,SOLUTION MANUAL FOR Computer Networking A
Top-Down Approach, 9th edition Kurose
Notes
1- The file is chapter after chapter.
2- We have shown you few pages sample.
3- The file contains all Appendix and Excel sheet
if it exists.
4- We have all what you need, we make update
at every time. There are many new editions
waiting you.
5- If you think you purchased the wrong file You
can contact us at every time, we can replace it
with true one.
Our email:
, Solutions Manual
Computer Networking:
A Top-Down Approach
Ninth Edition
James F. Kurose
Keith W. Ross
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
,This work is protected by United States copyright laws and is provided solely for
the use of instructors in teaching their courses and assessing student learning.
Dissemination or sale of any part of this work (including on the World Wide Web)
will destroy the integrity of the work and is not permitted. The work and materials
from it should never be made available to students except by instructors using
the accompanying text in their classes. All recipients of this work are expected to
abide by these restrictions and to honor the intended pedagogical purposes and
the needs of other instructors who rely on these materials.
Copyright © 2026 by Pearson Education, Inc. or its affiliates, 221 River Street,
Hoboken, NJ 07030. All Rights Reserved. Manufactured in the United States of
America. This publication is protected by copyright, and permission should be obtained
from the publisher prior to any prohibited reproduction, storage in a retrieval system, or
transmission in any form or by any means, electronic, mechanical, photocopying,
recording, or otherwise. For information regarding permissions, request forms, and the
appropriate contacts within the Pearson Education Global Rights and Permissions
department, please visit http://www.pearsoned.com/permissions/
Pearson uses AI, including to support the creation of content. We claim copyright to the
fullest extent permissible by law.
Pearson, and Pearson+ are exclusive trademarks owned by Pearson Education, Inc. or
its affiliates, in the United States, and/or other countries.
Unless otherwise indicated herein, any third-party trademarks, logos, or icons that may
appear in this work are the property of their respective owners, and any references to
third-party trademarks, logos, icons, or other trade dress are for demonstrative or
descriptive purposes only. Such references are not intended to imply any sponsorship,
endorsement, authorization, or promotion of Pearson’s products by the owners of such
marks, or any relationship between the owner and Pearson Education, Inc., or its
affiliates, authors, licensees, or distributors.
Copyright © 2026 Pearson Education, Inc. 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. A 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. DSL over telephone line: home or small office; 2. Cable to HFC: home; 3. 100 Mbps
switched Ethernet: enterprise; LEO satellite
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: DSL; cable modem; fiber-to-
the-home.
7. Ethernet LANs have transmission rates of 10 Mbps, 100 Mbps, 1 Gbps,10 Gbps, 100
Gbps, 400 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 at least four 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. Cellular Networks, including 4G and 5G, primarily for smartphones and mobile
hotspots. 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.
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
, c. Fixed Wireless Access (FWA), typically 4G or 5G based. For rural suburban
homes and offices without fiber or cable.
d. LEO Satellite Internet, used in remote locations with lower speed and higher
latency.
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
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
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
, 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.
17. a) 1000 km, 1 Mbps, 100 bytes
b) 100 km, 1 Mbps, 100 bytes
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. It adds header to each chunk, thereby
generating multiple packets from the file. The header in each packet includes the IP
address of the destination (end system B). The packet switch uses the destination IP
address in the packet 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 destination address.
21. The maximum emission rate is 500 packets/sec and the maximum transmission rate is
350 packets/sec. The corresponding traffic intensity is 500/350 =1.43 > 1. Loss will
eventually occur for each experiment; but the time when loss first occurs will be
different from one experiment to the next due to the randomness in the emission
process.
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.
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
,25. Routers process network, link and physical layers (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 Transport layer as well.) Link layer switches process link and physical
layers (layers 1 through2). Hosts process all five layers.
26. A self-replicating malware is a piece of code that cab enter and infect our devices,
and once it infects the host, from that host it seeks entry into other hosts over the Internet.
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.
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
,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
Messages from Server to ATM machine (display)
Msg name purpose
-------- -------
PASSWD Ask user for PIN (password)
OK last requested operation (PASSWD, WITHDRAWL)
OK
ERR last requested operation (PASSWD, WITHDRAWL)
in ERROR
AMOUNT <amt> sent in response to BALANCE request
BYE user done, display welcome screen at ATM
Correct operation:
client server
HELO (userid) --------------> (check if valid userid)
<------------- PASSWD
PASSWD <passwd> --------------> (check password)
<------------- OK (password is OK)
BALANCE -------------->
<------------- AMOUNT <amt>
WITHDRAWL <amt> --------------> check if enough $ to cover
withdrawl
<------------- OK
ATM dispenses $
BYE -------------->
<------------- BYE
In situation when there's not enough money:
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
, HELO (userid) --------------> (check if valid userid)
<------------- PASSWD
PASSWD <passwd> --------------> (check password)
<------------- OK (password is OK)
BALANCE -------------->
<------------- AMOUNT <amt>
WITHDRAWL <amt> --------------> check if enough $ to cover
withdrawl
<------------- ERR (not enough funds)
error msg displayed
no $ given out
BYE -------------->
<------------- BYE
Problem 2
At time N*(L/R) the first packet has reached the destination, the second packet is stored in
the last router, the third packet is stored in the next-to-last router, etc. At time N*(L/R) +
L/R, the second packet has reached the destination, the third packet is stored in the last
router, etc. Continuing with this logic, we see that at time N*(L/R) + (P-1)*(L/R) = (N+P-
1)*(L/R) all packets have reached the destination.
Problem 3
a) A circuit-switched network would be well suited to the application, because the
application involves long sessions with predictable smooth bandwidth requirements.
Since the transmission rate is known and not bursty, bandwidth can be reserved for each
application session without significant waste. In addition, the overhead costs of setting
up and tearing down connections are amortized over the lengthy duration of a typical
application session.
b) In the worst case, all the applications simultaneously transmit over one or more network
links. However, since each link has sufficient bandwidth to handle the sum of all of the
applications' data rates, no congestion (very little queuing) will occur. Given such
generous link capacities, the network does not need congestion control mechanisms.
Problem 4
a) Between the switch in the upper left and the switch in the upper right we can have 4
connections. Similarly we can have four connections between each of the 3 other pairs
of adjacent switches. Thus, this network can support up to 16 connections.
b) We can 4 connections passing through the switch in the upper-right-hand corner and
another 4 connections passing through the switch in the lower-left-hand corner, giving
a total of 8 connections.
c) Yes. For the connections between A and C, we route two connections through B and
two connections through D. For the connections between B and D, we route two
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
Top-Down Approach, 9th edition Kurose
Notes
1- The file is chapter after chapter.
2- We have shown you few pages sample.
3- The file contains all Appendix and Excel sheet
if it exists.
4- We have all what you need, we make update
at every time. There are many new editions
waiting you.
5- If you think you purchased the wrong file You
can contact us at every time, we can replace it
with true one.
Our email:
, Solutions Manual
Computer Networking:
A Top-Down Approach
Ninth Edition
James F. Kurose
Keith W. Ross
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
,This work is protected by United States copyright laws and is provided solely for
the use of instructors in teaching their courses and assessing student learning.
Dissemination or sale of any part of this work (including on the World Wide Web)
will destroy the integrity of the work and is not permitted. The work and materials
from it should never be made available to students except by instructors using
the accompanying text in their classes. All recipients of this work are expected to
abide by these restrictions and to honor the intended pedagogical purposes and
the needs of other instructors who rely on these materials.
Copyright © 2026 by Pearson Education, Inc. or its affiliates, 221 River Street,
Hoboken, NJ 07030. All Rights Reserved. Manufactured in the United States of
America. This publication is protected by copyright, and permission should be obtained
from the publisher prior to any prohibited reproduction, storage in a retrieval system, or
transmission in any form or by any means, electronic, mechanical, photocopying,
recording, or otherwise. For information regarding permissions, request forms, and the
appropriate contacts within the Pearson Education Global Rights and Permissions
department, please visit http://www.pearsoned.com/permissions/
Pearson uses AI, including to support the creation of content. We claim copyright to the
fullest extent permissible by law.
Pearson, and Pearson+ are exclusive trademarks owned by Pearson Education, Inc. or
its affiliates, in the United States, and/or other countries.
Unless otherwise indicated herein, any third-party trademarks, logos, or icons that may
appear in this work are the property of their respective owners, and any references to
third-party trademarks, logos, icons, or other trade dress are for demonstrative or
descriptive purposes only. Such references are not intended to imply any sponsorship,
endorsement, authorization, or promotion of Pearson’s products by the owners of such
marks, or any relationship between the owner and Pearson Education, Inc., or its
affiliates, authors, licensees, or distributors.
Copyright © 2026 Pearson Education, Inc. 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. A 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. DSL over telephone line: home or small office; 2. Cable to HFC: home; 3. 100 Mbps
switched Ethernet: enterprise; LEO satellite
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: DSL; cable modem; fiber-to-
the-home.
7. Ethernet LANs have transmission rates of 10 Mbps, 100 Mbps, 1 Gbps,10 Gbps, 100
Gbps, 400 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 at least four 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. Cellular Networks, including 4G and 5G, primarily for smartphones and mobile
hotspots. 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.
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
, c. Fixed Wireless Access (FWA), typically 4G or 5G based. For rural suburban
homes and offices without fiber or cable.
d. LEO Satellite Internet, used in remote locations with lower speed and higher
latency.
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
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
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
, 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.
17. a) 1000 km, 1 Mbps, 100 bytes
b) 100 km, 1 Mbps, 100 bytes
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. It adds header to each chunk, thereby
generating multiple packets from the file. The header in each packet includes the IP
address of the destination (end system B). The packet switch uses the destination IP
address in the packet 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 destination address.
21. The maximum emission rate is 500 packets/sec and the maximum transmission rate is
350 packets/sec. The corresponding traffic intensity is 500/350 =1.43 > 1. Loss will
eventually occur for each experiment; but the time when loss first occurs will be
different from one experiment to the next due to the randomness in the emission
process.
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.
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
,25. Routers process network, link and physical layers (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 Transport layer as well.) Link layer switches process link and physical
layers (layers 1 through2). Hosts process all five layers.
26. A self-replicating malware is a piece of code that cab enter and infect our devices,
and once it infects the host, from that host it seeks entry into other hosts over the Internet.
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.
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
,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
Messages from Server to ATM machine (display)
Msg name purpose
-------- -------
PASSWD Ask user for PIN (password)
OK last requested operation (PASSWD, WITHDRAWL)
OK
ERR last requested operation (PASSWD, WITHDRAWL)
in ERROR
AMOUNT <amt> sent in response to BALANCE request
BYE user done, display welcome screen at ATM
Correct operation:
client server
HELO (userid) --------------> (check if valid userid)
<------------- PASSWD
PASSWD <passwd> --------------> (check password)
<------------- OK (password is OK)
BALANCE -------------->
<------------- AMOUNT <amt>
WITHDRAWL <amt> --------------> check if enough $ to cover
withdrawl
<------------- OK
ATM dispenses $
BYE -------------->
<------------- BYE
In situation when there's not enough money:
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
, HELO (userid) --------------> (check if valid userid)
<------------- PASSWD
PASSWD <passwd> --------------> (check password)
<------------- OK (password is OK)
BALANCE -------------->
<------------- AMOUNT <amt>
WITHDRAWL <amt> --------------> check if enough $ to cover
withdrawl
<------------- ERR (not enough funds)
error msg displayed
no $ given out
BYE -------------->
<------------- BYE
Problem 2
At time N*(L/R) the first packet has reached the destination, the second packet is stored in
the last router, the third packet is stored in the next-to-last router, etc. At time N*(L/R) +
L/R, the second packet has reached the destination, the third packet is stored in the last
router, etc. Continuing with this logic, we see that at time N*(L/R) + (P-1)*(L/R) = (N+P-
1)*(L/R) all packets have reached the destination.
Problem 3
a) A circuit-switched network would be well suited to the application, because the
application involves long sessions with predictable smooth bandwidth requirements.
Since the transmission rate is known and not bursty, bandwidth can be reserved for each
application session without significant waste. In addition, the overhead costs of setting
up and tearing down connections are amortized over the lengthy duration of a typical
application session.
b) In the worst case, all the applications simultaneously transmit over one or more network
links. However, since each link has sufficient bandwidth to handle the sum of all of the
applications' data rates, no congestion (very little queuing) will occur. Given such
generous link capacities, the network does not need congestion control mechanisms.
Problem 4
a) Between the switch in the upper left and the switch in the upper right we can have 4
connections. Similarly we can have four connections between each of the 3 other pairs
of adjacent switches. Thus, this network can support up to 16 connections.
b) We can 4 connections passing through the switch in the upper-right-hand corner and
another 4 connections passing through the switch in the lower-left-hand corner, giving
a total of 8 connections.
c) Yes. For the connections between A and C, we route two connections through B and
two connections through D. For the connections between B and D, we route two
Copyright © 2026 Pearson Education, Inc. All Rights Reserved
