计算机网络第四版课后英文题目(4)

all the stations whose addresses are prime numbers suddenly become ready at once, how many bit slots are needed to resolve the contention?

11.A collection of 2n stations uses the adaptive tree walk protocol to arbitrate access to a shared cable. At a certain instant, two of them become ready. What are the minimum, maximum, and mean number of slots to walk the tree if 2n 1?

12.The wireless LANs that we studied used protocols such as MACA instead of using CSMA/CD. Under what conditions, if any, would it be possible to use CSMA/CD instead?

13.What properties do the WDMA and GSM channel access protocols have in common? See Chap. 2 for GSM.

14.Six stations, A through F, communicate using the MACA protocol. Is it possible that two transmissions take place simultaneously? Explain your answer.

15.A seven-story office building has 15 adjacent offices per floor. Each office contains a wall socket for a terminal in the front wall, so the sockets form a rectangular grid in the vertical plane, with a separation of 4 m between sockets, both horizontally and

vertically. Assuming that it is feasible to run a straight cable between any pair of sockets, horizontally, vertically, or

diagonally, how many meters of cable are needed to connect all sockets using

a. (a) a star configuration with a single router in the middle? b. (b) an 802.3 LAN?

16.What is the baud rate of the standard 10-Mbps Ethernet?

17.Sketch the Manchester encoding for the bit stream: 0001110101. 18.Sketch the differential Manchester encoding for the bit stream of the previous problem. Assume the line is initially in the low state. 19.A 1-km-long, 10-Mbps CSMA/CD LAN (not 802.3) has a propagation speed of 200 m/μsec. Repeaters are not allowed in this system. Data frames are 256 bits long, including 32 bits of header, checksum, and other overhead. The first bit slot after a successful transmission is reserved for the receiver to capture the channel in order to send a 32-bit acknowledgement frame. What is the effective data rate, excluding overhead, assuming that there are no collisions?

20.Two CSMA/CD stations are each trying to transmit long (multiframe) files. After each frame is sent, they contend for the channel, using the binary exponential backoff algorithm. What is the probability that the contention ends on round k, and what is the mean number of rounds per contention period?

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21.Consider building a CSMA/CD network running at 1 Gbps over a 1-km cable with no repeaters. The signal speed in the cable is 200,000 km/sec. What is the minimum frame size?

22.An IP packet to be transmitted by Ethernet is 60 bytes long, including all its headers. If LLC is not in use, is padding needed in the Ethernet frame, and if so, how many bytes?

23.Ethernet frames must be at least 64 bytes long to ensure that the transmitter is still going in the event of a collision at the far end of the cable. Fast Ethernet has the same 64-byte minimum frame size but can get the bits out ten times faster. How is it possible to maintain the same minimum frame size? 24.Some books quote the maximum size of an Ethernet frame as 1518 bytes instead of 1500 bytes. Are they wrong? Explain your answer.

25.The 1000Base-SX specification states that the clock shall run at 1250 MHz, even though gigabit Ethernet is only supposed to deliver 1 Gbps. Is this higher speed to provide for an extra margin of safety? If not, what is going on here?

26.How many frames per second can gigabit Ethernet handle? Think carefully and take into account all the relevant cases. Hint: the fact that it is gigabit Ethernet matters.

27.Name two networks that allow frames to be packed back-to-back. Why is this feature worth having?

28.In Fig. 4-27, four stations, A, B, C, and D, are shown. Which of the last two stations do you think is closest to A and why?

29.Suppose that an 11-Mbps 802.11b LAN is transmitting 64-byte frames back-to-back over a radio channel with a bit error rate of 10-7. How many frames per second will be damaged on average?

30.An 802.16 network has a channel width of 20 MHz. How many bits/sec can be sent to a subscriber station?

31.IEEE 802.16 supports four service classes. Which service class is the best choice for sending uncompressed video?

32.Give two reasons why networks might use an error-correcting code instead of error detection and retransmission. 33.From Fig. 4-35, we see that a Bluetooth device can be in two piconets at the same time. Is there any reason why one device cannot be the master in both of them at the same time?

34.Figure 4-25 shows several physical layer protocols. Which of these is closest to the Bluetooth physical layer protocol? What is the biggest difference between the two?

35.Bluetooth supports two types of links between a master and a slave. What are they and what is each one used for?

36.Beacon frames in the frequency hopping spread spectrum variant of 802.11 contain the dwell time. Do you think the analogous beacon

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frames in Bluetooth also contain the dwell time? Discuss your answer.

37.Consider the interconnected LANs showns in Fig. 4-44. Assume that hosts a and b are on LAN 1, c is on LAN 2, and d is on LAN 8. Initially, hash tables in all bridges are empty and the spanning tree shown in Fig 4-44(b) is used. Show how the hash tables of different bridges change after each of the following events happen in sequence, first (a) then (b) and so on.

a. (a) a sends to d. b. (b) c sends to a. c. (c) d sends to c.

d. (d) d moves to LAN 6. e. (e) d sends to a.

38.One consequence of using a spanning tree to forward frames in an extended LAN is that some bridges may not participate at all in forwarding frames. Identify three such bridges in Fig. 4-44. Is there any reason for keeping the …… 此处隐藏：9449字，全部文档内容请下载后查看。喜欢就下载吧 ……