,Computer Networks: A Systems Approach
Sixth Edition
Solutions Manual
Larry Peterson and Bruce Davie
2021
1
,Dear Instructor:
This Instructors’ Manual contains solutions to most of the exercises in the sixth edition
of Peterson and Davie’s Computer Networks: A Systems Approach.
Exercises are sorted (roughly) by section, not difficulty. While some exercises are
more difficult than others, none are intended to be fiendishly tricky. A few exercises
(notably, though not exclusively, the ones that involve calculating simple probabilities)
require a modest amount of mathematical background; most do not. There is a sidebar
summarizing much of the applicable basic probability theory in Chapter 2.
An occasional exercise is awkwardly or ambiguously worded in the text. This manual
sometimes suggests better versions; also see the errata at the web site.
Where appropriate, relevant supplemental files for these solutions (e.g. programs) have
been placed on the textbook web site,
https://www.elsevier.com/books-and-journals/book-companion/
978012818200. Useful other material can also be found there, such as errata, sample
programming assignments, PowerPoint lecture slides, and EPS figures. You can also
access the sources for the book, including figures, at
https://github.com/SystemsApproach.
If you have any questions about these support materials, please contact your Morgan
Kaufmann sales representative. If you would like to contribute your own teaching
materials, please contact us at .
We welcome bug reports and suggestions as to improvements for both the exercises
and the solutions; these may be sent to or you can
open issues and pull requests at https://github.com/SystemsApproach.
Larry Peterson
Bruce Davie
January 2021
, Chapter 1 1
Solutions for Chapter 1
4. We will count the transfer as completed when the last data bit arrives at its desti-
nation. An alternative interpretation would be to count until the last ACK arrives
back at the sender, in which case the time would be half an RTT (25 ms) longer.
(a) 2 initial RTT’s (100ms) + 1000KB/1.5Mbps (transmit) + RTT/2 (propaga-
tion = 25ms)
≈ 0.125 + 8Mbit/1.5Mbps = 0.125 + 5.333 sec = 5.658 sec. If we pay
more careful attention to when a mega is 106 versus 220 , we get
8,192,000 bits/1,500,000 bits/sec = 5.461 sec, for a total delay of 5.586 sec.
(b) To the above we add the time for 999 RTTs (the number of RTTs be-
tween when packet 1 arrives and packet 1000 arrives), for a total of 5.586 +
49.95 = 55.536.
(c) This is 49.5 RTTs, plus the initial 2, for 2.575 seconds.
(d) Right after the handshaking is done we send one packet. One RTT after the
handshaking we send two packets. At n RTTs past the initial handshaking
we have sent 1 + 2 + 4 + · · · + 2n = 2n+1 − 1 packets. At n = 9 we have thus
been able to send all 1,000 packets; the last batch arrives 0.5 RTT later.
Total time is 2+9.5 RTTs, or .575 sec.
5. The answer is in the book.
6. Propagation delay is 4×103 m/(2×108 m/sec) = 2×10−5 sec = 20 µs. 100 bytes/20 µs
is 5 bytes/µs, or 5 MB/sec, or 40 Mbit/sec. For 512-byte packets, this rises to
204.8 Mbit/sec.
7. The answer is in the book.
8. Postal addresses are strongly hierarchical (with a geographical hierarchy, which
network addressing may or may not use). Addresses also provide embedded
“routing information”. Unlike typical network addresses, postal addresses are
long and of variable length and contain a certain amount of redundant informa-
tion. This last attribute makes them more tolerant of minor errors and incon-
sistencies. Telephone numbers are more similar to network addresses (although
phone numbers are nowadays apparently more like network host names than ad-
dresses): they are (geographically) hierarchical, fixed-length, administratively
assigned, and in more-or-less one-to-one correspondence with nodes.
9. One might want addresses to serve as locators, providing hints as to how data
should be routed. One approach for this is to make addresses hierarchical.
Another property might be administratively assigned, versus, say, the factory-
assigned addresses used by Ethernet. Other address attributes that might be
relevant are fixed-length v. variable-length, and absolute v. relative (like file
names).
Sixth Edition
Solutions Manual
Larry Peterson and Bruce Davie
2021
1
,Dear Instructor:
This Instructors’ Manual contains solutions to most of the exercises in the sixth edition
of Peterson and Davie’s Computer Networks: A Systems Approach.
Exercises are sorted (roughly) by section, not difficulty. While some exercises are
more difficult than others, none are intended to be fiendishly tricky. A few exercises
(notably, though not exclusively, the ones that involve calculating simple probabilities)
require a modest amount of mathematical background; most do not. There is a sidebar
summarizing much of the applicable basic probability theory in Chapter 2.
An occasional exercise is awkwardly or ambiguously worded in the text. This manual
sometimes suggests better versions; also see the errata at the web site.
Where appropriate, relevant supplemental files for these solutions (e.g. programs) have
been placed on the textbook web site,
https://www.elsevier.com/books-and-journals/book-companion/
978012818200. Useful other material can also be found there, such as errata, sample
programming assignments, PowerPoint lecture slides, and EPS figures. You can also
access the sources for the book, including figures, at
https://github.com/SystemsApproach.
If you have any questions about these support materials, please contact your Morgan
Kaufmann sales representative. If you would like to contribute your own teaching
materials, please contact us at .
We welcome bug reports and suggestions as to improvements for both the exercises
and the solutions; these may be sent to or you can
open issues and pull requests at https://github.com/SystemsApproach.
Larry Peterson
Bruce Davie
January 2021
, Chapter 1 1
Solutions for Chapter 1
4. We will count the transfer as completed when the last data bit arrives at its desti-
nation. An alternative interpretation would be to count until the last ACK arrives
back at the sender, in which case the time would be half an RTT (25 ms) longer.
(a) 2 initial RTT’s (100ms) + 1000KB/1.5Mbps (transmit) + RTT/2 (propaga-
tion = 25ms)
≈ 0.125 + 8Mbit/1.5Mbps = 0.125 + 5.333 sec = 5.658 sec. If we pay
more careful attention to when a mega is 106 versus 220 , we get
8,192,000 bits/1,500,000 bits/sec = 5.461 sec, for a total delay of 5.586 sec.
(b) To the above we add the time for 999 RTTs (the number of RTTs be-
tween when packet 1 arrives and packet 1000 arrives), for a total of 5.586 +
49.95 = 55.536.
(c) This is 49.5 RTTs, plus the initial 2, for 2.575 seconds.
(d) Right after the handshaking is done we send one packet. One RTT after the
handshaking we send two packets. At n RTTs past the initial handshaking
we have sent 1 + 2 + 4 + · · · + 2n = 2n+1 − 1 packets. At n = 9 we have thus
been able to send all 1,000 packets; the last batch arrives 0.5 RTT later.
Total time is 2+9.5 RTTs, or .575 sec.
5. The answer is in the book.
6. Propagation delay is 4×103 m/(2×108 m/sec) = 2×10−5 sec = 20 µs. 100 bytes/20 µs
is 5 bytes/µs, or 5 MB/sec, or 40 Mbit/sec. For 512-byte packets, this rises to
204.8 Mbit/sec.
7. The answer is in the book.
8. Postal addresses are strongly hierarchical (with a geographical hierarchy, which
network addressing may or may not use). Addresses also provide embedded
“routing information”. Unlike typical network addresses, postal addresses are
long and of variable length and contain a certain amount of redundant informa-
tion. This last attribute makes them more tolerant of minor errors and incon-
sistencies. Telephone numbers are more similar to network addresses (although
phone numbers are nowadays apparently more like network host names than ad-
dresses): they are (geographically) hierarchical, fixed-length, administratively
assigned, and in more-or-less one-to-one correspondence with nodes.
9. One might want addresses to serve as locators, providing hints as to how data
should be routed. One approach for this is to make addresses hierarchical.
Another property might be administratively assigned, versus, say, the factory-
assigned addresses used by Ethernet. Other address attributes that might be
relevant are fixed-length v. variable-length, and absolute v. relative (like file
names).
