chapter2：物理层课堂练习
Chapter 2: Physical Layer(Clod-exam (25m))
Classno___________StuNo_______StuName_______________Grade________
Fill in the blanks(填空45%):
1. The functions of physical layer is to transmit ( ) from one cable to the other side of the cable.
2. The three kinds of guided transmission media are ( ) 、( ) and ( )
3. The range of frequencies transmitted without being strongly attenuated is called( )
暑假英语作文4. A connection that allows traffic in both directions simultaneously is called( ).
玛利亚 莎拉波娃5. A connection that allows traffic either way, but only one way at a time is called( )
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esl下载6. A connection that allows traffic only one way is called ( )
猴子用英文怎么说7. The two basic categories of multiplexing schemes are ( ) and ( )
8. Two different switching techniques are ud nowadays:( ) and ( ). The two differs in many respects, for example, ( ) requires that a circuit be t up end to end before communication begins.
10. Compared to copper, ( ) is not affected by electromagnetic noi.
True or Fal?(判断15%)
1. A Nyquist’s theorem,a noiless 3-kHz channel cannot transmit binary (i.e., two-level) signals at a rate exceeding 6000 bps.
2. According to Shannon’s theorem, a channel of 3000-Hz bandwidth with a signal to thermal noi ratio of 30 dB can never transmit much more than 30,000 bps.
3. Twisted pairs can only be ud for transmitting either analog or digital signals.
4. Multimode fiber has better transmission properties than Single-mode fiber, so normally
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it is more expensive.
5. Services with more bandwidth than standard telephone rvice are sometimes called broadband.
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Questions(40%):木偶战记
1. Television channels are 6 MHz wide. How many bits/c can be nt if four-level digital signals are ud? Assume a noiless channel.
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在线学日语2. Is the Nyquist theorem true for optical fiber or only for copper wire?
3. What is the esntial difference between message switching and packet switching?
4.If a binary signal is nt over a 3-kHz channel who signal-to-noi ratio is 20 dB, what is the maximum achievable data rate?
