition on the transmission delay T trans and thepropagation delay T prop has to be satisfied to guarantee that a node always detects a collision?A. T trans > T propB. T trans > 2T prop CORRECTC. T trans < T propD. 2T trans < T prop2.Alice and Bob communicate in an alphabet that has L letters. They use a monoalphabeticsubstitution cipher with key K. Assume that Trudy obtains a plaintext m and thecorresponding ciphertext c. Under what conditions can Trudy recover the key K completely?A. m contains at least 1-L unique letters. CORRECTB. Lm≥.C. Km≥.D. m is not empty.3.The WiMaX protocol:A. provides the maximum available data rate over a wireless channel.B. uses unlicensed spectrum, such as WiFi.C. provides a mechanism for scheduling. CORRECTD. All of the above options are correct.4.Two hosts simultaneously send data through a link of capacity 1Mbps. Host A generates datawith a rate of 1Mbps and uses TCP. Host B uses UDP and transmits a 100bytes packet every 1ms. Which host will obtain higher throughput?A. Host A.B. Host B. CORRECTC. They obtain roughly the same throughput.D. They experience congestion collapse and negligible throughput.5.What is the theoretical upper-bound on the number of simultaneous TCP/IPv4 connectionsthat a host with a single IP address can handle? (Ignore memory limitations.)B. 232C. 264CORRECTD. unlimited6.Host A sends a TCP segment (Seq = 43, ACK = 103), to which host B replies with a TCP segment (Seq = 103, ACK = 57). The payload of the first TCP segment isA. 14 bytes long. CORRECTB. 43 bytes long.C. 46 bytes long.D. 57 bytes long.E. 60 bytes long.7.The Distance-Vector algorithm is not:A. iterative.B. asynchronous.C. distributed.D. used in RIP.E. None of the above. CORRECT8.Longest prefix matching is used:A. in routers to know on which link interface to forward packets. CORRECTB. in classless addressing to use the address space more efficiently than in classful addressing.C. by NAT to increase the available address space in home networks.D. to assign subnet masks.E. None of the above.9.An authoritative DNS server knows a top-level domain server via:A. hostname.B. IP address. CORRECTC. canonical hostname.D. alias.E. domain.10.A user requests aWeb page that consists of some text and 3 images. The browser’s cache is empty. For this page, the client’s browser:A. sends 1 http request message and receives 1 http response messages.B. sends 1 http request message and receives 3 http response messages.C. sends 1 http request message and receives 4 http response messages.D. sends 3 http request messages and receives 3 http response messages.11.What is the advantage of using a layered model of networking?A. Simplified the networkB. For the purpose of standardizationC. Divides the complexity of internetworking into discrete, more easily learned operation subsetsD. All of the above CORRECT12.What is the name of protocol data unit(PDU)at the network layer of the OSI reference model?A. TransportB. FrameC. Packet CORRECTD. Segment13.Which is true when a broadcast is sent out in an Ethernet 802.3 LAN?A. The broadcast is sent only to the default gateway.B. The broadcast is sent only to the destination hardware address in the broadcast.C. The broadcast is sent to all devices in the collision domain. CORRECTD. The broadcast is sent to all devices in the broadcast domain.14.Segmentation of a data stream happens at which layer of the OSI model?A.PhysicalB.Data Link/doc/ee7d8dd65022aaea998f0fd2.html workD.Transport CORRECT15.Which of following international standard defines for Fast Ethernet?A.IEEE 802.3B.IEEE 802.3zC.IEEE 802.3u CORRECTD.IEEE 802.3ae16.What does the Data Link layer use to find hosts on a local network?A.Logical network addressesB.Port numbersC.Hardware addresses CORRECTD.Default gateways17.What were the key reasons the ISO released the OSI model?A.To allow companies to charge more for their equipmentB.To help vendors create interoperable network devices CORRECTC.To help vendors create and sell specialized software and hardware18.What is used at the Transport layer to stop a receiving host’s buffer from overflowing?A.SegmentationB.PacketsC.AcknowledgmentsD.Flow control CORRECT19.When data is encapsulated, which is the correct order?A.Data,frame,packet,segment,bitB.Segment,data,packet,frame,bitC.Data,segment,packet,frame,bit CORRECTD.Data,segment,frame,packet,bit20.What does the term“Base”indicate in 100Base-TX?A.The maximum distanceB.The type of wiring usedC.A LAN switch method using half duplexD.A signaling method for communication on the network CORRECT21.What is the maximum distance of 100Base-T?A.100 feetB.1000 feetC.100 meters CORRECTD.1000 meters22.Which of the following would describe a transport layer connection that would ensure reliable delivery?A.RoutingB.Acknowledgments CORRECTC.SwitchingD.System authentication23.Which of the following is not considered a reason for LAN congestion?A.Low bandwidthB.Too many users in a broadcast domainC.Broadcast stormsD.Routers CORRECT24.Which of the following are two basic types of dynamic routing?A.Static and defaultB.TCP and UDP exchangeD.None of the above25.If your LAN network is currently congested and you are using only hubs in your network,what would be the BEST solution to decrease congestion on your network?A.Cascade your hubs.B.Replace your hubs with switches. CORRECTC.Replace your hubs with routers.D.Add faster hubs.26.What technology is a used by most switches to resolve topology loops and ensure that data flows properly through a single network path?A.RIPB.STP CORRECTC.IGRPD.Store-and-forward27.Which of the following is one of the characteristics of IP?A.reliable and connectionlessB.unreliable and connectionless CORRECTC.reliable and connection-orientedD.unreliable and connection-oriented28.What is the valid host range for subnet 172.16.10.16(Mask 255.255.255.240)?A.172.16.10.20 through 172.16.10.22B.172.16.10.16 through 172.16.10.23C.172.16.10.17 through 172.16.10.31D.172.16.10.17 through 172.16.10.30 CORRECT29.What range of addresses can be used in the first octet of a Class B network address?A.1–126B.128–190C.128–191 CORRECTD.129–19230.Which of the following is not true?A.IP is connectionless and provides routing.B.ARP is used to find an IP address of a host. CORRECTC.UDP is connectionless.D.TCP is connection oriented.31.Which class of IP address provides a maximum of only 254 host addresses per network ID?B.Class BC.Class C CORRECTD.Class D32.Which protocol tool use ICMP?A.TelnetB.Ping CORRECTC.ARPD.FTP33.Which of the following is an IEEE standard for frame tagging?A.802.1XB.802.3ZC.802.1QD.802.3U CORRECT34.A client will use____to send emails to mail-server.A.POP3B.SMTP CORRECTC.TELNETD.FTP35.Which protocol used in PPP allows multiple Network layer protocols to be used during a connection?A.LCPB.NCP CORRECTC.HDLCD.X.2536.When too many packets are present in the subnet, performance degrades. What is this situation called?A.dead lockB.congestion CORRECT/doc/ee7d8dd65022aaea998f0fd2.html work fault/doc/ee7d8dd65022aaea998f0fd2.html work busy37.Which language can be used to realize the client-side dynamic web page generation?A.CGIB.ASP CORRECTC.JavaScript38.The two-wire connections between each subs criber’s telephone and the end office are known in the trade as the____.A.trunkB.local loopC.linkD.switch CORRECT39.When web page is transmitted over SSL, the protocol used is_____.A.HTTPB.SHTTPC.HTTPS CORRECTD.SSL40.Nyquist proved that if an arbitrary signal has been run through a low-pass filter of bandwidthH, the filtered signal can be completely reconstructed by making only_____(exact)samples per secondA.HB.0.5HC.2H CORRECTD.4H41.To convert a binary message to an ASCII message in email system, we can useencoding, which break up groups of 24 bits into four 6-bit units, with each unit being sent asa legal ASCII character. (Ref in page 262)A.base64 CORRECTB.quoted-printableC.SMTPD.POP342.A CRC generator polynomial is G(x)=X8+X5+X2+l.How many bits will the checksum be?A.7B.8 CORRECTC.9D.1043.If the length of sequence is 4 bits, the maximum sending window size should be____.A.13B.14C.15 CORRECTD.1644.In 802.11, to solve the_______station problem and the hidden station problem,we can useA. faultB.mobileC.exposed CORRECTD.wireless45.If the congestion window size is 20KB, and the receive window size is 30KB,what is themaximum bytes can the TCP entity transmit?A.20KB CORRECTB.30KBC.50KBD.10KB46.Port numbers below________are called well-known ports and are reserved for standardservices.A.256B.1024 CORRECTC.4096D.100047.________, which are overlay networks on top of public networks but with most of theproperties of private network.A.PBXB.VPN CORRECTC.CDMA 1XD.GPRS48.The problem of running out of IP addresses is not a theoretical problem that might occur atsome point in the distant future. Some people felt that a quick fix was needed for the short term. This quick fix came in the form of____________________.A.IP6B.DHCPC.RARPD.NAT CORRECT49.Public-key algorithms have the property that_______keys are used for encryption anddecryption and that the decryption key cannot be derived from the encryption key.These properties make it possible to publish the public key.A.one timeB.randomC.same50.The main public-key algorithm is___________which derives its strength from the fact that itis very difficult to factor large numbers.A.DESB.AESC.MD5D.RSA CORRECT51.Various schemes have been devised for digital signatures, using both symmetric-key and________-key algorithms.A.public CORRECTB.privateC.one timeD.one way52.Often, authentication is needed but secrecy is not, based on the idea of a one-way hashfunction that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string. This hash function, MD, often called a________.A.message digest CORRECTB.packet-switchedC.message-detectD.mini data53.URL(Uniform Resource Locator)have three parts: the________, the DNS name of themachine on which the page is located, and a local name uniquely indicating the specific page.A.protocol CORRECTB.addressC.port number/doc/ee7d8dd65022aaea998f0fd2.html54.HTTP1.1, which supports________connections. With them, it is possible to establish a TCPconnection, send a request and get a response, and then additional requests and get additional response.A.one timeB.persistent CORRECTC.stop and waitD.one-way55._______, when it is used, a bad frame that is received is discarded, but the good framesreceived after it are buffered.A.selective repeatD.stop and wait56.How does the FDM multiplexing schemes work like?A.each user having exclusive possession of some band CORRECTB.each user take turns, periodically getting the entire bandwidth for a litter burst of timeC.each user transmit over the entire frequency spectrum all the time with different codingD.each user transmit over a shared fiber using different wavelength57.When we use a modem, which use 16 phases signal to modulation, then how much can we get the maximum data rate in a 2400 baud channel(in noiseless channel)?A.400bpsB.2400bpsC.9.6kbps CORRECTD.14.4kbps58.______is a small java program that has been compiled into binary instruction running in JVM, and can be embedded into HTML pages, interpreted by JVM-capable browsers.A.JavaScriptB.JavaBeanC.Applet CORRECTD.JSP59.Which of the following best describes the function of the OSI reference model’s transport layer?A.It sends data by using flow control CORRECTB.It provides the best path for deliveryC.It determines network addressesD.It provides error-correcting60.What is the most efficient subnet mask to use on point-to-point WAN links?A.255.255.255.0B.255.255.255.224C.255.255.255.252 CORRECTD.255.255.255.248*************************61.Given the cutoff frequency is 3000Hz, the bit rate b=9600 bits/s, then the time required to send 8 bits 1 bit at a time will be 8/b sec, so the number of the highest harmonic passed through isA. 1C. 2.5D. 2062.If two codewords are a Hamming distance 2d+1 apart, it will require single-bit errorsto convert one into the other. Error-correcting can be done while bit-errors are atmost .A.2d, d+1B. 2d, dC.2 d+1, d CORRECTD. None of the above63.For sliding window protocol using go back N, supposing the sender window’s size is 16, then at most frames may be outstanding at any instant.A. 0B. 1C. 15 CORRECTD. 1664.If the physical line is poor, which of the following protocols may be work better?A. Stop-and -WaitB. One-Bit Sliding Window ProtocolC. Sliding Window Protocol Using Go Back ND. Sliding Window Protocol Using Selective Repeat CORRECT65.Services provided by Ethernet are unreliable. If the destination station receive a error data frame, it 。

计算机网络双语试题及答案一、选择题（共20题，每题2分，共40分）1. 当使用HTTP协议进行通信时，下列哪个是无连接的协议？A. TCPB. IPC. UDPD. FTP2. 在计算机网络中，IP地址的作用是什么？A. 标识主机在网络中的唯一地址B. 实现数据的可靠传输C. 进行主机之间的通信D. 提供远程访问服务3. 下列哪个不属于网络拓扑结构的类型？A. 总线型拓扑B. 环形拓扑C. 星型拓扑D. 布线型拓扑4. 在TCP/IP协议中，下列哪个协议用于将IP地址转换为物理地址？B. DHCPC. FTPD. ICMP5. 在计算机网络中，HTTP和HTTPS协议之间的区别是？A. HTTP使用明文传输，HTTPS使用加密传输B. HTTP使用UDP传输，HTTPS使用TCP传输C. HTTP使用IP地址，HTTPS使用域名D. HTTP使用GET请求，HTTPS使用POST请求6. 某计算机的IP地址是192.168.0.1，子网掩码是255.255.255.0，那么该计算机所在的网络号是？A. 192.168.0B. 192.168.0.1C. 192.168.0.255D. 192.168.0.07. 在计算机网络中，下列哪个协议用于将域名解析为IP地址？A. DNSB. FTPC. DHCP8. 在TCP/IP协议中，下列哪个协议用于控制数据传输的可靠性？A. ICMPB. UDPC. FTPD. TCP9. 在计算机网络中，什么是反向代理服务器（Reverse Proxy Server）？A. 将外部网络请求转发给内部服务器的服务器B. 将内部网络请求转发给外部服务器的服务器C. 将HTTP请求转发给HTTPS服务器的服务器D. 将HTTPS请求转发给HTTP服务器的服务器10. 在计算机网络中，下列哪个协议用于电子邮件的发送和接收？A. SMTPB. POP3C. HTTPD. FTP11. 在计算机网络中，下列哪个协议用于文件传输？B. SMTPC. UDPD. TCP12. 以下哪个不是IPv6地址的特点？A. 128位长度B. 冒号分隔的十六进制C. 有固定的网络号和主机号D. 全球唯一的地址13. 在计算机网络中，下列哪个技术不属于无线局域网技术？A. Wi-FiB. BluetoothC. NFCD. 4G14. 在网络中，下列哪个设备用于将不同网段的数据转发到目的主机？A. 集线器B. 路由器D. 网关15. 下列哪个网络拓扑结构具有较高的可容错性和可拓展性？A. 星型拓扑B. 总线型拓扑C. 环形拓扑D. 树型拓扑16. 在计算机网络中，下列哪个协议用于互联网上的主机进行网络配置？A. DHCPB. DNSC. HTTPD. FTP17. 在TCP/IP协议中，下列哪个协议用于检测并纠正数据传输中的错误？A. TCPB. ARPC. ICMPD. UDP18. 下列哪个是网络安全的常见攻击方式之一？A. DDoS攻击B. 数据库攻击C. 剪贴板攻击D. 社会工程学攻击19. 下列哪个不是局域网（LAN）的特点？A. 覆盖范围较小B. 速度较快C. 价格较高D. 结构较简单20. 在计算机网络中，下列哪个协议用于向局域网中的所有主机广播消息？A. UDPB. TCPC. DHCPD. ICMP二、问答题（共5题，每题10分，共50分）1. 请简要介绍HTTP协议的工作原理。

计算机⽹络英⽂版——提供给学⽣部分习题答案Solution of Selected Exercises from the End of Chapter ExercisesChapter 1 - Introduction And Overview1.4 To what aspects of networking does data communications refer?Answer:Data communications refers to the study of low-level mechanisms and technologies used to send information acrossa physical communication medium, such as a wire, radio wave, or light beam.1.5 What is packet-switching, and why is packet switching relevant to the Internet?Answer: Packet switching divides data into small blocks, called packets, and includes an identification of the intended recipient in each packet. Packet switching changed networking in a fundamental way, and provided the basis for the modern Internet. Packet switching allows multiple senders to transmit data over a shared network.1.8 What is a communication protocol? Conceptually, what two aspects of communication does a protocol specify? Answer: A communication protocol refer to a specification for network communication.Major aspects of a protocol are syntax (format) and semantics (meaning) of the protocol.1.9 What is a protocol suite, and what is the advantage of a suite?Answer:protocols are designed in complete, cooperative sets called suites or families, instead of creating each protocol in isolation. Each protocol in a suite handles one aspect of communication; together, the protocols in a suite cover all aspects of communication. The entire suite is designed to allow the protocols to work together efficiently. 1.11 List the layers in the TCP/IP model, and give a brief explanation of each.(See Textbook)1.14 Give a brief explain of the layers in the ISO Open System Interconnection model.(See Textbook)Chapter 3 - Internet Applications And Network Programming3.1 What are the two basic communication paradigms used in the Internet?Answer: There are various approaches, but according to textbook, we can specify them as Stream Paradigm and Message Paradigm.3.2 Give six characteristics of Internet stream communication.(See Textbook)3.3 Give six characteristics of Internet message communication.(See Textbook)3.4 If a sender uses the stream paradigm and always sends 1024 bytes at a time, what size blocks can the Internet deliverto a receiver?Answer: stream paradigm does not provide any guarantees for block sizes, so all depends on individual transfer.3.6 What are the three surprising aspects of the Internet’s message delivery semantics?Answer:The Internet’s message delivery has the followi ng undesirable characteristics:* Messages can be lost* Messages can be duplicated* Messages can be delivered out-of-order3.8 When two applications communicate over the Internet, which one is the server?Answer: T he application that waits for some other applications to contact is called server, and the application that contact other one is called client.3.14 What two identifiers are used to specify a particular server?Answer: A particular server is identified by the following identifiers:* An identifier for the computer on which a server runs (IP Address)* An identifier for a particular service on the computer (Port Number)Chapter 4 - Traditional Internet Applications4.1 What details does an application protocol specify?(See Textbook)4.3 What are the two key aspects of application protocols, and what does each include?(See Textbook)4.6 What are the four parts of a URL, and what punctuation is used to separate the parts?Answer: The URL into four components: a protocol, a computer name, a document name, and parameters. The computer name and protocol port are used to form a connection to the server on which the page resides. And the document name and parameters are used to request a specific page.4.7 What are the four HTTP request types, and when is each used?(See Textbook)4.12 When a user requests an FTP directory listing, how many TCP connections are formed? Explain.Answer: FTP uses two types of connections to perform its functionality, namely* A control connection is reserved for commands. Each time the server needs to download or upload a file, the server opens a new connection.* A data connection is used to transfer files.4.16 List the three types of protocols used with email, and describe each.(See Textbook)4.17 What are the characteristics of SMTP?(See Textbook)4.20 What are the two main email access protocols?Answer: Two major email access protocols are:* Post Office Protocol (POP)* Internet Mail Access Protocol (IMAP)Chapter 6- Information Sources and Signals6.4 State and describe the four fundamental characteristics of a sine wave.(See Textbook)6.9 What is the analog bandwidth of a signal?Answer: Analog bandwidth of signal can be defined as to be the difference between the highest and lowest frequencies of the constituent parts (i.e., the highest and lowest frequencies obtained by Fourier analysis)6.11 Suppose an engineer increases the number of possible signal levels from two to four. How many more bits can be sent in the same amount of time? Explain.Answer: The number of levels that can be represented by n bits is given by 2n . So if number of levels changes from 2→4, it means number of bits goes from 1→2612. What is the definition of baud?Answer: Baud is defined as the number of times that a signal can change per second.6.14 What is the bandwidth of a digital signal? Explain.Answer: According to the definition of analog bandwidth, a digital signal has infinite bandwidth because Fourier analysis of a digital signal produces an infinite set of sine waves with frequencies that grow to infinity.6.18 What is the chief advantage of a Differential Manchester Encoding?Answer: The most important property of differential encoding is that the encoding works correctly even if the two wires carrying the signal are accidentally reversed.6.20 If the maximum frequency audible to a human ear is 20,000 Hz, at what rate must the analog signal from a microphone be sampled when converting it to digital?Answer: The sampling rate = 2 × f max, so the signal should be sampled at 2x20,000 = 40,000 HzChapter 7 - Transmission Media7.2 What are the three energy types used when classifying physical media according to energy used?Answer: Three types of energy used when classifying physical media are electrical, electromechanical (radio), and light7.4 What three types of wiring are used to reduce interference form noise?(See Textbook)7.10 List the three forms of optical fiber, and give the general properties of each.(See Textbook)7.21 What is the relationship between bandwidth, signal levels, and data rate?Answer: If a transmission system uses K possible signal levels and has an anal og bandwidth B, Nyquist’s Theorem states that the maximum data rate in bits per second, D, is: D = 2 B log2K7.22 If two signal levels are used, what is the data rate that can be sent over a coaxial cable that has an analog bandwidthof 6.2 MHz?Answer: Using the D= 2 B log2 K relationship, D = 2*6.2*log22 = 2*6.2*1 = 12.4 Mbps7.24 If a system has an input power level of 9000, and an output power level of 3000, what is the difference when expressed in dB?Answer: Decibel is expressed as 10log10(P out/P in) → 10log10(3,000/9,000) = to be determined by reader7.23 If a system has an average power level of 100, an average noise level of 33.33, and a bandwidth of 100 MHz, whatis the effective limit on channel capacity?Answer: Shannon theorem specify the maximum data rate that could be achieved over a transmission system that experiences noise: C = Blog2 (1 + S/N) = 100,000,000 * log2 (1 + 100/33.33) = 100,000,000 * log24 = 200,000,000 = 200 Mbps7.25 If a telephone system can be created with a signal-to-noise ratio of 40 dB and an analog bandwidth of 3000 Hz, how many bits per second could be transmitted?Answer: First we should convert 40 dB to a real number, namely if 40 = 10 log10S/N→S/N = 10,000 , Using the Shannon’s capacity expression C = B log2(1 + S/N) → C = 3,000 log2 (1+ 10,000) = to be determined by readerCh 8 - Reliability And Channel Coding8.1 List and explain the three main sources of transmission errors.(See Textbook)8.3 In a burst error, how is burst length measured?Answer: For a burst error, the burst size, or length, is defined as the number of bits from the start of the corruption to the end of the corruption.8.4 What is a codeword?Answer: We can define the set of all possible messages to be a set of datawords, and define the set of all possible encoded versions to be a set of codewords. So each possible code sequence is considered to be a codeword.8.8 Compute the Hamming distance for the following pairs: (0000, 0001), (0101, 0001), (1111, 1001), and ( 0001, 1110). (See Textbook)8.11 Generate a RAC parity matrix for a (20, 12) coding of the dataword 100011011111.(See Textbook)8.15 Express the two values in the previous exercise as polynomials.Answer:X10+ X7 + X5 + X3 + XX4+ X2+ 1Ch 9 - Transmission Modes9.1 Describe the difference between serial and parallel transmission.Answer: Transmission modes can be divided into two fundamental categories:* Serial: one bit is sent at a time* Parallel: multiple bits are sent at the same time9.2 What are the advantages of parallel transmission? What is the chief disadvantage?Answer: A parallel mode of transmission has two chief advantages:* High speed: Because it can send N bits at the same time, a parallel interface can operate N times faster than an equivalent serial interface.* Match to underlying hardware: Internally, computer and communication hardware uses parallel circuitry.Thus, a parallel interface matches the internal hardware well.The main disadvantage of parallel transmission is number of cables required, for long distance communication, this is an important consideration.9.4 What is the chief characteristic of asynchronous transmission?Answer:Asynchronous transmission can occur at any time, with an arbitrary delay between the transmission of two data items, it allows the physical medium to be idle for an arbitrary time between two transmissions.Chapter 11 - Multiplexing And Demultiplexing11.2 What are the four basic types of multiplexing?(See Textbook)11.4 What is a guard band?Answer: For proper communication without interference, we should choose a set of carrier frequencies with a gap between them known as a guard band. The guard band reduces or eliminates the possible interference between neighboring carrier signals.11.8 Explain how a range of frequencies can be used to increase data rate.Answer:To increase the overall data rate, a sender divides the frequency range of the channel into K carriers, and sends 1 /K of the data over each carrier.11.12 Suppose N users compete using a statistical TDM system, and suppose the underlying physical transport can sendK bits per second. What is the minimum and maximum data rate that an individual user can experience?Answer: If we neglect the overhead generated by statistical TDM, a system will have two possibilities: * Minimum: If all channels have equal data then the rate will be K/N bps* Maximum: If only one channel active and the others are passive, then rate will be K bpsChapter 13 - Local Area Networks: Packets, Frames, And Topologies13.1 What is circuit switching, and what are its chief characteristics?Answer: The term circuit switching refers to a communication mechanism that establishes a path between a sender and receiver with guaranteed isolation from paths used by other pairs of senders and receivers. The circuit switching has the following main characteristics:* Point-to-point communication* Separate steps for circuit creation, use, and termination* Performance equivalent to an isolated physical path13.3 In a packet switching system, how does a sender transfer a large file?Answer: The packet switching system requires a sender to divide each message into blocks of data that are known as packets . The size of a packet varies; each packet switching technology defines a maximum packet size. So, a large file will be divided into smaller pieces and sent.13.5 What are the characteristics of LANs, MANs, and W ANs?Answer: There are lots of details that can be said and discussed for categorization of network types based on geography, few points are highlighted below:* Local Area Network (LAN): Least expensive; spans a single room or a single building* Metropolitan Area Network (MAN) Medium expense; spans a major city or a metroplex* Wide Area Network (WAN) Most expensive; spans sites in multiple cities13.6 Name the two sublayers of Layer 2 protocols defined by IEEE, and give the purpose of each.Answer: The Layer 2 protocols defined by IEEE defines two sub-layers as mentioned below:* Logical Link Control (LLC) Addressing and demultiplexing* Media Access Control (MAC) Access to shared media13.8 What are the four basic LAN topologies?Answer: The four basic LAN topologies are star, ring, mesh and bus.13.10 In a mesh network, how many connections are required among 20 computers?Answer: The expression to calculate number of connections in a mesh network is given by n (n-1)/2. So for 20 computers then number of connections required will be = 20 (20 – 1)/2 =19013.15 Give a definition of the term frame .Answer: In a packet-switched network, each frame corresponds to a packet processed at data link layer.Chapter 14 - The IEEE MAC Sub-Layer14.1 Explain the three basic approaches used to arbitrate access to a shared medium.(See Textbook)14.3 List the three main types of channelization and the characteristics of each.(See Textbook)14.6 What is a token, and how are tokens used to control network access?Answer: A special control message is called a token. In a token passing system, when no station has any packets to send, the token circulates among all stations continuously. When a station captures the token, it sends its data, and when transmission completed, it releases the token.14.8 Expand the acronym CSMA/CD, and explain each part.Answer: The acronym CSMA/CD stands for Carrier Sense Multi-Access with Collision Detection, which means the following: * Carrier Sense: Instead of allowing a station to transmit whenever a packet becomes ready, Ethernet requires each station to monitor the cable to detect whether another transmission is already in progress.* Multiple Access: The system allows multiple users/hosts to make use of a common/shared media* Collision Detection. A collision can occur if two stations wait for a transmission to stop, find the cable idle, and both start transmitting.14.10 Why does CSMA/CD use a random delay? (Hint: think of many identical computers on a network.)Answer: Randomization is used to avoid having multiple stations transmit simultaneously as soon as the cable is idle.That is, the standard specifies a maximum delay, d, and requires each station to choose a random delay less than d after a collision occurs. In most cases, when two stations each choose a random value, the station that chooses the smallest delay willChapter 15 - Wired LAN Technology (Ethernet And 802.3)15.1 How large is the maximum Ethernet frame, including the CRC?Answer: According to Fig. 15.1 a conventional Ethernet frame has the following fields:* Header: 14 bytes (fixed)* Payload: 46-1500 bytes (there is a minimum frame size because of collision detection)* CRC: 4 bytes (fixed)Accordingly an Ethernet frame will be maximum 1518 bytes and minimum 64 bytes15.3 In an 802.3 Ethernet frame, what is the maximum payload size?Answer: The 802.3 Ethernet makes use of 8-bytes of the original/conventional Ethernet for Logical Link Control / Sub-Network Attachment Point (LLC / SNAP) header instead of extending/increasing the header. This is for sake of backward compatibility. So the maximum pay load is reduced from 1500 bytes to 1492 bytes.15.6 How did a computer attach to a Thicknet Ethernet?Answer: Hardware used with Thicknet was divided into two major parts:* Transceiver: A network interface card (NIC) handled the digital aspects of communication, and a separate electronic device called a transceiver connected to the Ethernet cable and handled carrier detection, conversion of bits into appropriate voltages for transmission, and conversion of incoming signals to bits.* AUI: A physical cable known as an Attachment Unit Interface (AUI) connected a transceiver to a NIC in a computer. A transceiver was usually remote from a computer.15.7 How were computers attached to a Thinnet Ethernet?Answer: Thinnet Ethernet (formally named 10Base2) uses a thinner coaxial cable that was more flexible than Thicknet. The wiring scheme differed dramatically from Thicknet. Instead of using AUI connections between a computer and a transceiver, Thinnet integrates a transceiver directly on the NIC, and runs a coaxial cable from one computer to another.15.8 What is an Ethernet hub, and what wiring is used with a hub?Answer: An electronic device that serves as the central interconnection is known as a hub. Hubs were available in a variety of sizes, with the cost proportional to size. The hubs are becoming old-fashioned, and being replaced with switches.15.3 What category of twisted pair wiring is needed for a 10 Mbps network? 100 Mbps? 1000 Mbps?Answer: The three major categories of Ethernet and their wiring is listed below:* 10 Mbps: 10BaseT (Ethernet) Category 5* 100 Mbps: 100BaseT (Ethernet Fast) Category 5E* 1 Gbps: 1000BaseT (Gigabit Ethernet) Category 6Chapter 20 - Internetworking: Concepts, Architecture, and Protocols20.2 Will the Internet be replaced by a single networking technology? Why or why not?Answer: Incompatibilities make it impossible to form a large network merely by interconnecting the wires among networks. The beauty of the Internet is interconnection of wide range of technologies from various manufacturers.Diversity of the products and solutions is a richness instead of limitation as long as they all adopt the same set of protocols.20.3 What are the two reasons an organization does not use a single router to connect all its networks?Answer:An organization seldom uses a single router to connect all of its networks. There are two major reasons: * Because the router must forward each packet, the processor in a given router is insufficient to handle the traffic passing among an arbitrary number of networks.* Redundancy improves internet reliability. To avoid a single point of failure, protocol software continuously monitors internet connections and instructs routers to send traffic along alternative paths when a network or router fails.20.6 In the 5-layer reference model used with the TCP/IP Internet protocols, what is the purpose of each of the five layers?(See 1.11)Chapter 21- IP: Internet Addressing21.3 In the original classful address scheme, was it possible to determine the class of an address from the address itself? Explain.Answer:Yes, since in the classful addressing scheme initial bit(s) gives indication about the class being used.21.7 If an ISP assigned you a /28 address block, how many computers could you assign an address?Answer: When an organization is assigned /28 CIDR address, it means 28 bits out of 32 bits are fixed, so 32-28 = 4 bits available for user space. So number of users 24-2 = 4, since the all 0s and all 1s address are having special use and can’t be assigned to a user.21.8 If an ISP offers a / 17 address block for N dollars per month and a / 16 address block for 1.5 N dollars per month,which has the cheapest cost per computer?Answer: Number of addresses in /17 block 232-17 = 215Price per address: N /215 = N / 215Number of addresses in /16 block 232-16 = 216Price per address: 1.5N /216 = 0.75N/215 So /16 address block will be cheaper in comparison with the price given for /17 block.21.10 Suppose you are an ISP with a / 24 address block. Explain whether you accommodate a request from a customer who needs addresses for 255 computers. (Hint: consider the special addresses.)Answer: For a/24 address block, number of available addresses will be 232-24 = 28 = 256. However, a suffix with all 0s address is reserved for network ID and a suffix with all 1s address is reserved for broadcast address, so number of addresses that can be assigned to computers/hosts will be 256 -2 = 254.21.11 Suppose you are an ISP that owns a / 22 address block. Show the CIDR allocation you would use to allocateaddress blocks to four customers who need addresses for 60 computers each.Answer: The /22 address block can be assigned as follows:ddd.ddd.ddd.00/26ddd.ddd.ddd.01/26ddd.ddd.ddd.10/26ddd.ddd.ddd.11/26Chapter 22- Datagram Forwarding22.1 What are the two basic communication paradigms that designers consider when designing an internet?Answer:* Connection-oriented service * Connectionless service22.2 How does the Internet design accommodate heterogeneous networks that each have their own packet format?Answer: To overcome heterogeneity, the Internet Protocol defines a packet format that is independent of the underlying hardware. The result is a universal, virtual packet that can be transferred across the underlying hardware intact. The Internet packet format is not tied directly to any hardware. The underlying hardware does not understand or recognize an Internet packet.22.5 What is the maximum length of an IP datagram?In the current version of the Internet Protocol (IP version 4), a datagram can contain at most 64 K (65535) octets, including the header.22.7 If a datagram contains one 8-bit data value and no header options, what values will be found in header fields H.LEN and TOTAL LENGTH?Answer: H. LEN indicated header in 32-quantities, since no options, then this value will be 5. The TOTAL LENGTH indicated the number of bytes in a datagram including the header. This means 5x4 bytes + 1 (8-bits) = 21 bytesChapter 23 - Support Protocols And Technologies23.1 When a router uses a forwarding table to look up a next-hop address, the result is an IP address. What must happenbefore the datagram can be sent?Answer: Each router along the path uses the destination IP address in the datagram to select a next-hop address, encapsulates the datagram in a hardware frame, and transmits the frame across one network. A crucial step of the forwarding process requires a translation: forwarding uses IP addresses, and a frame transmitted across a physical network must contain the MAC address of the next hop.23.2 What term is used to describe the mapping between a protocol address and a hardware address?Answer: Translation from a computer’s IP address to an equivalent hardware address is known as address resolution, and an IP address is said to be resolved to the correct MAC address. The TCP/IP protocol being used for this is called Address Resolution Protocol (ARP). Address resolution is local to a network.23.5 How many octets does an ARP message occupy when used with IP and Ethernet addresses?Answer: According to Fig 23.3 an ARP message has 7-lines of each being 32-bit (4 bytes or octets), therefore,number of octets in an ARP can be determined as 7x4 = 28 octets23.10 What types of addresses are used in layers below ARP?Answer:ARP forms a conceptual boundary in the protocol stack; layers above ARP use IP addresses, and layers below ARP use MAC addresses.23.17 What is the chief difference between BOOTP and DHCP?Answer:The main difference is that the BOOTP protocol required manual administration. So before a computer could use BOOTP to obtain an address, a network administrator had to configure a BOOTP server to know the computer’s I P address. Chapter 24 - The Future IP (IPv6)24.3 List the major features of IPv6, and give a short description of each.(See Textbook)24.4 How large is the smallest IPv6 datagram header?Answer: IPv6 datagram header consists of a base header + zero or more extension header. Since, smallest header is being asked, we assume zero extension header and consider IPv6 will have only base header. If we look at IPv6 header format in Fig. 24.3, it shows that 10x4 bytes = 40 bytes.Chapter 26 - TCP: Reliable Transport Service26.2 List the features of TCP.(See Textbook)26.6 When using a sliding window of size N, how many packets can be sent without requiring a single ACK to be received?Answer: If the size of the window is N, then it means a sender can transmit up to N packets without waiting for an ACK, as long as other controls are in place.26.9 What is the chief cause of packet delay and loss in the Internet?Answer: The main cause of packet delay and loss in the Internet is congestion.Chapter 28 - Network Performance (QoS and DiffServ)28.1 List and describe the three primary measures of network performance.(See Textbook)28.2 Give five types of delay along with an explanation of each.(See Textbook)Chapter 30 - Network Security30.1 List the major security problems on the Internet, and give a short description of each.(See Textbook)30.2 Name the technique used in security attacks.(See Textbook)30.8 List and describe the eight basic security techniques.(See Textbook)。

HUST Examination Answer SheetCourse: Computer Networks (closed-book exam) Jan.2014 Department of Electronics and Information EngineeringSolution[Question 1] Network architecture(1) Draw the architecture diagrams of ISO/OSI reference model and TCP/IP network. (2) State the differences between the two architectures.(3) Mark the names of data unit and network equipment in the bottom 4 layers of ISO/OSI diagram.Solution:（1）ISO/OSI reference model TCP/IP modelDifferences:a) TCP/IP model is the actual architecture in the Internet, while OSI model is a theoreticalarchitecture.b) TCP/IP model does not imply strict layering, while OSI model implies strict layering. c) In TCP/IP model, IP serves as the focal point for the architecture.d) TCP/IP model allows for arbitrarily many different network technologies , ranging fromEthernet to wireless to single point-to-point links.e) TCP/IP model emphasize implementations of proposed protocols. (2)Physical : bit, repeater or hubData link : frame, Ethernet switch or bridge Internet : packet, routerTransport : message, gateway[Question 2] Principles of network designSelect ONE of the following principles, tell its main ideas and provide an example. (1) Keep it simple and stupid(2) Complex edge and simple core (3) Smart sender and dumb receiverSolution:(1) KISS: Keep It Simple and StupidIt means that you should make things simple in the designing. One example following it : Ethernet(2) Complex edge and simple coreIt means that the hosts are very complex and have many functions while the nodes are very simple and have few functions.One example following it : The design of router, or the functions of TCP and IP(3) Smart sender and dumb receiverIt means that the function of sender is more complex than that of the receiver, which is help to improve the robustness and performance of communication protocol. One example following it: The flow control of TCP protocol[Question 3] Error detection(1) Tell the main idea of error detection and error correction in communication.(2) Given the CRC polynomial x 4 + x 3 + 1, if the original message is 10110011010, what is the CRC message to send?(3) Suppose the first bit of the message in (2) is inverted due to the noise in transmission. How can the receiver detect it via CRC verification?Solution:(1)1087431()M x x x x x x x =+++++, 43()1C x x x =++. So k=4.a) Multiply M(x) by 2kto get 141211875()T x x x x x x x =+++++,b) Then divide T(x) by C(x) to get the remainder 0000.c) The message that should be transmitted is 101100110100000.(2)The message received is 001100110100000.Divide it by C(x), then the remainder is 1100.So it is not divisible by C(x).So the receiver knows that an error has occurred.(1) What are the essential components to realize reliable transmission?(2) Suppose two computers are communicated via Stop-and-wait protocol. The link bandwidth is 5kbps, and the one-way propagation delay is 20ms. To reach 80% or higher link utilization, what is the minimal frame size for this communication?(3) If it is upgraded to Sliding-Window protocol. To reach the same goal with (2), what is the minimal window size, how many bits are required to describe the frame sequence in window? (Suppose the frame size is 1 or 100Byte)Solution:(1)ACK, and timerActual_throughput = Data / Total_DelayTotal_Delay = RTT + Data / BWLink_Utilization = 100 * Actual_throughput / BWSo: Data/throughput = RTT + Data/BW(BW/throughput - 1) Data = BW*RTTData = BW*RTT/(1/Utilization -1)For the stop-and-wait protocol, for each RTT only one frame is sent,Thus Frame_size = Data = BW*RTT/(1/Utilization - 1) = 5kbps * 40ms / (1/0.8 - 1)= 200 bit / 0.25 = 800 bit = 100 ByteIf the students ignore the data transmission delay, their answer isframe_size = BW*RTT*Utilization = 5000 bit/sec * 40 / 1000 sec * 0.8 = 160 bit = 20 ByteIn this case, at least -2 score.(3)For the sliding-window protocol, in each RTT the data window can be transmitted at most.Thus Window_size = Data = BW*RTT/(1/Utilization - 1) = 5kbps * 40ms / (1/0.8 - 1)= 200 bit / 0.25 = 800 bit = 100 ByteIf the frame size is 100Byte, 1 frames are allowed.To indicate the frames in both sides of sender and receiver, the sequence number should describe 2 frames, thus the [log2(2) ]=1 bitIf the students ignore the data transmission delay, their answer iswindow_size = BW*RTT*Utilization = 5000 bit/sec * 40 / 1000 sec * 0.8 = 160 bit = 20 ByteIf the frame size is 100Byte, 1 frames are allowed.To indicate the frames in both sides of sender and receiver, the sequence number should describe 2 frames, thus the [log2(2) ]=1 bitIn this case, at least -2 score.(1) What is the main idea of CSMA/CD (Carrier Sense Multiple Access/Collision Detection) in traditional Ethernet? Can it be deployed for wireless local network, why?(2) Suppose one traditional Ethernet has 1km cable, the signal propagation speed is 2*105km/s, and the transmission rate is designed to be 100Mbps. What is the minimal frame size to support carrier sensing?Solution:(1) the main idea of CSMA/CD include two parts. One is carrier sensing, which means the node should detect the channel before sending any data. If the node finds the channel is idle, it begins to transmit. Otherwise, the node stop for next round. The second issues is collision detection, which means the node should detect the channel in the duration of its data transmission. If the node finds the channel become busy, or in other word, there is a collision, it should stop transmitting immediately.CSMA/CD cannot be deployed in wireless LAN, because the wireless radio transmitter and receiver can not work in dual mode. The wireless node cannot detect collision when it is transmitting data.(2)the minimal frame should be transmitted throughout the whole traditional Ethernet.Thus t = frame_size / transmit_rate = 2 * cable_length / prop_speed.Frame_size = 100 * 106 bits/sec * 2 * 103 m / (2 * 108)m/sec = 1000 bits = 125 Byte[Question 6] Switched network(1) What are the differences between circuit switching and packet switching?(2) For the following linear topology network, each link has 2ms propagation delay and 4 Mbps bandwidth.A B C DIf we use circuit switching, circuit setup requires a 1KB message to make one round-trip on the path, which incurs a 1ms delay at each switch after the message has been completely received. Then we can send the file as one contiguous bit stream. What is the delay for circuit switching to transmit n-byte from A to D?(3) If we use packet switching in the network of (2), we can break the file into 1KB packets, which has 24byte header and 1000byte payload. The switch takes 1ms process delay after receiving the packet, and then sent it continuously. What is the condition for packet switching to have less delay performance than circuit switching?Solution:(1)(2)T pkt = Packet_Size / Bandwidth = 1 KB / 4Mbps = 1024 *8 / (4 * 106) = 2.048 ms T p = 2 ms, T s = 1 ms,T t = n B / 4MbpsIn circuit switching, Total time duration:D = Singling_Delay + Transmission_Delay = 2 * Packet_Duration + Transmission_Delay = 2 * (T pkt * 2 + T p * 3 + T s * 2 + T pkt ) + (T p * 3 + T t ) = T pkt * 6 + T p * 9 + T s * 4 + T tThus, D = 2.048 * 6 + 2 * 9 + 1 * 4 + n * 8 bits / 4Mbps = 34.288 (ms) + 2n (us)(3)Main ideaThe reliability provided by endhost The reliability provided by thenetwork Information in packet Every packet has its dest-addrin header Every packet has its temp VCIlocally Forwarding action inswitch Every packet was treatedindependentlyThe packets are processed inthe manner of VCPackets received indestinationNot in sequenceIn sequenceT pkt = Packet_Size / Bandwidth = 1 KB / 4Mbps = 1024 *8 / (4 * 106) = 2.048 msT p = 2 ms,T s = 1 ms,T t = 1.024 * n B / 4MbpsIn packet switching, Total time duration:D = Delay_at_Switch * Switch_Num + Delay_at_last_hop= (T p + T pkt +T s)*2 + (T p + T t )= T pkt * 2 + T p * 3 + T s * 2 + T tThus, D = 2.048 * 2 + 2 * 3 + 1 * 2 + 1.024 * n B / 4Mbps= 12.096 (ms) + 2.048 n (us)In order to make34.288 (ms) + 2n (us) > 12.096 (ms) + 2.048 n (us)Thus 22.192(ms) > 0.048 n(us)n < 22.192 * 1000 / 0.048 = 462333 Byte = 451.5 KB[Question 7] Ethernet Switch(1) What are the differences between hub and switch in Ethernet?(2) Suppose one server and nine clients are connected via hub in 10Mbps Ethernet, what is the maximal bandwidth for the client-server connection?(3) If the hub is upgraded to switch, can the client-server connection obtain more bandwidth? if can, how much is it?Solution:(1)hub works in Layer2, it works as the shared media and relays the frames to all the nodes connecting to hub. Switch works in Layer2, it forwards the frames to the specific node according to the destination address embedded in the frame header.(2)the max bandwidth in client-server connection is 10Mbps/(1+9)= 1Mbps(3)the max bandwidth in client-server connection is 10Mbps/9 = 1.1111MbpsAdditional 0.1111 Mbps is obtained for each connection.[Question 8] Router(1) Somebody says that, ``the only difference between switch and router is that they do switch function based on the address in different layers.’’ Is it correct? Why?(2) If we obtain the following information from one router. What kind of routing protocol does itSolution:(1)it is not fully correct. The part talking about the forwarding function is correct, while it is not the only difference. Another but not the last difference is that, router has more functions on control plane, which do routing and find the paths for packets.(2)The routing protocol is RIP.The routing table is:Destination Next hop Interface192.168.1.0/24 * Fa 0/4192.168.2.0/24 * Fa 0/6192.168.10.0/24 192.168.1.1 Fa 0/4192.168.30.0/24 192.168.2.2 Fa 0/6[Question 9] Routing algorithm(1) State the main differences between distance vector routing and link state routing.(2) For the network given in the following figure, provide the steps of forward search in Dijkstra algorithm for node A finding the shortest path to node ESolution:(1) The idea of distance vector routing is to tell the neighbors about the learned topology to all the nodes in the network. The idea of link state routing is to tell all the nodes in network about the neighborhood topology.Step 1 2 3 4 5 6 7 8 9Confirmed (A,0,-) (A,0,-) (A,0,-)(D,2,D)(A,0,-)(D,2,D)(A,0,-)(D,2,D)(B,4,D)(A,0,-)(D,2,D)(B,4,D)(A,0,-)(D,2,D)(B,4,D)(E,6,D)(A,0,-)(D,2,D)(B,4,D)(E,6,D)(A,0,-)(D,2,D)(B,4,D)(E,6,D)(C,7,D)Tentative (B,5,B)(D,2,D)(B,5,B) (B,4,D)(E,7,D)(E,7,D)(E,6,D)(C,8,D)(C,8,D) (C,7,D)A→E A→D→EA→D→B→EA→D→B→E[Question 10] IP address allocationA company has one C class IP address of 200.1.1.*. It has four departments.(1) If each department has less than 25 computers. Provide a kind of IP address allocation. Give the network address, subnet mask, and the available IP address range for each department. (2) If the four departments have 72, 35, 34, 20 computers respectively. Provide the IP address allocation scheme again.Solution:(1)Since each department has less than 25 computers, even considering the additional two more IP address for gateway and broadcast, the 64-computer subnet is enough for them.One IP address allocation scheme is to even divide the 256 IP addresses into 4 subnets, each subnet allows 64 hosts.Another IP address allocation scheme is to even divide the 256 IP addresses into 4 subnets, each subnet allows 32 hosts.(2) Since one of the department has more requirements than 64, then the even distribution scheme[Question 11] TCP protocol(1) Somebody says that, ``because of the reliable transmission service in layer 2, there is no need to provide such service again within TCP protocol in layer 4’’. Is it correct? Why?(2) State the main rules of TCP connection setup according to the following figure. Explain every word and number in the figure.Solution:(1) It is wrong. TCP is based on the un-reliable IP layer, which only provides best effort service. If TCP wants to provide reliable transmission service, it has to realize this by itself.(2)TCP use three hand-shakes to setup the connection.According to the figure, there are two nodes. The sender is with IP address of 192.168.1.163 and the receiver 192.168.1.165 respectively.●At first, the sender send a request ``SYN’’to the receiver to setup the connection. Thismessage is with the sequence number of 424CF1DC;●Secondly, the receiver reply an acknowledgment message ``SYN/ACK’’ to the sender. Thismessage has two sequence numbers. The seq in the ACK is 424CF1DD, which is to confirm the last ``SYN’’ from sender. The seq in the SYN is 30318555, which is a new message from the receiver.●Thirdly, the sender reply an acknowledgment message ``ACK’’ to the receiver. The seq in theACK is 30318556, which is to confirm the last ``SYN’’ from receiver.In the end, both the sender and receiver knows that the other side is ready for this TCP connection.[Question 12] TCP congestion control(1) Both flow control and congestion control in TCP are realized by window based packet control. How can TCP get the window sizes in these two mechanisms?(2) Assume that TCP implements an extension that allows window sizes much larger than 64 KB. Suppose that you are using this extended TCP over a 1Gbps link with a latency of 150ms. TCP packet size is 1KB, and the max receive window is 1 MB. Suppose there is no real congestion and packet loss in transmission. How many RTTs does it take until slow start opens the send window to 1 MB? How long does it take to send the complete file? ( Suppose file size is 10MB )Solution:(1) In flow control, TCP sender knows the window size by the field of advertise-window replied from the receiver. In congestion control, TCP sender learns the window size adaptively by AIMD( Additive Increase and Multiplicative Decrease) mechanism responding to the packet lossevent.(2)When TCP realizes congestion control mechanism, its effective send window size will be min (CongestionWindow, AdvertizedWindow). In original design of TCP header, the field of AdvertizedWindow is 16 bit, which is 216=26*210=64 KB. So the maximum effective window of original TCP sender is 64KB. The assumption of the first sentence in this question relaxes such constraint for TCP.In slow start, the send window starts from w0=1 packet, which is 1 KB. For each RTT after a successful transmission, the window size will be doubled. After i RTT, it will be 2i * w0. Let 2i * 1KB = 1MB, soi = log2(1MB/1KB) = log2(210) = 10.It will take 10 RTTs to reach 1MB send window.Case 1: if the receiver window remains as 1MBIn the first 10 RTTs, total (1 + 2 + 4 + … + 210) * 1KB has been transmitted.Which is (211 - 1) * 1KB = 2 MB - 1 KB, the rest file is 10MB - (2MB - 1KB) = 8MB + 1KBIn the reset transmission, each RTT can only support 1MB transmission.Thus, additional 9 RTTs are required. Total 19 RTT = 19 * 150ms = 2.85 sCase 2: if the receiver window can be changed.Since there is no congestion and loss, the maximum send window will be the bandwidth * delay for this TCP connection.w max= 1G bps * 150ms = 109 * 150 * 10-3= 150 *106 bit = 18.75 * 106 byte = 17.88 MB.So, this 10 MB file can be transferred before reaching w max. In another word, it can be sent in its slow start phase. Assume x RTT is required to send this file, then:(1 + 2 + 4 + … + 2x) * 1KB ≥ 10 MB2 * 2x–1 ≥ 10 * 1024x ≥ log2(10241) – 1 = 12.3Thus x = 13, it will take 13 RTTs to transfer this file. 13RTT = = sTotal delay = 13RTT + Filesize/BW = 13 * 150ms+ 10MB / 1Gbps =1.95 + 0.08 * 1.024^2=2.03 s11。

Chapter 1 Computer Networks and the Internet1．The ( ) is a worldwide computernetwork, that is, a network that interconnectsmillionsofcomputing devices throughout theworld. ppt3 A public InternetB IntranetC switch netD television net2．Which kind of media is not a guidedmedia ( )A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channel3．Which kind of media is a guided media ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN4．The units of data exchanged by a link-layer protocol are called ( ).A FramesB SegmentsC DatagramsD bit streams5．Which of the following optionbelongs to the circuit-switchednetworks ( )A FDMB TDMC VCnetworksD both A and B 6．( )makes sure that neither sideof a connection overwhelms theother side by sending too manypackets too fast.A Reliable data transferB Flow controlC Congestion controlD Handshaking procedure7．( ) means that the switch mustreceive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM8．Datagramnetworksandvirtual-circuit networks differ in that ( ).A datagram networks are circuit-switched networks, and virtual-circuit networks are packet-switched networks.B datagram networks are packet-switched networks, and virtual-circuit networks are circuit-switched networks.C datagram networks use destination addresses and virtual-circuit networks use VC. numbers to forward packets toward their destination.D datagram networks use VC. numbers and virtual-circuit networks use destination addresses to forward packetstoward their destination.9．In the following options, which one is not a guided media ( )A twisted-pairwireB fiber opticsC coaxial cableD satellite10．Processing delay does not include the time to ( ).A examine the packet ’s headerB wait to transmit the packet onto the linkC determine where to direct thepacketD check bit-error in the packet 11．In the following four descriptions, which one is correct ( )A The traffic intensity must begreater than 1.B The fraction of lost packetsincreases as the trafficintensity decreases.C If the traffic intensity isclose to zero, the averagequeuing delay will be close tozero.D If the traffic intensity isclose to one, the averagequeuing delay will be close toone.12．The Internet’s network layer is responsible for movingnetwork-layer packets known as( ) from one host to another.A frameB datagramC segmentD message13．The protocols of various layersare called ( ).A the protocol stackB TCP/IPC ISPD network protocol14．There are two classes ofpacket-switched networks: ( )networks and virtual-circuitnetworks.A datagramB circuit-switchedC televisionD telephone15．Access networks can be looselyclassified into threecategories: residential access,company access and ( ) access.A cabledB wirelessC campusD city areaQuestion 16～17Suppose, a is the average rate at which packets arrive at the queue,R is the transmission rate, and all packets consist of L bits, then thetraffic intensity is ( 16 ), and it should no greater than ( 17 ).16． A LR ／aB La ／RC Ra ／LD LR ／a 17．A 2B 1C 0D -118．In the Internet, the equivalentconcept to end systems is ( ).A hostsB serversC clientsD routers19．In the Internet, end systems are connected together by ( ).A copper wireB coaxial cableC communication linksD fiber optics 20．End systems access to the Internet through its ( ). A modemsB protocolsC ISPD sockets21．End systems, packet switches,and other pieces of the Internet, run ( ) that control thesending and receiving ofinformation within theInternet.A programsB processesC applicationsD protocols22．There are many private networks,such as many corporate andgovernment networks, whosehosts cannot exchange messages with hosts outside of the private network. These private networks are often referred to as ( ).A internetsB LANC intranetsD WAN23．The internet allows ( ) runningon its end systems to exchangedata with each other.A clients applicationsB server applicationsC P2P applicationsD distributed applications24．The Internet provides two services to its distributed applications: a connectionlessunreliable service and ()service.A flowcontrolB connection-oriented reliableC congestion controlD TCP25．It defines the format and theorder of messages exchangedbetween two or morecommunicating entities, as wellas the actions taken on thetransmission and/or receipt ofa message or other event. Thesentence describes ( ).A InternetB protocolC intranetD network26．In the following options, which does not define in protocol ( )A the format of messagesexchanged between two or morecommunicating entitiesB the order of messagesexchanged between two or morecommunicating entitiesC the actions taken on thetransmission of a message orother eventD the transmission signals aredigital signals or analogsignals27．In the following options, which is defined in protocol ( )A the actions taken on thetransmission and/or receiptof a message or other event B the objects exchanged between communicating entities C the content in the exchangedmessagesD the location of the hosts28．In the following options, whichdoes not belong to the network edge( )A end systemsB routersC clientsD servers29．In the following options, whichbelongs to the network core ( )A end systemsB routersC clientsD servers30．In the following options, whichis not the bundled with theInternet’sconnection-oriented service( )A reliable data transferB guarantee of thetransmission timeC flow controlD congestion-control31．An application can rely on theconnection to deliver all of itsdata without error and in theproper order. The sentencedescribes ( ). A flow controlB congestion-controlC reliable datatransferD connection-oriented service 32．It makes sure that neither sideof a connection overwhelms theother side by sending too manypackets too fast. The sentence describes ( ). A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer33．It helps prevent the Internetfrom entering a state of gridlock. When a packet switchbecomes congested, its bufferscan overflow and packet loss canoccur. The sentence describes( ).A flowcontrolB congestion-controlC connection-oriented serviceD reliable data transfer 34．TheInternet ’sconnection-oriented service has aname, it is ( ).A TCPB UDPC TCP/IPD IP35．In the following options, which service does not be provided to an application by TCP( )A reliable transportB flow controlC video conferencingD congestion control36．The Internet ’s connectionless service is called ( ).A TCPB UDPC TCP/IPD IP37．In the following options, which does not use TCP( )A SMTPB internet telephoneC FTPD HTTP38．In the following options, which does not use UDP( )A InternetphoneB video conferencingC streamingmultimediaD telnet39．There are two fundamentalapproaches to building a network core, ( ) and packet switching.A electrical current switchingB circuit switchingC data switchingD message switching40．In ( ) networks, the resourcesneeded along a path to provide for communication between the end system are reserved for theduration of the communicationsession.A packet-switchedB data-switchedC circuit-switchedD message-switched41．In ( ) networks, the resources are not reserved; a session’smessages use the resources ondemand, and as a consequence,may have to wait for access tocommunication link.A packet-switchedB data-switchedC circuit-switchedD message-switched42．In a circuit-switched network, if each link has n circuits, foreach link used by the end-to-endconnection, the connection gets( ) of the link’s bandwidthfor the duration of the connection.A a fraction 1/nB allC 1/2D n times43．For ( ), the transmission rateof a circuit is equal to theframe rate multiplied by thenumber of bits in a slot.A CDMAB packet-switched networkC TDMD FDM44．( ) means that the switch mustreceive the entire packetbefore it can begin to transmitthe first bit of the packet ontothe outbound link.A Queuing delayB Store-and-forwardtransmissionC Packet lossD Propagation45．The network that forwardspackets according to host destination addresses is called( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram46．The network that forwardspackets according tovirtual-circuit numbers iscalled ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram47．In the following entries, whichis not a kind of access network( )A residentialaccessB company accessC wirelessaccessD local access48．Suppose there is exactly onepacket switch between a sendinghost and a receiving host. The transmission rates between thesending host and the switch and between the switch and the receiving host are R 1 and R 2,respectively. Assuming that theswitch uses store-and-forwardpacket switching, what is thetotal end-to-end delay to senda packet of length L (Ignorequeuing delay, propagationdelay, and processing delay.) ( ) A L /R 1＋L /R 2B L /R 1C L /R 2D none of the above49．The time required to examine thepacket ’s header and determinewhere to direct the packet ispart of the ( ). A queuing delayB processing delayC propagation delayD transmission delay50．The time required to propagatefrom the beginning of the linkto the next router is ( ). A queuing delayB processing delayC propagation delayD transmission delay51．Consider sending a packet of3000bits over a path of 5 links. Eachlink transmits at 1000bps. Queuingdelays, propagation delay and processing delay are negligible. (6 points)(1).Suppose the network is apacket-switched virtual circuitnetwork. VC setup time is seconds.Suppose the sending layers add atotal of 500 bits of header to eachpacket. How long does it take to sendthe file from source to destination(2).Suppose the network is a packet-switched datagram networkand a connectionless service is used.Now suppose each packet has 200 bitsof header. How long does it take tosend the file(3).Suppose that the network is acircuit-switched network. Furthersuppose that the transmission rate of the circuit between source anddestination is 200bps. Assumingsetup time and 200 bits of header appended to the packet, how longdoes it take to send the packetS olution:(1).t=5*(3000+500)/1000+=( 2).t=5*(3000+200)/1000=16s( 3).t=(3000+200)/200+=。

Chapter 1 Computer Networks and the Internet1．The ( ) is a worldwide computer network, that is, a network that interconnects millions of computing devices throughout the world.ppt3A public InternetB IntranetC switch netD television net2．Which kind of media is not a guided media? ( )A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channel3．Which kind of media is a guided media? ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN4．The units of data exchanged by a link-layer protocol are called ( ).A FramesB SegmentsC DatagramsD bit streams5．Which of the following option belongs to the circuit-switched networks? ( )A FDMB TDMC VC networksD both A and B6．( )makes sure that neither side of a connection overwhelms the other side by sending too many packets too fast.A Reliable data transferB Flow controlC Congestion controlD Handshaking procedure7．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM8．Datagram networks and virtual-circuit networks differ in that ( ).A datagram networks are circuit-switched networks, andvirtual-circuit networks are packet-switched networks.B datagram networks are packet-switched networks, andvirtual-circuit networks are circuit-switched networks.C datagram networks use destination addresses and virtual-circuitnetworks use VC. numbers to forward packets toward theirdestination.D datagram networks use VC. numbers and virtual-circuit networksuse destination addresses to forward packets toward their destination. 9．In the following options, which one is not a guided media? ( )A twisted-pair wireB fiber opticsC coaxial cableD satellite10．Processing delay does not include the time to ( ).A examine the packet’s headerB wait to transmit the packet onto the linkC determine where to direct the packetD check bit-error in the packet11．In the following four descriptions, which one is correct? ( )A The traffic intensity must be greater than 1.B The fraction of lost packets increases as the traffic intensitydecreases.C If the traffic intensity is close to zero, the average queuing delaywill be close to zero.D If the traffic intensity is close to one, the average queuing delaywill be close to one.12．The Internet’s network layer is responsible for moving network-layer packets known as ( ) from one host to another.A frameB datagramC segmentD message13．The protocols of various layers are called ( ).A the protocol stackB TCP/IPC ISPD network protocol14．There are two classes of packet-switched networks: ( ) networks and virtual-circuit networks.A datagramB circuit-switchedC televisionD telephone15．Access networks can be loosely classified into three categories: residential access, company access and ( ) access.A cabledB wirelessC campusD city areaQuestion 16～17Suppose, a is the average rate at which packets arrive at the queue, R is the transmission rate, and all packets consist of L bits, then the traffic intensity is ( 16 ), and it should no greater than ( 17 ).16． A LR／aB La／RC Ra／LD LR／a17．A 2B 1C 0D -118．In the Internet, the equivalent concept to end systems is ( ).A hostsB serversC clientsD routers19．In the Internet, end systems are connected together by ( ).A copper wireB coaxial cableC communication linksD fiber optics20．End systems access to the Internet through its ( ).A modemsB protocolsC ISPD sockets21．End systems, packet switches, and other pieces of the Internet, run ( ) that control the sending and receiving of information within theInternet.A programsB processesC applicationsD protocols22．There are many private networks, such as many corporate and government networks, whose hosts cannot exchange messages withhosts outside of the private network. These private networks are often referred to as ( ).A internetsB LANC intranetsD WAN23．The internet allows ( ) running on its end systems to exchange data with each other.A clients applicationsB server applicationsC P2P applicationsD distributed applications24．The Internet provides two services to its distributed applications: a connectionless unreliable service and () service.A flow controlB connection-oriented reliableC congestion controlD TCP25．It defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on thetransmission and/or receipt of a message or other event. The sentence describes ( ).A InternetB protocolC intranetD network26．In the following options, which does not define in protocol? ( )A the format of messages exchanged between two or morecommunicating entitiesB the order of messages exchanged between two or morecommunicating entitiesC the actions taken on the transmission of a message or other eventD the transmission signals are digital signals or analog signals 27．In the following options, which is defined in protocol? ( )A the actions taken on the transmission and/or receipt of a message orother eventB the objects exchanged between communicating entitiesC the content in the exchanged messagesD the location of the hosts28．In the following options, which does not belong to the network edge? ( )A end systemsB routersC clientsD servers29．In the following options, which belongs to the network core? ( )A end systemsB routersC clientsD servers30．In the following options, which is not the bundled with the Internet’s connection-oriented service? ( )A reliable data transferB guarantee of the transmission timeC flow controlD congestion-control31．An application can rely on the connection to deliver all of its data without error and in the proper order. The sentence describes ( ).A flow controlB congestion-controlC reliable data transferD connection-oriented service32．It makes sure that neither side of a connection overwhelms the other side by sending too many packets too fast. The sentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer33．It helps prevent the Internet from entering a state of gridlock. When a packet switch becomes congested, its buffers can overflow and packet loss can occur. The sentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer34．The Internet’s connection-oriented service has a name, it is ( ).A TCPB UDPC TCP/IPD IP35．In the following options, which service does not be provided to an application by TCP?( )A reliable transportB flow controlC video conferencingD congestion control36．The Internet’s connectionless service is called ( ).A TCPB UDPC TCP/IPD IP37．In the following options, which does not use TCP?( )A SMTPB internet telephoneC FTPD HTTP 38．In the following options, which does not use UDP?( )A Internet phoneB video conferencingC streaming multimediaD telnet39．There are two fundamental approaches to building a network core, ( ) and packet switching.A electrical current switchingB circuit switchingC data switchingD message switching40．In ( ) networks, the resources needed along a path to provide for communication between the end system are reserved for the duration of the communication session.A packet-switchedB data-switchedC circuit-switchedD message-switched41．In ( ) networks, the resources are not reserved; a session’s messages use the resources on demand, and as a consequence, may have to wait for access to communication link.A packet-switchedB data-switchedC circuit-switchedD message-switched42．In a circuit-switched network, if each link has n circuits, for each link used by the end-to-end connection, the connection gets ( ) of thelink’s bandwidth for the duration of the connection.A a fraction 1/nB allC 1/2D n times43．For ( ), the transmission rate of a circuit is equal to the frame rate multiplied by the number of bits in a slot.A CDMAB packet-switched networkC TDMD FDM44．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Queuing delayB Store-and-forward transmissionC Packet lossD Propagation45．The network that forwards packets according to host destination addresses is called ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram46．The network that forwards packets according to virtual-circuit numbers is called ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram47．In the following entries, which is not a kind of access network?( )A residential accessB company accessC wireless accessD local access48．Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are R1 and R2,respectively. Assuming that the switch uses store-and-forward packetswitching, what is the total end-to-end delay to send a packet of length L? (Ignore queuing delay, propagation delay, and processing delay.)( )A L/R1＋L/R2B L/R1C L/R2D none of the above49．The time required to examine the packet’s header and determine where to direct the packet is part of the ( ).A queuing delayB processing delayC propagation delayD transmission delay50．The time required to propagate from the beginning of the link to the next router is ( ).A queuing delayB processing delayC propagation delayD transmission delay51．Consider sending a packet of 3000bits over a path of 5 links. Each link transmits at 1000bps. Queuing delays, propagation delay and processing delay are negligible. (6 points)(1).Suppose the network is a packet-switched virtual circuit network. VC setup time is 0.1 seconds. Suppose the sending layers add a total of 500 bits of header to each packet. How long does it take to send the file from source to destination?(2).Suppose the network is a packet-switched datagram network and a connectionless service is used. Now suppose each packet has 200 bits of header. How long does it take to send the file?(3).Suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between source and destination is 200bps. Assuming 0.02s setup time and 200 bits of header appended to the packet, how long does it take to send the packet?Solution: (1). t=5*(3000+500)/1 000+0.1=17.6s(2). t=5*(3000+200)/1 000=16s(3). t=(3000+200)/200+0.02=16.02s 相对压力一般指表压，是测量系统相对于大气压的压力值。

计算机网络英文题库附答案c h a p t e r精编W O R D版IBM system office room 【A0816H-A0912AAAHH-GX8Q8-GNTHHJ8】Chapter 1 Computer Networks and the Internet 1．The ( ) is a worldwide computer network, that is, a network that interconnects millions of computing devices throughout the world.ppt3A public InternetB IntranetC switch netD television net2．Which kind of media is not a guided media ( )A twisted-pair copper wireB a coaxial cableC fiber opticsD digital satellite channel3．Which kind of media is a guided media ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN4．The units of data exchanged by a link-layer protocol are called ( ).A FramesB SegmentsC DatagramsD bit streams5．Which of the following option belongs to the circuit-switched networks ( )A FDMB TDMC VC networksD both A and B6．( )makes sure that neither side of aconnection overwhelms the other side bysending too many packets too fast.A Reliable data transferB Flow controlC Congestion controlD Handshaking procedure7．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link.A Store-and-forward transmissionB FDMC End-to-end connectionD TDM8．Datagram networks and virtual-circuit networks differ in that ( ).A datagram networks are circuit-switchednetworks, and virtual-circuit networks arepacket-switched networks.B datagram networks are packet-switchednetworks, and virtual-circuit networks arecircuit-switched networks.C datagram networks use destinationaddresses and virtual-circuit networks useVC. numbers to forward packets towardtheir destination.D datagram networks use VC. numbersand virtual-circuit networks use destinationaddresses to forward packets toward theirdestination.9．In the following options, which one is not a guided media ( )A twisted-pair wireB fiber opticsC coaxial cableD satellite10．Processing delay does not include the time to ( ).A examine the packet’s headerB wait to transmit the packet onto the linkC determine where to direct the packetD check bit-error in the packet11．In the following four descriptions, which one is correct ( )A The traffic intensity must be greaterthan 1.B The fraction of lost packets increases asthe traffic intensity decreases.C If the traffic intensity is close to zero,the average queuing delay will be close tozero.D If the traffic intensity is close to one, theaverage queuing delay will be close to one.12．The Internet’s network layer isresponsible for moving network-layerpackets known as ( ) from one host toanother.A frameB datagramC segmentD message13．The protocols of various layers are called ( ).A the protocol stackB TCP/IPC ISPD network protocol14．There are two classes of packet-switched networks: ( ) networks and virtual-circuitnetworks.A datagramB circuit-switchedC televisionD telephone15．Access networks can be loosely classified into three categories: residential access,company access and ( ) access.A cabledB wirelessC campusD city areaQuestion 16～17Suppose, a is the average rate at which packets arrive at the queue, R is the transmission rate, and all packets consist of L bits, then the traffic intensity is ( 16 ), and it should no greater than ( 17 ).16．A LR／aB La／RC Ra／LD LR／a 17．A 2B 1C 0D -118．In the Internet, the equivalent concept to end systems is ( ).A hostsB serversC clientsD routers19．In the Internet, end systems are connected together by ( ).A copper wireB coaxial cableC communication linksD fiber optics20．End systems access to the Internet through its ( ).A modemsB protocolsC ISPD sockets21．End systems, packet switches, and other pieces of the Internet, run ( ) that controlthe sending and receiving of informationwithin the Internet.A programsB processesC applicationsD protocols22．There are many private networks, such as many corporate and government networks,whose hosts cannot exchange messageswith hosts outside of the private network.These private networks are often referredto as ( ).A internetsB LANC intranetsD WAN23．The internet allows ( ) running on its end systems to exchange data with each other.A clients applicationsB server applicationsC P2P applicationsD distributed applications24．The Internet provides two services to its distributed applications: a connectionlessunreliable service and () service.A flow controlB connection-oriented reliableC congestion controlD TCP25．It defines the format and the order of messages exchanged between two or morecommunicating entities, as well as theactions taken on the transmission and/orreceipt of a message or other event. Thesentence describes ( ).A InternetB protocolC intranetD network26．In the following options, which does not define in protocol ( )A the format of messages exchangedbetween two or more communicatingentitiesB the order of messages exchangedbetween two or more communicatingentitiesC the actions taken on the transmission ofa message or other eventD the transmission signals are digitalsignals or analog signals27．In the following options, which is defined in protocol ( )A the actions taken on the transmissionand/or receipt of a message or othereventB the objects exchanged between communicating entitiesC the content in the exchanged messagesD the location of the hosts28．In the following options, which does not belong to the network edge ( )A end systemsB routersC clientsD servers29．In the following options, which belongs to the network core ( )A end systemsB routersC clientsD servers30．In the following options, which is not the bundled with the Internet’s connection-oriented service( )A reliable data transferB guarantee of the transmission timeC flow controlD congestion-control31．An application can rely on the connection to deliver all of its data without error andin the proper order. The sentencedescribes ( ).A flow controlB congestion-controlC reliable data transferD connection-oriented service32．It makes sure that neither side of aconnection overwhelms the other side bysending too many packets too fast. Thesentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer33．It helps prevent the Internet from enteringa state of gridlock. When a packet switchbecomes congested, its buffers canoverflow and packet loss can occur. Thesentence describes ( ).A flow controlB congestion-controlC connection-oriented serviceD reliable data transfer34．The Internet’s connection-oriented service has a name, it is ( ).A TCPB UDPC TCP/IPD IP 35．In the following options, which service does not be provided to an application by TCP( )A reliable transportB flow controlC video conferencingD congestion control36．The Internet’s connectionless service is called ( ).A TCPB UDPC TCP/IPD IP37．In the following options, which does not use TCP()A SMTPB internet telephoneC FTPD HTTP38．In the following options, which does not use UDP( )A Internet phoneB video conferencingC streaming multimediaD telnet39．There are two fundamental approaches to building a network core, ( ) and packetswitching.A electrical current switchingB circuit switchingC data switchingD message switching40．In ( ) networks, the resources needed along a path to provide forcommunication between the end systemare reserved for the duration of thecommunication session.A packet-switchedB data-switchedC circuit-switchedD message-switched41．In ( ) networks, the resources are not reserved; a session’s messages use theresources on demand, and as aconsequence, may have to wait for accessto communication link.A packet-switchedB data-switchedC circuit-switchedD message-switched42．In a circuit-switched network, if each link has n circuits, for each link used by theend-to-end connection, the connectiongets ( ) of the link’s bandwidth for theduration of the connection.A a fraction 1/nB allC 1/2D n times43．For ( ), the transmission rate of a circuit is equal to the frame rate multiplied by thenumber of bits in a slot.A CDMAB packet-switched networkC TDMD FDM 44．( ) means that the switch must receive the entire packet before it can begin totransmit the first bit of the packet onto theoutbound link.A Queuing delayB Store-and-forward transmissionC Packet lossD Propagation45．The network that forwards packetsaccording to host destination addresses iscalled ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram46．The network that forwards packetsaccording to virtual-circuit numbers iscalled ( ) network.A circuit-switchedB packet-switchedC virtual-circuitD datagram47．In the following entries, which is not a kind of access network()A residential accessB company accessC wireless accessD local access48．Suppose there is exactly one packet switch between a sending host and a receivinghost. The transmission rates between thesending host and the switch and betweenthe switch and the receiving host are R1and R2, respectively. Assuming that theswitch uses store-and-forward packetswitching, what is the total end-to-enddelay to send a packet of length L (Ignorequeuing delay, propagation delay, andprocessing delay.) ( )A L/R1＋L/R2B L/R1C L/R2D none of the above49．The time required to examine thepacket’s header and determine where todirect the packet is part of the ( ).A queuing delayB processing delayC propagation delayD transmission delay50．The time required to propagate from the beginning of the link to the next router is( ).A queuing delayB processing delayC propagation delayD transmission delay51．Consider sending a packet of 3000bits over a path of 5 links. Each link transmits at 1000bps. Queuing delays, propagation delay and processing delay are negligible. (6 points) (1).Suppose the network is a packet-switched virtual circuit network. VC setup time is 0.1 seconds. Suppose the sending layers add a total of 500 bits of header to each packet. How long does it take to send the file from source to destination?(2).Suppose the network is a packet-switched datagram network and a connectionless serviceis used. Now suppose each packet has 200 bitsof header. How long does it take to send the file?(3).Suppose that the network is a circuit-switched network. Further suppose that the transmission rate of the circuit between sourceand destination is 200bps. Assuming 0.02s setuptime and 200 bits of header appended to the packet, how long does it take to send the packet?So lution:(1).t=5*(3000+500)/1000+0.1=17.6s( 2).t=5*(3000+200)/1000=16s( 3).t=(3000+200)/200+0.02=16.02s。

计算机网络第四版(课后练习+答案)计算机网络第四版(课后练习+答案)Introduction:计算机网络是现代信息技术的基础，它涉及到计算机与计算机之间如何进行数据交换和通信。

《计算机网络第四版》是一本权威指南，提供了大量的课后练习和答案，帮助读者加强对计算机网络的理解。

本文将对《计算机网络第四版》课后练习和答案进行综述，以便读者更好地掌握网络通信的关键概念和原理。

Chapter 1: Introduction to Networking在第一章中，课后练习的内容涵盖了计算机网络的基本概念和发展历程。

学习者可以通过这些练习加深对网络通信的了解，例如描述计算机网络的基本组成部分、定义OSI模型的七层结构以及解释分组交换和电路交换的区别。

Chapter 2: Network Models第二章课后练习着重介绍了计算机网络的各种模型，包括OSI模型和TCP/IP模型。

练习题目涵盖了每个模型的层次结构和功能，同时还要求学习者能够比较这两个模型之间的异同点。

Chapter 3: Physical Layer and Media物理层和传输介质是计算机网络的基础，第三章课后练习起到了巩固和扩展这些概念的作用。

学习者将通过回答问题和解决实际情况的案例，深入理解诸如数据信号的调制和解调、传输介质的特性以及常见的物理层设备等内容。

Chapter 4: Data Link Layer数据链路层构建在物理层之上，并处理节点到节点之间的数据传输。

第四章的课后练习要求学习者熟练掌握数据链路层的基本概念，包括帧的封装和解封装、错误检测和纠正技术以及介绍局域网和广域网等。

Chapter 5: Network Layer网络层负责数据包的转发和路由选择，在第五章的练习题中，学习者需要回答关于IP地址的分配和路由表的设计的问题，深入理解网络层的功能和特性。

还会涉及到IP协议的各种细节，例如子网划分、地址转换和网络控制协议等。

Chapter 6: Transport Layer传输层提供端到端的可靠数据传输服务，第六章的课后练习通过设计案例和讨论问题的方式，帮助学习者掌握TCP和UDP协议的细节和应用场景。

第一章(1.2 1.3节)5.Calculate the total time required to transfer a 1,000-KB file in the following cases, assuming an RTT of 100 ms, a packet size of 1-KB data, and an initial 2 ×RTT of “handshaking” before data is sent.(a) The bandwidth is 1.5 Mbps, and data packets can be sent continuously.(b) The bandwidth is 1.5 Mbps, but after we finish sending each data packetwe must wait one RTT before sending the next.(c) The bandwidth is “infinite,”meaning that we take transmit time to bezero, and up to 20 packets can be sent per RTT.(d) The bandwidth is infinite, and during the first RTT we can send onepacket (21−1), during the second RTT we can send two packets (22−1),during the third we can send four (23−1), and so on. (A justification forsuch an exponential increase will be given in Chapter 6.)7. Consider a point-to-point link 2 km in length. At what bandwidth would propagation delay (at a speed of 2 × 108m/sec) equal transmit delay for 100-byte packets? What about 512-byte packets?13.How “wide” is a bit on a 1-Gbps link? How long is a bit in copper wire, where the speed of propagation is 2.3 × 108 m/s?15.Suppose a 100-Mbps point-to-point link is being set up between Earth and a new lunar colony. The distance from the moon to Earth is approximately 385,000 km, and data travels over the link at the speed of light—3 × 108 m/s.(a) Calculate the minimum RTT for the link.(b) Using the RTT as the delay, calculate the delay × bandwidth product forthe link.(c) What is the significance of he delay × bandwidth product computedin (b)?(d) A camera on the lunar base takes pictures of Earth and saves them in digitalformat to disk. Suppose Mission Control on Earth wishes to download themost current image, which is 25 MB. What is the minimum amount of time that will elapse between when the request for the data goes out andthe transfer is finished?18. Calculate the latency (from first bit sent to last bit received) for the following:(a) A 10-Mbps Ethernet with a single store-and-forward switch in the path,and a packet size of 5,000 bits. Assume that each link introduces a propaga-tion delay of 10 µs, and that the switch begins retransmitting immediatelyafter it has finished receiving the packet.(b) Same as (a) but with three switches.(c) Same as (a) but assume the switch implements “cut-through”switching: itis able to begin retransmitting the packet after the first 200 bits have beenreceived.第二章（除2.7 2.9 节）1.Show the NRZ, Manchester, and NRZI encodings for the bit pattern shown in Figure2.46. Assume that the NRZI signal starts out low.23.Consider an ARQ algorithm running over a 20-km point-to-point fiber link.(a) Compute the propagation delay for this link, assuming that the speed oflight is 2 × 108 m/s in the fiber.(b) Suggest a suitable timeout value for the ARQ algorithm to use.(c) Why might it still be possible for the ARQ algorithm to time out andretransmit a frame, given this timeout value?26.The text suggests that the sliding window protocol can be used to implement flow control. We can imagine doing this by having the receiver delay ACKs, that is, not send the ACK until there is free buffer space to hold the next frame. In doing so, each ACK would simultaneously acknowledge the receipt of the last frame and tell the source that there is now free buffer space available to hold the next frame. Explain why implementing flow control in this way is not a good idea.44.Let A and B be two stations attempting to transmit on an Ethernet. Each has steady queue of frames ready to send; A’s frames will be numbered A 1, A2 , and so on, and B’s similarly. Let T = 51.2 µs be the exponential backoff base unit. SupposeA andB simultaneously attempt to send frame 1, collide, and happen to choose backoff times of 0 × T and 1 × T, respectively, meaning A wins the race and transmits A 1 while B waits. At the end of this transmission, B will attempt to retransmit B1 while A will attempt to transmit A2 . These first attempts will collide, but now A backs off for either 0 × T or 1 × T, while B backs off for time equal to one of 0 × T, . . . , 3 × T.(a) Give the probability that A wins this second backoff race immediately after this firstcollision , that is, A’s first choice of backoff time k × 51.2 is less than B’s.(b) Suppose A wins this second backoff race. A transmits A 3 , and when it isfinished, A and B collide again as A tries to transmit A4 and B tries once more to transmit B1. Give the probability that A wins this third backoff race immediately after the first collision.(c) Give a reasonable lower bound for the probability that A wins all the re- maining backoff races.(d) What then happens to the frame B1?This scenario is known as the Ethernet capture effect.48. Repeat the previous exercise, now with the assumption that Ethernet is p -persistent with p = 0.33 (that is, a waiting station transmits immediately with probability p when the line goes idle, and otherwise defers one 51.2-µs slot time and repeats the process). Your timeline should meet criterion (1) of the previous problem, but in lieu of criterion (2), you should show at least one collision and at least one run of four deferrals on an idle line. Again, note that many solutions are possible.第三章（3.1 3.2节）ing the example network given in Figure 3.30, give the virtual circuit tables for all the switches after each of the following connections is established. Assume that the sequence of connections is cumulative, that is, the first connection is still up when the second connection is established, and so on. Also assume that the VCI assignment always picks the lowest unused VCI on each link, starting with 0.(a) Host A connects to host B.(b) Host C connects to host G.(c) Host E connects to host I.(d) Host D connects to host B.(e) Host F connects to host J.(f) Host H connects to host A.3.For the network given in Figure 3.31, give the datagram forwarding table for each node. The links are labeled with relative costs; your tables should forward each packet via the lowest-cost path to its destination.5. Consider the virtual circuit switches in Figure 3.33. Table 3.6 lists, for each switch, what port, VCI (or VCI, interface) pairs are connected to other. Connections are bidirectional. List all endpoint-to-endpoint connections.13. Given the extended LAN shown in Figure 3.34, indicate which ports are not selected by the spanning tree algorithm.15. Consider the arrangement of learning bridges shown in Figure 3.35. Assuming all are initially empty, give the forwarding tables for each of the bridges B1–B4 after the following transmissions:■ A sends to C.■ C sends to A.■ D sends to C.Identify ports with the unique neighbor reached directly from that port, thatis, the ports for B1 are to be labeled “A” and “B2.”17.Consider hosts X, Y, Z, W and learning bridges B1, B2, B3, with initially empty forwarding tables, as in Figure 3.36.(a) Suppose X sends to Z. Which bridges learn where X is? Does Y’s networkinterface see this packet?(b) Suppose Z now sends to X. Which bridges learn where Z is? Does Y’s network interface see this packet?(c) Suppose Y now sends to X. Which bridges learn where Y is? Does Z’s net-work interface see this packet?(d) Finally, suppose Z sends to Y. Which bridges learn where Z is? Does W’snetwork interface see this packet?第四章（4.1 4.2 4.3.1 4.3.5 4.5 节）4.Suppose a TCP message that contains 2,048 bytes of data and 20 bytes of TCP header is passed to IP for delivery across two networks of the Internet (i.e., from the source host to a router to the destination host). The first network uses 14-byte headers and has an MTU of 1,024 bytes; the second uses 8-byte headers with an MTU of 512 bytes. Each network’s MTU gives the size of the largest IP datagram that can be carried in a link layer frame. Give the sizes and offsets of the sequence of fragments delivered to the network layer at the destination host. Assume all IP headers are 20 bytes.21.Suppose a router has built up the routing table shown in Table 4.14. The router can deliver packets directly over interfaces 0 and 1, or it can forward packets to routers R2, R3, or R4. Describe what the router does with a packet addressed to each of the following destinations:(a) 128.96.39.10.(b) 128.96.40.12.(c) 128.96.40.151.(d) 192.4.153.17.(e) 192.4.153.90.45.Table 4.16 is a routing table using CIDR. Address bytes are in hexadecimal. The notation “/12” in C4.50.0.0/12 denotes a netmask with 12 leading 1 bits, that is, FF.F0.0.0. Note that the last three entries cover every address and thus serve in lieu of a default route. State to what next hop the following will be delivered.(a) C4.5E.13.87.(b) C4.5E.22.09.(c) C3.41.80.02.(d) 5E.43.91.12.(e) C4.6D.31.2E.(f) C4.6B.31.2E.第五章（5.1 5.2节）10. You are hired to design a reliable byte-stream protocol that uses a sliding window (like TCP). This protocol will run over a 1-Gbps network. The RTT of the network is 140 ms, and the maximum segment lifetime is 60 seconds. How many bits would you include in the AdvertisedWindow and SequenceNum fields of your protocol header?第六章（6.5节）第九章（9.1节）。

计算机网络英文复习题1、请简述英文“network”是什么含义？并举出一个具体的网络应用实例。

“Network”的英文意思是网络。

网络是由多个节点（nodes）通过各种协议（protocols）进行连接，以实现信息的交换和共享的一种系统。

网络应用实例包括：电子邮件（Email）、万维网（World Wide Web）、文件传输（FTP）、远程登录（Telnet）等。

2、什么是局域网（Local Area Network，LAN）？请举例说明。

局域网（LAN）是一种在有限区域内（如一座大楼、一个校园或一个工厂等）连接计算机和其他设备的高速网络。

例如，家庭网络、办公室网络和校园网络等都是局域网的例子。

3、什么是广域网（Wide Area Network，WAN）？请举例说明。

广域网（WAN）是一种跨越较大地理范围的网络，通常由多个局域网组成，并通过各种传输媒介（如光纤、卫星等）连接在一起。

例如，因特网（Internet）就是一种广域网的例子。

4、请简述TCP/IP协议是什么？并列举其中两个主要的协议。

TCP/IP协议是一种在网络通信中广泛使用的协议套件，它包含了传输控制协议（TCP）和互联网协议（IP）。

这两个协议是TCP/IP协议的重要组成部分。

此外，TCP/IP协议还包括其他一些协议，如HTTP、FTP等。

5、什么是IP？请简述其结构。

IP是互联网协议（IP）中用来唯一标识网络主机或设备的。

它通常由四个数字组成，每个数字在0-255之间。

这些数字由点号分隔，形如 x.x.x.x。

例如，192.168.1.1就是一个IP的例子。

6、什么是DNS？请简述其作用。

DNS（Domain Name System）是域名系统，它可以将网站的域名解析为对应的IP，从而让用户可以通过域名访问网站。

DNS的作用是在用户访问网站时进行解析，将域名转化为对应的IP，这样用户就可以通过浏览器访问网站了。

计算机网络复习题一、选择题1、OSI模型将计算机网络分为几个层次？A. 4个B. 6个C. 7个D. 8个2、TCP/IP协议包含哪两个主要的协议？A. TCP和HTTPB. TCP和UDPC. HTTP和FTPD. FTP和SMTP3、以下哪个协议用于传输电子邮件？A. SMTPB. IMAPC. POP3D. FTP4、以下哪个网络设备用于将网络分成若干个子网？A.路由器B.交换机C.网关D.集线器5、以太网使用什么类型的传输方式？A.异步传输B.同步传输C.基带传输D.宽带传输二、填空题1、OSI模型的第一层是_________层，负责在计算机之间建立连接。

计算机英语考试试题及答案Introduction：计算机英语考试是测试学生在计算机领域具备的英语水平和技能的考试，旨在评估学生综合运用英语和计算机知识的能力。

本文将提供一些计算机英语考试的典型试题及其答案，以帮助读者更好地理解和准备此类考试。

Section 1: 填空题1. HTML是一种用于创建（1）的（2）标准。

答案：1. 网页； 2. 标记语言2. CSS是用于定义和（1）网页的外观和布局的样式（2）。

答案：1. 美化； 2. 表达语言Section 2: 选择题3. 在计算机网络中，TCP/IP代表的是：a) 网络协议 b) 网页设计语言c) 数据库管理系统 d) 电子邮件协议答案：a) 网络协议4. 下列哪项属于非编程语言？a) Java b) Pythonc) SQL d) HTML答案：d) HTMLSection 3: 阅读理解阅读下面的一段话，然后回答问题。

The cloud computing model allows users to access applications, information, data storage, and computing power via the internet. Instead of relying on local servers or personal devices, users can utilize cloud services provided by third-party providers. This model offers benefits such as scalability, flexibility, and cost-effectiveness. However, it also raises concerns regarding data security and privacy.5. What is the main benefit of cloud computing?答案：The main benefit of cloud computing is scalability, flexibility, and cost-effectiveness.6. The cloud computing model relies on ________.答案：The cloud computing model relies on accessing applications, information, data storage, and computing power via the internet.Section 4: 编程题7. 请写一个简单的Python程序来计算斐波那契数列的前n项，并将结果打印出来。

Chapter 1 Computer Networks and the Internet 1．The The ( ( ) ) is is is a a a worldwide worldwide worldwide computer computer computer network, network, network, that that that is, is, is, a a a network network network that that interconnects millions of computing devices throughout the world. ppt3 A public Internet B Intranet C switch net D television net 2．Which kind of media is not a guided media? ( ) A twisted-pair copper wire B a coaxial cable C fiber optics D digital satellite channel 3．Which kind of media is a guided media? ( ) A geostationary satellite B low-altitude satellite C fiber optics D wireless LAN 4．The units of data exchanged by a link-layer protocol are called ( ). A Frames B Segments C Datagrams D bit streams 5．Which of the following option belongs to the circuit-switched networks? ( ) A FDM B TDM C VC networks D both A and B 6．( )makes sure that that neither neither neither side side side of of of a a a connection overwhelms connection overwhelms the the other other side by sending too many packets too fast. A Reliable data transfer B Flow control C Congestion control D Handshaking procedure 7．( ) means that the switch must receive the entire packet before it can begin to transmit the first bit of the packet onto the outbound link. A Store-and-forward transmission B FDM C End-to-end connection D TDM 8．Datagram networks and virtual-circuit networks differ in that ( ). A datagram networks are circuit-switched networks, and virtual-circuit networks are packet-switched networks. B datagram networks are packet-switched networks, and virtual-circuit networks are circuit-switched networks. C datagram networks use destination addresses and virtual-circuit networks use VC. numbers to forward packets toward their destination. D datagram networks use VC. numbers and virtual-circuit networks use destination addresses to forward packets toward their destination. 9．In the following options, which one is not a guided media? ( ) A twisted-pair wire B fiber optics C coaxial cable D satellite 10．Processing delay does not include the time to ( ). A examine the packet ’s header B wait to transmit the packet onto the link C determine where to direct the packet D check bit-error in the packet 11．In the following four descriptions, which one is correct? ( ) A The traffic intensity must be greater than 1. B The fraction of lost packets increases as the traffic intensity decreases. C If the traffic intensity is close to zero, the average queuing delaywill be close to zero. D If the traffic intensity is close to one, the average queuing delay will be close to one. 12．The The Internet Internet Internet’’s s network network network layer layer layer is is is responsible responsible responsible for for for moving moving moving network-layer network-layer packets known as ( ) from one host to another. A frame B datagram C segment D message 13．The protocols of various layers are called ( ). A the protocol stack B TCP/IP C ISP D network protocol 14．There are two classes of packet-switched networks: ( ) networks and virtual-circuit networks. A datagram B circuit-switched C television D telephone 15．Access networks can be loosely classified into three categories: residential access, company access and ( ) access. A cabled B wireless C campus D city area Question 16～17 Suppose, a is the average rate at which packets arrive at the queue, R is the the transmission transmission transmission rate, rate, rate, and and and all all all packets packets packets consist consist consist of of L bits, bits, then then then the the the traffic traffic intensity is ( 16 ), and it should no greater than ( 17 ). 16． A LR ／aB La ／RC Ra ／L D LR ／a 17．A 2 B 1 C 0 D -1 18．In the Internet, the equivalent concept to end systems is ( ). A hosts B servers C clients D routers 19．In the Internet, end systems are connected together by ( ). A copper wire B coaxial cable C communication links D fiber optics 20．End systems access to the Internet through its ( ). A modems B protocols C ISP D sockets 21．End systems, packet switches, and other pieces of the Internet, run ( ) that control the sending and receiving of information within the Internet. A programs B processes C applications D protocols 22．There are many private networks, such as many corporate and government networks, whose hosts cannot exchange messages with hosts outside of the private network. These private networks are often referred to as ( ). A internets B LANC intranets D W AN 23．The internet allows ( ) running on its end systems to exchange data with each other. A clients applications B server applications C P2P applications D distributed applications 24．The Internet provides two services to its distributed applications: a connectionless unreliable service and () service. A flow control B connection-oriented reliable C congestion control D TCP 25．It defines the format and the order of messages exchanged between twoor more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event. The sentence describes ( ). A Internet B protocol C intranet D network 26．In the following options, which does not define in protocol? ( ) A the format of messages exchanged between two or more communicating entities B the order of messages exchanged between two or more communicating entities C the actions taken on the transmission of a message or other evenD the transmission signals are digital signals or analog signals 27．In the following options, which is defined in protocol? ( ) A the actions taken on the transmission and/or receipt of a message oother event B the objects exchanged between communicating entities C the content in the exchanged messages D the location of the hosts 28．In the following options, which does not belong to the network edge( ) A end systems B routers C clients D servers 29．In the following options, which belongs to the network core? ( ) A end systems B routers C clients D servers 30．In the following options, which is not the bundled with the Internet ’s connection-oriented service? ( ) A reliable data transfer B guarantee of the transmission time C flow control D congestion-control 31．An application can rely on the connection to deliver all of its data without error and in the proper order. The sentence describes ( ). A flow control B congestion-control C reliable data transfer D connection-oriented service 32．It makes sure that neither side of a connection overwhelms the other side by sending too many packets too fast. The sentence describes ( ). A flow control B congestion-control C connection-oriented service D reliable data transfer 33．It helps prevent the Internet from entering a state of gridlock. When a packet switch becomes congested, its buffers can overflow and packet loss can occur. The sentence describes ( ). A flow control B congestion-control C connection-oriented service D reliable data transfer 34．The Internet ’s connection-oriented service has a name, it is ( ). A TCP B UDP C TCP/IP D IP 35．In In the the the following following following options, options, options, which which which service service service does does does not not not be be be provided provided provided to to to an an application by TCP?( ) A reliable transport B flow control C video conferencing D congestion control 36．The Internet ’s connectionless service is called ( ). A TCP B UDP C TCP/IP D IP 37．In the following options, which does not use TCP?( ) A SMTP B internet telephone C FTP D HTTP 38．In the following options, which does not use UDP?( ) A Internet phone B video conferencing C streaming multimedia D telnet 39．There are two fundamental approaches to building a network core, ( ) and packet switching. A electrical current switching B circuit switching C data switching D message switching 40．In ( ) networks, the resources needed along a path to provide for communication between the end system are reserved for the duration ofthe communication session. A packet-switched B data-switched C circuit-switched D message-switched 41．In ( ) networks, the resources are not reserved; a session’s messages use the resources on demand, and as a consequence, may have to wait for access to communication link. A packet-switched B data-switched C circuit-switched D message-switched 42．In a circuit-switched network, if each link has n circuits, for each link used by the end-to-end connection, the connection gets ( ) of the link link’’s bandwidth for the duration of the connection. A a fraction 1/n B all C 1/2 D n times 43．For ( ), the transmission rate of a circuit is equal to the frame rate multiplied by the number of bits in a slot. A CDMA B packet-switched network C TDM D FDM 44．( ) means that the switch must receive the entire packet before it canbegin to transmit the first bit of the packet onto the outbound link. A Queuing delay B Store-and-forward transmission C Packet loss D Propagation 45．The network that forwards packets according to host destination addresses is called ( ) network. A circuit-switched B packet-switched C virtual-circuit D datagram 46．The network that forwards packets according to virtual-circuit numbers is called ( ) network. A circuit-switched B packet-switched C virtual-circuit D datagram 47．In the following entries, which is not a kind of access network?( ) A residential access B company access C wireless access D local access 48．Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are R 1 and R 2, respectively. Assuming that the switch uses store-and-forward packet switching, what is the total end-to-end delay to send a packet of length L ? (Ignore queuing delay, propagation delay, and processing delay.) ( )A L /R 1＋L /R 2 B L /R 1C L /R 2D none of the above 49．The time required to examine the packet ’s header and determine where to direct the packet is part of the ( ). A queuing delay B processing delay C propagation delay D transmission delay 50．The time required to propagate from the beginning of the link to the next router is ( ). A queuing delay B processing delay C propagation delay D transmission delay 51．Consider sending a packet of 3000bits over a path of 5 links. Each link transmits transmits at at at 1000bps. 1000bps. 1000bps. Queuing Queuing Queuing delays, delays, delays, propagation propagation propagation delay delay delay and and and processing processing delay are negligible. (6 points) (1).Suppose (1).Suppose the the the network network network is is is a a a packet-switched packet-switched packet-switched virtual virtual virtual circuit circuit circuit network. network. network. VC VC setup time is 0.1 seconds. Suppose the sending layers add a total of 500 bits of header to each packet. How long does it take to send the file from source to destination? (2).Suppose the the network network network is is is a a a packet-switched packet-switched datagram datagram network network network and and and a a connectionless connectionless service service service is is is used. used. used. Now Now Now suppose suppose suppose each each each packet packet packet has has has 200 200 200 bits bits bits of of header. How long does it take to send the file? (3).Suppose that the network is a circuit-switched network. Further suppose that that the the the transmission transmission transmission rate rate rate of of of the the the circuit circuit circuit between between between source source source and and and destination destination destination is is 200bps. Assuming 0.02s setup time and 200 bits of header appended to the packet, how long does it take to send the packet? Solution: (1). t=5*(3000+500)/1000+0.1=17.6s(2). t=5*(3000+200)/1000=16s(3). t=(3000+200)/200+0.02=16.02s。