【正文】 e is always an initial connection cost incurred in setting up the circuit. It is costeffective only in those situations where once the circuit is set up ( ).A. the voice conversation beginsB. there is no any intervention on the part of the subnetC. there is a message to be transmittedD. there is a guaranteed steady flow of information transfer答案：D17. A major problem facing the radio munication industry is the limitation of ( ).A. the LSI technologyB. the poor service performanceC. the available radio frequency spectrumD. the size of the mobile transceivers答案：C18. LargeScale Integrated circuit technology reduced ( ) so that they easily fit into the standard automobile.A. the costs of the transceiversB. the size of mobile transceiversC. the number of the channelsD. the frequency band of the transceiver答案：B19. A basic cellular system consists of three parts: a mobile unit, ( ).A. a cell site, and a mobile telephone switching officeB. a cellular processor and a cellular switchC. a control unit and a power plantD. an antenna and a data terminal答案：A20. Each mobile unit can only use one channel at a time for its munication link, ( ).A. the channel is fixed when the call is madeB. but the channel is not fixedC. and the channel is a highspeed data linkD. and many mobile units use the same channel答案：B21. The cellular switch, which can be either analog or digital, switches calls ( ).A. to connect mobile subscribers to the nationwide telephone networkB. to connect fixed telephone subscribers to one anotherC. to link together many fixed telephone usersD. using the microwave radio links答案：A22. People on the ARPNET quickly discovered that they could ( ) .A. municate to one another by telephoneB. exchange messages and conduct electronic “conferences” with distantC. conduct data munications D. get all kinds of information services, such as science, education答案：B23. Today thousands of network and millions of puters are connected to the Internet. It is growing so quickly ( ) how many users “On the Net”.A. that anybody knows B. that you can tell us C. that anyone can say exactly D. that nobody can say exactly答案：D24. The Internet is an international collection of puter networks that ( ), connected together through backbone systems.A. all understand a standard system of addresses and mandsB. all have the bridges and gatewaysC. all use the same addresses and the serversD. all understand importance of munications答案：A25. The Internet is the largest repository of information which can provide very very large network resources. The network resources can be divided into ( ).A. munication resources and puter resourcesB. servers resources and bridges resourcesC. facilities resources and information resourcesD. hardware resources and software resources答案：C26. As more and more systems join the Internet, and as more and more forms of information can be converted to digital form , ( ).A. the amount of stuff available to Internet users continues to growB. the Internet bees very busyC. the number of Internet users bees very largeD. the information in Internet is shared by more people.答案：A27. Before you can use the Internet, you must ( ).A. understand the regulations of the InternetB. choose a way to move data between the Internet and your PCC. install a serverD. study the concept of the munications答案：B28. ( ) is a networked hypertext protocol and user interface.A. Asynchronous serial interface B. EmailC. Internet D. World wide web答案：D29. If the signal is very large pared to the noise level, then ( ).A. the signaltonoise ratio is poorB. a perfect message can take placeC. it’s a terrestrial systemD. the noise power is very strong答案：B30. If we consider binary transmission, the plete information about a particular message will always be obtained ( ).A. by detecting the shape of the transmitted signalB. by detecting the level of the transmitted signalC. by calculating the parameters of the transmitted signalD. by detecting the presence or absence of the pulse答案：D31. At the receive terminal ( ) to separate the 8digit sequences into the appropriate channels.A. PCM is used B. a demultiplexer is neededC. the frame code is arranged D. the coder is required答案：B32. It is ( ) which is of the most interest to the munication engineer.A. the method for overing noisy environmentsB. the relationship of the true signal to the noise signalC. the binary transmissionD. the quality of the transmission答案：B33. The codec is arranged ( ), and code this value into the 8digit sequence.A. to do these operationsB. to perform these functionsC. to transmit the voice channelsD. to sample the amplitude value答案：D34. Digital transmission ( ) for overing noisy environments.A. provides a programB. provides a powerful methodC. provides the thermal lowlevel noiseD. provides the signaltonoise ratio答案：B35. The signal ( ) is very weak.A. within terrestrial systemB. within munication equipmentC. received from a satellite D. in a particular message答案：C36. The shape of the transmitted signal are most easily affected by the noise and attenuation ( ).A. introduced by the transmission pathB. introduced by the satelliteC. introduced by the equipmentD. introduced by the codec答案：A37. The demultiplexer knows which group of 8digits relates to channel ( ).A. by choosing digital transmissionB. by identifying the synchronization wordC. by word interleavingD. by binary transmission答案：B21 /