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Computer Networking: A Top-Down Approach

James Kurose, Keith Ross

Chapter 1

Computer Networks and the Internet - all with Video Answers

Educators

Chapter Questions

Problem 1

What is the difference between a host and an end system? List several different types of end systems. Is a Web server an end system?

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01:45

Problem 2

The word protocol is often used to describe diplomatic relations. How does Wikipedia describe diplomatic protocol?

Jennifer Stoner
Jennifer Stoner
Numerade Educator

Problem 3

$$
\text { Why are standards important for protocols? }
$$

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Problem 4

List six access technologies. Classify each one as home access, enterprise access, or wide-area wireless access.

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Problem 5

Is HFC transmission rate dedicated or shared among users? Are collisions possible in a downstream HFC channel? Why or why not?

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01:48

Problem 6

List the available residential access technologies in your city. For each type of access, provide the advertised downstream rate, upstream rate, and monthly price.

Michael Cooper
Michael Cooper
Numerade Educator

Problem 7

$$
\text { What is the transmission rate of Ethernet LANs? }
$$

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Problem 8

$$
\text { What are some of the physical media that Ethernet can run over? }
$$

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Problem 9

Dial-up modems, HFC, DSL and FTTH are all used for residentia access. For each of these access technologies, provide a range of transmission rates and comment on whether the transmission rate

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02:15

Problem 10

Describe the most popular wireless Internet access technologies today. Compare and contrast them.

Eric Goldman
Eric Goldman
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Problem 11

Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are $R_1$ and $R_2$, respectively. Assuming that the switch uses store-and-forward packet switching, what is the total end-to-end delay to send a packet of length $L$ ? (Ignore queuing, propagation delay, and processing delay.)

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Problem 12

What advantage does a circuit-switched network have over a packet-switched network? What advantages does TDM have over FDM in a circuit-switched network?

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Problem 13

Suppose users share a 2 Mbps link. Also suppose each user transmits continuously at 1 Mbps when transmitting, but each user transmits only 20 percent of the time. (See the discussion of statistical multiplexing in Section 1.3.)
a. When circuit switching is used, how many users can be supported?
b. For the remainder of this problem, suppose packet switching is used. Why will there be essentially no queuing delay before the link if two or fewer users transmit at the same time? Why will there be a queuing delay if three users transmit at the same time?
c. Find the probability that a given user is transmitting.
d. Suppose now there are three users. Find the probability that at any given time, all three users are transmitting simultaneously. Find the fraction of time during which the aueue grows.

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01:23

Problem 14

Why will two ISPs at the same level of the hierarchy often peer with each other? How does an IXP earn money?

Kaylee Mcclellan
Kaylee Mcclellan
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Problem 15

Some content providers have created their own networks. Describe Google's network. What motivates content providers to create these networks?

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Problem 16

Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end-to-end delay. Which of these delays are constant and which are variable?

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Problem 17

Visit the Transmission Versus Propagation Delay applet at the companion Web site. Among the rates, propagation delay, and packet sizes available, find a combination for which the sender finishes transmitting before the first bit of the packet reaches the receiver. Find another combination for which the first bit of the packet reaches the receiver before the sender finishes transmitting.

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02:53

Problem 18

How long does it take a packet of length 1,000 bytes to propagate over a link of distance $2,500 \mathrm{~km}$, propagation speed $2.5 \cdot 10^8 \mathrm{~m} / \mathrm{s}$, and transmission rate $2 \mathrm{Mbps}$ ? More generally, how long does it take a packet of length $L$ to propagate over a link of distance $d$, propagation speed $s$, and transmission

Samriddhi Singh
Samriddhi Singh
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Problem 19

Suppose Host A wants to send a large file to Host B. The path from Host A to Host $B$ has three links, of rates $R_1=500 \mathrm{kbps}, R_2=2 \mathrm{Mbps}$, and $R_3=1 \mathrm{Mbps}$.
a. Assuming no other traffic in the network, what is the throughput for the file transfer?
b. Suppose the file is 4 million bytes. Dividing the file size by the throughput, roughlly how long will it take to transfer the file to Host B?
c. Repeat (a) and (b), but now with $R_2$ reduced to $100 \mathrm{kbps}$.

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Problem 20

Suppose end system A wants to send a large file to end system B. At a very high level, describe how end system A creates packets from the file. When one of these packets arrives to a router, what information in the packet does the router use to dctermine the link onto which the packet is forwarded?
Why is packet switching in the Internet analogous to driving from one city to another and asking directions along the way?

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Problem 21

Visit the Queuing and Loss applet at the companion Web site. What is the maximum emission rate and the minimum transmission rate? With those rates, what is the traffic intensity? Run the applet with these rates and determine how long it takes for packet loss to occur. Then repeat the experiment a second time and determine again how long it takes for packet loss to occur. Are the values different? Why or why not?

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01:21

Problem 22

List five tasks that a layer can perform. Is it possible that one (or more) of these tasks could be performed by two (or more) layers?

Jennifer Stoner
Jennifer Stoner
Numerade Educator
01:21

Problem 23

What are the five layers in the Internet protocol stack? What are the principal responsibilities of each of these layers?

Jennifer Stoner
Jennifer Stoner
Numerade Educator
01:40

Problem 24

What is an application-layer message? A transport-layer segment? A network-layer datagram? A link-layer frame?

Vysakh M
Vysakh M
Numerade Educator
01:40

Problem 25

Which layers in the Internet protocol stack does a router process? Which layers does a link-layer switch process? Which layers does a host process?

Vysakh M
Vysakh M
Numerade Educator
01:13

Problem 26

\text { What is the difference between a virus and a worm? }

Joanna Quigley
Joanna Quigley
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02:16

Problem 27

\text { Describe how a botnet can be created and how it can be used for a DDoS attack. }

Jennifer Stoner
Jennifer Stoner
Numerade Educator
02:12

Problem 28

Suppose Alice and Bob are sending packets to each other over a computer network. Suppose Trudy positions herself in the network so that she can capture all the packets sent by Alice and send whatever she wants to Bob; she can also capture all the packets sent by Bob and send whatever she wants to Alice. List some of the malicious things Trudy can do from this position.

Kris Bright
Kris Bright
Numerade Educator