bài giải bài tập truyền số liệu

1 CHAPTER 1 Introduction Solutions to Odd-Numbered Review Questions and Exercises Review Questions 1. The five components of a data communication system are the sender, receiver, transmission medium, message, and protocol. 3. The three criteria are performance, reliability, and security. 5. Line configurations (or types of connections) are point-to-point and multipoint. 7. In half-duplex transmission, only one entity can send at a time; in a full-duplex transmission, both entities can send at the same time. 9. The number of cables for each type of network is: a. Mesh: n (n – 1) / 2 b. Star: n c. Ring: n – 1 d. Bus: one backbone and n drop lines 11. An internet is an interconnection of networks. The Internet is the name of a spe- cific worldwide network 13. Standards are needed to create and maintain an open and competitive market for manufacturers, to coordinate protocol rules, and thus guarantee compatibility of data communication technologies. Exercises 15. With 16 bits, we can represent up to 2 16 different colors. 17. a. Mesh topology: If one connection fails, the other connections will still be work- ing. b. Star topology: The other devices will still be able to send data through the hub; there will be no access to the device which has the failed connection to the hub. c. Bus Topology: All transmission stops if the failure is in the bus. If the drop-line fails, only the corresponding device cannot operate. 2 d. Ring Topology: The failed connection may disable the whole network unless it is a dual ring or there is a by-pass mechanism. 19. Theoretically, in a ring topology, unplugging one station, interrupts the ring. How- ever, most ring networks use a mechanism that bypasses the station; the ring can continue its operation. 21. See Figure 1.1 23. a. E-mail is not an interactive application. Even if it is delivered immediately, it may stay in the mail-box of the receiver for a while. It is not sensitive to delay. b. We normally do not expect a file to be copied immediately. It is not very sensi- tive to delay. c. Surfing the Internet is the an application very sensitive to delay. We except to get access to the site we are searching. 25. The telephone network was originally designed for voice communication; the Internet was originally designed for data communication. The two networks are similar in the fact that both are made of interconnections of small networks. The telephone network, as we will see in future chapters, is mostly a circuit-switched network; the Internet is mostly a packet-switched network. Figure 1.1 Solution to Exercise 21 Station Station Station Repeater Station Station Station Repeater Station Station Station Repeater Hub 1 CHAPTER 2 Network Models Solutions to Odd-Numbered Review Questions and Exercises Review Questions 1. The Internet model, as discussed in this chapter, include physical, data link, net- work, transport, and application layers. 3. The application layer supports the user. 5. Peer-to-peer processes are processes on two or more devices communicating at a same layer 7. Headers and trailers are control data added at the beginning and the end of each data unit at each layer of the sender and removed at the corresponding layers of the receiver. They provide source and destination addresses, synchronization points, information for error detection, etc. 9. The data link layer is responsible for a. framing data bits b. providing the physical addresses of the sender/receiver c. data rate control d. detection and correction of damaged and lost frames 11. The transport layer oversees the process-to-process delivery of the entire message. It is responsible for a. dividing the message into manageable segments b. reassembling it at the destination c. flow and error control 13. The application layer services include file transfer, remote access, shared data- base management, and mail services. Exercises 15. The International Standards Organization, or the International Organization of Standards, (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network com- munications is the Open Systems Interconnection (OSI) model. SolStd-02.fm Page 1 Saturday, January 21, 2006 9:52 AM 2 17. a. Reliable process-to-process delivery: transport layer b. Route selection: network layer c. Defining frames: data link layer d. Providing user services: application layer e. Transmission of bits across the medium: physical layer 19. a. Format and code conversion services: presentation layer b. Establishing, managing, and terminating sessions: session layer c. Ensuring reliable transmission of data: data link and transport layers d. Log-in and log-out procedures: session layer e. Providing independence from different data representation: presentation layer 21. See Figure 2.1. 23. Before using the destination address in an intermediate or the destination node, the packet goes through error checking that may help the node find the corruption (with a high probability) and discard the packet. Normally the upper layer protocol will inform the source to resend the packet. 25. The errors between the nodes can be detected by the data link layer control, but the error at the node (between input port and output port) of the node cannot be detected by the data link layer. Figure 2.1 Solution to Exercise 21 B/42 C/82 A/40 Sender Sender LAN1 LAN2 R1 D/80 T2 42 40 iDatajA D T2 80 82 iDatajA D SolStd-02.fm Page 2 Saturday, January 21, 2006 9:52 AM 1 CHAPTER 3 Data and Signals Solutions to Odd-Numbered Review Questions and Exercises Review Questions 1. Frequency and period are the inverse of each other. T = 1/ f and f = 1/T. 3. Using Fourier analysis. Fourier series gives the frequency domain of a periodic signal; Fourier analysis gives the frequency domain of a nonperiodic signal. 5. Baseband transmission means sending a digital or an analog signal without modu- lation using a low-pass channel. Broadband transmission means modulating a digital or an analog signal using a band-pass channel. 7. The Nyquist theorem defines the maximum bit rate of a noiseless channel. 9. Optical signals have very high frequencies. A high frequency means a short wave length because the wave length is inversely proportional to the frequency (λ = v/f), where v is the propagation speed in the media. 11. The frequency domain of a voice signal is normally continuous because voice is a nonperiodic signal. 13. This is baseband transmission because no modulation is involved. 15. This is broadband transmission because it involves modulation. Exercises 17. a. f = 1 / T = 1 / (5 s) = 0.2 Hz b. f = 1 / T = 1 / (12 μs) =83333 Hz = 83.333 × 10 3 Hz = 83.333 KHz c. f = 1 / T = 1 / (220 ns) = 4550000 Hz = 4.55× 10 6 Hz = 4.55 MHz 19. See Figure 3.1 21. Each signal is a simple signal in this case. The bandwidth of a simple signal is zero. So the bandwidth of both signals are the same. 23. a. (10 / 1000) s = 0.01 s b. (8 / 1000) s = 0. 008 s = 8 ms 2 c. ((100,000 × 8) / 1000) s = 800 s 25. The signal makes 8 cycles in 4 ms. The frequency is 8 /(4 ms) = 2 KHz 27. The signal is periodic, so the frequency domain is made of discrete frequencies. as shown in Figure 3.2. 29. Using the first harmonic, data rate = 2 × 6 MHz = 12 Mbps Using three harmonics, data rate = (2 × 6 MHz) /3 = 4 Mbps Using five harmonics, data rate = (2 × 6 MHz) /5 = 2.4 Mbps 31. –10 = 10 log 10 (P 2 / 5) → log 10 (P 2 / 5) = −1 → (P 2 / 5) = 10 −1 → P 2 = 0.5 W 33. 100,000 bits / 5 Kbps = 20 s 35. 1 μm × 1000 = 1000 μm = 1 mm 37. We have 4,000 log 2 (1 + 10 / 0.005) = 43,866 bps 39. To represent 1024 colors, we need log 2 1024 = 10 (see Appendix C) bits. The total number of bits are, therefore, 1200 × 1000 × 10 = 12,000,000 bits 41. We have SNR= (signal power)/(noise power). However, power is proportional to the square of voltage. This means we have Figure 3.1 Solution to Exercise 19 Figure 3.2 Solution to Exercise 27 0 20 50 100 20 0 Frequency domain Bandwidth = 200 − 0 = 200 Amplitude 10 volts Frequenc y 30 KHz 10 KHz 3 SNR = [(signal voltage) 2 ] / [(noise voltage) 2 ] = [(signal voltage) / (noise voltage)] 2 = 20 2 = 400 We then have SNR dB = 10 log 10 SNR ≈ 26.02 43. a. The data rate is doubled (C 2 = 2 × C 1 ). b. When the SNR is doubled, the data rate increases slightly. We can say that, approximately, (C 2 = C 1 + 1). 45. We have transmission time = (packet length)/(bandwidth) = (8,000,000 bits) / (200,000 bps) = 40 s 47. a. Number of bits = bandwidth × delay = 1 Mbps × 2 ms = 2000 bits b. Number of bits = bandwidth × delay = 10 Mbps × 2 ms = 20,000 bits c. Number of bits = bandwidth × delay = 100 Mbps × 2 ms = 200,000 bits 4 1 CHAPTER 4 Digital Transmission Solutions to Odd-Numbered Review Questions and Exercises Review Questions 1. The three different techniques described in this chapter are line coding, block cod- ing, and scrambling. 3. The data rate defines the number of data elements (bits) sent in 1s. The unit is bits per second (bps). The signal rate is the number of signal elements sent in 1s. The unit is the baud. 5. When the voltage level in a digital signal is constant for a while, the spectrum cre- ates very low frequencies, called DC components, that present problems for a sys- tem that cannot pass low frequencies. 7. In this chapter, we introduced unipolar, polar, bipolar, multilevel, and multitran- sition coding. 9. Scrambling, as discussed in this chapter, is a technique that substitutes long zero- level pulses with a combination of other levels without increasing the number of bits. 11. In parallel transmission we send data several bits at a time. In serial transmission we send data one bit at a time. Exercises 13. We use the formula s = c × N × (1/r) for each case. We let c = 1/2. a. r = 1 → s = (1/2) × (1 Mbps) × 1/1 = 500 kbaud b. r = 1/2 → s = (1/2) × (1 Mbps) × 1/(1/2) = 1 Mbaud c. r = 2 → s = (1/2) × (1 Mbps) × 1/2 = 250 Kbaud d. r = 4/3 → s = (1/2) × (1 Mbps) × 1/(4/3) = 375 Kbaud 15. See Figure 4.1 Bandwidth is proportional to (3/8)N which is within the range in Table 4.1 (B = 0 to N) for the NRZ-L scheme. 17. See Figure 4.2. Bandwidth is proportional to (12.5 / 8) N which is within the range in Table 4.1 (B = N to B = 2N) for the Manchester scheme. 2 19. See Figure 4.3. B is proportional to (5.25 / 16) N which is inside range in Table 4.1 (B = 0 to N/2) for 2B/1Q. 21. The data stream can be found as a. NRZ-I: 10011001. b. Differential Manchester: 11000100. c. AMI: 01110001. 23. The data rate is 100 Kbps. For each case, we first need to calculate the value f/N. We then use Figure 4.8 in the text to find P (energy per Hz). All calculations are approximations. a. f /N = 0/100 = 0 → P = 0.0 b. f /N = 50/100 = 1/2 → P = 0.3 c. f /N = 100/100 = 1 → P = 0.4 d. f /N = 150/100 = 1.5 → P = 0.0 Figure 4.1 Solution to Exercise 15 Figure 4.2 Solution to Exercise 17 00000000 11111111 00110011 01010101 Case a Case b Case c Case d Average Number of Changes = (0 + 0 + 8 + 4) / 4 = 3 for N = 8 B (3 / 8) N 00000000 11111111 00110011 01010101 Case a Case b Case c Case d Average Number of Changes = (15 + 15+ 8 + 12) / 4 = 12.5 for N = 8 B (12.5 / 8) N