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《计算机网络：自顶向下方法》第4版的解答指南本书是Jim Kurose和Keith Ross合著的《计算机网络：自顶向下方法》第4版的复习问题和习题答案，版本日期为2007年10月29日。这个文档仅供教师使用，严禁复制或分发给他人，包括其他教师。请不要在公共网站上发布任何解决方案。如果你需要最新的解答手册，可以直接向作者申请。所有内容版权1996-2007年由J.F. Kurose和K.W. Ross持有，保留所有权利。第1章复习问题 1. "主机"和"端系统"这两个词在本书中互换使用。端系统包括个人电脑、工作站、Web服务器、邮件服务器、互联网连接的PDA、WebTV等。 2. 这个例子用外交礼仪来类比网络通信。假设A国大使Alice邀请B国大使Bob参加晚宴。Alice不会直接打电话给Bob说：“现在就来我们的餐桌”。她会提出一个日期和时间。Bob可能会回应说那天他没空，但另一个日期可以。Alice和Bob来回发送“消息”，直到他们就日期和时间达成一致。然后，Bob在约定的时间到达使馆，希望不超过约定时间的15分钟前后。外交礼仪还允许Alice或Bob在有合理理由的情况下礼貌地取消约定。 3. 通常，网络程序包含两个在不同主机上运行的程序进行通信。启动通信的程序是客户端。通常，客户端程序请求并接收服务器程序的服务。 4. 1. 拨号调制解调器通过电话线：住宅用户；2. 数字用户线路（DSL）通过电话线：住宅用户计算机网络的自顶向下方法是一种从应用层开始理解网络的视角，逐层向下深入到物理层。这种方法让学生首先了解网络如何为用户服务，然后再深入研究实现这些服务的技术细节。在第1章中，我们已经接触到网络的基本概念，如主机和端系统的角色，以及客户端-服务器模型的工作原理。此外，还讨论了两种常见的家庭上网方式：拨号调制解调器和DSL。在学习过程中，复习问题和习题旨在巩固对这些基本概念的理解，帮助学生将理论与实际应用相结合。例如，通过类比法解释网络通信的过程，让学生更好地理解主机间如何交换信息。而客户端-服务器模型的介绍则强调了网络服务提供和请求的动态。对于拨号调制解调器和DSL的区分，可以帮助学生了解不同接入技术的特点和应用场景，这对于理解网络架构和性能评估至关重要。随着章节的深入，学生将进一步学习网络的层次结构，每层的功能，以及它们如何协同工作来实现全球范围内的数据传输。

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Computer Networking: A Top-Down Approach

Featuring the Internet, 4

Edition

Solutions to Review Questions and Problems

Version Date: October 29, 2007

This document contains the solutions to review questions and problems for the 4th

edition of Computer Networking: A Top-Down Approach Featuring the Internet by Jim

Kurose and Keith Ross. These solutions are being made available to instructors ONLY.

Please do NOT copy or distribute this document to others (even other instructors). Please

do not post any solutions on a publicly-available Web site. We’ll be happy to provide a

copy (up-to-date) of this solution manual ourselves to anyone who asks.

Chapter 1 Review Questions

1. There is no difference. Throughout this text, the words “host” and “end system” are

used interchangeably. End systems include PCs, workstations, Web servers, mail

servers, Internet-connected PDAs, WebTVs, etc.

2. Suppose Alice, an ambassador of country A wants to invite Bob, an ambassador of

country B, over for dinner. Alice doesn’t simply just call Bob on the phone and say,

“come to our dinner table now”. Instead, she calls Bob and suggests a date and time.

Bob may respond by saying he’s not available that particular date, but he is available

another date. Alice and Bob continue to send “messages” back and forth until they

agree on a date and time. Bob then shows up at the embassy on the agreed date,

hopefully not more than 15 minutes before or after the agreed time. Diplomatic

protocols also allow for either Alice or Bob to politely cancel the engagement if they

have reasonable excuses.

3. A networking program usually has two programs, each running on a different host,

communicating with each other. The program that initiates the communication is the

client. Typically, the client program requests and receives services from the server

program.

4. 1. Dial-up modem over telephone line: residential; 2. DSL over telephone line:

residential or small office; 3. Cable to HFC: residential; 4. 100 Mbps switched

Etherent: company; 5. Wireless LAN: mobile; 6. Cellular mobile access (for example,

WAP): mobile

5. HFC bandwidth is shared among the users. On the downstream channel, all packets

emanate from a single source, namely, the head end. Thus, there are no collisions in

the downstream channel.

6. Current possibilities include: dial-up; DSL; cable modem; fiber-to-the-home.

7. Ethernet LANs have transmission rates of 10 Mbps, 100 Mbps, 1 Gbps and 10 Gbps.

For an X Mbps Ethernet (where X = 10, 100, 1,000 or 10,000), a user can

continuously transmit at the rate X Mbps if that user is the only person sending data.

If there are more than one active user, then each user cannot continuously transmit at

X Mbps.

8. Ethernet most commonly runs over twisted-pair copper wire and “thin” coaxial cable.

It also can run over fibers optic links and thick coaxial cable.

9. Dial up modems: up to 56 Kbps, bandwidth is dedicated; ISDN: up to 128 kbps,

bandwidth is dedicated; ADSL: downstream channel is .5-8 Mbps, upstream channel

is up to 1 Mbps, bandwidth is dedicated; HFC, downstream channel is 10-30 Mbps

and upstream channel is usually less than a few Mbps, bandwidth is shared.

10. There are two most popular wireless Internet access technologies today:

a) Wireless LAN

In a wireless LAN, wireless users transmit/receive packets to/from a base station

(wireless access point) within a radius of few tens of meters. The base station is

typically connected to the wired Internet and thus serves to connect wireless users

to the wired network.

b) Wide-area wireless access network

In these systems, packets are transmitted over the same wireless infrastructure

used for cellular telephony, with the base station thus being managed by a

telecommunications provider. This provides wireless access to users within a

radius of tens of kilometers of the base station.

11. A circuit-switched network can guarantee a certain amount of end-to-end bandwidth

for the duration of a call. Most packet-switched networks today (including the

Internet) cannot make any end-to-end guarantees for bandwidth.

12. In a packet switched network, the packets from different sources flowing on a link do

not follow any fixed, pre-defined pattern. In TDM circuit switching, each host gets

the same slot in a revolving TDM frame.

13. At time t

the sending host begins to transmit. At time t

= L/R

, the sending host

completes transmission and the entire packet is received at the router (no propagation

delay). Because the router has the entire packet at time t1, it can begin to transmit the

packet to the receiving host at time t

. At time t

= t

+ L/R

, the router completes

transmission and the entire packet is received at the receiving host (again, no

propagation delay). Thus, the end-to-end delay is L/R

+ L/R

14. A tier-1 ISP connects to all other tier-1 ISPs; a tier-2 ISP connects to only a few of

the tier-1 ISPs. Also, a tier-2 ISP is a customer of one or more tier-1.

15. a) 2 users can be supported because each user requires half of the link bandwidth.

b) Since each user requires 1Mbps when transmitting, if two or fewer users transmit

simultaneously, a maximum of 2Mbps will be required. Since the available

bandwidth of the shared link is 2Mbps, there will be no queuing delay before the

link. Whereas, if three users transmit simultaneously, the bandwidth required

will be 3Mbps which is more than the available bandwidth of the shared link. In

this case, there will be queuing delay before the link.

c) Probability that a given user is transmitting = 0.2

d) Probability that all three users are transmitting simultaneously =

= (0.2)

= 0.008. Since the queue grows when all the users are transmitting, the

fraction of time during which the queue grows (which is equal to the probability

that all three users are transmitting simultaneously) is 0.008.

16. The delay components are processing delays, transmission delays, propagation

delays, and queuing delays. All of these delays are fixed, except for the queuing

delays, which are variable.

17. Java Applet

18. 10msec; d/s; no; no

19. a) 500 kbps

b) 64 seconds

c) 100kbps; 320 seconds

20. End system A breaks the large file into chunks. To each chunk, it adds header

generating multiple packets from the file. The header in each packet includes the

address of the destination: end system B. The packet switch uses the destination

address to determine the outgoing link. Asking which road to take is analogous to a

packet asking which outgoing link it should be forwarded on, given the packet’s

address.

21. Java Applet

22. Five generic tasks are error control, flow control, segmentation and reassembly,

multiplexing, and connection setup. Yes, these tasks can be duplicated at different

layers. For example, error control is often provided at more than one layer.

23. The five layers in the Internet protocol stack are – from top to bottom – the

application layer, the transport layer, the network layer, the link layer, and the

physical layer. The principal responsibilities are outlined in Section 1.5.1.

24. Application-layer message: data which an application wants to send and passed onto

the transport layer; transport-layer segment: generated by the transport layer and

encapsulates application-layer message with transport layer header; network-layer

datagram: encapsulates transport-layer segment with a network-layer header; link-

layer frame: encapsulates network-layer datagram with a link-layer header.

25. Routers process layers 1 through 3. (This is a little bit of a white lie, as modern

routers sometimes act as firewalls or caching components, and process layer four as

well.) Link layer switches process layers 1 through 2. Hosts process all five layers.

26. a) Virus

Requires some form of human interaction to spread. Classic example: E-mail

viruses.

b)Worms

No user replication needed. Worm in infected host scans IP addresses and port

numbers, looking for vulnerable processes to infect.

c) Trojan horse

Hidden, devious part of some otherwise useful software.

27. Creation of a botnet requires an attacker to find vulnerability in some application or

system (e.g. exploiting the buffer overflow vulnerability that might exist in an

application). After finding the vulnerability, the attacker needs to scan for hosts that

are vulnerable. The target is basically to compromise a series of systems by

exploiting that particular vulnerability. Any system that is part of the botnet can

automatically scan its environment and propagate by exploiting the vulnerability. An

important property of such botnets is that the originator of the botnet can remotely

control and issue commands to all the nodes in the botnet. Hence, it becomes

possible for the attacker to issue a command to all the nodes, that target a single

node (for example, all nodes in the botnet might be commanded by the attacker to

send a TCP SYN message to the target, which might result in a TCP SYN flood

attack at the target).

28. Trudy can pretend to be Bob to Alice (and vice-versa) and partially or completely

modify the message(s) being sent from Bob to Alice. For example, she can easily

change the phrase “Alice, I owe you $1000” to “Alice, I owe you $10,000”.

Furthermore, Trudy can even drop the packets that are being sent by Bob to Alice

(and vise-versa), even if the packets from Bob to Alice are encrypted.

Chapter 1 Problems:

Problem 1.

There is no single right answer to this question. Many protocols would do the trick.

Here's a simple answer below:

Messages from ATM machine to Server

Msg name purpose

-------- -------

HELO <userid> Let server know that there is a card in the

ATM machine

ATM card transmits user ID to Server

PASSWD <passwd> User enters PIN, which is sent to server

BALANCE User requests balance

WITHDRAWL <amount> User asks to withdraw money

BYE user all done

剩余63页未读，继续阅读

评论收藏

内容反馈

zhaofey1985

2011-12-01

答案不错，而且是word的~~
zhangyiryudo

2011-09-25

没有原题，没有书，答案还行
z3w1h4

2013-01-29

很不错，解释得很清楚，刚好老师用的就是这版本
yetiyoohoo

2011-11-05

答案很好，用处很大，对照起来了解自己写的是否正确，感谢分享
xkj5090379087

2011-09-26

图片有点小，不过字很大，还是能看的。

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