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                                   CHAPTER SIX ANSWERS TO REVIEW QUESTIONS
 

1.(a) rain simplex                                  (f) gas furnace full-duplex
   (b) looking in a mirror full-duplex       (g) video game simplex
   (c) single-lane bridge half-duplex        (h) automatic garage door half- duplex
   (d) CB radio half-duplex                    (i) snowball fight  full-duplex
   (e) television simplex                          (j) classroom lecture half-duplex

2. Analog.

3. Amplitude modulation.

4. Frequency modulation is the type of modulation affected very little by storms.

5. Phase shift keying.

6. Echo suppressors.

7. The types of noise that can occur on a communications network are impulse noise, white noise, attenuation, crosstalk, line failure, and delay distortion.

8. Two alternative names for white noise are thermal noise and Gaussian noise.

9. Repeaters.

10. Yes, 1200 + 1500 = 2700Hz while a Voice Grade line = 3400Hz.

11. Delay distortion is corrected by using an equalizer to ensure that all data arrives at the same time.

12. Odd parity is used.

13. Parity checking is only 50 percent effective because an even number of changed bits will go undetected.

14. Longitudinal redundancy check is the type of parity that creates a block control character.

15. A polynomial equation is used to create a string of bits. The string is added to the transmission. At the receiving end, the same string of bits is used and if the result is the same, no errors exist.

16. The automatic repeat request (ARQ) technique, which resends the packet sent in error with all the packets that follow it, is go-back-N ARQ.

17. Negative acknowledgment (NAK).

18. Some of the various ways to prevent errors on the data communication network are increase shielding, conditioning, lowering transmission speed, and changing to a different circuit.

19. The efficiency of a line with a block of 500 characters sent on synchronous communications with 12 SYN characters used is 97.7 percent.

20. Integrated Services Digital Network (ISDN) is the name of the network used for digital transmission and available to the home PC user.