Solution Manual for Computer Networking, 8th Edition by
James Kurose
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
,Computer Networking: A Top-Down Approach, 8th Edition
Solutions to Review Questions and Problems
Version Date: August 2020
This document contains the solutions to review questions and problems for the 8th edition of
Computer Networking: A Top-Down Approach 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.
Acknowledgments: Over the years, several students and colleagues have helped us prepare this
solutions manual. Special thanks goes to Honggang Zhang, Rakesh Kumar, Prithula Dhungel, Vijay
Annapureddy, Yifan Zhou. Also thanks to all the readers who have made suggestions and
corrected errors.
All material © copyright 1996-2020 by J.F. Kurose and K.W. Ross. All rights reserved
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
,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, PDAs,
Internet-connected game consoles, etc.
2. From Wikipedia: Diplomatic protocol is commonly described as a set of international courtesy
rules. These well-established and time-honored rules have made it easier for nations and
people to live and work together. Part of protocol has always been the acknowledgment of the
hierarchical standing of all present. Protocol rules are based on the principles of civility.
3. Standards are important for protocols so that people can create networking systems and
products that interoperate.
4. 1. Dial-up modem over telephone line: home; 2. DSL over telephone line: home or small
office; 3. Cable to HFC: home; 4. 100 Mbps switched Ethernet: enterprise.
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. In most American cities, the 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.
8. Today, Ethernet most commonly runs over twisted-pair copper wire. It also can run over fibers
optic links.
9. ADSL: up to 24 Mbps downstream and 2.5 Mbps upstream, bandwidth is dedicated; HFC, rates
up to 42.8 Mbps and upstream rates of up to 30.7 Mbps, bandwidth is shared. FTTH: 2-
10Mbps upload; 10-20 Mbps download; bandwidth is not shared.
10. There are two popular wireless Internet access technologies today:
a. Wifi (802.11) In a wireless LAN, wireless users transmit/receive packets to/from an
base station (i.e., 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. 3G and 4G wide-area wireless access networks. 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. At time t0 the sending host begins to transmit. At time t1 = L/R1, 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
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
, packet to the receiving host at time t1. At time t2 = t1 + L/R2, 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/R1 + L/R2.
12. 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. FDM requires sophisticated analog hardware to
shift signal into appropriate frequency bands.
13. 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)3 = 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.
14. If the two ISPs do not peer with each other, then when they send traffic to each other they
have to send the traffic through a provider ISP (intermediary), to which they have to pay for
carrying the traffic. By peering with each other directly, the two ISPs can reduce their
payments to their provider ISPs. An Internet Exchange Points (IXP) (typically in a standalone
building with its own switches) is a meeting point where multiple ISPs can connect and/or
peer together. An ISP earns its money by charging each of the the ISPs that connect to the IXP
a relatively small fee, which may depend on the amount of traffic sent to or received from the
IXP.
15. Google's private network connects together all its data centers, big and small. Traffic between
the Google data centers passes over its private network rather than over the public Internet.
Many of these data centers are located in, or close to, lower tier ISPs. Therefore, when Google
delivers content to a user, it often can bypass higher tier ISPs. What motivates content
providers to create these networks? First, the content provider has more control over the user
experience, since it has to use few intermediary ISPs. Second, it can save money by sending
less traffic into provider networks. Third, if ISPs decide to charge more money to highly
profitable content providers (in countries where net neutrality doesn't apply), the content
providers can avoid these extra payments.
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.
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
James Kurose
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
,Computer Networking: A Top-Down Approach, 8th Edition
Solutions to Review Questions and Problems
Version Date: August 2020
This document contains the solutions to review questions and problems for the 8th edition of
Computer Networking: A Top-Down Approach 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.
Acknowledgments: Over the years, several students and colleagues have helped us prepare this
solutions manual. Special thanks goes to Honggang Zhang, Rakesh Kumar, Prithula Dhungel, Vijay
Annapureddy, Yifan Zhou. Also thanks to all the readers who have made suggestions and
corrected errors.
All material © copyright 1996-2020 by J.F. Kurose and K.W. Ross. All rights reserved
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
,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, PDAs,
Internet-connected game consoles, etc.
2. From Wikipedia: Diplomatic protocol is commonly described as a set of international courtesy
rules. These well-established and time-honored rules have made it easier for nations and
people to live and work together. Part of protocol has always been the acknowledgment of the
hierarchical standing of all present. Protocol rules are based on the principles of civility.
3. Standards are important for protocols so that people can create networking systems and
products that interoperate.
4. 1. Dial-up modem over telephone line: home; 2. DSL over telephone line: home or small
office; 3. Cable to HFC: home; 4. 100 Mbps switched Ethernet: enterprise.
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. In most American cities, the 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.
8. Today, Ethernet most commonly runs over twisted-pair copper wire. It also can run over fibers
optic links.
9. ADSL: up to 24 Mbps downstream and 2.5 Mbps upstream, bandwidth is dedicated; HFC, rates
up to 42.8 Mbps and upstream rates of up to 30.7 Mbps, bandwidth is shared. FTTH: 2-
10Mbps upload; 10-20 Mbps download; bandwidth is not shared.
10. There are two popular wireless Internet access technologies today:
a. Wifi (802.11) In a wireless LAN, wireless users transmit/receive packets to/from an
base station (i.e., 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. 3G and 4G wide-area wireless access networks. 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. At time t0 the sending host begins to transmit. At time t1 = L/R1, 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
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
, packet to the receiving host at time t1. At time t2 = t1 + L/R2, 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/R1 + L/R2.
12. 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. FDM requires sophisticated analog hardware to
shift signal into appropriate frequency bands.
13. 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)3 = 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.
14. If the two ISPs do not peer with each other, then when they send traffic to each other they
have to send the traffic through a provider ISP (intermediary), to which they have to pay for
carrying the traffic. By peering with each other directly, the two ISPs can reduce their
payments to their provider ISPs. An Internet Exchange Points (IXP) (typically in a standalone
building with its own switches) is a meeting point where multiple ISPs can connect and/or
peer together. An ISP earns its money by charging each of the the ISPs that connect to the IXP
a relatively small fee, which may depend on the amount of traffic sent to or received from the
IXP.
15. Google's private network connects together all its data centers, big and small. Traffic between
the Google data centers passes over its private network rather than over the public Internet.
Many of these data centers are located in, or close to, lower tier ISPs. Therefore, when Google
delivers content to a user, it often can bypass higher tier ISPs. What motivates content
providers to create these networks? First, the content provider has more control over the user
experience, since it has to use few intermediary ISPs. Second, it can save money by sending
less traffic into provider networks. Third, if ISPs decide to charge more money to highly
profitable content providers (in countries where net neutrality doesn't apply), the content
providers can avoid these extra payments.
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.
© 2020 Pearson Education, Hoboken, NJ. All rights reserved.
