REVIEW: Ch 1, 2, 3, 4, 10 and 29.
1.
a. Name any four standards organizations involved in standards creation. ISO, ITU-T, ANSI, IEEE, EIA
b. What are the five components that make up a data communication system.
Message, sender, receiver, medium and protocol.
c. The value of a simple sine wave at time zero is its maximum positive value. What is the phase shift? 90 degrees
d. What is the name of the layer that lies between the network layer and the physical layer? data link layer
e. What is the period of a sine wave that has a frequency of 10000 Hz? 100 microseconds
f. A line has a signal-to-noise ratio of 1000 and a bandwidth of 4000KHz. What is the maximum data rate supported
by this line? Capacity = Bandwidth*log2(1+SNR)
g. What is the frequency of a signal that has a constant value of 10 volts? zero Hertz.
h. What is the name of the layer that is responsible for the source-to-destination of a packet across multiple network
links?
Network layer
i. What is the name of the layer that is responsible for the process-to-process delivery of the entire message.
transport layer
j. Name the layer that is responsible for the translation if the sending system uses ASCII encoding and the receiving
station uses EBCDIC encoding.
presentation
k. What are units of period and frequency?
What is a bit interval and what is its counterpart in an analog signal? time needed to send one bit; a period.
l. Name factors that would determine the performance of data communication network.
m. The attenuation of a signal is -10 dB. What is the final signal power if it was originally 5W?
n. What should be the sampling rate for a signal with components ranging from 10KHz to 100 KHz. 200, 000
samples per second
o. A signal is decomposed into three sine waves with frequencies of 50, 75, and 200 Hz. What is the bandwidth of the
signal? 150 Hz
p. What is the bit rate of a signal if the bit interval is 10 microseconds? 100, 000bps (100 Kbps)
u. Draw the waveform for the data stream 00011100 using Manchester encoding.
v. Following figure is the Manchester encoding of a data stream. What is the data stream?
00011100
What would be the data stream if the above figure is an output of differential Manchester coding? 10010010
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4.
Construct the Hamming code for the data 1011001. Use even parity. Show the steps.
The code 101011010100110 is received. Using CRC find out the remainder. The divisor is 110101. Identify if there is
any error in the received code. Justify your answer.
If we want to transmit 1000 ASCII characters (7 bit) asynchrounously. What is the minimum number of extra bits
needed? What is the efficiency in percentage?
For seven-bit ASCII: 7000 bits for data, 1000 stop bits, 1000 start bits, for a total of 9000 bits. This
means 78% of bits transmitted are data (7000/9000). Note that if a parity bit is used to make each
character eight bits long, the calculation would be different.
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8.
What are the three types of transmission impairement? Explain each. Pg. 69 section 3.6
What does a deciBel measure? Write it’s formula.
What is the relationship between propagation time and propagation speed. Explain.
Draw on the same diagram the time-domain plot of two sine waves (for only 1 s) with the following characteristics: Signal
A-amplitude 25V, frequency 5, phase 0; Signal B-amplitude 10V, frequency 5, phase 90.
9. For a data unit of 16 bits, find the minimum number of redundancy bits needed to correct one single-bit error. Show the
positions of the redundancy bits in Hamming code (similar to figure 10.14).
10. What is the maximum effect of a 2-ms burst of a noise on data transmitted at 12000 bps.
11. What is cryptography? What is the basis of symmetric key cryptography?
12. What is the concept behind substitutional cryptography and transpositional cryptography?
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1. _______ refers to the structure or format of the data, the order in which they are presented. Syntax
2. _______ refers to the meaning of each section of bits. Semantics
1
3. The frequency of a signal is inversely related to its _______. period
4. Which error detection method involves polynomials? CRC
5. In cyclic redundancy checking, what is the CRC? The remainder
6. At the CRC checker, _______ means that the data unit is damaged. a nonzero remainder
7. Encryption and decryption are functions of the ______________ layer. presentation
8. The _______ of a signal is the width of its frequency spectrum. bandwidth
9. A simple sine wave completes one cycle in _______ degrees. 360
10. A bit interval of 10 milliseconds means a bit rate of _______bps. 100
11. In a _______ topology, a dedicated link connects a device to a central controller. star
12. The data link layer lies between the _______ layer and the network layer. physical
13. If the data unit is 111111, the divisor 1010, and the remainder 110, what is the dividend at the receiver? 111111110
15. The Hamming code is a method of_______. error detection and correction
16. In CRC there is no error if the remainder at the receiver is ________ . zero
17. At the CRC generator, _______ added to the data unit before the division process. Os are
18. A signal has a constant value of 10 volts. Its frequency is _______ Hz.
19. Error detection is usually done in the _______ layer of the OSI model.
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45.
zero
data link
The _______ of a signal is the collection of all its component frequencies. frequency spectrum
A _______ is a physical communication pathway that transfers data from one device to another. link
The _______ of a signal is its number of cycles per second. frequency
There are n devices arranged in a ring topology. A device is deleted. There are now _______ links of cable. n - 1 39.
E-mail is a service handled by the _______ layer. application
In the _______ transmission mode, both stations can transmit and receive at the same time. full-duplex
_______ rate is the number of bits per second; _______ rate is the number of signal units per second. Bit; baud
A sampling rate of _______ million samples per second is needed for a signal with components ranging from 10MHz to
100 MHz.
200
The network layer lies between the transport layer and the _______ layer. data link
_______ addresses on headers change as a packet moves from network to network but the _______ do not.
Physical; logical
The _______ is the number of bits sent in one second. bit rate
_______ transmission features start bits, stop bits, and gaps between data units. Asynchronous
A digital signal has its 0 bits represented by 0 volts and its 1 bit represented by -5 volts or 5 volts. This is _______
encoding. bipolar
Write three elements of a protocol? Syntax, semantics, and timing.
What is the bit rate for a signal in which 8 bits last 1 microseconds? 8000kbps (8Mbps)
Forty-five physical channels link _______ devices arranged in a mesh topology. ten
Review Questions and Exercises
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