CNS-ST 3.1: DIGITAL & DATA COMMUNICATIONS

DIGITAL COMMUNICATION

1. The first digital code was the: Morse code

2. Advantage of digital over analog transmission. Noise immunity

3. Hartleys Law is: I = ktB

4. The Shannon-Hartley theorem is: C = 2Blog(2M)

5. The Shannon Limit is given by: C = B log2 (1 + S/N)

6. In North America, companding uses: the Law (mu law)

7. A typical codec in a telephone system sends and receives: 8-bit numbers

8. In delta modulation, granular noise is produced when: the signal does not change

9. Which coding scheme requires DC continuity: unipolar NRZ

10. Number of independent symbols that can be propagated out through a communications system which is a function of bandwidth. Information capacity

11. Refers to the rate of change of a signal on a transmission medium after encoding and modulation have occurred. Baud rate

12. What is the relationship of bit rate and baud in FSK and PSK? Equal

13. What is the relationship of bit rate and baud in QPSK and 8-PSK? Bit rate is greater than baud

14. A digital modulation technique also known as on-off keying. Amplitude Shift Keying or ASK

15. From of digital modulation using its modulation signal (a binary pulse stream) that varies between two discrete voltage levels. FSK

16. In FSK, a figure of merit used to express the degree of modulation. H-factor

17. Most common modulation technique used for radio telegraphy. FSK

18. It is a type of FSK where the mark and space frequencies are synchronized with the input binary rate. Continuous-Phase Frequency-Shift Keying or CPFSK

19. The most common circuit used for demodulating binary FSK signals. Phase locked loop

20. A form of digital modulation similar to PSK except the digital information is contained in both the amplitude and the phase of the transmitted carrier. Quadrature Amplitude Modulation

21. If is often used to compare the performance of one digital modulation technique to another Bandwidth efficiency, Information density of Spectral efficiency

22. It is the ratio of the transmission bit rate to the minimum bandwidth required for a particular modulation scheme. Bandwidth efficiency, Information density of Spectral efficiency

23. For an 8-PSK system, operating with an information bit rate of 24 kbps, determine the bandwidth efficiency. 3 bits/cycle

24. For a 16-PSK and a transmission system with a 10 kHz bandwidth, determine the maximum bit rate. 40,000 bps

25. A common method of achieving carrier recovery for BPSK. Squaring loop

26. A modulation technique where data rates I excess of 56 kbps can be achieved over telephone circuits. Trellis code modulation

27. It is a theoretical expectation of the bit error rate in the system. Probability of errors

28. It is a function of the carrier-to-noise power ratio and the number of possible encoding conditions used. Probability of error

29. It is the ratio of the average carrier power to the thermal noise power. Carrier-to-noise ratio

30. It is the thermal noise power normalized to 1-Hz bandwidth. Noise power density

31. It is used to compare two or more digital modulation systems that use different transmission rates, modulation scheme or encoding techniques. Energy per bit-to-noise power density ratio

32. The phase relationship between signaling elements for BPSK is the optimum signaling form and occurs only when two binary signal levels are allowed and when one signal is the exact negative of the other. Antipodal signaling

33. An eye pattern shows a good channel when: the eye is maximally open

34. What you see in an eye pattern is the effect of: intersymbol interference

35. High-frequency radioteletype systems commonly use: FSK

36. In digital modulation, such as FSK, the rate of change of frequency at the input is called bit rate

37. The fundamental frequency of a binary square wave. 1/2 bit rate

38. In digital communications, employing FSK, baud rate is _____ of bit rate. Equal

39. Form of angle modulated constant envelope digital modulation. Phase-shift keying

40. The threshold point of QPSK system is + or 0.785

41. A form of digital modulation similar to PSK, it transmit 2 separate information signal using 2 AM carriers at the same frequency but differ in phase by 90O. QUAM

42. Table that list all the possible combinations of variables. Truth table

43. The term used to define jitter above 10 Hz is _____. Wander

44. He is credited with inventing PCM in 1937. Alex H. Reeves

45. In PCM, the circuit that periodically samples the analog input and converts it to PAM. Sample and hold

46. In PCM, it converts the PAM samples to parallel PCM codes. Analog-to-Digital Converter (ADC)

47. Modern digital systems use a _____ to demodulate a PAM signal. LPF

48. A signal which varies between 3 levels. Bipolar code

49. There are how many transistors in CMOS inverter? 2

50. Variation of the PCM that uses a single but PCM code. Delta modulation

51. In delta modulation method, what causes error in the demodulated signal? Slope overload

52. In PCM, according to Nyquist sampling theorem to avoid distortions, the minimum sampling rate should be ____ value of the highest audio frequency. Twice

53. The disadvantage of PC systems is that it requires a large bandwidth

54. Companding is employed in PCM system to protect small signals from quantizing distortion

55. An integrated circuit that performs the PCM encoding and decoding functions. Codec

56. Method of encoding audio signals used in US standard 1.544 Mbps 24-channel PCM system. Mu-law

57. A digital modulation technique in which the polarity of the transmitted pulse indicates whether the demodulator output should rise or fall at each pulse. Delta modulation

58. In PCM sampling, the time when the FET is on is called Acquisition

59. The most common method used for sampling voice signals in PCM systems. Flat-top sampling

60. What is the result if the input of the ADC is changing while performing conversion? Aperture distortion

61. The result whenever the sampling rate is less than twice the highest audio frequency. Alias or Foldover distortion

62. It is a process of converting an infinite number of possibilities to a fine number of conditions. Quantization

63. The magnitude of a quantum in quantization of PCM codes. Resolution

64. It is a numerical indication of how efficiently a PCM code is utilized. Coding efficiency

65. BW efficiency is also known as information capacity

66. Devices used for digitizing speech signals only. Vocoders

67. Type of PCM that uses single-bit PCM code to achieve digital transmission of analog signals. Delta modulation

68. A digital modulation technique that does not need to recover the phase coherent carrier. Differential phase shift keying

69. In Boolean Algebra, functions expressed as sum of minterms of product of maxterms are said to be in what form? Canonical

70. The slope of the analog signal is greater than the delta modulator can maintain. Slope overload

71. In is a delta modulation system where the step size of the Digital-to-Analog converter is automatically varied, depending on the analog input signal. Adaptive Delta Modulation

72. The type of PCM which is designed to take advantage of the sample-to-sample redundancies in the typical speech waveform. Differential PCM

73. An error detection, that requires a human being at the received terminal to analyze the received data and make decisions on its integrity symbol substitution *

74. Most reliable scheme for error detection. CRC *

75. Error control in HF radio data transmission. ARQ *

76. A convenient technique for determining the effects of the degradations introduced into the pulses as they travel to the regenerator. Eye patterns

77. It is the transmission of information in any form from one source to one or more destinations. Multiplexing

78. It is a form of phase-division multiplexing where two data channels modulate the same carrier frequency that is shifted 90 degrees in phase. Quadrature Amplitude Modulation or QAM

79. It is the most prevalent encoding technique used for TDM signals. Pulse Code Modulation or PCM

80. One eigth-bit PCM code is called _____. TDM frame

81. The time it takes to transmit one TDM frame is called _____. Frame time

82. T1 stands for Transmission one

83. In T1, it is equal to the reciprocal of the sample rate. Frame time

84. The PCM code for each channel occupies a fixed time slot called _____. Epoch

85. It is a low-quality video transmission for use between non-decided subscribers. Picturephone

86. A transmission of binary data which involves the transmission of two non-zero voltage level. Bipolar

87. It can be used to categorize the type of transmission. Duty cycle

88. If the active time of the binary pulse if less than 100% of the bit time. Return to zero (RZ)

89. What is the category of data transmission if the binary pulse is maintained for the entire bit time. Non return to zero (NRZ)

90. Encoding wherein, the most commonly used characters are represented with the fewest number of bits. Huffman Encoding *

91. Variation of biphase that is used for encoding SMPTE (Society of Motion Picture and Television Engineers) time code data and for recording on video tapes. Biphase-M

92. What uses convolutional coding technique? Trellis Coding *

93. These are used for transmission of PCM encoded time-division multiplexed digital signal. T carriers

94. Statistical TDMs are also called Intelligent TDMs, Stat mux or Asynchronous TDM

95. A chip that combines the codec and filter functions in the same LSI chip Combo Chip

96. It is the basic building block of FDM hierarchy. Message channel

97. An FDM hierarchy which is formed by frequency-division multiplexing five groups containing 12 channels each for a combined bandwidth of 240 kHz. Basic Supergroup

98. Basic supergroup frequency range. 312 to 522 kHz *

99. What is the final output of a multiplexer? Composite baseband

100. What type of mastergroup that is used for low-capacity microwave systems? L600

101. What type of mastergroup that can be further multiplexed and used for higher-capacity microwave radio systems? U600

102. How many voice channels are there in a mastergroup? 600 *

103. How many voice channels are there in a jumbogroup? 3600 *

104. How many groups are there in a supermastergroup of CCITTs FDM Hierarchy? 75 *

105. How many voice channels are there in a DS-2 Digital Signal Hierarchy. 96 *

106. In FDM, what is the carrier frequency of supergroup 10 in L600 mastergroup? 3100 kHz *

107. The number of voiceband channel of North American TDM communications system signaling rate of 44.736 Mbps _____. 672 *

108. It comprises of either a single L600 mastergroup or up to 3 U600 mastergroups Radio channel

109. TDMA is used instead of TDM when: the signals come from different sources *

110. A DS-1 signal contains: 24-channels *

111. The number of bits per sample is DS-1 is: 8 *

112. The number of samples per second in DS-1 is: 8 k *

113. The bit rate for each channel in DS-1 is: 64 kb/s *

114. In DS-1, bits are transmitted over a T-1 cable at: 1.544 MB/s *

115. Besides data bits, a DS-1 frame contains a: framing bit *

116. The number of framing bits in DS-1 is: 1 *

117. Framing bits in DS-1 are used to: synchronize the transmitter and receiver *

118. So-called stolen bits in DS-1 are used to: carrying signaling *

119. In DS-1, a bit is stolen out of each channel: every sixth frame *

120. A T-1 cable uses: bipolar RZ AMI coding *

121. A typical T-1 line uses: twisted-pair wire *

122. The number of frames in a superframe is: 12 *

123. Moving signals from one line to another is called: space switching *

124. Moving PCM samples from one time-slot to another is called: time switching *

125. A digital space switch is a: crosspoint switch *

126. The term chip rate is used in describing: direct-sequence method *

127. Processing gain is another term for: spreading gain *

128. A receiver for frequency-hopping spread-spectrum would be: a narrowband receiver *

129. A receiver for direct-sequence spread-spectrum would be: a wideband receiver *

130. For optimal performance, CDMA requires the use of: orthogonal PN sequences *

131. The five-level teletype code was invented by: Emile Baudot *

132. In telegraphy, a word consists of ____ characters. 7 and 1/2 *

133. In synchronous transmission, the receiver syncs-up with the transmitter by using: the data bits *

134. To maintain synchronization in synchronous transmission: long strings of 1s and 0s must not be allowed *

135. HDLC: is a bit-oriented protocol *

136. The use of flags in SDLC requires: bit-stuffing *

137. ARQ is used to: correct bit errors *

138. VRC is another name for: Parity*

139. Run-length encoding is used to: compress data *

140. When messages are intended for all the subscribers on the network it is called ____. Broadcasting

141. When messages are intended for a specific group of subscribers in the network it is called _____. Multicasting

142. Refers to the structure of the data within the message, which includes the sequence in which the data is sent Syntax

143. Refers to the meaning of each section of data. Semantics

144. It is an object or procedure considered by an authority of by general consent as a basis for comparison Standard

145. The process of adding or removing protocol data unit called ____. Encapsulation/decapsulation

146. The OSI layer that is responsible for the transmission of bits. Physical layer

147. The OSI layer that manages traffic on the link. Data link layer

148. The OSI layer that has inter-host communication. Session layer

149. The OSI layer that accepts and structures the message for the application. Presentation

150. The OSIL layer that serves as an interface for the user to the network. Application layer

151. The OSI layer that is task with the end-to-end accountability through a network. Network layer

152. The OSI layer that ensures and controls the end-to-end integrity of data message, by providing reliable, transparent transfer of data. Transport layer

153. A system that allows personal computer to access files, print to a local printer, and have and use one or more disk and CD drives. Local operating system

154. It describes the layout or appearance of a network, it describes how the computers, cables and other components within the data communications network are interconnected bot physically and logically. Network topology

155. The typical SNA topology is Hierarchical Topology *

156. Typical PBX configuration is Star Topology *

157. Topology which is relatively immune to bottlenecks. Mesh Topology *

158. It is a network access method used primarily with LANs configured in a ring topology using either baseband or broadband transmission formats. Token passing

159. Topology of the Classical Ethernet system. Bus *

160. ____ are omnipresent lack-and-white stripped stickers that seem to appear on virtually ever consumer item. Bar codes

161. Classification of bar codes that has gaps or space between characters and each character within the bar code is independent of every other character. Discrete code

162. A classification of bar code that does not include spaces between characters. Continuous code

163. A classification of bar code that stores data in two dimensions in contrast with a conventional linear bar code, which stores data long only one axis. 2D code

164. One of the most popular code which consists of 36 unique codes representing 10 digits and 26 uppercase letters. Code 39 or Code 3 of 9 or 3 of 9 Code

165. Code 39 is an example of what type of bar code. Discrete code

166. Classifications of errors where two or more non-consecutive bits within a given data string are in error. Multi-bit errors

167. Classification of errors where two or more consecutive bits within a given data string are in error. Burst error

168. The message that never arrives at the destination or one that arrives but is damaged to the extent that it is unrecognizable. Lost message

169. A message that is not recognized at the destination that contains one or more transmission errors. Damaged message

170. Determine the noise margin for an RS 232 interface with driver signal voltages of +/- 6V 3V and 19V

171. The specs of the old Bell type 103 modem were: 300 bps, full-duplex, FSK *

172. The ITU is under the auspices of: the U.N. *

173. High-speed modems equalize the line to compensate for: uneven phase and frequency response *

174. The bits send to allow equalization are called: a training sequence *

175. The V.90 standard is issued by: the ITU *

176. It describes the function of a family of interchange circuits. V.24 *

177. Protocol use to connect packet switching networks. X.75 *

178. The output rate of CCITT V.26. 1200 bauds *

179. Technique that allows corrections of data of the receiver. FEC *

180. MNP2, MNP3, MNP4 and MNP10 are all: error-correction protocols *

181. MNP5 and V.42 bits are both: data-compression schemes *

182. In RS-232, flow control is done using: RTS/CTS handshake & XON/OFF characters

183. The official name for RS-232C is: EIA-232D *

184. What is the signal rate of RS-232 normally used as an interface between DTE and DCE? 20 kbps *

185. In RS-232, a modem would be: a DCE *

186. In RS-232, a personal computer would be: a DTE *

187. On a DB-9 RS-232 connector, signal ground is pin: 5 *

188. On a DB-25 RS-232 connector, signal ground is pin: 7 *

189. RS-232C has how many pins? 25 pins *

190. RS-232 signal rate when used as an interface between DTE and DCE? 20 kbps *

191. The minimum lines required for RS-232 are: TD, RD, and signal ground *

192. Hardware flow control uses: RTS and CTS *

193. Which voltage represents a binary zero on an RS-232 data pin: +15 volts or +12 volts or +9 volts

194. A splitter at the subscriber end is not required for: ADSL lite *

195. Synchronous data transported by asynchronous modems is called ____. Isochronous

196. Synchronous modems cost more than asynchronous modems because ______. They must contain clock recovery circuits *

197. The Bell system 103 compatible modems is capable of duplex operation over two-wire telephone lines at a bit rate of ____. 300 bps

198. Asynchronous modes use what modulation techniques? ASK or FSK

199. Speed of asynchronous modems less than 2400 bps

200. Mode of transmission in PDN, wherein the data are transferred from source to the network then to the destination in an asynchronous data format? Start/stop *

201. The bell system 202 modem is an asynchronous 1200-baud transceiver utilizing FSK with a transmission bit rate of 1200 bps

202. Synchronous modes use what modulation technique? PSK and QAM

203. Asynchronous data modulation. FSK *

204. Digital modulation scheme modems commonly used PSK *

205. The total information processed of a system. Throughput *

206. Transmission rates of synchronous modems 2400 bps to 56,000 bps

207. Communication system where transmit and receive clock free-run at approximately the same speed. Asynchronous *

208. What protocol can achieve code transparency with flags? Bit-oriental protocol *

209. Characters transmitted other than data. Overhead *

210. A start bit is normally logic 0 *

211. In data communications circuits, synchronous data format is used to achieve what type of synchronization? Bit *

212. Type of synchronization where in the beginning and end of a character code is identified. Character synchronization *

213. What do you call a text code that makes use of 16-bit long code words? Unicode *

214. Function of data link control that specifies the means of detecting and correcting transmission errors error control

215. Error-detection protocol that uses the checksum method. Xmodem *

216. It is how the primary designates the secondary as a designation of recipient of data. Selection

217. Classification of protocol that interprets a frame of data as a group of successive bit combined into predetermined pattern of fixed length, usually 8 bits each. Character-oriented protocols or Byte-oriented protocols

218. The first file transfer protocol designed to facilitate transferring data between two personal computers over the public switched telephone network. Xmodem protocol

219. The circuit switch is a _____ switch. Transparent

220. A form of switching which is store and forward. Message switching

221. A form of switching which is hold and forward. Packing switching

222. It is logically equivalent to making telephone call through the DDD network except no direct end-to-end connection is made Virtual call

223. Packets which is self-contained and travels through the network independent of other packets of the same message by whatever means available. Datagram

224. A service provided by B-ISDN provider that offers a bi-directional end-to-end data transmission in real time. conversational service *

225. Uses connecting medium as a multi-channel device. Broadband transmission *

226. In asynchronous transfer mode cell format, the ______ indicates the mode source and packet destination. Virtual channel identifier *

227. The ISDN channel B designates _____. Bearer of Bearer of data

228. The ISDN channel D designates _____ which contains control information. Data

229. The Basic Rate Interface (BRI) of ISDN has a total bit rate or ____. 192 kbps

230. The primary rate interface consists of _____. 23B + D channels; 1.544 Mbps (US, Canada, Japan and Korea) 30B + D channel; 2.048 Mbps (Europe)

231. What is the minimum frame length for a 10-base 5 with a maximum segment length of 500 meters with a maximum of five segments. 512 bits

232. CSMA stands for: Carrier Sense Multiple Access *

233. The Internet is: a network of networks *

234. Dumb terminals are still used: in networks requiring central monitoring *

235. In a circuit-switched network: each channel carries only one data stream *

236. On networks, long messages are divided into chunks called: packets *

237. When two or more PCs try to access a baseband network cable at the same time, it is called: Contention

238. One type of network that never has a collision is: token-passing *

239. In an Ethernet-based network, a switch can be used to reduce the number of: Collisions *

240. The effect of too many collisions is: the network slows down *

241. MAU stands for: Multistation Access Unit *

242. The standard that describes Ethernet-type networks is: IEEE 802.3

243. Ethernet was invented by: Xerox

244. Ethernet is a baseband transmission system designed by _____ Robert Metcalfe and David Boggs

245. In data communication, the T in 10BaseT represents _____. The type of cable used *

246. The cable mostly used by the 10 and 100 Mbps Ethernet installation. ISTP *

247. Ethernet Standard that is sometimes called frozen yellow garden hose 10Base-5

248. An Ethernet running at 10Mbits /second uses: Manchester encoding *

249. Data transfer uses handshaking principle. Synchronous Data Transfer *

250. Data transfer scheme that used handshaking. Synchronous data transfer scheme *

251. Ethernet access method is ______. CSMA/CD *

252. Rate of Ethernet CSMH/CD. 10 Mbps *

253. A 100BaseT cable uses: twisted-pair copper wires *

254. The work Base in 10BaseT means: the cable carriers baseband signals *

255. 10BaseT cable typically uses: an RJ45 connector *

256. A hub: sends incoming packets out to all other terminals connected to it *

257. A switch: sends incoming packets out to specific ports *

258. An advantage of using a switch instead of a hub is: it reduces the number of collisions in large networks *

259. Using one node in the network to hold all the application software is done in: client-server networks *

260. The software that runs a client-server network must be: Multitasking b *

261. A thin client is: basically a PC with no disk drives *

262. Packet switching is based on: store-and-forward *

263. SNA stands for: Systems Network Architectures *

264. Bad frames are usually detected by the: link layer *

265. Together, TCP/IP consists of: 5 layers *

266. The lifetime of a packet in an IP network: depends on number of hops between nodes *

267. UPD stands for: User Datagram Protocol *

268. HTTP stand for: Hypertext Transport Protocol *

269. HTTP allows the use of: Browsers *

270. HTML stands for: Hypertext Markup Language *

271. HTML allows: web page layout *

272. FTP us used to: transfer files between a server on the network and user *

273. SMTP stands for: Simple Mail Transport Protocol *

274. A DNS:

translates word to numbers *

275. An internet connected to the Internet is often protected by: a firewall *