陕西师范大学 计算机网络课后习题指导 Solutions for Problem Sets of Computer Networking 王涛秦石醉张阳阳张敏江等编著 6/25/2015 本书提供教材：Computer Networking A Top-down Approach6 th edition的配套习题指导， 习题及相关资源的原始版权归原作者所有
陕西师范大学 计算机网络课后习题指导 Solutions for Problem Sets of Computer Networking 王涛 秦石醉 张阳阳 张敏江等 编著 6/25/2015 本书提供教材：Computer Networking A Top-down Approach 6th edition 的配套习题指导， 习题及相关资源的原始版权归原作者所有
说明 本书系陕西师范大学内部教学参考使用，编者对教程所包含内容没有权利要求， 一切权利归Computer Networking A Top--down Approach6 th edition原作者及出版 社所有。 本书由王涛、秦石醉、张阳阳、张敏江等人编著，部分内容参考自网络公开资源。 编写过程难免有错误，请谅解。 本书习题基于英文经典计算机网络教材Computer Networking A Top-dowm Approach”第六版
说明 本书系陕西师范大学内部教学参考使用，编者对教程所包含内容没有权利要求， 一切权利归 Computer Networking A Top-down Approach 6th edition 原作者及出版 社所有。 本书由王涛、秦石醉、张阳阳、张敏江等人编著，部分内容参考自网络公开资源。 编写过程难免有错误，请谅解。 本书习题基于英文经典计算机网络教材“Computer Networking A Top-down Approach”第六版
Table of Contents 说明 0 Chapter 1 Computer Networks and the Internet. .1 Chapter 2 Application Layer .19 Chapter 3 Transport Layer..... 36 Chapter 4 The Network Layer........ 69 Chapter 5 The Link Layer:Links,Access Networks,and LANs..............93 Chapter 6 Wireless and Mobile Networks... 110 Chapter 7 Multimedia Networking..... 117 Chapter 8 Security in Computer Networks.... .133 Chapter 9 Network Management....... 145
Table of Contents 说明.................................................................................................................... 0 Chapter 1 Computer Networks and the Internet ......................................... 1 Chapter 2 Application Layer ........................................................................19 Chapter 3 Transport Layer...........................................................................36 Chapter 4 The Network Layer......................................................................69 Chapter 5 The Link Layer: Links, Access Networks, and LANs..............93 Chapter 6 Wireless and Mobile Networks.................................................110 Chapter 7 Multimedia Networking ............................................................117 Chapter 8 Security in Computer Networks...............................................133 Chapter 9 Network Management...............................................................145
计算机网络课后习题指导 陕西师范大学 Chapter 1 Computer Networks and the Internet PI.Design and describe an application-level protocol to be used between an automatic teller machine and a bank's centralized computer.Your protocol should allow a user's card and password to be anaccount withdrawal to be made (that is,money disbursed to the user).Your protocol entities should be able to handle the all-too-common case in which there is not enough money in the account to cover the withdrawal.Specify your protocol by listing the messages exchanged and the action taken by theautomatic teller machine or the bank's centralized computer on transmission and messaes Sketch the operation of your simple withdrawal with diagram similar to that in Figure 12.Explicitly state the assumptions made by your protocol about the underlying end-to-end transport service. 答：本题不止一个答案，很多协议都能解决这个问趣，下面是一个简单的例 子： HELO <userid> 2 now that there。card in the user all done ATM(p) Me purpose opn.) ERR
计算机网络课后习题指导 陕西师范大学 1 Chapter 1 Computer Networks and the Internet P1. Design and describe an application-level protocol to be used between an automatic teller machine and a bank’s centralized computer. Your protocol should allow a user’s card and password to be verified, the account balance (which is maintained at the centralized computer) to be queried, and anaccount withdrawal to be made (that is, money disbursed to the user). Your protocol entities should be able to handle the all-too-common case in which there is not enough money in the account to cover the withdrawal. Specify your protocol by listing the messages exchanged and the action taken by theautomatic teller machine or the bank’s centralized computer on transmission and receipt of messages. Sketch the operation of your protocol for the case of a simple withdrawal with no errors, using a diagram similar to that in Figure 1.2. Explicitly state the assumptions made by your protocol about the underlying end-to-end transport service. 答：本题不止一个答案，很多协议都能解决这个问题，下面是一个简单的例 子：
计算机网络课后习题指导 陕西师范大学 Correct operation client server HE10(u银Rxid) 华 BALANCE Insitiwhen theret eh moy Ho世aerid) k it valid uaerid) PASSKD〈gawd BALANCE ERR (not enough funds) P2.Equation 1.1 gives a formula for the end-to-end delay of sending one packet of length L over N links of transmission rateR.Generalize this formula for sending Psuch packets back-to-back over the N links 答：由一个分组端到端时延公式：dn-o-end=N可得，当连续发送P个分 组时，得到时延为：demd-to-end=N后×P。 P3.Consider an application that transmits data at a steady rate (for example,the sender generates an N-bit unit of data every k time units,where k is small and fixed).Also,when such an application starts,it will continue running for a relatively long period of time.Answer the following questions, briefly justifying your answer: a Would a packet-switched network or a circuit-switched network be more appropriate for this application?Why? b.Suppose that a packet-switched network is used and the only traffic in this network comes from such applications as described above.Furthermore.assume that the sum of the application data rates is less than the capacities of each and every link.Is some form of congestion control needed? Why? 答：a.电路交换网更适合所描述的应用，因为这个应用要求在可预测的平滑带宽上进行长期 的会话。由于传输速率是已知，且波动不大 因此可 以给 应用会话话路预留带宽而不会有 太多的浪费。另外，我们不需要太过担心由长时间典型会话应用积累起来的，建立和拆除电 路时耗费的开销时间。 b.由于所给的带宽足够大，因此该网络中不需要拥塞控制机制。最坏的情况下（几乎可能拥 2
计算机网络课后习题指导 陕西师范大学 2 P2. Equation 1.1 gives a formula for the end-to-end delay of sending one packet of length L over N links of transmission rate R. Generalize this formula for sending P such packets back-to-back over the N links. 答：由一个分组端到端时延公式：d = 可得，当连续发送 P 个分 组时，得到时延为：d = × 。 P3. Consider an application that transmits data at a steady rate (for example, the sender generates an N-bit unit of data every k time units, where k is small and fixed). Also, when such an application starts, it will continue running for a relatively long period of time. Answer the following questions, briefly justifying your answer: a. Would a packet-switched network or a circuit-switched network be more appropriate for this application? Why? b. Suppose that a packet-switched network is used and the only traffic in this network comes from such applications as described above. Furthermore, assume that the sum of the application data rates is less than the capacities of each and every link. Is some form of congestion control needed? Why? 答：a. 电路交换网更适合所描述的应用，因为这个应用要求在可预测的平滑带宽上进行长期 的会话。由于传输速率是已知，且波动不大，因此可以给各应用会话话路预留带宽而不会有 太多的浪费。另外，我们不需要太过担心由长时间典型会话应用积累起来的，建立和拆除电 路时耗费的开销时间。 b. 由于所给的带宽足够大，因此该网络中不需要拥塞控制机制。最坏的情况下（几乎可能拥