Florida State University Computer Science Department

CEN 5515 - Data & Computer Communications - Fall 1997

Homework Problem Sheet

Homework 1: due September 4 - Assigned Readings

Public Policy Papers:
J. Hops, "Turning the Tide," J. Berry, "Who Will Tax the Web?"

1. Hops presents novel suggestions. What are the pros & cons of such fees? Do you support these? Why?

2. Berry introduces a different approach to generating revenue. Is the Wyden/Cox bill "fair?"
Why or why not? Would you support either Hops' or Berry's approach?

Privacy Papers:
P. G. Neumann, "Identity-related Misuse," B. N. Meeks, "Privacy Lost, Anytime, Anywhere"

3. Do you find it surprising that there is so little interest in the privacy issue?
What is your role as a computer scientist? Is Brin's suggestion the ultimate solution?

The International Internet:
B. Gregston, "The European Picture," G. Mesher, The Internet in Asia"

4. The European & Asian Internet experience is different than that in the USA. Why are
censorship laws more likely to pass in Europe than in the USA? Evaluate Lord Habgood's
comment & the author's response.

E-Commerce Papers:
J. Berry, "Death of a Middle-man," H. Anderson, "Money & Internet," D. Zgodzinski,
"Stage is Set for Easier Credit Card Sales," S. Hamilton, "E-commerce for the 21st Century"

5. Mail order shopping is a large industry in the USA. Is e-commerce likely to have
comparable success? As people are on-line anyway, will they do their shopping there?
Explain your view.
Have you or will you soon, make purchases on-line?

6. Are you convinced by Anderson's arguments? Will such changes happen in the time-frame he suggests?
What happens if there is a huge power outage as has happened in the North-east?

7. Will banks as we know them now disappear? How do you envision the financial establishment in ten years?

Internet Governance
W. A. Foster et al, "Who Governs the Internet?" J. Snyder, "Dangerous Ideas," R. Wiggins,
"The Top-level Domain Name Controversy," L. Garber & P. Korzeniowski, "Internet Splits
over Domain Name Controversy"

8. What do you predict will happen in the TLD controversy & why? Foster et al suggest
"competition is replacing collaboration" - can the Internet work in this new mode? Are the
European complaints valid?

NC vs PC
J. Ubois, "Betting the Ranch," S. J. Vaughan-Nichols, "To NC or not to NC?"

9. Ellison has great credibility. Are his arguments in support of NC convincing?
Which of these two very different predictions do you support & why?

The Wired World
J. Kisheimer, "Bailing Out of the Wired World," C.D. Martin, "Three Takes on the Digital Age"

10. Give your opinion of Stoll's comments. Are Martin's criticisms of Stoll's book valid?

Academic Concerns
T. M. Ciolek, "Today's WWW - Tomorrow's MMM?" B. A. Masters, "Curses Cloud
Internet's Blessings," R. Fox, "NewsTrack - Term Paper Access"

11. Are the concerns expressed in these papers significant?

Homework 2: due - September 18

1. Double the fundamental frequency to 2 Mhz using the same square wave as in Figure
14(a) of the Data Communication Principle's handout. What is the data rate? What is the
relationship to the sample done in class?

2. A character-interleaved time-division multiplexer is used to combine the data streams of a
number of 110-bps asynchronous terminals for data transmission over a 2400-bps digital
line. Each terminal sends characters consisting of 7 data bits, 1 parity bit, 1 start bit, and
2 stop bits. Assume that one synchronization character is sent every 19 data characters
and, in addition, at least 3% of the line capacity is reserved for pulse stuffing to
accomodate speed variations from the various terminals.

a) Determine the number of bits per character.
b) Determine the number of terminals that can be accomodated by the multiplexer.

3. Assume that two 600-bps terminals, five 300-bps terminals, and a number of 150-bps terminals
are to be time-muliplexed in a character-interleaved format over a 4800-bps digital line. The
terminals send 10 bits/character, and one synchronization character is inserted for every 99 data
characters. All the terminals are asynchronous, and 3% of the line capacity is allocated for pulse
stuffing to accomodate variations in the terminal clock rates. Determine the number of 150-bps
terminals that can be accomodated.

4. Ten 9600-bps lines are to be multiplexed using TDM. Ignoring overhead bits, what is the total
capacity required for synchronous TDM? Assuming that we wish to limit average line utilization to
0.8, and assuming that each line is busy 50% of the time, what is the capacity required for
statistical TDM?

Homework 3: due - October 7

4, 7 (Message: 1101 0110 11; polynomial: x⁴ + x + 1), 9, 14, 15, 25, 27
(Assume 1KB packets. Consider for a given host, that situation that would give a maximum
throughput for that host.)
Undergraduates - omit 25, 27

Homework 4: due October 16

5, 6, 8, 13, 18 (Let T(n) = complexity of an n x n Batcher network.
Then compute T(n) as a recursive function.)
Undergraduates - omit 18

Homework 5: due October 28

1, 5 (at least 2 reasons), 6, 7, 13 (d) & (e), 16, 21
Undergraduates - omit 6

Homework 6: due - November 4

10, 20,

1. Two blue armies are each poised on opposite hills preparing to attack a single red army
in the valley. The red army can defeat either of the blue armies separately but will fail to
defeat both blue armies if they attack simultaneously. The blue armies communicate via an
unreliable communications system (a foot soldier). The commander, with one of the blue
armies, would like to attack at noon. His problem is this: If he sends a message ordering
the attack, he cannot be sure it will get through. He could ask for acknowledgment but that might
not get through. Is there a protocol that the two blue armies can use to avoid defeat?

Homework 7: due - November 13

6 (a), 7(a), 10, 21, 24

1. Perform encryption using the RSA algorithm for the following (i.e. determine n, d or e
as needed, and C):

a) p = 3, q = 11, d = 7; M = 5
b) p = 5, q = 11, e = 3; M = 9.

Undergraduates - omit 21

Homework 8: due - November 20

7, 8, 14, 17, 19 (b) - Assume each packet has completely arrived in the queue at the
times indicated. Also assume that the transmission rate is one packet per time
unit and it takes one time unit to transmit a packet. Note that the calculation is done
at the beginning of a round robin cycle, i.e. after the computation, do a round robin
cycle to maintain fairness.

Homework 9: due - December 4

problems 3, 5, 6, 15 -note comments on 3 & 6 below

3 - There are 3 factors to consider: latency, bandwidth, and the size of the data
transferred. Consider a high-speed network with 100ms latency, 155 Mbps of bandwidth
and a 1KB data block, versus an I/O bus with 500 ns latency, 1 Gbps of bandwidth, and a
64-byte data block (i.e., one cache line).

6 - Assume it takes 12 cycles to transfer a 48-byte cell payload: 1 cycle per 4-byte word.

Undergraduates - omit 15

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