Self-Test
& Supply the missing word(s) in each statement.
Choose the letter that best answers each question.
1. Data communications is the transmission of _____ information.
2. True or false. Audio and video signals may be transmitted using data communications techniques.
3. The earliest form of data communications was the _____.
4. The earliest form of radio data communications is known as _____.
5. The Morse code is made up of combinations of _____ and _____ to represent characters.
6. Give the Morse code for the following characters (see Fig. 12-2): K, 8, ,. (page 310-Frenzel)
7. The 5-bit code used in teletype systems is called the _____ code.
8. A system of data communications using type writer like devices to send and receive coded messages is known as _____.
9. If in the Baudot code the character 11011 is sent and then the code 00111, the character _____ is received.
10. The most widely used binary data code is _____ which uses 7 bits to represent characters.
11. An 8-bit data code used in IBM systems is known as _____.
12. Write the ASCII codes for the following characters: B, 3, ?
13. What ASCII character is transmitted to ring a bell? BEL = _____.
14. The two types of data transmission are _____.
15. True or false. Serial data transfers are faster than parallel transfers.
16. The digital circuit often used to perform parallel-to-serial and serial-to-parallel data conversions is the _____
17. In asynchronous transmissions, _____ and _____ bits are used to signal the beginning and end of a character.
18. The speed of a serial data transmission is usually expressed in _____.
19. The number of symbols occurring per second in a data transmission is called the _____.
20. True or false. There can be more than i bit per baud in data transmissions.
21. True or false. Asynchronous transmission is faster than synchronous transmission.
22. In synchronous data transmission, data is sent in _____ of characters with special codes to signal the beginning and end.
23. In serial data transmission, a binary 0 is called a(n) _____ and a binary 1 is called a(n) _____.
24. The study of efficient information transfer is known as _____.
25. The amount of information transmitted is proportional to the system _____ and the _____ allowed for transmission.
26. The channel capacity of a 5-kHz bandwidth binary system is _____ bits/s assuming no noise.
27. If an 8-level encoding scheme is used in a 100 kHz bandwidth system, the channel capacity is _____ bits/s.
28. True or false. Multilevel or multisymbol binary encoding schemes permit more data to be transmitted in less time, assuming a constant symbol interval.
29. By using a multisymbol encoding scheme, a higher bit rate can' be achieved with _____ (more, less) bandwidth.
30. The channel capacity of a 6-MHz channel with an SIN ratio of 25 dB is _____ Mbits/s.
31. The minimum allowable bandwidth for a binary signal with a bit rate of 200 kbits/s is _____ kHz.
32. A modem contains both _____ and _____ circuits.
33. Modems convert _____ signals to _____ signals and vice versa.
34. The transmission medium most widely used with modems is the _____.
35. Modems are the interface between _____.
36. _____ modulation is used in low speed modems.
37. In FSK, binary 0 and I levels are represented by different _____.
38. In an FSKs modem, a high frequency represents a(n) _____ and a low frequency represents a(n) _____.
39. The typical frequencies used in a full duplex FSK modem are as follows:
- originate 0 _____ Hz and 1 _____ Hz;
- answer 0 _____ Hz and 1 _____ Hz.
40. The IC used to perform serial-to-parallel and parallel-to-serial conversions and other operations in a modem is known as a(n) _____.
41. The modulation method that represents bits as different phase shifts of a carrier is known as _____.
42. In BPSK, phase shifts of _____ degrees and _____ degrees used to represent bif\ary 0 and binary 1, respectively.
43. The circuit used to produce BPSK is a(n) _____.
44. The circuit-used to demodulate BPSK is a(n) _____.
45. A(n) _____ circuit is used to generate the carrier to be used in demodulating a BPSK signal.
46. A carrier recovery circuit is not needed with _____ PSK modulation.
47. The key circuit used in a DPSK modulator is the _____.
48. The number of different phase shifts used in QPSK is _____.
49. In QPSK, how many bits are represented by each phase shift?
50. The number of bits represented by each phase shift in 16-PSK is _____.
51. The circuit used to create a dibit is known as a(n) _____.
52. A circuit that converts a 2-bit binary code into one of four dc voltage levels is known as a _____.
53. Quadrature amplitude modulation is a combination of _____ modulation and _____ modulation.
54. True or false. Modems must transmit signals in the 300-Hz to 3-kHz range.
55. True or false. Carrier recovery is not required in a QPSK demodulator.
56. True or false. When QPSK is used, the bit rate is faster than the baud (symbol) rate.
57. True or false. Each phase and/or amplitude change can represent only one bit.
58. True or false. With QAM, a 9600 bits/s signal can be transmitted within a 3000-Hz bandwidth.
59. Rules and procedures that describe how data will be transmitted and received are referred to as _____.
60. List five methods of error detection and correction.
61. The process of exchanging signals between transmitter and receiver to indicate status or availability is called _____.
62. A popular protocol used in personal computer data communications is known as _____.
63. A string of characters making up a message or part of a message is referred to as a(n) _____ of data.
64. Stop and start bits are used with, _____ (asynchronous, synchronous) data.
65. Synchronous protocols usually begin with the _____ character.
66. The characters that indicate message number, destination, or other facts are collectively referred to as the _____.
67. The _____ character designates the beginning of a message, while the character _____ indicates its end.
68. One simple but time-consuming way to ensure an error-free transmission is to send the data multiple times. This is called _____.
69. One type of special self checking error code is the _____ code.
70. Errors in data transmission are usually caused by _____.
71. The ratio of the number of bit errors to the total number of bits transmitted is known as the _____.
72. A bit added to the transmitted character to help indicate an error is called the _____ bit.
73. A number added to the end of a data block to assist in detecting errors is known as the _____
74. Write the correct parity bits for each number.
a. Odd: 0011000 _____
b. Even: 1111101 _____
c. Odd: 0101101 _____
d. Even: 1000110 _____
75. Another name for parity is _____.
76. The basic building block of a parity generator circuit is the _____ gate.
77. Performing an exclusive OR on corresponding bits in successive data words produces a(n) word.
78. An error-detection system that uses a BCC at the end of a block is known as a(n) _____.
79. Dividing the data block by a constant produces a quotient that is discarded and a remainder called the _____ character.
80. The CRC circuit is basically a(n) _____.
81. True or false. If a bit error cart be identified, it can be corrected.
82. The telephone system is an example of a _____.
83. True or false. A cable TV system is considered a network.
84. Most networks re smaller and cover shorter distances and are referred to as _____.
85. The acronym PBX means _____.
86. True or false. PBXs cannot be used with digital data.
87. The three main types of LAN topologies are _____.
88. A PBX is a type of _____ topology LAN.
89. An LAN that uses a central controller for multiple stations is the _____ topology.
90. One type of LAN connects multiple terminals and PCs to a large central _____ computer.
91. A LAN in which the message is passed from one station to the next until the destination is reached is called a(n) _____.
92. The stations or users in a network are referred to as _____.
93. A network in which all stations attach to a common cable is called a(n) _____.
94. 94: The fastest network configuration is the _____.
95. In a(n) _____ LAN configuration, if one station fails, the whole system fails.
96. A connection from a LAN to a mainframe computer is known as a(n) _____.
97. A connection from one LAN to another is called a(n), _____.
98. The three transmission media used in LANs are _____.
99. An extended variation of the bus topology is called the _____.
100. List the three main disadvantages of twisted pair cable.
101. _____ is the most widely used medium in LANs.
102. The medium that permits the highest data rates is _____.
103. The longest transmission distances can be achieved with _____ medium.
104. Give the average maximum data rates in Mbits/s for each medium: twisted pair, coax, fiber-optic cable.
105. The digital, voice, or video voltages are referred to as _____ signals.
106. When the basic data signal is sent directly over the medium, the type of operation is said to be _____.
107. _____ operation uses modulation techniques and FDM techniques to increase speed and the number of operational channels.
108. Broadband operation requires the use of a(n) _____ at each node.
109. Spread spectrum is both a _____ and a _____ technique.
110. The two main types of spread spectrum are _____ and _____.
111. In a frequency-hopping SS system, a _____ circuit generates the transmitter frequency.
112. In a frequency-hopping SS system, a _____ circuit selects the frequency produced by the synthesizer.
113. True or false. The hop rate is slower than the bit rate of the digital data.
114. To a narrowband receiver, an SS signal appears as a type of _____.
115. Two or more stations using SS and sharing a common band are identified and distinguished from one another by their unique _____.
116. The length of time a frequency-hopping SS transmitter stays on one frequency is called the _____.
117. In a direct-sequence SS transmitter, the data signal is mixed with a PSN signal in an _____ circuit.
118. True or false. In a direct-sequence SS system, the chip rate is faster than the data rate.
119. The type of modulation used with direct sequence SS is usually _____.
120. The most difficult part of SS communications is initiating and maintaining _____ prior to and during transmission.
121. The process of comparing one direct sequence SS signal to another in an effort to obtain a match is called _____.
122. The two main benefits of SS are _____ and _____.
123. The main circuit used in making a PSN code generator is a _____.
124. The frequencies allocated to spread spectrum by the FCC for civilian applications are _____, _____, and _____ MHz.
125. Two growing applications for SS are _____ and _____.
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