计算机网络课后作业以与答案(中英文对照)
计算机网络（第5版）课后习题答案完整版
计算机网络（第5版）课后习题答案完整版《计算机网络》课后习题答案<完整版>第一章概述1-1 计算机网络向用户可以提供哪些服务？答：计算机网络向用户提供的最重要的功能有两个，连通性和共享。
1-2 试简述分组交换的特点答：分组交换实质上是在“存储——转发”基础上发展起来的。
它兼有电路交换和报文交换的优点。
分组交换在线路上采用动态复用技术传送按一定长度分割为许多小段的数据——分组。
每个分组标识后，在一条物理线路上采用动态复用的技术，同时传送多个数据分组。
把来自用户发端的数据暂存在交换机的存储器内，接着在网内转发。
到达接收端，再去掉分组头将各数据字段按顺序重新装配成完整的报文。
分组交换比电路交换的电路利用率高，比报文交换的传输时延小，交互性好。
1-3 试从多个方面比较电路交换、报文交换和分组交换的主要优缺点。
答：（1）电路交换电路交换就是计算机终端之间通信时，一方发起呼叫，独占一条物理线路。
当交换机完成接续，对方收到发起端的信号，双方即可进行通信。
在整个通信过程中双方一直占用该电路。
它的特点是实时性强，时延小，交换设备成本较低。
但同时也带来线路利用率低，电路接续时间长，通信效率低，不同类型终端用户之间不能通信等缺点。
电路交换比较适用于信息量大、长报文，经常使用的固定用户之间的通信。
（2）报文交换将用户的报文存储在交换机的存储器中。
当所需要的输出电路空闲时，再将该报文发向接收交换机或终端，它以“存储——转发”方式在网内传输数据。
报文交换的优点是中继电路利用率高，可以多个用户同时在一条线路上传送，可实现不同速率、不同规程的终端间互通。
但它的缺点也是显而易见的。
以报文为单位进行存储转发，网络传输时延大，且占用大量的交换机内存和外存，不能满足对实时性要求高的用户。
报文交换适用于传输的报文较短、实时性要求较低的网络用户之间的通信，如公用电报网。
（3）分组交换分组交换实质上是在“存储——转发”基础上发展起来的。
计算机网络习题答案(二)英文
Chapter 5: Data CodingFill In the Blank5-1.It is much easier for a machine to process a code if all the characters in the code have _____.5-2.The number of possible combinations or characters in a coding system are called _____.5-3.The minimum number of bits that would be required to encode only the 26 characters of the alphabet is _____.5-4.The three different groups of character assignments that are normally made in a coding system are _____, _____, and _____.5-5.The coding system that has enough bit combinations to encode all of the characters in all of the worlds languages is called _____.5-6.Three major types of data compression are called _____, _____, and _____. 5-7.Arguably, the most important data coding scheme because it is the mostly widely used is _____.5-8.In an even parity system, a 1 bit is added to a character’s code when necessary to make the total number of 1 bits representing the character an _____ number.5-9.Character compression is also known as _____.5-10. Character stripping removes the leading and trailing _____ characters from a message and adds them back at the receiving end.5-11.R un length encoding replaces _____ characters or repetitive groups of characters with a different, much shorter group of characters.5-12. A measure of how few bits are required to accurately convey the meaning of a character is called _____ _____.5-13. Bits that are used to determine the code points in a code are called _____ _____.5-14. The _____ code is an 8-bit code that has 256 code points.True or False5-1.The term binary digit is abbreviated bit.5-2.Machines cannot send Morse code because the coded characters have different numbers of code elements.5-3.It is more difficult for a machine to process a code if all of the bits are of the same duration.5-4.When even parity is used, a 0 bit is added, if necessary, to make the total number of 0 bits in the character an even number.5-5.The escape character in a coding system is a different character than the one that is generated when you press the ESC key on the keyboard of a PC.5-6.ASCII is a 7-bit code.5-7.Unicode provides enough code points so that all characters in all languages of the world have a unique 16-bit code point.5-8.Code efficiency is a measure of how many extra bits are used beyond those required to convey the meaning of a character.5-9.Data compression is the process of reducing the number of bits used to represent a character, or reducing the number of characters before they are transmitted.5-10.C haracter stripping is the process of removing control characters from a message before it is transmitted.5-11.T he binary digits are 1 and 2.5-12.A code is a predetermined set of symbols that have variable meanings.5-13.M orse code is not considered a binary code, because its two elements are of different length.5-14.A binary code works well for machines communicating by electrical means because the 1 bits and 2 bits can be represented by a current flow that is either on or off.5-15.F or transmission efficiency, it is ideal to have a coding system that uses a minimum number of bits to represent each character.5-16.M ost coding systems include a technique called an escape character.5-17.T he necessity to support escape characters complicates the design of equipment that is to code and decode the data.5-18.T he ASCII code is the most widely used code in computers and communications networks today.5-19.U nicode is a 16-bit character code.Multiple Choice5-1. Characters that control the positioning of information on a workstation screen or paper are called _____.a. page control charactersb. format effector charactersc. device control charactersd. screen control characterse. a and b5-2. It is much easier for a machine to process a code if the code has the following attributes: _____.a. it is a true binary codeb. all of the characters have the same number of bitsc. all of the bits are perfectly formedd. all of the bits are the same duratione. a and cf. All of the above.5-3. The unique sequence of bits assigned to represent the various characters of a code are called _____.a. code pointsb. character assignmentsc. control charactersd. character algorithmse. None of the above.5-4.The purpose of escape characters is to _____.a. allow a program to abort a message prematurelyb. implement a priority system by allowing one message to be prematurelyended so another can be sent on the circuitc. act as an alternate escape control character when more than 8 bits areneededd. indicate that the characters that follow are to be interpreted as having analternate meaninge. indicate that a PDU has been received correctly5-5. The ASCII code is also known as the _____.a. International Telegraph Alphabet 5b. extended ASCII codec. 8-bit coded. PC codee. EBCDIC code5-6. The EBCDIC code _____.a. was developed by IBMb. is an 8-bit codec. has 256 code pointsd. is used on older IBM mainframe computerse. All of the above.f. None of the above.5-7. Unicode _____.a. is a 16-bit codeb. was developed by a group of companiesc. supports the characters of all languagesd. All of the above.e. None of the above.5-8. Code efficiency is calculated _____.a. by minimizing the number of bits transmitted for a given messageb. by dividing the information bits by the total number of bits in a characterc. by dividing the total number of bits by the information bits in a characterd. by measuring the error rate at the receiving end of a transmission5-9. Three major types of data compression are _____.a. character removal, run length encoding, and bit compressionb. bit stripping, double clocking, and character strippingc. character compression, Huffman coding, and character strippingd. character stripping, run length encoding, and character compressione. over clocking, transmission digitizing, and double ACKing5-10. A 10-bit code could represent how many characters?a. 100b. 210 -1c. 29d. 512e. 2105-11.The number of possible combinations or characters in a coding system is called the _____.a. character assignmentb. code pointsc. control characterd. code limite. binary code5-12.Many coding systems include an extra bit, called a _____ , for checking purposes.a. parity bitb. padding bitc. control bitd. binary digite. checking bit5-13.When an ESC character is sent as a part of the data, it means that _____.a. the transmission is being abortedb. this is the end of the transmissionc. the characters that follow are to be interpreted as having an alternate meaningd. the characters that follow are encryptede. the transmission should be ignored5-14. Graphic characters _____.a. can be displayed on a workstation screenb. are special characters only used by graphic artistsc. are only present in specialized code systemsd. can also be used as format effector characters5-15Code conversion _____.a. changes one character to another for security purposesb. changes the characters in one coding system to those of another coding systemc. can be readily performed by a computerd. All of the above.e. b and cChapter 6: Data Communication FundamentalsFILL IN THE BLANK6-1. The three attribute s of a sine wave are its _____ , _____ , and _____.6-2. The FM radio band in the United States extends from 88 MHz to 108 MHz. Its bandwidth is _____.6-3. A signal drop of 10 dB represents a drop in power of _____times.6-4. A radio signal with a frequency of 101 MHz falls within the _____radio band.6-5. Speech with frequencies above _____is attenuate d and not transmitted through the public telephone network.6-6. Changing a communication signal by alter ing its amplitude, frequency, or phase is called _____.6-7. The unit of signaling rate on a communication circuit is called _____.6-8. The unit of measure of a circuit's data carrying rate is called _____6-9. Sending a tribit on a circuit requires _____(how many) unique signal changes to be transmitted?6-10. A circuit that allows transmission in one direction only is called a _____ circuit.6-11. A circuit that allows transmission in either direction but not at the same time is called a _____circuit.6-12. A circuit that allows transmission in both directions simultaneously is called a _____circuit.6-13. A circuit that allows all of the bits in a character to be transmitted simultaneously is called a _____circuit.6-14. A circuit in which the bits of a character are transmitted one after the other on a single communication path is called a _____circuit.6-15. The mechanism by which character synchronization occurs in asynchronous transmission is called _____and _____bits.6-16. The means by which the receiver knows which bits to group together to form a character is called _____.6-17. When each block of data to be transmitted is surrounded with synchronizing and other control characters the transmission is called _____.6-18. When each character to be transmitted is surrounded with start and stop bits, the transmission is called _____.6-19. The _____condition is the idle condition on a line. Conventionally it is the same as the signal for a 1 bit.6-20. The purpose of the _____in synchronous transmission is to maintain synchronization between the transmitting node and the receiving node.6-21. _____modulation is better suited for high-speed analog transmission because the receiver more easily detects changes in _____than changes in amplitude or frequency.6-22. _____equalizers assume that the circuit meets a n average set of loss, noise, and distortion parameter s, and shape the transmitted signal accordingly.6-23. _____equalizers examine the actual parameters of the circuit being used, and shape the signal to match its specific characteristics.6-24. Modems that use the V.34 standard use a sophisticated modulation technique called _____, and they assume that most of the actual transmission will occur on _____circuits.6-25. High-speed modems achieve a high throughput rate by using sophisticated modulation and __________techniques.6-26. A _____ensures that the signal entering a digital circuit has properly shaped, square pulses, and is precisely timed.6-27. The time it takes the modems on an HDX circuit to reverse their function –the time for the transmitting modem to switch to being the receiver, and the receiving modem to switch to being the transmitter—is called _____.6-28. The advantages of _____transmission over _____transmission include better data integrity; higher capacity circuits; easier integration of voice, data and other signals; better security and privacy; and lower cost.6-29. The type of digital modulation that takes 8,000 samples per second but uses only 4 bits per sample to code the difference between the values of two samples is called _____.6-30. An _____converts analog signals to a digital format.6-31. The difference between the actual value (height) of an analog signal and the nearest integer value, which is assigned when the signal is digitized, is called_____.6-32. When the number of data bits in a character is divided by the total number of bits required to transmit the character, the __________is being calculated. TRUE OR FALSE6-1. Signaling is the propagation of a signal on a medium.6-2. Playing the A key above middle C on a piano results in a digital signal that has 880 pulses per second.6-3. Sound waves, electrical waves, and electromagnetic waves have essentially different characteristics.6-4. A digital signal level is measured in decibels.6-5. The loss of signal strength between two points on a communication circuit is called attenuation.6-6. The amplitude and phase of a voice signal remain constant while its frequency changes.6-7. ADPCM is accomplished by shifting each channel to a different part of the frequency spectrum.6-8. The speed of a circuit is measured in baud.6-9. A 2,400 baud signal can carry data at a maximum rate of 7,200 bps.6-10. When 2 bits of information are coded into one signal change, they are called bi-bits.6-11. The most common digital signals are unipolar.6-12. When transmitting digital signals on an analog circuit, a modem is used.6-13. An analog signal that has been digitized can be closely restored to its original analog shape by a D/A converter.6-14. PCM is the ITU-T’s recommended method for digitizing voice at 32 Kbps. 6-15. In a modem, equalizer circuitry compensates for the variability of the actual transmission line used.6-16. Line turnaround time in a modem can be a significant part of the total transmission time.6-17. Modems can never handle full-duplex transmission.6-18. Phase modulation is the technique of chang ing a digital signal’s phase in order to modulate it.6-19. V.34-bis modems assume that most data transmission occurs on digital lines.6-20. The transmission speed between a pair of V.90 modems is symmetric.6-21. Cable modems for each CATV system are unique.6-22. Modem eliminator s are a low-cost alternative to modems on LAN circuits.6-23. There are very few practical uses for simplex transmission.6-24. Parallel mode transmission is widely used on WANs to achieve high throughput.6-25. Asynchronous transmission is widely used today.6-26. Start bits precede every data block in synchronous transmission.6-27. To jam a spread spectrum signal, one simply broadcasts a jamming signal on the spread spectrum signal’s carrier frequency.MULTIPLE CHOICE6-1. The reasons that digital transmission is superior to analog transmission are _____.a. better data integrityb. higher capacityc. easier integrationd. better security and privacye. lower costf. All of the above.g. only a, b, c, and d6-2. A modem is a form of a _____.a. A/D converterb. D/A converterc. codecd. DTEe. None of the above.f. a and b6-3. The three attributes of an analog signal discussed in the chapter are _____.a. frequency, decibels, and modulationb. phase, frequency, and amplitudec. amplitude, carrier, and sined. bit rate, speed, and error ratee. unipolarity, quantization, and equilibrium6-4. Parallel transmission occurs _____.a. during spread spectrum transmissionb. when a PC sends data to a printer using a serial cablec. on most WAN circuitsd. All of the above.e. None of the above.6-5. Differential Manchester coding _____.a. is often used on WANsb. is almost never usedc. is subservient to Manchester codingd. requires an analog circuit to work properlye. None of the above.6-6. The most widely used interface standard between PCs and modems is _____.a. point-to-pointb. USBc. RS-232-Dd. RS-232-Ce. X.256-7. The X.21 interface standard _____.a. is a replacement for RS-232-Cb. defines the interface to a digital circuitc. uses a PL-259 connectord. All of the above.e. None of the above.6-8. A network interface card _____.a. provides the interface from a PC to a networkb. provides the interface from one network to anotherc. provides the interface from a modem to a networkd. converts signals from analog to digitale. None of the above.6-9. When two modems send signals to each other for the process of establishing transmission parameters, it is called _____.a. synchronizingb. call setupc. call establishmentd. MOST (acronym for modem startup)e. handshaking6-10. Hertz is the unit of measure for _____.a. baudb. bit ratec. trellis code modulationd. cycles per seconde. data ratef. None of the above.6-11. The difference between the exact height of an analog signal and the nearest integer value when a digitizing sample is taken is called _____.a. digitizing discrepancyb. digitizing errorc. quantizing noised. digitizing discernmente. a and cf. b and c6-12. QAM uses a combination of _____and _____to generate quadbits.a. phase changes and relative amplitudesb. phase changes and dibitsc. phase changes and frequency changesd. amplitude changes and frequency changese. amplitude changes and dibitsChapter 7: Data Link Control ProtocolsFILL IN THE BLANK7-1. A set of rules that define the exact format of messages exchanged between computers or between computers and people is called a _____.7-2. Data link protocols are necessary so that all of the devices on the network are operating by the same set of rules and are able to _____with each other.7-3. The part of a protocol consisting of the rules that specify the way the receiving terminal signals the sending terminal if it has received data correctly, how and under what circumstances the line will be turned around, and whether the receiving terminal can accept more data is called _____.7-4. The part of the protocol consisting of rules specifying what happens when an error is detected, what to do if communications suddenly and unexplainably cease, and the way communications are reestablished after they are broken is called _____.7-5. The part of a protocol consisting of rules for ending the communications under normal and abnormal circumstances is called _____.7-6. The ability of data terminal equipment (DTE) to be able to transmit and receive any bit pattern as data is called _____.7-7. Predetermined communication parameters are those that are set _____by switches or specified as parameters in software.7-8. When a central or control station asks each station on the circuit or network if it has traffic to send, it is using a line control technique called _____.7-9. When any station that has traffic looks to see if the circuit is free, and if it is, begins sending its traffic the line control technique is called _____.7-10. In a polling system, one way that priority can be given to a terminal is by listing its address in the polling list _____.7-11. The _____of a message contains and conveys information about the message, such as the destination node’s address, a sequence number, and perhaps a date and time.7-12. BISYNC is defined to only support the 6-bit transcode (SBT), EBCDIC, and _____.7-13. Character synchronization is accomplished in BISYNC by sending _____ characters at the beginning and periodically in the middle of each transmission.7-14. Compared to BISYNC, DDCMP and other byte-count protocols implement transparency in a much more _____manner.7-15. The HDLC ___ field is used to mark the beginning and ending of frames.7-16. The technique that ensures a flag’s uniqueness by not allowing any other sequence of six consecutive 1 bits in the data stream is called _____.7-17. A protocol that is primarily used by PC workstations to send IP overdial-up lines, typically when dial ing in to an ISP for connection to the Internet, is called _____.7-18. The _____protocol was developed by IBM and then generalize d to become HDLC.7-19. SDLC is a _____of HDLC.7-20. SDLC is a subset of _____.7-21. A _____changes one protocol to another, when, for example, a message is sent between two networks that use different protocols.7-22. A sophisticated check character at the end of each block of data is called a _____.7-23. A technique used to ensure that a fast transmitting node does not send data faster than a receiving node can receive and process it is called _____.7-24. The flow control technique that allows multiple frames to be in transit on the line at one time is called _____.TRUE OR FALSE7-1. Data link protocols are concerned with the transmission of data through an entire network.7-2. All protocols use the same bit patterns as control characters.7-3. Data transparency allows a protocol to be able to transmit and receive any bit patterns as data.7-4. A protocol is implemented by transmitting certain bit patterns or characters on the communication circuit.7-5. The code used for the data is independent of the protocol being used.7-6. Because of collision s, contention systems are rarely used for line access.7-7. Poll ing systems require several stations on the circuit to act as master stations.7-8. Hub polling is the most common implementation of a polling system.7-9. Polling systems are dependent on the data code being used.7-10. Token passing systems require one station on the circuit to take responsibility to ensure that there are always multiple tokens circulating on the circuit.7-11. Data messages normally consist of three parts: the header, text, and trailer. 7-12. The ACK character normally acknowledges the receipt of a block of data. 7-13. Stop-and-wait flow control is inherently efficient because of its simplicity. 7-14. Stop-and-wait flow control allows multiple blocks of data to be in transit on the line at one time.7-15. PPP has largely replaced the SLIP protocol because it has better error detection.7-16. KERMIT is error checked but is a very slow protocol.7-17. A bit-oriented protocol uses multiple control characters to mark the start and end of parts of a message.7-18. HDLC is a bit-oriented protocol.7-19. SLDC is a byte-count-oriented protocol.7-20. The best known bit-oriented protocol is BISYNC.7-21. SDLC was an outgrowth of the original work on HDLC.7-22. SDLC operates in one of three modes; however, one mode is rarely used. 7-23. The basic operational unit for HDLC is a PDU.7-24. HDLC uses a FRA character to mark the beginnings and ends of frames. 7-25. BISYNC supports only selected data codes.7-26. BISYNC supports transparency.7-27. DDCMP has largely been replaced by HDLC.7-28. Go-back-n is an implementation of sliding window flow control.7-29. The LAP protocols are variant s of HDLC.7-30. PPP is a widely used synchronous protocol for dialing into the Internet through an ISP.MULTIPLE CHOICE7-1. In HDLC, when a 0 bit is inserted after all strings of five consecutive 1 bits, the term applied is _____.a. zeroingb. bit stuffingc. synchronizingd. oneinge. string breaking7-2. When two stations on a circuit transmit at the same time, a(n)_____occurs.a. altercationb. divisionc. pollingd. bit stuffinge. collision7-3. In order to know what stations to poll and in what sequence, the master station uses a _____.a. message headerb. polling listc. start of header characterd. polling PDAe. cyclic redundancy check7-4. When a receiver must acknowledge every block of data before the next block is sent, the _____type of flow control is being used.a. stop-and-waitb. stop-and-checkc. stop-and-flopd. sliding framee. sliding window7-5. The name of the flow control protocol in which the sending station, on receipt of a NAK, resends the damaged or out of sequence frame and all frames after it is _____.a. selective rejectb. TCPc. selective repeatd. send all before ne. HDLC7-6. HDLC is an example of _____.a. sliding window flow controlb. a serial line interface protocolc. an asynchronous protocold. All of the above.e. None of the above.7-7. When an HDLC node receives a flag character, it knows that _____.a. an error has occurredb. it should signal the sender to stop sending trafficc. a frame is beginning or endingd. it should switch to transparent modee. None of the above.7-8. HDLC’s information frames _____.a. are used to send an NAK when a frame is received incorrectlyb. are used to establish the way the protocol will proceedc. are used to send information from one node to a router for flow controld. contain the data field that holds the information being transmittede. are not used in ABM mode7-9. The part of a message that contains the destination address is called the_____.a. headerb. address PDUc. textd. trailere. flag7-10. Software or hardware that changes one protocol to another is called a_____ .a. CODECb. protocol converterc. modemd. routere. encryptor7-11. Contention systems work best _____.a. on circuits that have only more than two DTEsb. when the speed of the circuit is relatively fastc. on circuits that have heavy message trafficd. All of the above.e. None of the above.7-12. Desirable attributes for a data link protocol to have are _____.a. transparencyb. efficiencyc. bit linearityd. a, b, and ce. a and b7-13. Techniques to ensure that a fast transmitting node does not send data faster than the receiving node can receive and process it are called _____ .a. token passingb. flow controlc. parity checkingd. cyclic redundancy checkinge. error control7-14. The LAPD protocol is used _____.a. between an X.25 DTE and a packet switching networkb. on an ISDN D channelc. on frame relay networksd. on value added networkse. as a substitute for TCP/IP7-15. Go-back-n and selective repeat are two common implementations of _____.a. bit oriented protocolsb. byte protocolsc. byte-count oriented protocolsd. sliding window flow controle. transmission control protocolsChapter 8: Transmission MediaFILL IN THE BLANK8-1. A type of media that provides some type of physical path, such as wire, cable, or optical fiber, along which the signal moves from end to end is called _______ or guided media.8-2. Air is an example of _______ media.8-3. Twisted pair wire is an example of _______ media.8-4. The best media to use in homes and offices where costs must be kept low and bandwidth requirements are moderate is ____.8-5. The most appropriate media to use when there is a need for very high bandwidth and high security is _____.8-6. The most appropriate media to use when there is a need for high bandwidth and to broadcast to a wide area is ____.8-7. Wire containing at least three twists per foot and that is about the same as normal telephone cable installed in most office buildings is called _____.8-8. _____ cable normally contains four pairs of wires and is the type that is most commonly being installed in new homes and businesses, particularly when it is known that a computer network will be used.8-9. The shielding in shielded twisted pair wire provides a degree of _____ _____ in electrically noisy environments.8-10. _____ is advantageous when tap s in the cable need to be made—it is easier to tap than optical fiber.8-11. The characteristic of _____ include: high bandwidth, difficult to tap and splice; not subject to electrical interference, cable is very small diameter and lightweight.8-12. A _____ is required to operate a microwave transmitter.8-13. _____ _____ is the delay that occurs because light and radio signals only travel at 186,000 miles per second.8-14. Satellites in _____ orbits circle the earth at 22,300 miles.8-15. Satellites in _____ orbits are approximately 6,000 miles high.8-16. _____ works by modulating a laser light beam instead of broadcasting a radio wave.8-17. _____ is a fiber that has a glass core approximately 9 microns in diameter. 8-18. Data are placed on an optical fiber with a light source, either an LED or a _____.8-19. When UTP is used in a data application it is normally terminate d with a _____ jack.8-20. A type of satellite commonly used to send television programming into homes is called a _____.TRUE OR FALSE8-1. Optical fiber is an example of an unguided medium.8-2. Guided media are also known as wireless media.8-3. Wireless media are the most common media used today.8-4. Optical fiber emits an electro-optical field when carrying communications signals.8-5. CAT 3 cable is most frequently used for telephone transmission in older buildings.8-6. CAT 5 cable is commonly being installed in new homes and businesses.8-7. An advantage of UTP wire is its relatively low cost.8-8. Coaxial cable can be tapped easily.8-9. Optical fiber can be tapped easily.。
(完整版)计算机网络课后作业以及答案(中英文对照)
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。
计算机网络第五版答案完整版
计算机网络第五版答案完整版Computers have become an integral part of our lives, and computer networking plays a crucial role in connecting various devices and enabling communication between them. In the fifth edition of the book "Computer Networks," the authors provide comprehensive answers and solutions to various exercises and questions, giving readers a complete understanding of the concepts and principles of computer networking.1. Introduction to Computer NetworksComputer networks are essential for transmitting data and enabling communication between devices. In this chapter, the authors explain the basics of networks, including the OSI model, network topology, and types of networks. They also provide answers to exercises that help readers grasp the fundamental concepts of computer networking.2. Physical LayerThe physical layer is responsible for transmitting raw bits over a communication channel. The authors cover topics such as analog and digital signals, transmission media, and modulation techniques. Through detailed explanations and examples, readers gain a solid understanding of the physical layer's functions and mechanisms.3. Data Link LayerThe data link layer ensures reliable data transfer between two connected nodes. This chapter focuses on topics like error detection and correction, flow control, and media access control. The authors provide accurateanswers to questions related to these concepts, enabling readers to comprehend the data link layer's role in establishing error-free communication.4. Network LayerThe network layer facilitates the delivery of data packets across multiple networks. Addressing, routing algorithms, and internet protocols are among the key topics discussed in this chapter. By examining the provided answers, readers can enhance their knowledge of the network layer's functionalities and protocols.5. Transport LayerThe transport layer provides end-to-end communication between applications running on different hosts. This chapter explores topics like multiplexing, demultiplexing, reliable data transfer protocols, and congestion control. The authors offer complete solutions to exercises, allowing readers to grasp the complexities and mechanisms of the transport layer.6. Application LayerThe application layer enables network applications to communicate with each other. This chapter covers topics such as domain name system (DNS), email protocols, and World Wide Web (WWW) protocols. The authors present accurate and detailed answers, enabling readers to understand the application layer's role in facilitating various network services.7. Network SecurityNetwork security is essential to protect data from unauthorized access and malicious activities. This chapter discusses topics like symmetric and asymmetric encryption, public key infrastructure (PKI), and network security protocols. The authors provide comprehensive answers, helping readers to comprehend the importance of network security and the techniques used to safeguard data.8. Multimedia NetworkingIn the modern era, multimedia applications require robust networking capabilities. This chapter delves into topics such as streaming and real-time applications, multimedia protocols, and quality of service (QoS) mechanisms. By examining the provided answers, readers can gain a deeper understanding of the challenges and solutions in multimedia networking.9. Network ManagementEfficient network management is crucial for ensuring the smooth operation of computer networks. This chapter covers topics like Simple Network Management Protocol (SNMP), network monitoring, and network troubleshooting. The authors provide accurate and comprehensive answers, allowing readers to learn about the tools and techniques used in network management.By providing complete and accurate answers to exercises, the fifth edition of "Computer Networks" equips readers with the knowledge and understanding required to master the field of computer networking. The authors' attention to detail, clear explanations, and concise yet informative solutions make this book an invaluable resource for students, professionals, and anyone interested in computer networks.。
计网课后习题答案(英文)
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。
计算机网络英文——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 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。
计算机网络英文题库(附答案)chapter1
Chapter 1 Computer Networks and the Internet networks use VC. numbers to forward packets toward their1．The ( ) is a worldwide computer network, that is, a network that destination.interconnects millions of computing devices throughout the world. D datagram networks use VC. numbers and virtual-circuit networks ppt3 use destination addresses to forward packets toward their destination.A public Internet 9．In the following options, which one is not a guided media? ( )B Intranet A twisted-pair wireC switch net B fiber opticsD television net C coaxial cable2．Which kind of media is not a guided media? ( ) D satelliteA twisted-pair copper wire 10．Processing delay does not include the time to ( ).B a coaxial cable A examine the packet’s headerC fiber optics B wait to transmit the packet onto the linkD digital satellite channel C determine where to direct the packetD check bit-error in the packet3．Which kind of media is a guided media? ( )11．In the following four descriptions, which one is correct? ( )A geostationary satelliteB low-altitude satelliteC fiber opticsD wireless LAN 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 delay 4．The units of data exchanged by a link-layer protocol are called ( ).will be close to zero. A FramesD If the traffic intensity is close to one, the average queuing delay B Segmentswill be close to one. C Datagrams12．The Internet’s network layer is responsible for moving network-layer D bit streamspackets known as ( ) from one host to another. 5．Which of the following option belongs to the circuit-switched networks?A frame ( )B datagram A FDMC segment B TDMD message C VC networks13．The protocols of various layers are called ( ). D both A and BA the protocol stack 6．( )makes sure that neither side of a connection overwhelms the otherB TCP/IPside by sending too many packets too fast.C ISPA Reliable data transferD network protocolB Flow control14．There are two classes of packet-switched networks: ( ) networks andC Congestion controlvirtual-circuit networks.D Handshaking procedureA datagram7．( ) means that the switch must receive the entire packet before it canB circuit-switchedbegin to transmit the first bit of the packet onto the outbound link.C television A Store-and-forward transmissionB FDMD telephoneC End-to-end connection 15．Access networks can be loosely classified into three categories:D TDM residential access, company access and ( ) access.8．Datagram networks and virtual-circuit networks differ in that ( ).A cabledA datagram networks are circuit-switched networks, andB wirelessvirtual-circuit networks are packet-switched networks.B datagram networks are packet-switched networks, andC campusD city areavirtual-circuit networks are circuit-switched networks.Question 16～17 C datagram networks use destination addresses and virtual-circuit1D distributed applicationsSuppose, a is the average rate at which packets arrive at the queue, R is24．The Internet provides two services to its distributed applications: a the transmission rate, and all packets consist of L bits, then the trafficintensity is ( 16 ), and it should no greater than ( 17 ). connectionless unreliable service and () service.A flow control16． A LR／aB connection-oriented reliableB La／RC congestion controlC Ra／LD TCP25．It defines the format and the order of messages exchanged between twoD LR／aor more communicating entities, as well as the actions taken on the 17．A 2B 1 transmission and/or receipt of a message or other event. The sentence describes ( ).C 0A InternetD -1B protocol 18．In the Internet, the equivalent concept to end systems is ( ).C intranet A hostsD network B servers26．In the following options, which does not define in protocol? ( )C clientsA the format of messages exchanged between two or more D routerscommunicating entities 19．In the Internet, end systems are connected together by ( ).B the order of messages exchanged between two or more A copper wirecommunicating entities B coaxial cableC the actions taken on the transmission of a message or other eventC communication linksD the transmission signals are digital signals or analog signals 模拟D fiber optics信号20．End systems access to the Internet through its ( ).27．In the following options, which is defined in protocol? ( ) A modemsA the actions taken on the transmission and/or receipt of a message orB protocolsother eventC ISPB the objects exchanged between communicating entities D socketsC the content in the exchanged messages21．End systems, packet switches, and other pieces of the Internet, run ( )D the location of the hosts that control the sending and receiving of information within the28．In the following options, which does not belong to the network edge?Internet.( )A programsA end systemsB processesB routersC applicationsC clientsD protocolsD servers22．There are many private networks, such as many corporate and29．In the following options, which belongs to the network core? ( ) government networks, whose hosts cannot exchange messages withA end systemshosts outside of the private network. These private networks are oftenB routersreferred to as ( ).C clientsA internetsD serversB LAN30．In the following options, which is not the bundled with the Internet ’s C intranetsconnection-oriented service? ( ) D WANA reliable data transfer23．The internet allows ( ) running on its end systems to exchange dataB guarantee of the transmission timewith each other.C flow control***A clients applicationsD congestion-controlB server applications31．An application can rely on the connection to deliver all of its data C P2P applicationswithout error and in the proper order. The sentence describes ( ).2***A flow control C data switchingB congestion-control D message switchingC reliable data transfer 40．In ( ) networks, the resources needed along a path to provide forD connection-oriented service communication between the end system are reserved for the duration 持续of the communication session. 32．It makes sure that neither side of a connection overwhelms 淹没压倒the other side by sending too many packets too fast. The sentence A packet-switcheddescribes ( ). B data-switchedA flow control C circuit-switchedB congestion-control D message-switchedC connection-oriented service 41．In ( ) networks, the resources are not reserved; a session’s messagesD reliable data transfer use the resources on demand, and as a consequence, may have to wait 33．It helps prevent the Internet from entering a state of gridlock. When a for access to communication link.packet switch becomes congested, its buffers can overflow and packet A packet-switchedloss can occur. The sentence describes ( ). B data-switchedA flow control C circuit-switchedB congestion-control D message-switchedC connection-oriented service 42．In a circuit-switched network, if each link has n circuits, for each linkD reliable data transfer used by the end-to-end connection, the connection gets ( ) of the 34．The Internet’s connection-oriented service has a name, it is ( ). link ’s bandwidth for the duration of the connection.A TCP A a fraction 1/nB UDP B allC TCP/IP C 1/2D IP D n times35．In the following options, which service does not be provided to an 43．For ( ), the transmission rate of a circuit is equal to the frame rate application by TCP?( ) multiplied by the number of bits in a slot.A reliable transport A CDMAB flow control B packet-switched networkC video conferencing C TDMD congestion control D FDM36．The Internet’s connectionless service is called ( ). 44．( ) means that the switch must receive the entire packet before it canA TCP begin to transmit the first bit of the packet onto the outbound link.B UDP A Queuing delayC TCP/IP B Store-and-forward transmissionD IP C Packet loss37．In the following options, which does not use TCP?( ) D PropagationA SMTP 45．The network that forwards packets according to host destinationB internet telephone addresses is called ( ) network.C FTP A circuit-switchedD HTTP B packet-switched38．In the following options, which does not use UDP?( ) C virtual-circuitA Internet phone D datagramB video conferencing 46．The network that forwards packets according to virtual-circuit numbersC streaming multimedia is called ( ) network.D telnet A circuit-switched39．There are two fundamental approaches to building a network core, ( ) B packet-switchedand packet switching. C virtual-circuitA electrical current switching D datagramB circuit switching3。
计算机网络双语试题及答案
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。
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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。
假设该图像没有被压缩。
请问，通过56kbps的调制解调器信道来传输这幅图像需要多长时间？通过1Mbps的电缆调制解调器呢？通过10Mbps的以太网呢？通过100Mbps的以太网呢?)答：The image is 1024*768*3 bytes or 2359296 bytes.This is 18874368 bit. At 56,000 bits/sec, it takes about 337.042 sec. At 1,000,000 bits/sec, it takes about 18.874 sec. At 10,000,000 bits/sec, it takes about 1.887 sec. At 100,000,000 bits/sec, it takes about 0.189 sec.Chapter22-2. A noiseless 4-kHz channel is sampled every 1 msec. What is the maximum data rate?(一条无噪声4kHz信道按照每1ms一次进行采样，请问最大数据传输率是多少？)答：无噪声信道最大数据传输率公式：最大数据传输率=2Hlog2V b/s。
因此最大数据传输率决定于每次采样所产生的比特数，如果每次采样产生16bits，那么数据传输率可达128kbps；如果每次采样产生1024bits，那么可达8.2Mbps。
注意这是对无噪声信道而言的，实际信道总是有噪声的，其最大数据传输率由香农定律给出。
2-4. If a binary signal is sent over a 3-kHz channel whose signal-to-noise ratio is 20 dB, what is the maximum achievable data rate?(如果在一条3kHz的信道上发送一个二进制信号，该信道的信噪比为20dB，则最大可达到的数据传输率为多少？)答：信噪比为20 dB 即S/N =100由于log2101≈6.658，由香农定理，该信道的信道容量为3log2(1+100)=19.98kbps。
又根据乃奎斯特定理，发送二进制信号的3kHz 信道的最大数据传输速率为2*3*log22=6kbps。
所以可以取得的最大数据传输速率为6kbps。
2-5. What signal-to-noise ratio is needed to put a T1 carrier on a 50-kHz line?(在50kHz的线路上使用1T线路需要多大的信噪比？)答：为发送T1 信号，我们需要所以，在50kHz 线路上使用T1 载波需要93dB 的信噪比。
2-34. A signal is transmitted digitally over a 4-kHz noiseless channel with one sample every 125 µsec. How many bits per second are actually sent for each of these encoding methods?(a) CCITT 2.048 Mbps standard.(b) DPCM with a 4-bit relative signal value.(c) Delta modulation.（一个信号在4kHz的无噪声信道上以数字方式进行传输，没125us采样一次。
请问，按照以下的编码方法，每秒钟实际发送多少位？（a）CCITT 2.048Mbps标准。
（b）有4位相对信号值的DPCM。
（c）增量调制。
）答：a．CCITT 2.048Mbps 标准用32 个8 位数据样本组成一个125的基本帧，30 个信道用于传信息，2 个信道用于传控制信号。
在每一个4kHz 信道上发送的数据率就是8*8000=64kbps。
b．差分脉码调制（DPCM）是一种压缩传输信息量的方法，它发送的不是每一次抽样的二进制编码值，而是两次抽样的差值的二进制编码。
现在相对差值是4 位，所以对应每个4kHz 信道实际发送的比特速率为4*8000=32bps。
c．增量调制的基本思想是：当抽样时间间隔s t 很短时，模拟数据在两次抽样之间的变化很小，可以选择一个合适的量化值作为阶距。
把两次抽样的差别近似为不是增加一个就是减少一个。
这样只需用1bit 二进制信息就可以表示一次抽样结果，而不会引入很大误差。
因此，此时对应每个4kHz 信道实际发送的数据速率为1*8000=8kHz。
2-43. Suppose that x bits of user data are to be transmitted over a k-hop path in a packet-switched network as a series of packets, each containingp data bits and h header bits,with x >> p+h.The bit rate of the lines is b bps and the propagation delay is negligible.What value of p minimizes the total delay?(假定x位用户数据将以一系列分组形式，在一个分组交换网络中沿着一条共有k跳的路径向前传播，每个分组包含p位数据和h位的头，这里x>>p+h。
线路的传输率为b bps，传播延迟忽略不计。
请问，什么样的p值使总延迟最小？)答：所需要的分组总数是x /p，因此总的数据加上头信息交通量为(p+h)*x/p 位。
源端发送这些位需要时间为(p+h)*x/pb中间的路由器重传最后一个分组所花的总时间为(k-1)*(p+h)/ b因此我们得到的总的延迟为对该函数求p 的导数，得到令得到因为p＞0，所以故时能使总的延迟最小。
2-53. A CDMA receiver gets the following chips: (-1 +1 -3 +1 -1 -3 +1 +1). Assuming the chip sequences defined in Fig. 2-45(b), which stations transmitted, and which bits did each one send?(一个CDMA接收器得到了下面的时间片：(-1 +1 -3 +1 -1 -3 +1 +1)。
假设时间片序列如图2.45（b）中所定义，请问哪些移动站传输了数据？每个站发送了什么位?)答：Just compute the four normalized inner products:（1+1 3+1 1 3+1+1）d（1 1 1+1+1 1+1+1）/8=1（1+1 3+1 1 3+1+1）d（1 1+1 1+1+1+1 1）/8=1（1+1 3+1 1 3+1+1）d（1+1 1+1+1+1 1 1）/8=0（1+1 3+1 1 3+1+1）d（1+1 1 1 1 1+1 1）/8=1The result is that A and D sent 1 bits, B sent a 0 bit, and C was silent.Chapter33-3.The following data fragment occurs in the middle of a data stream for which the byte-stuffing algorithm described in the text is used: A B ESC C ESC FLAG FLAG D. What is the output after stuffing?(数据片断（A B ESC C ESC FLAG FLAG D）出现在一个数据流的中间，而成帧方式采用的是本章介绍的字节填充算法，请问经过填充之后的输出时什么？)答：After stuffing, we get A B ESC ESC C ESC ESC ESC FLAG ESC FLAG D.3-15. A bit stream 10011101 is transmitted using the standard CRC method described in the text. The generator polynomial is x3 + 1. Show the actual bit string transmitted. Suppose the third bit from the left is inverted during transmission. Show that this error is detected at the receiver's end.(利用本章中介绍的标准多项式CRC方法来传输位流1001101。