When analog signals are digitized using the G.711 codec， voice samples are encapsulated into protocol data units （PDUs） involving which three headers？ （）

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• Which two statements are true about analog to digital conversion of voice signals for use in digital telephony networks？（）

  A . The three required steps in the analog to digital conversion are sampling，encoding，and compression. B . The three required steps in the analog to digital conversion are sampling，quantization，and compression. C . The three required steps in the analog to digital conversion are sampling，quantization，and encoding. D . The output of the sampling process is a pulse code modulation （PCM） signal. E . The output of the sampling process is a pulse amplitude modulation （PAM） signal.

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• By how much is a signal’s strength reduced when the signal passes through an object thatintroduces 3 dB of attenuation？（）

  A . 1/6 B . 1/4 C . 1/3 D . 1/2

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• All of the following are distress signals under the Rules EXCEPT（）.

  A . International Code Signal "AA" B . orange-colored smoke C . red flares D . the repeated raising and lowering of outstretched arm

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• When you are firing a pyrotechnic distress signal，it should be aimed（）.

  A . horizontally and directly abeam of your vessel B . at the vessel whose attention you want to attract C . into the wind D . at greater than 60 degrees above the horizo

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• When whistle signals are used for launching lifeboats，one short blast means（）.

  A . use the float-free method only B . lower all boats C . raise all boats D . drill is over，secure all boat

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• Operational amplifiers, used primarily in analog circuits, are characterized by（）

  A . high input impedance, high gain and low output impedance B . high input impedance, high gain and high output impedance C . low input impedance, low gain and high output impedance D . low input impedance, high gain and low output impedance

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• What is the term that is used to describe the process of converting a signal from digital to analog？（）

  A .  packetization B .  quantization C .  decoding D .  sampling

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• When a router converts analog signals to digital signals， what three steps are always included in the process？（）

  A . involution B . encoding C . sampling D . quantization E . compression F . companding

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• Mariners are warned that fog signals should（）be relied upon implicity.

  A . always B . never C . sonetimes D . sometime

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• When you are firing a pyrotechnic distress signal，it should be aimed at（）.

  A . straight overhead B . at the vessel whose attention you are trying to get C . into the wind D . about 60 degrees above the horizo

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• What are two steps that are taken when a router converts a voice signal from analog to digital form？（）

  A . sampling B . packetization C . quantization D . serializatio

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• All of the following are distress signals EXCEPT（）.

  A . the continuous sounding of any fog signal apparatus B . giving five or more short and rapid blasts of the whistle C . firing a gun at intervals of about a minute D . a barrel with burning oil in it，on deck

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• When a vessel signals her distress by means of a gun or other explosive signal，the firing should be at intervals of approximately（）.

  A . 10 minutes B . 1 minute C . 1 hour D . 3 minute

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• When a router converts analog signals to digital signals， what three steps are always included in the process？ （）

  A .  involution B .  encoding C .  sampling D .  quantization E .  compression F .  companding

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• Signaling devices which are required on inflatable liferafts include（）.

  A . a rocket shoulder rifle B . an oil lantern C . red flares D . an air hor

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• When two vessels are in sight of one another and NOT in or near an area of restricted visibility，any of the following signals may be given EXCEPT（）.

  A . a light signal of at least five short and rapid flashes B . one prolonged，one short，one prolonged，and one short whistle blasts C . four short whistle blasts D . two short whistle blast

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• Analog signal and digital signal are two kinds of signals in the form of control.

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• Hand signals are not involved into cultural awareness.

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• In face－to－face communication, non－verbal signals are not as important as verbal messIn face-to-face communication, non-verbal signals are not as important as verbal messages.（）

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• The highest frequency of a signal is ,sampling angular frequency is , , in order to avoid aliasing when sampling this signal, what pre-processing is required before sampling （）

  A．quantization B．denoising C．modulation D．anti-aliasingfiltering

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• The first step to process an analog signal digitally is to（）

  A．encode it by using the binary coding scheme B．quantize it in amplitude C．sample it at discrete time instant D．pass it through a D/A converte

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• A continuous signal is also called because its waveform is often analogous to that of the physical variable（）

  A．an analog signal B．a discrete signal C．a digital signal D．a sampled signal

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