Chapter 1. Introduction Section 1.1. Uses of Computer Networks Section 1.2. Network Hardware Section 1.3. Network Software Section 1.4. Reference Models Section 1.5. Example Networks Section 1.6. Network Standardization Section 1.7. Metric Units Section 1.8. Outline of the Rest of the Book Section 1.9. Summary Chapter 2. The Physical Layer
Section 2.1. The Theoretical Basis for Data Communication Section 2.2. Guided Transmission Media Section 2.3. Wireless Transmission Section 2.4. Communication Satellites Section 2.5. The Public Switched Telephone Network Section 2.6. The Mobile Telephone System Section 2.7. Cable Television Section 2.8. Summary Chapter 3. The Data Link Layer Section 3.1. Data Link Layer Design Issues Section 3.2. Error Detection and Correction Section 3.3. Elementary Data Link Protocols Section 3.4. Sliding Window Protocols Section 3.5. Protocol Verification Section 3.6. Example Data Link Protocols Section 3.7. Summary
Chapter 4. The Medium Access Control Sublayer Section 4.1. The Channel Allocation Problem Section 4.2. Multiple Access Protocols Section 4.3. Ethernet Section 4.4. Wireless LANs Section 4.5. Broadband Wireless Section 4.6. Bluetooth Section 4.7. Data Link Layer Switching Section 4.8. Summary
Chapter 5. The Network Layer Section 5.1. Network Layer Design Issues Section 5.2. Routing Algorithms Section 5.3. Congestion Control Algorithms
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Section 5.4. Quality of Service Section 5.5. Internetworking
Section 5.6. The Network Layer in the Internet Section 5.7. Summary
Chapter 6. The Transport Layer Section 6.1. The Transport Service
Section 6.2. Elements of Transport Protocols Section 6.3. A Simple Transport Protocol
Section 6.4. The Internet Transport Protocols: UDP Section 6.5. The Internet Transport Protocols: TCP Section 6.6. Performance Issues Section 6.7. Summary Chapter 7. The Application Layer Section 7.1. DNS—The Domain Name System Section 7.2. Electronic Mail Section 7.3. The World Wide Web Section 7.4. Multimedia Section 7.5. Summary Chapter 8. Network Security Section 8.1. Cryptography Section 8.2. Symmetric-Key Algorithms Section 8.3. Public-Key Algorithms Section 8.4. Digital Signatures Section 8.5. Management of Public Keys Section 8.6. Communication Security Section 8.7. Authentication Protocols Section 8.8. E-Mail Security Section 8.9. Web Security Section 8.10. Social Issues Section 8.11. Summary Chapter 9. Reading List and Bibliography Section 9.1. Suggestions for Further Reading Section 9.1.1. Introduction and General Works Section 9.2. Alphabetical Bibliography
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计算机网络课后题目
第一章
1. Imagine that you have trained your St. Bernard, Bernie, to carry a box of three 8mm tapes instead of a flask of brandy. (When your disk fills up, you consider that an emergency.) These tapes each contain 7 gigabytes. The dog can travel to your side, wherever you may be, at 18 km/hour. For what range of distances does Bernie have a higher data rate than a transmission line whose data rate (excluding overhead) is 150 Mbps?
2. An alternative to a LAN is simply a big timesharing system with terminals for all users. Give two advantages of a client-server system using a LAN.
3. The performance of a client-server system is influenced by two network factors: the bandwidth of the network (how many bits/sec it can transport) and the latency (how many seconds it takes for the first bit to get from the client to the server). Give an example of a network that exhibits high bandwidth and high latency. Then give an example of one with low bandwidth and low latency.
4. Besides bandwidth and latency, what other parameter is needed to give a good characterization of the quality of service offered by a network used for digitized voice traffic?
5. A factor in the delay of a store-and-forward packet-switching system is how long it takes to store and forward a packet through a switch. If switching time is 10 μsec, is this likely to be a major factor in the response of a client-server system where the client is in New York and the server is in California? Assume the
propagation speed in copper and fiber to be 2/3 the speed of light in vacuum. 6. A client-server system uses a satellite network, with the satellite at a height of 40,000 km. What is the best-case delay in response to a request?
7. In the future, when everyone has a home terminal connected to a computer network, instant public referendums on important pending legislation will become possible. Ultimately, existing
legislatures could be eliminated, to let the will of the people be expressed directly. The positive aspects of such a direct democracy are fairly obvious; discuss some of the negative aspects.
8. A collection of five routers is to be connected in a point-to-point subnet. Between each pair of routers, the designers may put a high-speed line, a medium-speed line, a low-speed line, or no line.
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If it takes 100 ms of computer time to generate and inspect each topology, how long will it take to inspect all of them?
9. A group of 2n - 1 routers are interconnected in a centralized binary tree, with a router at each tree node. Router i communicates with router j by sending a message to the root of the tree. The root then sends the message back down to j. Derive an approximate expression for the mean number of hops per message for large n, assuming that all router pairs are equally likely.
10.A disadvantage of a broadcast subnet is the capacity wasted when multiple hosts attempt to access the channel at the same time. As a simplistic example, suppose that time is divided into discrete slots, with each of the n hosts attempting to use the channel with probability p during each slot. What fraction of the slots are wasted due to collisions?
11.What are two reasons for using layered protocols?
12.The president of the Specialty Paint Corp. gets the idea to work with a local beer brewer to produce an invisible beer can (as an anti-litter measure). The president tells her legal department to look into it, and they in turn ask engineering for help. As a result, the chief engineer calls his counterpart at the other company to discuss the technical aspects of the project. The engineers then report back to their respective legal departments, which then confer by telephone to arrange the legal aspects. Finally, the two corporate presidents discuss the financial side of the deal. Is this an example of a multilayer protocol in the sense of the OSI model? 13.What is the principal difference between connectionless communication and connection-oriented communication?
14.Two networks each provide reliable connection-oriented service. One of them offers a reliable byte stream and the other offers a reliable message stream. Are these identical? If so, why is the distinction made? If not, give an example of how they differ. 15.What does ''negotiation'' mean when discussing network protocols? Give an example.
16.In Fig. 1-19, a service is shown. Are any other services implicit in this figure? If so, where? If not, why not?
17.In some networks, the data link layer handles transmission errors by requesting damaged frames to be retransmitted. If the probability of a frame's being damaged is p, what is the mean number of transmissions required to send a frame? Assume that acknowledgements are never lost.
18.Which of the OSI layers handles each of the following:
a. (a) Dividing the transmitted bit stream into frames. b. (b) Determining which route through the subnet to use.
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19.If the unit exchanged at the data link level is called a frame and the unit exchanged at the network level is called a packet, do frames encapsulate packets or do packets encapsulate frames? Explain your answer.
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?
21.List two ways in which the OSI reference model and the TCP/IP reference model are the same. Now list two ways in which they differ. 22.What is the main difference between TCP and UDP?
23.The subnet of Fig. 1-25(b) was designed to withstand a nuclear war. How many bombs would it take to partition the nodes into two disconnected sets? Assume that any bomb wipes out a node and all of the links connected to it.
24.The Internet is roughly doubling in size every 18 months. Although no one really knows for sure, one estimate put the number of hosts on it at 100 million in 2001. Use these data to compute the expected number of Internet hosts in the year 2010. Do you believe this? Explain why or why not.
25.When a file is transferred between two computers, two acknowledgement strategies are possible. In the first one, the file is chopped up into packets, which are individually acknowledged by the receiver, but the file transfer as a whole is not acknowledged. In the second one, the packets are not acknowledged individually, but the entire file is acknowledged when it arrives. Discuss these two approaches.
26.Why does ATM use small, fixed-length cells?
27.How long was a bit on the original 802.3 standard in meters? Use a transmission speed of 10 Mbps and assume the propagation speed in coax is 2/3 the speed of light in vacuum.
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?
29.Ethernet and wireless networks have some similarities and some differences. One property of Ethernet is that only one frame at a time can be transmitted on an Ethernet. Does 802.11 share this property with Ethernet? Discuss your answer. 30.Wireless networks are easy to install, which makes them inexpensive since installation costs usually far overshadow equipment costs. Nevertheless, they also have some disadvantages. Name two of them. 31.List two advantages and two disadvantages of having international standards for network protocols.
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