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Tutorial topic 7
Data Communications #1
[2000 Final]
1 Digital data is encoded on conventional telephone lines by…
(A) Voltage levels
(B) Two pairs of light frequencies, one pair for outgoing data, and one pair for incoming data
(C) Modulation
(D) Gnomes
[1]
[2000 Final]
2 Serial data …
(A) Is preferred because it is intrinsically capable of being transmitted faster than parallel data
(B) Is only able to be transmitted on simplex and half-duplex links
(C) Must incorporate some mechanism for synchronising the sender and the receiver
(D) Can get out of order in the wires
[1]
[2000 Final]
3 In Quadrature Amplitude Modulation …
(A) The missing part of the sine wave contains information
(B) Different carrier wave frequencies are used for 0s and 1s
(C) Only one bit can be encoded per signalling element, though signalling elements may be more than a single wavelength long
(D) Bits last for different times, depending on whether they are 0 or 1
[1]
[2000 Final]
4 Error detection…
(A) Is not necessary in today's highly reliable networks
(B) Must take place before data is transmitted
(C) Cannot occur if communication is restricted to a single direction
(D) Relies on incorporation of extra bits into the data stream
[1]
[2001 Final]
5 Which of the following is true of fibre optics?
(A) An optic fibre has a much higher bandwidth than a coaxial cable.
(B) Signals carried by optical fibres are degraded by external electromagnetic fields.
(C) A optic fibre must be at least 1mm thick.
(D) An optic fibre is normally use to carry signals in both directions at the same time.
[1]
[2001 Final]
6 QAM is a method of signal modulation. Which of the following statements is true?
(A) QAM is used by a computer to communicate with a modem.
(B) QAM combines amplitude and frequency modulation.
(C) QAM is used by the parallel port on a PC.
(D) QAM combines phase and amplitude modulation.
[1]
[1996 Final]
7 Describe how frequency modulation works.
[2]
[1996 Final]
8 What is meant by the baud rate of a channel, and what is the relationship between baud rate and capacity (bits per second).
[3]
[2000 Final]
9 Suppose that a computer application is sending information that is coded using 6 symbols: a,b,c,d,e,f. Experience shows that these 6 symbols occur with the frequencies:
Symbol Frequency
a 24%
d 15%
b 18%
e 9%
c 29%
f 5%
Construct an efficient Huffman Code for these symbol frequencies and explain your method? What is the bit sequence that would be used to encode the data sequence efface?
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