計算機網(wǎng)絡第五版(andrew)官方英文版答案

1、COMPUTER NETWORKSFIFTH EDITIONPROBLEM SOLUTIONSANDREW S. TANENBAUMVrije Universiteit Amsterdam, The NetherlandsandDAVID WETHERALLUniversity of Washington Seattle, WAPRENTICE HALLUpper Saddle River, NJPROBLEM SOLUTIONS 1S

2、OLUTIONS TO CHAPTER 1 PROBLEMS1. The dog can carry 21 gigabytes, or 168 gigabits. A speed of 18 km/hour equals 0.005 km/sec. The time to travel distance x km is x /0.005 = 200x sec, yielding a data rate of 168/200x Gbps

3、or 840/x Mbps. For x < 5.6 km, the dog has a higher rate than the communication line.(i) If dog’s speed is doubled, maximum value of x is also doubled.(ii) If tape capacity is doubled, value of x is also doubled.(iii)

4、 If data rate of the transmission line is doubled, value of x is halved.2. The LAN model can be grown incrementally. If the LAN is just a long cable. it cannot be brought down by a single failure (if the servers are repl

5、icated) It is probably cheaper. It provides more computing power and better interactive interfaces.3. A transcontinental fiber link might have many gigabits/sec of bandwidth, but the latency will also be high due to the

6、speed of light propagation over thousands of kilometers. In contrast, a 56-kbps modem calling a computer in the same building has low bandwidth and low latency.4. A uniform delivery time is needed for voice as well as vi

7、deo, so the amount of jitter in the network is important. This could be expressed as the standard deviation of the delivery time. Having short delay but large variability is ac- tually worse than a somewhat longer delay

8、and low variability. For financial transaction traffic, reliability and security are very important.5. No. The speed of propagation is 200,000 km/sec or 200 meters/μsec. In 10 μsec the signal travels 2 km. Thus, each swi

9、tch adds the equivalent of 2 km of extra cable. If the client and server are separated by 5000 km, traversing even 50 switches adds only 100 km to the total path, which is only 2%. Thus, switching delay is not a major fa

10、ctor under these circumstances.6. The request has to go up and down, and the response has to go up and down. The total path length traversed is thus 160,000 km. The speed of light in air and vacuum is 300,000 km/sec, so

11、the propagation delay alone is 160,000/300,000 sec or about 533 msec.7. There is obviously no single correct answer here, but the following points seem relevant. The present system has a great deal of inertia (checks and

12、 bal- ances) built into it. This inertia may serve to keep the legal, economic, and social systems from being turned upside down every time a different party comes to power. Also, many people hold strong opinions on cont